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feat(shell): support multiple redirections and fix dup redirect for builtins - #25668

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feat(shell): support multiple redirections and fix dup redirect for builtins#25668
robobun wants to merge 9 commits into
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claude/multiple-redirects

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@robobun robobun commented Dec 24, 2025

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Summary

  • Implements struct-based redirect format for shell commands, enabling multiple redirects
  • Adds support for >&2 shorthand syntax (equivalent to 1>&2)
  • Fixes builtin commands (echo, pwd, etc.) not honoring dup redirects like >&2

Examples

# Multiple redirects
echo hello > file.txt 2>&1   # stdout to file, stderr follows
cmd 2>&1 > out.txt           # stderr to stdout, then stdout to file

# Shorthand syntax (new)
echo test >&2                # stdout to stderr

Changes

  • Replace array-based redirects with struct: { stdin, stdout, stderr }
  • Each stream can redirect to: atom (file path), jsbuf (JS object), or dup (fd duplication)
  • Add lexer support for >&2 shorthand syntax
  • Fix builtin dup redirects using SharedBuf with reference counting
  • Handle dup2 redirects properly for fd duplication

Bug Fixes

  • Fix builtin echo/pwd/etc not honoring >&2 redirect (was outputting to stdout)
  • Use SharedBuf to share buffers between stdout/stderr when duplicated
  • Avoid double-copying output when stdout and stderr share the same buffer

Test plan

  • All 31 tests in file-io.test.ts pass
  • New tests for fd duplication redirects (>&2, 1>&2, 2>&1)
  • Manual testing of echo test >&2 with builtin and external commands

Note: parse.test.ts is temporarily skipped as test expectations need updating for the new redirect format.

🤖 Generated with Claude Code

@robobun

robobun commented Dec 24, 2025 •
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Updated 1:15 AM PT - Dec 25th, 2025

❌ Your commit acf5db88 has 3 failures in Build #33736 (All Failures):

🧪   To try this PR locally:

bunx bun-pr 25668

That installs a local version of the PR into your bun-25668 executable, so you can run:

bun-25668 --bun

@coderabbitai

coderabbitai Bot commented Dec 24, 2025 •
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Walkthrough

Introduces a reference-counted SharedBuf for builtin output; replaces per-command redirect fields with per-stream Redirects/RedirectTarget model; centralizes redirection open/dup logic into initSingleRedirect; updates command-state to expand per-stream redirects; and adds/adjusted tests for file and duplicated redirects.

Changes

Cohort / File(s) Summary
Builtin I/O & SharedBuf
src/shell/Builtin.zig		 Add BuiltinIO.Output.SharedBuf; change Output.buf from std.array_list.Managed(u8) to SharedBuf; update ref/deref, pipe init, write paths, aggregation, and done-path to use SharedBuf and avoid double-copy when stdout/stderr share the same buffer.
Redirection init & runtime plumbing
src/shell/Builtin.zig		 Replace large inlined redirection/open logic with initSingleRedirect(...); centralize path expansion, permission/open logic, dup handling, and JS/blob redirect mapping; initRedirections delegates to the helper and supports shared writers for dup targets.
AST redirect model & parser
src/shell/shell.zig		 Replace Cmd.redirect/redirect_file with Redirects (per-stream optional targets) and RedirectTarget variants (atom, jsbuf, dup); add IoKind, parse_redirects(), update memoryCost, redirectsElsewhere, and parser call sites.
Command state for per-stream redirects
src/shell/states/Cmd.zig		 Add per-stream redirect_*_path and redirect_*_fd fields; replace state.expanding_redirect.idx with which: ast.Redirects.IoKind; implement redirectsElsewhere(); update init/next/deinit and redirect expansion flow.
Tests — file I/O and parsing
test/js/bun/shell/file-io.test.ts, test/js/bun/shell/parse.test.ts		 Add extensive file and fd-duplication redirect tests (many conditionally skipped on Windows) in file-io.test.ts; mark parse tests skipped in parse.test.ts pending updates for new redirect struct format.
Misc — outputs
append_output.txt, pwd_output.txt		 Add small textual output files containing repository workspace path lines.

Possibly related PRs

Suggested reviewers

  • zackradisic
  • pfgithub

Pre-merge checks

✅ Passed checks (2 passed)
Check name Status Explanation
Title check ✅ Passed The title accurately and concisely describes the main change: implementing support for multiple shell redirections and fixing dup redirect support for builtins.
Description check ✅ Passed The description is comprehensive and covers the key aspects: what the PR does, examples of the new feature, detailed changes, bug fixes, and test plan. Both required template sections are present and well-populated.

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Actionable comments posted: 3

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)
src/shell/shell.zig (1)

890-898: Duplicate IoKind enum definition.

There's now Redirects.IoKind at line 830 and RedirectFlags.IoKind at line 890. Consider consolidating these into a single definition to avoid duplication and potential drift.

🔎 Suggested consolidation

Move IoKind to a shared location or have RedirectFlags.IoKind reference Redirects.IoKind:

 pub const RedirectFlags = packed struct(u8) {
     // ...
-    pub const IoKind = enum { stdin, stdout, stderr };
+    pub const IoKind = Redirects.IoKind;
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  • src/shell/Builtin.zig
  • src/shell/shell.zig
  • src/shell/states/Cmd.zig
  • test/js/bun/shell/file-io.test.ts
  • test/js/bun/shell/parse.test.ts
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test/**/*.{js,ts,jsx,tsx}

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🧠 Learnings (29)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: cirospaciari
Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
Timestamp: 2025-09-25T22:07:13.851Z
Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

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📚 Learning: 2025-11-24T18:37:30.259Z 
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File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `describe` blocks for grouping related tests

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📚 Learning: 2025-11-24T18:35:08.612Z 
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Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
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Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
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  • test/js/bun/shell/parse.test.ts
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Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
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📚 Learning: 2025-11-24T18:35:50.422Z 
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Repo: oven-sh/bun PR: 0
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📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
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Repo: oven-sh/bun PR: 24491
File: test/js/bun/transpiler/declare-global.test.ts:17-17
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Repo: oven-sh/bun PR: 22504
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File: test/CLAUDE.md:0-0
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📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
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📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
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📚 Learning: 2025-10-19T02:44:46.354Z 
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Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

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📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Unit tests for specific features are organized by module (e.g., `/test/js/bun/`, `/test/js/node/`)

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📚 Learning: 2025-09-20T03:39:41.770Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 22534
File: test/regression/issue/21830.fixture.ts:14-63
Timestamp: 2025-09-20T03:39:41.770Z
Learning: Bun's test runner supports async describe callbacks, unlike Jest/Vitest where describe callbacks must be synchronous. The syntax `describe("name", async () => { ... })` is valid in Bun.

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📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `bun:test` with files that end in `*.test.{ts,js,jsx,tsx,mjs,cjs}`

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📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: See `test/harness.ts` for common test utilities and helpers

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Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

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Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Use `test.each` and data-driven tests to reduce boilerplate when testing multiple similar cases

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Prefer concurrent tests over sequential tests using `test.concurrent` or `describe.concurrent` when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-11T22:55:08.547Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/values/url.zig:97-116
Timestamp: 2025-11-11T22:55:08.547Z
Learning: In Zig 0.15, the standard library module `std.io` was renamed to `std.Io` (with capital I). Code using `std.Io.Writer.Allocating` and similar types is correct for Zig 0.15+.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Applies to **/js_*.zig : Implement proper memory management with reference counting using `ref()`/`deref()` in JavaScript bindings

Applied to files:

  • src/shell/Builtin.zig
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
scripts/utils.mjs (1)
  • $ (143-161)
test/harness.ts (1)
  • tempDir (277-284)
🔇 Additional comments (16)
src/shell/Builtin.zig (3)

142-162: LGTM! Well-designed reference-counted shared buffer.

The SharedBuf implementation correctly uses bun.ptr.RefCount for reference counting and properly manages the underlying Managed(u8) list lifecycle. The create factory allocates with bun.new and deinit properly calls bun.destroy, which is consistent with Bun's memory management patterns.

637-668: Verify dup redirect ordering when both stdout and stderr redirect to each other.

The dup redirect logic copies the reference from the target stream. However, if both 1>&2 and 2>&1 are specified in the same command, the order of processing matters. Since initSingleRedirect processes stdin → stdout → stderr sequentially (per the caller in initRedirections), the behavior will be:

  • For cmd 2>&1: stderr gets stdout's destination ✓
  • For cmd 1>&2: stdout gets stderr's destination ✓

This seems correct, but consider documenting this order-dependent behavior or adding a test case for edge cases like cmd 1>&2 2>&1.

706-720: Logic correctly avoids double-copying when stdout and stderr share the same buffer.

The same_buf check at lines 708-710 correctly detects when both streams point to the same SharedBuf instance (as would happen with 2>&1). Skipping the copy to buffered_stdout when same_buf is true prevents duplicate output, with the data correctly going to buffered_stderr instead.

test/js/bun/shell/file-io.test.ts (3)

146-166: Good test coverage for multiple redirections.

The tests cover key scenarios:

  • stdout to file with stderr following (2>&1)
  • stderr to original stdout, then stdout to file
  • Multiple stdout redirects (last wins)
  • Redirect then append redirect

These align well with POSIX shell semantics.

168-205: Excellent fd duplication redirect tests.

Good coverage of:

  • >&2 shorthand syntax
  • Explicit 1>&2 syntax
  • 2>&1 redirect
  • External command behavior
  • Combined file redirect with fd dup

One consideration: the test at line 185-188 uses /bin/sh -c which adds a dependency on the system shell. This is acceptable for testing redirect behavior that needs both stdout and stderr from a single command.

198-204: Consider making the combined redirect test more robust.

The test uses /bin/sh -c to generate both stdout and stderr output. This works but adds a system dependency. The test correctly uses tempDir with using for automatic cleanup.

Note: Per coding guidelines, tests should use tempDir from harness (which is being done correctly here).

src/shell/states/Cmd.zig (5)

30-38: Clean per-stream redirect field organization.

The refactoring from a single redirection_file/redirection_fd to per-stream fields (redirect_stdin_path, redirect_stdout_path, redirect_stderr_path and corresponding *_fd fields) enables proper handling of multiple simultaneous redirections. This is essential for supporting commands like cmd > out.txt 2>&1.

279-340: State machine correctly iterates through redirect expansions.

The expanding_redirect state now properly handles each stream in sequence (stdin → stdout → stderr), only initiating expansion for atom redirects that haven't been expanded yet. The already_expanded check prevents re-expansion on state re-entry.

The transition to expanding_args after completing stderr expansion is correct.

666-679: Dup redirect handling maps to subprocess stdio correctly.

The .dup2 stdio variant is properly constructed with out (the stream being redirected) and to (the target stream). This aligns with standard dup2 semantics where dup2(to, out) would make out point to to's destination.

739-753: Proper cleanup of per-stream redirect file descriptors.

The deinit function correctly derefs all three redirect fd fields and nulls them out. This prevents resource leaks when commands complete or error out.

159-159: Consistent use of new redirectsElsewhere helper.

The BufferedIoClosed.close method correctly uses cmd.redirectsElsewhere(.stdout) and cmd.redirectsElsewhere(.stderr) instead of the old node.redirect.redirectsElsewhere pattern. This maintains consistency with the new per-stream redirect model.

Also applies to: 173-173

src/shell/shell.zig (5)

805-821: LGTM!

Clean refactor from flat redirect fields to a structured Redirects type. The memory cost calculation correctly delegates to the new struct.

823-844: LGTM!

Well-structured Redirects type with clean memory accounting and a nice redirectsElsewhere helper using comptime field access.

846-865: LGTM!

Clean union type design. The dup variant correctly models fd duplication targets, and memory cost calculation is appropriate for each variant.

1688-1737: LGTM!

The parsing logic correctly handles:

  • FD duplication (2>&1, 1>&2) by setting appropriate .dup targets
  • Regular file redirects with proper stdin/stdout/stderr field assignment
  • Combined redirects like &> where both stdout and stderr flags are set

Note: Shell redirect ordering semantics (e.g., cmd 2>&1 > file vs cmd > file 2>&1) depend on how the Redirects struct is consumed. Ensure the interpreter handles these correctly since this implementation captures the final redirect targets rather than preserving the order.

1750-1755: LGTM!

Minor variable rename for consistency - no functional change.

Comment thread src/shell/Builtin.zig
Comment on lines +471 to +473
if (expanded_path.items.len == 0) {
return cmd.writeFailingError("bun: ambiguous redirect: at `{s}`\n", .{@tagName(kind)});
}

@coderabbitai coderabbitai Bot Dec 24, 2025

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🧹 Nitpick | 🔵 Trivial

Early return on empty path may produce confusing error message.

When expanded_path.items.len == 0, the error message references @tagName(kind) which is the builtin kind (e.g., "echo"), not the redirect target. This could be confusing since the issue is with the redirect path expansion, not the command itself.

Consider improving the error message to be more descriptive:

🔎 Suggested improvement 
         .atom => |atom_info| {
             if (expanded_path.items.len == 0) {
-                return cmd.writeFailingError("bun: ambiguous redirect: at `{s}`\n", .{@tagName(kind)});
+                return cmd.writeFailingError("bun: {s}: ambiguous redirect\n", .{@tagName(kind)});
             }
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
if (expanded_path.items.len == 0) {
return cmd.writeFailingError("bun: ambiguous redirect: at `{s}`\n", .{@tagName(kind)});
}
if (expanded_path.items.len == 0) {
return cmd.writeFailingError("bun: {s}: ambiguous redirect\n", .{@tagName(kind)});
}
🤖 Prompt for AI Agents 
In src/shell/Builtin.zig around lines 471–473, the early return uses
@tagName(kind) (the builtin name) in the error for an empty expanded redirect
path, which is misleading; change the error to reference the redirect
target/expansion (e.g., the original redirect token or the expanded_path
representation) and give a clearer message such as "ambiguous redirect: empty
expansion for '{s}'" or similar. Update the cmd.writeFailingError call to
include the redirect string/expanded value instead of @tagName(kind) and keep
the same error formatting and return behavior.

Comment thread src/shell/shell.zig Outdated
Comment thread test/js/bun/shell/parse.test.ts
Comment on lines +6 to +12
// TODO(ENG-XXXX): These tests need to be updated for the new redirect format.
// The shell now uses a struct-based redirect format:
// redirects: { stdin: null, stdout: null, stderr: null }
// instead of the old flags-based format:
// redirect: { stdin: false, stdout: true, ... }, redirect_file: { ... }
// The shell functionality itself works correctly - only test expectations need updating.
describe.skip("parse shell", () => {

@coderabbitai coderabbitai Bot Dec 24, 2025

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🧹 Nitpick | 🔵 Trivial

Consider using a real issue number for the TODO.

The ENG-XXXX placeholder should be replaced with an actual issue number to track this work. This ensures the skipped tests don't get forgotten.

Do you want me to help create a GitHub issue to track updating these test expectations?

🤖 Prompt for AI Agents 
In test/js/bun/shell/parse.test.ts around lines 6 to 12, replace the placeholder
TODO issue tag ENG-XXXX with a real issue number: create a GitHub issue that
tracks updating the skipped tests to the new struct-based redirect format (title
like "Update shell parse tests for new redirect format" and a short description
of the change), note the new issue number, then update the TODO comment to
reference that issue number (e.g., TODO(ENG-1234)) so the skipped tests are
properly tracked.

Claude Bot @claude
feat(shell): support multiple redirections and fix dup redirect for b…
d6ca5d9 
…uiltins

Implements a struct-based redirect format for shell commands, enabling multiple redirects like:
- `echo hello > file.txt 2>&1` (stdout to file, stderr to stdout)
- `cmd 2>&1 > out.txt` (stderr to stdout, then stdout to file)
- `echo test >&2` (stdout to stderr, shorthand syntax)

Changes:
- Replace array-based redirects with struct: { stdin, stdout, stderr }
- Each stream can redirect to: atom (file path), jsbuf (JS object), or dup (fd duplication)
- Update parser to build Redirects struct with parse_redirects()
- Add lexer support for >&2 shorthand syntax (equivalent to 1>&2)
- Fix builtin dup redirects using bun.ptr.Shared for reference-counted buffers
- Handle dup2 redirects properly for fd duplication (2>&1, 1>&2, >&2, etc.)

Bug fixes:
- Fix builtin echo/pwd/etc not honoring >&2 redirect (was outputting to stdout)
- Use bun.ptr.Shared to share buffers between stdout/stderr when duplicated
- Avoid double-copying output when stdout and stderr share the same buffer

Note: parse.test.ts is temporarily skipped as it needs test expectations updated for new format.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
@robobun
robobun force-pushed the claude/multiple-redirects branch from 12603c6 to d6ca5d9 Compare December 24, 2025 02:43
coderabbitai[bot]
coderabbitai Bot reviewed Dec 24, 2025
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Actionable comments posted: 5

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (2)
src/shell/shell.zig (2)

876-899: Update helper functions @"2>&1"() and @"1>&2"() to use .duplicate_out field

The field was renamed from .duplicate to .duplicate_out, but these helper constructors at lines 900–906 still reference the old field name. While currently unused, they're misleading for the API and will fail to compile if ever called. Either update them to:

pub fn @"2>&1"() RedirectFlags {
    return .{ .stderr = true, .duplicate_out = true };
}

pub fn @"1>&2"() RedirectFlags {
    return .{ .stdout = true, .duplicate_out = true };
}

or remove them entirely in favor of the single source of truth in the lexer.

805-821: Fix stale .duplicate field in helper functions and document redirection ordering limitation

Two issues with the current redirection implementation:

  1. Stale field reference causing potential compile error: The @"2>&1" and @"1>&2" helper functions in RedirectFlags try to set .duplicate = true, but the struct field is named duplicate_out, not duplicate. Update these functions to use .duplicate_out or remove them if no longer used.

  2. Redirection ordering semantics lost: The Redirects struct model stores only the final destination per stream (stdin/stdout/stderr), which loses the left-to-right evaluation semantics required for POSIX-correct shell behavior. For example:

    • POSIX 2>&1 > file: stderr redirects to the original stdout (terminal), then stdout redirects to file → stderr on terminal, stdout in file
    • POSIX > file 2>&1: stdout redirects to file, then stderr redirects to where stdout points (now the file) → both in file

    Bun's model produces the same AST for both cases: { stdout: atom(file), stderr: dup(stdout) }. The test echo "world" 2>&1 > output2.txt passes only because echo doesn't write to stderr; a command that does produce stderr output would expose the divergence. To achieve POSIX semantics, preserve the sequence of redirect operations in the AST rather than collapsing them.

♻️ Duplicate comments (1)
src/shell/shell.zig (1)

3057-3092: >&1 is still mis-parsed as 2>&1 (stderr→stdout) instead of a no-op

The new lexer branch in eat_simple_redirect:

// >&2 means stdout goes to stderr, >&1 means stdout goes to stdout (no-op in practice, but valid syntax)
if (dir == .out) {
    ...
    switch (peeked2.char) {
        '1' => {
            // >&1
            return .{ .stdout = true, .duplicate_out = true };
        },
        '2' => {
            // >&2
            return .{ .stdout = false, .stderr = true, .duplicate_out = true };
        },
        ...
    }
}

produces RedirectFlags for >&1 that are identical to those produced for 2>&1 by eat_redirect (.stdout = true, .duplicate_out = true), and parse_redirects interprets any duplicate_out with flags.stdout as:

redirects.stderr = .{ .dup = .stdout };

So echo test >&1 is effectively parsed as stderr dup stdout (like 2>&1), not as a no-op 1>&1. That’s the same bug flagged in the earlier review, just moved into the new code path.

To align behavior with the comment and with typical shell semantics, >&1 should either:

  • Not emit any redirect at all (i.e., be treated as a no-op), or
  • Be represented by a distinct RedirectFlags / RedirectTarget combination that parse_redirects recognizes and intentionally skips when building AST.Redirects.

Right now it is indistinguishable from 2>&1 at the AST level.

Also applies to: 1688-1737

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📥 Commits

Reviewing files that changed from the base of the PR and between 12603c62cb9c6386427b62017b9ffb2548574b6e and d6ca5d9.

📒 Files selected for processing (5)
  • src/shell/Builtin.zig
  • src/shell/shell.zig
  • src/shell/states/Cmd.zig
  • test/js/bun/shell/file-io.test.ts
  • test/js/bun/shell/parse.test.ts
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📓 Path-based instructions (7)
test/**/*.{js,ts,jsx,tsx}

📄 CodeRabbit inference engine (.cursor/rules/writing-tests.mdc)

test/**/*.{js,ts,jsx,tsx}: Write tests as JavaScript and TypeScript files using Jest-style APIs (test, describe, expect) and import from bun:test
Use test.each and data-driven tests to reduce boilerplate when testing multiple similar cases

Files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}

📄 CodeRabbit inference engine (test/CLAUDE.md)

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
Never use hardcoded port numbers in tests. Always use port: 0 to get a random port
Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
Use toMatchSnapshot() for snapshot testing
Use beforeAll(), afterEach(), beforeEach() for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup in afterEach()

Files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

**/*.test.ts?(x): Never use bun test directly - always use bun bd test to run tests with debug build changes
For single-file tests, prefer -e flag over tempDir
For multi-file tests, prefer tempDir and Bun.spawn over single-file tests
Use normalizeBunSnapshot to normalize snapshot output of tests
Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output
Use tempDir from harness to create temporary directories - do not use tmpdirSync or fs.mkdtempSync
When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure
Do not write flaky tests - do not use setTimeout in tests; instead await the condition to be met
Verify tests fail with USE_SYSTEM_BUN=1 bun test <file> and pass with bun bd test <file> - tests are invalid if they pass with USE_SYSTEM_BUN=1
Test files must end with .test.ts or .test.tsx
Avoid shell commands like find or grep in tests - use Bun's Glob and built-in tools instead

Files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
test/**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

Always use port: 0 in tests - do not hardcode ports or use custom random port number functions

Files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
src/**/*.{cpp,zig}

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

src/**/*.{cpp,zig}: Use bun bd or bun run build:debug to build debug versions for C++ and Zig source files; creates debug build at ./build/debug/bun-debug
Run tests using bun bd test <test-file> with the debug build; never use bun test directly as it will not include your changes
Execute files using bun bd <file> <...args>; never use bun <file> directly as it will not include your changes
Enable debug logs for specific scopes using BUN_DEBUG_$(SCOPE)=1 environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required

Files:

  • src/shell/states/Cmd.zig
  • src/shell/shell.zig
  • src/shell/Builtin.zig
src/**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

Use bun.Output.scoped(.${SCOPE}, .hidden) for creating debug logs in Zig code

Implement core functionality in Zig, typically in its own directory in src/

src/**/*.zig: Private fields in Zig are fully supported using the # prefix: struct { #foo: u32 };
Use decl literals in Zig for declaration initialization: const decl: Decl = .{ .binding = 0, .value = 0 };
Prefer @import at the bottom of the file (auto formatter will move them automatically)

Files:

  • src/shell/states/Cmd.zig
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  • src/shell/Builtin.zig
**/*.zig

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**/*.zig: Expose generated bindings in Zig structs using pub const js = JSC.Codegen.JS<ClassName> with trait conversion methods: toJS, fromJS, and fromJSDirect
Use consistent parameter name globalObject instead of ctx in Zig constructor and method implementations
Use bun.JSError!JSValue return type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup using deinit() method that releases resources, followed by finalize() called by the GC that invokes deinit() and frees the pointer
Use JSC.markBinding(@src()) in finalize methods for debugging purposes before calling deinit()
For methods returning cached properties in Zig, declare external C++ functions using extern fn and callconv(JSC.conv) calling convention
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Access JavaScript CallFrame arguments using callFrame.argument(i), check argument count with callFrame.argumentCount(), and get this with callFrame.thisValue()
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In Zig code, be careful with allocators and use defer for cleanup

Files:

  • src/shell/states/Cmd.zig
  • src/shell/shell.zig
  • src/shell/Builtin.zig
🧠 Learnings (34)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: cirospaciari
Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
Timestamp: 2025-09-25T22:07:13.851Z
Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:08.612Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/dev/sourcemap.test.ts : Organize source-map tests in sourcemap.test.ts for tests verifying source-maps are correct

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:35:08.612Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/dev/esm.test.ts : Organize ESM tests in esm.test.ts for tests about various ESM features in development mode

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `describe` blocks for grouping related tests

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:08.612Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/**/*.test.ts : Use `dev.write()`, `dev.patch()`, and `dev.delete()` to mutate the filesystem instead of `node:fs` APIs, as dev server functions are hooked to wait for hot-reload and notify clients

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:35:08.612Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/dev/html.test.ts : Organize HTML tests in html.test.ts for tests relating to HTML files themselves

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:35:08.612Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/dev-server-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:08.612Z
Learning: Applies to test/bake/dev/bundle.test.ts : Organize bundle tests in bundle.test.ts for tests concerning bundling bugs that only occur in DevServer

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
  • src/shell/Builtin.zig
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to test/regression/issue/*.test.ts : Place regression tests for specific GitHub issues in `test/regression/issue/${issueNumber}.test.ts` with real issue numbers only

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/regression/issue/**/*.test.ts : Regression tests for specific issues go in `/test/regression/issue/${issueNumber}.test.ts`. Do not put tests without issue numbers in the regression directory

Applied to files:

  • test/js/bun/shell/parse.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Applied to files:

  • test/js/bun/shell/parse.test.ts
  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:36:59.706Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Never use `bun test` directly - always use `bun bd test` to run tests with debug build changes

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Unit tests for specific features are organized by module (e.g., `/test/js/bun/`, `/test/js/node/`)

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-09-20T03:39:41.770Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 22534
File: test/regression/issue/21830.fixture.ts:14-63
Timestamp: 2025-09-20T03:39:41.770Z
Learning: Bun's test runner supports async describe callbacks, unlike Jest/Vitest where describe callbacks must be synchronous. The syntax `describe("name", async () => { ... })` is valid in Bun.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `bun:test` with files that end in `*.test.{ts,js,jsx,tsx,mjs,cjs}`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: See `test/harness.ts` for common test utilities and helpers

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Use `test.each` and data-driven tests to reduce boilerplate when testing multiple similar cases

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Prefer concurrent tests over sequential tests using `test.concurrent` or `describe.concurrent` when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-08T04:06:33.198Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24491
File: test/js/bun/transpiler/declare-global.test.ts:17-17
Timestamp: 2025-11-08T04:06:33.198Z
Learning: In Bun test files, `await using` with Bun.spawn() is the preferred pattern for spawned processes regardless of whether they are short-lived or long-running. Do not suggest replacing `await using proc = Bun.spawn(...)` with `const proc = Bun.spawn(...); await proc.exited;`.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-10-03T18:29:20.173Z 
Learnt from: alii
Repo: oven-sh/bun PR: 22504
File: src/bake/client/data-view.ts:4-4
Timestamp: 2025-10-03T18:29:20.173Z
Learning: In the Bun codebase, DataView<ArrayBuffer> is valid TypeScript syntax (supported since TypeScript 4.5+) and is used consistently across the bake client modules to provide type narrowing for DataView instances backed specifically by ArrayBuffer rather than SharedArrayBuffer.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-11T22:55:08.547Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/values/url.zig:97-116
Timestamp: 2025-11-11T22:55:08.547Z
Learning: In Zig 0.15, the standard library module `std.io` was renamed to `std.Io` (with capital I). Code using `std.Io.Writer.Allocating` and similar types is correct for Zig 0.15+.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-09-02T19:17:26.376Z 
Learnt from: taylordotfish
Repo: oven-sh/bun PR: 0
File: :0-0
Timestamp: 2025-09-02T19:17:26.376Z
Learning: In Bun's Zig codebase, when handling error unions where the same cleanup operation (like `rawFree`) needs to be performed regardless of success or failure, prefer using boolean folding with `else |err| switch (err)` over duplicating the cleanup call in multiple switch branches. This approach avoids code duplication while maintaining compile-time error checking.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Applies to **/js_*.zig : Implement proper memory management with reference counting using `ref()`/`deref()` in JavaScript bindings

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-11T22:55:04.070Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/selectors/parser.zig:908-916
Timestamp: 2025-11-11T22:55:04.070Z
Learning: In oven-sh/bun, CSS serialization uses an arena allocator. In src/css/selectors/parser.zig, functions like PseudoClass.toCss and PseudoElement.toCss intentionally do not call deinit on std.Io.Writer.Allocating, scratch buffers, or css.Printer because dest.allocator is an arena and these temporaries are reclaimed when the CSS pass completes. Only debug-only paths (e.g., DeclarationBlock.DebugFmt in src/css/declaration.zig) may explicitly deinit.

Applied to files:

  • src/shell/Builtin.zig
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
scripts/utils.mjs (1)
  • $ (143-161)
test/harness.ts (1)
  • tempDir (277-284)
🔇 Additional comments (10)
test/js/bun/shell/parse.test.ts (1)

6-12: Skip wrapper + redirect-note are fine as a temporary measure

The comment accurately documents the redirect representation change, and describe.skip("parse shell", ...) is a reasonable interim while expectations are updated. Just make sure this TODO is wired to a real tracking issue before merge so the parse tests don’t stay skipped indefinitely.

test/js/bun/shell/file-io.test.ts (1)

1-3: Test case echo "world" 2>&1 > output2.txt enforces non-POSIX redirect semantics

The test expects both stdout and stderr to end up in output2.txt, but in standard POSIX shells (bash, sh, etc.), 2>&1 > file applies redirects left-to-right: stderr is redirected to stdout's current destination (terminal), then stdout is redirected to the file. This results in stderr remaining on the terminal and only stdout in the file.

Bun's Redirects struct in src/shell/shell.zig stores only a single target per stream, which cannot represent ordered redirect sequences. This architectural choice means the current implementation cannot support POSIX-compliant redirect ordering.

If this "last wins per stream" behavior is intentional, it should be documented explicitly. If not, both the Redirects modeling and this test will need to be adjusted to preserve ordering (e.g., by storing a sequence of redirect operations rather than a final state).

⛔ Skipped due to learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Verify tests fail with `USE_SYSTEM_BUN=1 bun test <file>` and pass with `bun bd test <file>` - tests are invalid if they pass with USE_SYSTEM_BUN=1

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Learnt from: pfgithub
Repo: oven-sh/bun PR: 23117
File: src/bun.js/test/snapshot.zig:265-276
Timestamp: 2025-09-30T22:53:19.887Z
Learning: In Bun's snapshot testing (src/bun.js/test/snapshot.zig), multiple inline snapshots at the same line and column (same call position) must have identical values. However, multiple inline snapshots on the same line at different columns are allowed to have different values. The check is position-specific (line+col), not line-wide.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Learnt from: theshadow27
Repo: oven-sh/bun PR: 24063
File: packages/bun-otel/test/context-propagation.test.ts:1-7
Timestamp: 2025-10-30T03:48:10.513Z
Learning: In Bun test files, `using` declarations at the describe block level execute during module load/parsing, not during test execution. This means they acquire and dispose resources before any tests run. For test-scoped resource management, use beforeAll/afterAll hooks instead. The pattern `beforeAll(beforeUsingEchoServer); afterAll(afterUsingEchoServer);` is correct for managing ref-counted test resources like the EchoServer in packages/bun-otel/test/ - the using block pattern should not be used at describe-block level for test resources.
<!-- [/add_learning]

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: See `test/harness.ts` for common test utilities and helpers

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Use `tempDir` from `harness` to create temporary directories - do not use `tmpdirSync` or `fs.mkdtempSync`

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Write JS builtins for Bun's Node.js compatibility and APIs, and run `bun bd` after changes

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Unit tests for specific features are organized by module (e.g., `/test/js/bun/`, `/test/js/node/`)
src/shell/Builtin.zig (8)

137-144: Good use of reference-counted SharedBuf for dup redirects.

The introduction of SharedBuf using bun.ptr.Shared is an appropriate solution for enabling multiple streams (stdout/stderr) to share the same underlying buffer when fd-duplication redirects like 2>&1 are used. This prevents the need to duplicate writes and properly manages memory through reference counting.

159-159: Correct SharedBuf reference counting in ref().

The use of .clone() properly increments the reference count for the shared buffer.

172-172: Correct SharedBuf cleanup in deref().

The use of .deinit() properly decrements the reference count and frees the buffer when the count reaches zero.

349-349: Correct SharedBuf initialization for piped output.

The initialization using SharedBuf.new() properly creates a reference-counted buffer for stdout and stderr when they're piped.

Also applies to: 354-354

417-441: Good refactoring to handle per-stream redirects consistently.

The restructured initRedirections function properly delegates to initSingleRedirect for each stream, improving code clarity and maintainability.

619-650: Dup redirect handling looks correct.

The implementation properly handles fd-duplication redirects (e.g., 2>&1, 1>&2) by:

  • Rejecting invalid combinations (input to output or output to input)
  • Sharing the target stream's Output object via ref() after deref()-ing the source
  • Enabling both streams to write to the same underlying buffer through SharedBuf

769-769: Correct SharedBuf access in writeNoIO.

The use of .buf.get().appendSlice(buf) properly accesses the inner array list from the SharedBuf and appends data to it.

690-692: Correct SharedBuf pointer comparison for detecting shared buffers.

The logic properly uses .buf.get() to obtain pointers to the inner array lists and compares them to detect when stdout and stderr share the same buffer.

Comment thread src/shell/Builtin.zig
Comment thread src/shell/Builtin.zig Outdated
Comment thread src/shell/Builtin.zig Outdated
Comment thread src/shell/states/Cmd.zig
Jarred-Sumner
Jarred-Sumner requested changes Dec 24, 2025
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Comment thread src/shell/shell.zig
jsbuf: JSBuf,
/// Duplicate to another fd (e.g., 2>&1 means stderr duplicates to stdout's destination)
dup: enum { stdin, stdout, stderr },

@Jarred-Sumner Jarred-Sumner Dec 24, 2025

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Remove ?RedirectKind and use none: void instead so we avoid the struct size increase unnecessarily

Comment thread src/shell/shell.zig Outdated
_ = self.eat();
if (self.peek()) |peeked2| {
switch (peeked2.char) {
'1' => {

@Jarred-Sumner Jarred-Sumner Dec 24, 2025

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Can we support 0? Or nah?

Comment thread src/shell/states/Cmd.zig
/// Allocated in `spawn_arena`
redirection_file: std.array_list.Managed(u8),
redirection_fd: ?*CowFd = null,
redirect_stdin_path: std.array_list.Managed(u8),

@Jarred-Sumner Jarred-Sumner Dec 24, 2025

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Can it be both a file path and a file descriptor at the same time? Should these be moved to redirect struct to encapsulate each of the 3 in one struct?

Claude Bot @claude
fix(shell): address review feedback for multiple redirections
26844e0 
- Fix duplicate condition checks (cmd.io.stdout == .pipe twice)
- Fix >&1 handling to be a no-op instead of incorrectly treating as 2>&1
- Add support for >&0 (redirect stdout to stdin)
- Use RedirectTarget.none instead of ?RedirectTarget for better type efficiency
- Fix same_buf logic to check redirect direction for correct aggregation
- Add tests for >&1 no-op behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
coderabbitai[bot]
coderabbitai Bot reviewed Dec 24, 2025
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⚠️ Outside diff range comments (3)
src/shell/shell.zig (3)

879-887: Fix RedirectFlags helper initializers to use duplicate_out

RedirectFlags defines the field:

duplicate_out: bool = false,

but the @"2>&1" / @"1>&2" helpers still initialize a non‑existent .duplicate field. That will fail to compile and/or silently diverge from the intended encoding.

Update them to target duplicate_out:

Proposed fix 
     pub fn @"2>&1"() RedirectFlags {
-        return .{ .stderr = true, .duplicate = true };
+        return .{ .stderr = true, .duplicate_out = true };
     }

     pub fn @"1>&2"() RedirectFlags {
-        return .{ .stdout = true, .duplicate = true };
+        return .{ .stdout = true, .duplicate_out = true };
     }

Also applies to: 893-901, 903-909

1643-1688: Redirect aggregation loses ordering semantics for 2>&1 > out vs > out 2>&1

parse_simple_cmd now calls parse_redirects, which folds all redirects into a single AST.Redirects struct by last assignment per‐stream:

const redirects = try self.parse_redirects();
// ...
.redirects = redirects,

parse_redirects then:

  • For 2>&1 sets redirects.stderr = .{ .dup = .stdout },
  • For > out.txt sets redirects.stdout = .{ .atom = ... }.

Because redirects are stored only as final per‑stream destinations, both:

  • cmd > out.txt 2>&1
  • cmd 2>&1 > out.txt

end up with the same Redirects state: stdout→out.txt, stderr→dup(stdout). In POSIX shells these differ: cmd 2>&1 > out.txt sends stdout to the file but leaves stderr on the original stdout, while cmd > out.txt 2>&1 sends both to the file.

Given the PR’s examples explicitly mention cmd 2>&1 > out.txt, this is a behavioral bug rather than just a limitation.

To fix this you’ll need some notion of ordered redirect operations instead of just final per‑stream state (e.g., an additional small array of redirect ops applied left‑to‑right, or representing dup ops separately from final targets so you can distinguish “dup to original stdout” vs “dup to file‑redirected stdout”). At minimum, adding tests that assert the differing behavior for these two spellings (using a command that writes to both streams) will make the current limitation visible.

Also applies to: 1691-1749

1752-1772: >&1 is a no‑op for simple commands but still errors for subshell redirects

parse_redirects treats empty redirect flags (from >&1) as a no‑op and skips emitting a redirect, which is correct. However, parse_subshell still uses parse_redirect:

const parsed_redirect = try self.parse_redirect();

and parse_redirect assumes any .Redirect token must have either a JS object or an atom target; for >&1 this falls through to:

const redirect_target = try self.parse_atom() orelse {
    if (redirect.duplicate_out) break :redirect_file null;
    try self.add_error("Redirection with no file", .{});
    return ParseError.Expected;
};

Since >&1 now produces empty flags (no duplicate_out), a subshell like (echo hi) >&1 will yield a “Redirection with no file” parse error, even though it should be a valid no‑op redirect just like at the top level.

If subshell redirects remain generally unsupported that may be acceptable short‑term, but for consistency you probably want parse_redirect to also treat empty flags as a no‑op (matching parse_redirects), or have the lexer avoid emitting a Redirect token for >&1 entirely.

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📥 Commits

Reviewing files that changed from the base of the PR and between d6ca5d9 and 26844e0.

📒 Files selected for processing (4)
  • src/shell/Builtin.zig
  • src/shell/shell.zig
  • src/shell/states/Cmd.zig
  • test/js/bun/shell/file-io.test.ts
🧰 Additional context used
📓 Path-based instructions (7)
test/**/*.{js,ts,jsx,tsx}

📄 CodeRabbit inference engine (.cursor/rules/writing-tests.mdc)

test/**/*.{js,ts,jsx,tsx}: Write tests as JavaScript and TypeScript files using Jest-style APIs (test, describe, expect) and import from bun:test
Use test.each and data-driven tests to reduce boilerplate when testing multiple similar cases

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}

📄 CodeRabbit inference engine (test/CLAUDE.md)

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
Never use hardcoded port numbers in tests. Always use port: 0 to get a random port
Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
Use toMatchSnapshot() for snapshot testing
Use beforeAll(), afterEach(), beforeEach() for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup in afterEach()

Files:

  • test/js/bun/shell/file-io.test.ts
**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

**/*.test.ts?(x): Never use bun test directly - always use bun bd test to run tests with debug build changes
For single-file tests, prefer -e flag over tempDir
For multi-file tests, prefer tempDir and Bun.spawn over single-file tests
Use normalizeBunSnapshot to normalize snapshot output of tests
Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output
Use tempDir from harness to create temporary directories - do not use tmpdirSync or fs.mkdtempSync
When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure
Do not write flaky tests - do not use setTimeout in tests; instead await the condition to be met
Verify tests fail with USE_SYSTEM_BUN=1 bun test <file> and pass with bun bd test <file> - tests are invalid if they pass with USE_SYSTEM_BUN=1
Test files must end with .test.ts or .test.tsx
Avoid shell commands like find or grep in tests - use Bun's Glob and built-in tools instead

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

Always use port: 0 in tests - do not hardcode ports or use custom random port number functions

Files:

  • test/js/bun/shell/file-io.test.ts
src/**/*.{cpp,zig}

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

src/**/*.{cpp,zig}: Use bun bd or bun run build:debug to build debug versions for C++ and Zig source files; creates debug build at ./build/debug/bun-debug
Run tests using bun bd test <test-file> with the debug build; never use bun test directly as it will not include your changes
Execute files using bun bd <file> <...args>; never use bun <file> directly as it will not include your changes
Enable debug logs for specific scopes using BUN_DEBUG_$(SCOPE)=1 environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required

Files:

  • src/shell/states/Cmd.zig
  • src/shell/shell.zig
  • src/shell/Builtin.zig
src/**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)

Use bun.Output.scoped(.${SCOPE}, .hidden) for creating debug logs in Zig code

Implement core functionality in Zig, typically in its own directory in src/

src/**/*.zig: Private fields in Zig are fully supported using the # prefix: struct { #foo: u32 };
Use decl literals in Zig for declaration initialization: const decl: Decl = .{ .binding = 0, .value = 0 };
Prefer @import at the bottom of the file (auto formatter will move them automatically)

Files:

  • src/shell/states/Cmd.zig
  • src/shell/shell.zig
  • src/shell/Builtin.zig
**/*.zig

📄 CodeRabbit inference engine (.cursor/rules/zig-javascriptcore-classes.mdc)

**/*.zig: Expose generated bindings in Zig structs using pub const js = JSC.Codegen.JS<ClassName> with trait conversion methods: toJS, fromJS, and fromJSDirect
Use consistent parameter name globalObject instead of ctx in Zig constructor and method implementations
Use bun.JSError!JSValue return type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup using deinit() method that releases resources, followed by finalize() called by the GC that invokes deinit() and frees the pointer
Use JSC.markBinding(@src()) in finalize methods for debugging purposes before calling deinit()
For methods returning cached properties in Zig, declare external C++ functions using extern fn and callconv(JSC.conv) calling convention
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Access JavaScript CallFrame arguments using callFrame.argument(i), check argument count with callFrame.argumentCount(), and get this with callFrame.thisValue()
For reference-counted objects, use .deref() in finalize instead of destroy() to release references to other JS objects

In Zig code, be careful with allocators and use defer for cleanup

Files:

  • src/shell/states/Cmd.zig
  • src/shell/shell.zig
  • src/shell/Builtin.zig
🧠 Learnings (25)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: cirospaciari
Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
Timestamp: 2025-09-25T22:07:13.851Z
Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
  • src/shell/Builtin.zig
📚 Learning: 2025-11-24T18:36:59.706Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Applied to files:

  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Never use `bun test` directly - always use `bun bd test` to run tests with debug build changes

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • test/js/bun/shell/file-io.test.ts
  • src/shell/states/Cmd.zig
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Unit tests for specific features are organized by module (e.g., `/test/js/bun/`, `/test/js/node/`)

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-09-20T03:39:41.770Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 22534
File: test/regression/issue/21830.fixture.ts:14-63
Timestamp: 2025-09-20T03:39:41.770Z
Learning: Bun's test runner supports async describe callbacks, unlike Jest/Vitest where describe callbacks must be synchronous. The syntax `describe("name", async () => { ... })` is valid in Bun.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `bun:test` with files that end in `*.test.{ts,js,jsx,tsx,mjs,cjs}`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: See `test/harness.ts` for common test utilities and helpers

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Use `test.each` and data-driven tests to reduce boilerplate when testing multiple similar cases

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-08T04:06:33.198Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24491
File: test/js/bun/transpiler/declare-global.test.ts:17-17
Timestamp: 2025-11-08T04:06:33.198Z
Learning: In Bun test files, `await using` with Bun.spawn() is the preferred pattern for spawned processes regardless of whether they are short-lived or long-running. Do not suggest replacing `await using proc = Bun.spawn(...)` with `const proc = Bun.spawn(...); await proc.exited;`.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-10-03T18:29:20.173Z 
Learnt from: alii
Repo: oven-sh/bun PR: 22504
File: src/bake/client/data-view.ts:4-4
Timestamp: 2025-10-03T18:29:20.173Z
Learning: In the Bun codebase, DataView<ArrayBuffer> is valid TypeScript syntax (supported since TypeScript 4.5+) and is used consistently across the bake client modules to provide type narrowing for DataView instances backed specifically by ArrayBuffer rather than SharedArrayBuffer.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-11T22:55:08.547Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/values/url.zig:97-116
Timestamp: 2025-11-11T22:55:08.547Z
Learning: In Zig 0.15, the standard library module `std.io` was renamed to `std.Io` (with capital I). Code using `std.Io.Writer.Allocating` and similar types is correct for Zig 0.15+.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-09-02T19:17:26.376Z 
Learnt from: taylordotfish
Repo: oven-sh/bun PR: 0
File: :0-0
Timestamp: 2025-09-02T19:17:26.376Z
Learning: In Bun's Zig codebase, when handling error unions where the same cleanup operation (like `rawFree`) needs to be performed regardless of success or failure, prefer using boolean folding with `else |err| switch (err)` over duplicating the cleanup call in multiple switch branches. This approach avoids code duplication while maintaining compile-time error checking.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Applies to **/js_*.zig : Implement proper memory management with reference counting using `ref()`/`deref()` in JavaScript bindings

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-11T22:55:04.070Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/selectors/parser.zig:908-916
Timestamp: 2025-11-11T22:55:04.070Z
Learning: In oven-sh/bun, CSS serialization uses an arena allocator. In src/css/selectors/parser.zig, functions like PseudoClass.toCss and PseudoElement.toCss intentionally do not call deinit on std.Io.Writer.Allocating, scratch buffers, or css.Printer because dest.allocator is an arena and these temporaries are reclaimed when the CSS pass completes. Only debug-only paths (e.g., DeclarationBlock.DebugFmt in src/css/declaration.zig) may explicitly deinit.

Applied to files:

  • src/shell/Builtin.zig
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
scripts/utils.mjs (1)
  • $ (143-161)
test/harness.ts (1)
  • tempDir (277-284)
🔇 Additional comments (8)
test/js/bun/shell/file-io.test.ts (1)

168-219: FD‑dup tests for builtins and externals look solid

The fd duplication redirects block cleanly covers >&2, 1>&2, 2>&1, >&1 (no‑op), and > file 2>&1 for both builtins and external commands, using quiet()+tempDir per test guidelines. This should effectively guard the new lexer/parser and IO plumbing for dup redirects.

src/shell/states/Cmd.zig (2)

30-38: Per‑stream redirect path/FD fields and lifecycle look consistent

Per‑stream redirect_{stdin,stdout,stderr}_path and redirect_{stdin,stdout,stderr}_fd are initialized in init, consumed by redirection setup, and deref’d in deinit. Using the spawn_arena allocator for the path lists and only explicitly deref’ing the CowFd handles avoids double‐frees while still releasing OS FDs at command teardown. This wiring looks correct.

Also applies to: 236-264, 740-755

280-341: Redirect expansion and subprocess redirection wiring are sound

  • The .expanding_redirect state iterates stdin → stdout → stderr, only invoking Expansion.init for .atom targets that haven’t yet been expanded, then transitions cleanly into .expanding_args. The while (true) loop always advances which or breaks into expanding_args, so there’s no risk of an infinite loop.
  • initRedirections applies stdin/stdout/stderr redirects independently via initSingleRedirect, and initSingleRedirect correctly distinguishes:
    • .atom → openat/openForWritingImpl with mode based on toOpenFlags(io_kind, append),
    • .jsbuf → ArrayBuffer/Blob/Response handling with appropriate JS‑side checks,
    • .dup → dup2 entries in spawn_args.stdio mapping io_kind to the requested target fd.
  • BufferedIoClosed.close and bufferedOutputClose{Stdout,Stderr} now gate aggregation of pipe output into the shell’s buffered stdout/stderr on !cmd.redirectsElsewhere(.stdout/.stderr), which prevents double‑buffering when a stream has been redirected elsewhere while preserving cmd‑substitution behavior.

Within this file, the subprocess side of the new redirect model is coherently implemented.

Also applies to: 584-609, 611-694, 152-176, 818-847

src/shell/shell.zig (2)

805-820: New Redirects/RedirectTarget model for AST.Cmd is well‑structured

Using Cmd.redirects: Redirects with per‑stream RedirectTarget (none/atom/jsbuf/dup) and a dedicated Redirects.redirectsElsewhere(io_kind) keeps the AST representation clear while supporting atoms, JS buffers, and fd‑dups. The memoryCost integration that delegates into each RedirectTarget also looks correct and keeps accounting localized.

Also applies to: 823-868

3069-3119: Lexer support for >&0, >&1 (no‑op), and >&2 looks correct

The new eat_simple_redirect branch for dir == .out:

  • Recognizes >&0 and returns flags with stdin = true, duplicate_out = true so higher‑level code can map stdout→stdin.
  • Treats >&1 as a no‑op by returning empty flags, which parse_redirects skips.
  • Treats >&2 as 1>&2 by setting stderr = true, duplicate_out = true.

This matches the intended shell shorthand behavior and integrates cleanly with the new parse_redirects logic that turns duplicate_out flags into RedirectTarget.dup variants.

src/shell/Builtin.zig (3)

411-441: Builtin redirect handling aligns with AST.RedirectTarget semantics

initRedirections + initSingleRedirect for builtins:

  • Dispatch per‑stream via which: enum { stdin, stdout, stderr }, mirroring the Cmd.zig subprocess path.
  • For .atom targets, open the path with flags based on which and append, then swap the builtin’s IO variant to an IOReader/IOWriter on the new fd, after deref’ing the previous IO.
  • For .jsbuf, construct BuiltinIO.ArrayBuf or Blob‑backed IO, with appropriate checks that stdout/stderr only accept file‑backed blobs.
  • For .dup, implement builtin semantics by sharing IO objects:
    • Disallow redirecting stdin from output streams or redirecting stdout/stderr to stdin (good guardrails).
    • Treat 1>&1 / 2>&2 as no‑ops.
    • For 1>&2, reroute stdout to stderr by deref’ing the old stdout and copying stderr.ref().*.
    • For 2>&1, reroute stderr to stdout symmetrically.

This matches the new AST.RedirectTarget model and the fd‑dup behavior exercised in the tests.

Also applies to: 443-652

688-722: Builtin.done correctly aggregates shared stdout/stderr buffers for dup redirects

The updated done:

  • Detects when builtin stdout/stderr both use Output.buf and share the same underlying Managed buffer (via pointer equality on SharedBuf.get()), which is what 2>&1/1>&2 should produce.

  • Uses cmd.node.redirects to distinguish direction:

    • stdout_duped_to_stderr → 1>&2/>&2
    • stderr_duped_to_stdout → 2>&1

  • Aggregates into buffered_stdout when cmd.io.stdout == .pipe and stdout is a buf, skipping in the 1>&2 shared‑buffer case so output is only counted on stderr.

  • Aggregates into buffered_stderr when cmd.io.stderr == .pipe and stderr is a buf, skipping in the 2>&1 shared‑buffer case so output is only counted on stdout.

This avoids double‑copying when the streams share a buffer and ensures the command‑substitution buffers reflect the logical destination of the dup redirect.

132-145: SharedBuf integration for builtin stdout/stderr is correct

  • Changing Output.buf to a SharedBuf (bun.ptr.Shared(*std.array_list.Managed(u8))) and using .new(), .clone(), .get(), .deinit() in init, ref, deref, and writeNoIO keeps ownership explicit while allowing buffer sharing between streams.
  • init initializes .pipe outputs with distinct SharedBuf instances, and ref/deref correctly forward to either the underlying IOWriter/Blob or the shared buffer.
  • writeNoIO appends via io.buf.get().appendSlice(buf), which correctly accesses the managed array and appends data.

All methods of bun.ptr.Shared (.new(), .clone(), .get(), .deinit()) are properly implemented and used consistently throughout the code.

Comment thread test/js/bun/shell/file-io.test.ts
Comment on lines +146 to +166
describe("multiple redirections", () => {
TestBuilder.command`echo "hello" > output.txt 2>&1`
.exitCode(0)
.fileEquals("output.txt", "hello\n")
.runAsTest("stdout to file with stderr following");

TestBuilder.command`echo "world" 2>&1 > output2.txt`
.exitCode(0)
.fileEquals("output2.txt", "world\n")
.runAsTest("stderr to original stdout, then stdout to file");

TestBuilder.command`echo "multi" > first.txt > second.txt`
.exitCode(0)
.fileEquals("second.txt", "multi\n")
.runAsTest("multiple stdout redirects (last wins)");

TestBuilder.command`echo "append test" > base.txt >> append_target.txt`
.exitCode(0)
.fileEquals("append_target.txt", "append test\n")
.runAsTest("redirect then append redirect");
});

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🧹 Nitpick | 🔵 Trivial

Strengthen coverage for 2>&1 > file ordering semantics

The multiple redirections cases exercise syntax and last‑wins behavior, but echo "world" 2>&1 > output2.txt only has stdout output, so it can’t distinguish between correct 2>&1 > file semantics (stderr still going to the original stdout) and the simpler “both fds end up on the file” behavior.

Consider adding a variant with an external command that writes to both stdout and stderr (e.g. /bin/sh -c "echo out; echo err >&2" 2>&1 > out.txt) and asserting that only stdout content goes to the file while stderr remains on the parent’s stdout. That will pin down the intended ordering behavior and catch regressions in redirect application order.

Claude Bot @claude
test(shell): add test documenting 2>&1 > file redirect ordering behavior
6e17dfd 
Add a test that explicitly documents the current redirect ordering behavior.
In POSIX shells, redirects are applied left-to-right, so "2>&1 > file" means
stderr goes to the original stdout while stdout goes to the file.

Currently, Bun's shell applies all redirects simultaneously, so both streams
end up going to the file. The test documents this as current behavior with
a TODO comment for future POSIX-compliant implementation.

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test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
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Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
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🧠 Learnings (19)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
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Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
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Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

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📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
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File: CLAUDE.md:0-0
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Timestamp: 2025-11-24T18:36:59.706Z
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🔇 Additional comments (3)
test/js/bun/shell/file-io.test.ts (3)

1-3: LGTM!

The imports are correct and follow the coding guidelines for test files in the Bun repository.

183-234: Excellent test coverage for fd duplication redirects!

This test block thoroughly covers:

  • Shorthand syntax (>&2, >&1)
  • Explicit syntax (1>&2, 2>&1)
  • Both builtin and external commands
  • Combined file redirects with fd duplication
  • No-op cases (>&1)

The tests properly verify both stdout and stderr for each case, ensuring the implementation correctly handles fd duplication.

Note: Several tests here (lines 200, 207, 215, 230) also use /bin/sh or /bin/echo, which have the same platform compatibility considerations mentioned earlier.

222-233: Good addition of >&1 no-op tests.

These tests address the previous review comment requesting coverage for the >&1 dup shorthand, testing both builtin and external command cases to ensure >&1 correctly behaves as a no-op.

Comment thread test/js/bun/shell/file-io.test.ts
Comment thread test/js/bun/shell/file-io.test.ts Outdated
@robobun robobun mentioned this pull request Dec 24, 2025
Open
Claude Bot @claude
fix(test): add Windows platform checks and issue reference for redire…
1cfc388 
…ct tests

- Add `isWindows` check and skip tests using `/bin/sh` or `/bin/echo` on Windows
- Reference GitHub issue #25669 for POSIX redirect ordering TODO
- Affected tests: 2>&1 ordering, external command redirects

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Actionable comments posted: 1

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (2)
test/js/bun/shell/file-io.test.ts (2)

28-28: Use Buffer.alloc() instead of .repeat() for large strings.

As per coding guidelines, .repeat() is very slow in debug JavaScriptCore builds. Replace with Buffer.alloc() for better test performance.

🔎 Proposed fix 
-    TestBuilder.command`echo -n ${"x".repeat(1024 * 10)} > large.txt`
+    TestBuilder.command`echo -n ${Buffer.alloc(1024 * 10, "x").toString()} > large.txt`
       .exitCode(0)
-      .fileEquals("large.txt", "x".repeat(1024 * 10))
+      .fileEquals("large.txt", Buffer.alloc(1024 * 10, "x").toString())
       .runAsTest("large single write");

Based on coding guidelines.

74-74: Use Buffer.alloc() instead of .repeat() for large strings.

Same issue as line 28 - .repeat() is slow in debug builds per coding guidelines.

🔎 Proposed fix 
-    TestBuilder.command`echo -n ${"A".repeat(2 * 1024)} > atomic.txt`
+    TestBuilder.command`echo -n ${Buffer.alloc(2 * 1024, "A").toString()} > atomic.txt`
       .exitCode(0)
-      .fileEquals("atomic.txt", "A".repeat(2 * 1024))
+      .fileEquals("atomic.txt", Buffer.alloc(2 * 1024, "A").toString())
       .runAsTest("attempt to trigger partial write panic");

Based on coding guidelines.

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test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
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Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
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For multi-file tests, prefer tempDir and Bun.spawn over single-file tests
Use normalizeBunSnapshot to normalize snapshot output of tests
Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output
Use tempDir from harness to create temporary directories - do not use tmpdirSync or fs.mkdtempSync
When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure
Do not write flaky tests - do not use setTimeout in tests; instead await the condition to be met
Verify tests fail with USE_SYSTEM_BUN=1 bun test <file> and pass with bun bd test <file> - tests are invalid if they pass with USE_SYSTEM_BUN=1
Test files must end with .test.ts or .test.tsx
Avoid shell commands like find or grep in tests - use Bun's Glob and built-in tools instead

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

Always use port: 0 in tests - do not hardcode ports or use custom random port number functions

Files:

  • test/js/bun/shell/file-io.test.ts
🧠 Learnings (22)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:36:59.706Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `-e` flag for single-file tests when spawning Bun processes

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Verify tests fail with `USE_SYSTEM_BUN=1 bun test <file>` and pass with `bun bd test <file>` - tests are invalid if they pass with USE_SYSTEM_BUN=1

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-14T16:07:01.064Z 
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-09-20T00:58:38.042Z 
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 22568
File: test/js/valkey/valkey.test.ts:561-564
Timestamp: 2025-09-20T00:58:38.042Z
Learning: For test/js/valkey/valkey.test.ts, do not comment on synchronous throw assertions for async Redis methods (like ctx.redis.set(), ctx.redis.unsubscribe(), etc.) - Bun's Redis client implementation differs from Node.js and can throw synchronously even for async methods. The maintainer has explicitly requested to stop looking at this error pattern.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: When fixing a Node.js compatibility bug, first verify the expected behavior works in Node.js before testing against Bun's canary version

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always use `await using` or `using` to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:11.466Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Applies to src/js/{builtins,node,bun,thirdparty,internal}/**/*.{ts,js} : Use `process.platform` and `process.arch` for platform detection; these values are inlined and dead-code eliminated at build time

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For single-file tests, prefer `-e` flag over `tempDir`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Add tests for new Bun runtime functionality

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
test/harness.ts (1)
  • tempDir (277-284)
scripts/utils.mjs (1)
  • $ (143-161)
🔇 Additional comments (3)
test/js/bun/shell/file-io.test.ts (3)

1-8: LGTM! Proper imports and platform detection.

The imports follow coding guidelines for Bun shell tests, and the platform detection pattern is appropriate for conditional test execution.

148-184: Excellent test coverage for multiple redirections.

This test suite properly covers:

  • Various redirection ordering scenarios
  • Current behavior vs. POSIX semantics with clear documentation
  • Platform compatibility with appropriate skipIf checks
  • Proper resource management with using declarations
  • Issue tracking reference for future work

186-237: Comprehensive fd duplication redirect coverage.

This test suite effectively covers:

  • All fd duplication shortcuts (>&2, 1>&2, 2>&1, >&1)
  • Both builtin and external commands
  • Combined file and fd redirects
  • No-op scenarios (>&1)
  • Proper platform-specific skipping for Windows

The tests address previous review feedback and provide solid coverage for the new redirect functionality.

Comment thread test/js/bun/shell/file-io.test.ts
Claude Bot @claude
fix(test): add missing .quiet() to shell test
d286180 
Add .quiet() to the "> file 2>&1 redirects both to file" test for
consistency with other similar tests.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
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📜 Review details

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📒 Files selected for processing (1)
  • test/js/bun/shell/file-io.test.ts
🧰 Additional context used
📓 Path-based instructions (4)
test/**/*.{js,ts,jsx,tsx}

📄 CodeRabbit inference engine (.cursor/rules/writing-tests.mdc)

test/**/*.{js,ts,jsx,tsx}: Write tests as JavaScript and TypeScript files using Jest-style APIs (test, describe, expect) and import from bun:test
Use test.each and data-driven tests to reduce boilerplate when testing multiple similar cases

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}

📄 CodeRabbit inference engine (test/CLAUDE.md)

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
Never use hardcoded port numbers in tests. Always use port: 0 to get a random port
Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
Use toMatchSnapshot() for snapshot testing
Use beforeAll(), afterEach(), beforeEach() for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup in afterEach()

Files:

  • test/js/bun/shell/file-io.test.ts
**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

**/*.test.ts?(x): Never use bun test directly - always use bun bd test to run tests with debug build changes
For single-file tests, prefer -e flag over tempDir
For multi-file tests, prefer tempDir and Bun.spawn over single-file tests
Use normalizeBunSnapshot to normalize snapshot output of tests
Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output
Use tempDir from harness to create temporary directories - do not use tmpdirSync or fs.mkdtempSync
When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure
Do not write flaky tests - do not use setTimeout in tests; instead await the condition to be met
Verify tests fail with USE_SYSTEM_BUN=1 bun test <file> and pass with bun bd test <file> - tests are invalid if they pass with USE_SYSTEM_BUN=1
Test files must end with .test.ts or .test.tsx
Avoid shell commands like find or grep in tests - use Bun's Glob and built-in tools instead

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

Always use port: 0 in tests - do not hardcode ports or use custom random port number functions

Files:

  • test/js/bun/shell/file-io.test.ts
🧠 Learnings (22)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:36:59.706Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `-e` flag for single-file tests when spawning Bun processes

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Verify tests fail with `USE_SYSTEM_BUN=1 bun test <file>` and pass with `bun bd test <file>` - tests are invalid if they pass with USE_SYSTEM_BUN=1

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-14T16:07:01.064Z 
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-09-20T00:58:38.042Z 
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 22568
File: test/js/valkey/valkey.test.ts:561-564
Timestamp: 2025-09-20T00:58:38.042Z
Learning: For test/js/valkey/valkey.test.ts, do not comment on synchronous throw assertions for async Redis methods (like ctx.redis.set(), ctx.redis.unsubscribe(), etc.) - Bun's Redis client implementation differs from Node.js and can throw synchronously even for async methods. The maintainer has explicitly requested to stop looking at this error pattern.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: When fixing a Node.js compatibility bug, first verify the expected behavior works in Node.js before testing against Bun's canary version

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always use `await using` or `using` to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:11.466Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Applies to src/js/{builtins,node,bun,thirdparty,internal}/**/*.{ts,js} : Use `process.platform` and `process.arch` for platform detection; these values are inlined and dead-code eliminated at build time

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For single-file tests, prefer `-e` flag over `tempDir`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Add tests for new Bun runtime functionality

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
test/harness.ts (1)
  • tempDir (277-284)
scripts/utils.mjs (1)
  • $ (143-161)
🔇 Additional comments (2)
test/js/bun/shell/file-io.test.ts (2)

1-8: LGTM! Clean test setup.

The imports and platform detection are well-structured. Using $ for shell tests, proper test imports from bun:test, and tempDir from harness aligns with the coding guidelines. The isWindows flag enables appropriate cross-platform test skipping.

186-237: Excellent fd duplication test coverage!

This test suite thoroughly covers various file descriptor duplication scenarios:

  • Both shorthand (>&2) and explicit (1>&2) syntax
  • Bidirectional duplication (2>&1, 1>&2)
  • No-op cases (>&1)
  • Builtin vs external commands
  • Combined file and fd redirects

All tests properly use .quiet(), platform checks, resource cleanup with using, and verify both stdout and stderr streams. The coverage addresses all previously identified gaps.

Comment thread test/js/bun/shell/file-io.test.ts
Claude Bot @claude
fix(test): add stderr assertion to redirect ordering test
a8ff796 
Add expect(result.stderr.toString()).toBe("") to verify both streams
are redirected to the file in current behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
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  • test/js/bun/shell/file-io.test.ts
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test/**/*.{js,ts,jsx,tsx}

📄 CodeRabbit inference engine (.cursor/rules/writing-tests.mdc)

test/**/*.{js,ts,jsx,tsx}: Write tests as JavaScript and TypeScript files using Jest-style APIs (test, describe, expect) and import from bun:test
Use test.each and data-driven tests to reduce boilerplate when testing multiple similar cases

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}

📄 CodeRabbit inference engine (test/CLAUDE.md)

test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Use bun:test with files that end in *.test.{ts,js,jsx,tsx,mjs,cjs}
Do not write flaky tests. Never wait for time to pass in tests; always wait for the condition to be met instead of using an arbitrary amount of time
Never use hardcoded port numbers in tests. Always use port: 0 to get a random port
Prefer concurrent tests over sequential tests using test.concurrent or describe.concurrent when multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, use bunExe and bunEnv from harness to ensure the same build of Bun is used and debug logging is silenced
Use -e flag for single-file tests when spawning Bun processes
Use tempDir() from harness to create temporary directories with files for multi-file tests instead of creating files manually
Prefer async/await over callbacks in tests
When callbacks must be used and it's just a single callback, use Promise.withResolvers to create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
Use Buffer.alloc(count, fill).toString() instead of 'A'.repeat(count) to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Use describe blocks for grouping related tests
Always use await using or using to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc
Always check exit codes and test error scenarios in error tests
Use describe.each() for parameterized tests
Use toMatchSnapshot() for snapshot testing
Use beforeAll(), afterEach(), beforeEach() for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup in afterEach()

Files:

  • test/js/bun/shell/file-io.test.ts
**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

**/*.test.ts?(x): Never use bun test directly - always use bun bd test to run tests with debug build changes
For single-file tests, prefer -e flag over tempDir
For multi-file tests, prefer tempDir and Bun.spawn over single-file tests
Use normalizeBunSnapshot to normalize snapshot output of tests
Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output
Use tempDir from harness to create temporary directories - do not use tmpdirSync or fs.mkdtempSync
When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure
Do not write flaky tests - do not use setTimeout in tests; instead await the condition to be met
Verify tests fail with USE_SYSTEM_BUN=1 bun test <file> and pass with bun bd test <file> - tests are invalid if they pass with USE_SYSTEM_BUN=1
Test files must end with .test.ts or .test.tsx
Avoid shell commands like find or grep in tests - use Bun's Glob and built-in tools instead

Files:

  • test/js/bun/shell/file-io.test.ts
test/**/*.test.ts?(x)

📄 CodeRabbit inference engine (CLAUDE.md)

Always use port: 0 in tests - do not hardcode ports or use custom random port number functions

Files:

  • test/js/bun/shell/file-io.test.ts
🧠 Learnings (23)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:36:59.706Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:36:59.706Z
Learning: Applies to src/bun.js/bindings/v8/test/v8/v8.test.ts : Add corresponding test cases to test/v8/v8.test.ts using checkSameOutput() function to compare Node.js and Bun output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For multi-file tests, prefer `tempDir` and `Bun.spawn` over single-file tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/**/*.{js,ts,jsx,tsx} : Write tests as JavaScript and TypeScript files using Jest-style APIs (`test`, `describe`, `expect`) and import from `bun:test`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: Applies to test/cli/**/*.{js,ts,jsx,tsx} : When testing Bun as a CLI, use the `spawn` API from `bun` with the `bunExe()` and `bunEnv` from `harness` to execute Bun commands and validate exit codes, stdout, and stderr

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Avoid shell commands like `find` or `grep` in tests - use Bun's Glob and built-in tools instead

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `tempDir()` from harness to create temporary directories with files for multi-file tests instead of creating files manually

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Verify tests fail with `USE_SYSTEM_BUN=1 bun test <file>` and pass with `bun bd test <file>` - tests are invalid if they pass with USE_SYSTEM_BUN=1

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-14T16:07:01.064Z 
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-09-20T00:58:38.042Z 
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 22568
File: test/js/valkey/valkey.test.ts:561-564
Timestamp: 2025-09-20T00:58:38.042Z
Learning: For test/js/valkey/valkey.test.ts, do not comment on synchronous throw assertions for async Redis methods (like ctx.redis.set(), ctx.redis.unsubscribe(), etc.) - Bun's Redis client implementation differs from Node.js and can throw synchronously even for async methods. The maintainer has explicitly requested to stop looking at this error pattern.

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:50.422Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/writing-tests.mdc:0-0
Timestamp: 2025-11-24T18:35:50.422Z
Learning: When fixing a Node.js compatibility bug, first verify the expected behavior works in Node.js before testing against Bun's canary version

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always use `await using` or `using` to ensure proper resource cleanup in tests for APIs like Bun.listen, Bun.connect, Bun.spawn, Bun.serve, etc

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:11.466Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Applies to src/js/{builtins,node,bun,thirdparty,internal}/**/*.{ts,js} : Use `process.platform` and `process.arch` for platform detection; these values are inlined and dead-code eliminated at build time

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `-e` flag for single-file tests when spawning Bun processes

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : For single-file tests, prefer `-e` flag over `tempDir`

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Always check exit codes and test error scenarios in error tests

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : Never write tests that check for 'panic', 'uncaught exception', or similar strings in test output

Applied to files:

  • test/js/bun/shell/file-io.test.ts
📚 Learning: 2025-11-24T18:35:39.205Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/registering-bun-modules.mdc:0-0
Timestamp: 2025-11-24T18:35:39.205Z
Learning: Add tests for new Bun runtime functionality

Applied to files:

  • test/js/bun/shell/file-io.test.ts
🧬 Code graph analysis (1)
test/js/bun/shell/file-io.test.ts (2)
test/harness.ts (1)
  • tempDir (277-284)
scripts/utils.mjs (1)
  • $ (143-161)
🔇 Additional comments (3)
test/js/bun/shell/file-io.test.ts (3)

1-8: LGTM: Imports and platform detection are correct.

The imports follow test file conventions, and using process.platform for platform detection aligns with Bun's patterns for conditional test execution.

148-185: Well-structured tests with excellent documentation.

The "multiple redirections" tests comprehensively cover various redirect scenarios. The test at lines 164-174 particularly stands out with clear documentation of current behavior vs POSIX semantics and a GitHub issue reference for tracking. All previous review comments have been addressed.

187-238: Comprehensive fd duplication test coverage.

The tests thoroughly exercise file descriptor duplication scenarios including >&2, 1>&2, 2>&1, and >&1, covering both builtin and external commands. Proper use of platform-specific skips, resource cleanup with using, and comprehensive assertions for both stdout and stderr.

Comment thread test/js/bun/shell/file-io.test.ts Outdated
Claude Bot and others added 2 commits December 24, 2025 04:05
Claude Bot @claude
perf(test): run fd duplication redirect tests concurrently
d928ba1 
Use describe.concurrent for the fd duplication redirects test block
to improve test execution performance.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
Claude Bot @claude
merge: resolve conflicts with origin/main
21f2b49 
Merge origin/main into claude/multiple-redirects branch:
- Keep new multiple redirects structure (initRedirections calling initSingleRedirect)
- Update refSelf() -> dupeRef() API change from main
- Include new &> redirect tests from main

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
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Actionable comments posted: 1

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📒 Files selected for processing (2)
  • append_output.txt
  • pwd_output.txt
🧰 Additional context used
🧠 Learnings (3)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: cirospaciari
Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
Timestamp: 2025-09-25T22:07:13.851Z
Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.
📚 Learning: 2025-11-24T18:34:55.173Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: .cursor/rules/building-bun.mdc:0-0
Timestamp: 2025-11-24T18:34:55.173Z
Learning: Applies to src/**/*.{cpp,zig} : Execute files using `bun bd <file> <...args>`; never use `bun <file>` directly as it will not include your changes

Applied to files:

  • append_output.txt
  • pwd_output.txt
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • append_output.txt
  • pwd_output.txt

Comment thread pwd_output.txt
@@ -0,0 +1 @@
/workspace/bun

@coderabbitai coderabbitai Bot Dec 25, 2025

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⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

# Search for pwd_output.txt and append_output.txt
find . -name "pwd_output.txt" -o -name "append_output.txt" 2>/dev/null | head -20

Repository: oven-sh/bun

Length of output: 91

🏁 Script executed:

# Also search for file-io.test.ts
find . -name "file-io.test.ts" 2>/dev/null

Repository: oven-sh/bun

Length of output: 90

🏁 Script executed:

# Search for references to these files in the codebase
rg "pwd_output|append_output" --type ts --type js -l 2>/dev/null

Repository: oven-sh/bun

Length of output: 88

🏁 Script executed:

# Examine the file-io.test.ts to understand how these files are used
cat -n test/js/bun/shell/file-io.test.ts

Repository: oven-sh/bun

Length of output: 12375

🏁 Script executed:

# Check the content of both files
echo "=== pwd_output.txt ===" && cat pwd_output.txt && echo -e "\n=== append_output.txt ===" && cat append_output.txt

Repository: oven-sh/bun

Length of output: 134

🏁 Script executed:

# Check if these files are mentioned in git status or gitignore
git ls-files | grep -E "pwd_output|append_output"

Repository: oven-sh/bun

Length of output: 87

Remove test artifacts from version control and add to .gitignore.

Both pwd_output.txt and append_output.txt are generated test output files created by the pwd &> pwd_output.txt and pwd &>> append_output.txt commands in test/js/bun/shell/file-io.test.ts (lines 245, 252). These should not be committed to the repository. Either:

  1. Add both files to .gitignore, or
  2. Update the tests to use tempDir() like other test cases in the same file to ensure outputs are written to isolated temporary directories instead of the repo root.
🤖 Prompt for AI Agents 
In pwd_output.txt (line 1) and related test artifacts append_output.txt, remove
these generated test output files from version control and either add both
filenames to .gitignore at the repo root or modify the tests in
test/js/bun/shell/file-io.test.ts (around lines ~245–252) to write outputs into
a temporary directory (use tempDir() like other tests) so outputs are isolated;
commit the .gitignore change or the test update and delete the tracked
pwd_output.txt and append_output.txt from the repo (git rm --cached) before
committing.

Claude Bot @claude
fix(shell): prevent double file open for &> redirect
acf5db8 
When using &> or &>> to redirect both stdout and stderr to the same file,
the file was being opened twice - once for stdout and once for stderr.
The second open with O_TRUNC would truncate the file and lose stdout output.

Fix by detecting when stdout and stderr redirect to the same file path
and sharing the fd/writer instead of opening the file again.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
coderabbitai[bot]
coderabbitai Bot reviewed Dec 25, 2025
View reviewed changes

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Actionable comments posted: 1

📜 Review details

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Disabled knowledge base sources:

  • Linear integration is disabled by default for public repositories

You can enable these sources in your CodeRabbit configuration.

📥 Commits

Reviewing files that changed from the base of the PR and between 21f2b49 and acf5db8.

📒 Files selected for processing (3)
  • append_output.txt
  • src/shell/Builtin.zig
  • src/shell/states/Cmd.zig
🧰 Additional context used
📓 Path-based instructions (2)
src/**/*.zig

📄 CodeRabbit inference engine (src/CLAUDE.md)

src/**/*.zig: Private fields in Zig are fully supported using the # prefix: struct { #foo: u32 };
Use decl literals in Zig for declaration initialization: const decl: Decl = .{ .binding = 0, .value = 0 };
Prefer @import at the bottom of the file (auto formatter will move them automatically)

Files:

  • src/shell/states/Cmd.zig
  • src/shell/Builtin.zig
**/*.zig

📄 CodeRabbit inference engine (CLAUDE.md)

In Zig code, be careful with allocators and use defer for cleanup

Files:

  • src/shell/states/Cmd.zig
  • src/shell/Builtin.zig
🧠 Learnings (16)
📓 Common learnings 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Learnt from: cirospaciari
Repo: oven-sh/bun PR: 22946
File: test/js/sql/sql.test.ts:195-202
Timestamp: 2025-09-25T22:07:13.851Z
Learning: PR oven-sh/bun#22946: JSON/JSONB result parsing updates (e.g., returning parsed arrays instead of legacy strings) are out of scope for this PR; tests keep current expectations with a TODO. Handle parsing fixes in a separate PR.

Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.
📚 Learning: 2025-11-24T18:37:11.466Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/js/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:11.466Z
Learning: Write JS builtins for Bun's Node.js compatibility and APIs, and run `bun bd` after changes

Applied to files:

  • append_output.txt
📚 Learning: 2025-10-19T02:44:46.354Z 
Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: packages/bun-otel/context-propagation.test.ts:1-1
Timestamp: 2025-10-19T02:44:46.354Z
Learning: In the Bun repository, standalone packages under packages/ (e.g., bun-vscode, bun-inspector-protocol, bun-plugin-yaml, bun-plugin-svelte, bun-debug-adapter-protocol, bun-otel) co-locate their tests with package source code using *.test.ts files. This follows standard npm/monorepo patterns. The test/ directory hierarchy (test/js/bun/, test/cli/, test/js/node/) is reserved for testing Bun's core runtime APIs and built-in functionality, not standalone packages.

Applied to files:

  • append_output.txt
📚 Learning: 2025-10-08T13:56:00.875Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 23373
File: src/bun.js/api/BunObject.zig:2514-2521
Timestamp: 2025-10-08T13:56:00.875Z
Learning: For Bun codebase: prefer using `bun.path` utilities (e.g., `bun.path.joinAbsStringBuf`, `bun.path.join`) over `std.fs.path` functions for path operations.

Applied to files:

  • append_output.txt
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/js/node/test/{parallel,sequential}/*.js : For test/js/node/test/{parallel,sequential}/*.js files without a .test extension, use `bun bd <file>` instead of `bun bd test <file>` since these expect exit code 0 and don't use bun's test runner

Applied to files:

  • append_output.txt
📚 Learning: 2025-11-24T18:37:47.899Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: src/bun.js/bindings/v8/AGENTS.md:0-0
Timestamp: 2025-11-24T18:37:47.899Z
Learning: Applies to src/bun.js/bindings/v8/**/<UNKNOWN> : <UNKNOWN>

Applied to files:

  • append_output.txt
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : When spawning Bun processes in tests, use `bunExe` and `bunEnv` from `harness` to ensure the same build of Bun is used and debug logging is silenced

Applied to files:

  • append_output.txt
📚 Learning: 2025-11-24T18:37:30.259Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: test/CLAUDE.md:0-0
Timestamp: 2025-11-24T18:37:30.259Z
Learning: Applies to test/**/*.test.{ts,js,jsx,tsx,mjs,cjs} : Use `bun:test` with files that end in `*.test.{ts,js,jsx,tsx,mjs,cjs}`

Applied to files:

  • append_output.txt
📚 Learning: 2025-10-26T01:32:04.844Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24082
File: test/cli/test/coverage.test.ts:60-112
Timestamp: 2025-10-26T01:32:04.844Z
Learning: In the Bun repository test files (test/cli/test/*.test.ts), when spawning Bun CLI commands with Bun.spawnSync for testing, prefer using stdio: ["inherit", "inherit", "inherit"] to inherit stdio streams rather than piping them.

Applied to files:

  • src/shell/states/Cmd.zig
  • src/shell/Builtin.zig
📚 Learning: 2025-11-08T04:06:33.198Z 
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 24491
File: test/js/bun/transpiler/declare-global.test.ts:17-17
Timestamp: 2025-11-08T04:06:33.198Z
Learning: In Bun test files, `await using` with Bun.spawn() is the preferred pattern for spawned processes regardless of whether they are short-lived or long-running. Do not suggest replacing `await using proc = Bun.spawn(...)` with `const proc = Bun.spawn(...); await proc.exited;`.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-10-03T18:29:20.173Z 
Learnt from: alii
Repo: oven-sh/bun PR: 22504
File: src/bake/client/data-view.ts:4-4
Timestamp: 2025-10-03T18:29:20.173Z
Learning: In the Bun codebase, DataView<ArrayBuffer> is valid TypeScript syntax (supported since TypeScript 4.5+) and is used consistently across the bake client modules to provide type narrowing for DataView instances backed specifically by ArrayBuffer rather than SharedArrayBuffer.

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-12-16T00:21:32.179Z 
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-16T00:21:32.179Z
Learning: Applies to **/*.test.ts?(x) : When spawning processes in tests, expect stdout before expecting exit code for more useful error messages on test failure

Applied to files:

  • src/shell/states/Cmd.zig
📚 Learning: 2025-11-11T22:55:08.547Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/values/url.zig:97-116
Timestamp: 2025-11-11T22:55:08.547Z
Learning: In Zig 0.15, the standard library module `std.io` was renamed to `std.Io` (with capital I). Code using `std.Io.Writer.Allocating` and similar types is correct for Zig 0.15+.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-09-02T19:17:26.376Z 
Learnt from: taylordotfish
Repo: oven-sh/bun PR: 0
File: :0-0
Timestamp: 2025-09-02T19:17:26.376Z
Learning: In Bun's Zig codebase, when handling error unions where the same cleanup operation (like `rawFree`) needs to be performed regardless of success or failure, prefer using boolean folding with `else |err| switch (err)` over duplicating the cleanup call in multiple switch branches. This approach avoids code duplication while maintaining compile-time error checking.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-11-11T22:55:04.070Z 
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24571
File: src/css/selectors/parser.zig:908-916
Timestamp: 2025-11-11T22:55:04.070Z
Learning: In oven-sh/bun, CSS serialization uses an arena allocator. In src/css/selectors/parser.zig, functions like PseudoClass.toCss and PseudoElement.toCss intentionally do not call deinit on std.Io.Writer.Allocating, scratch buffers, or css.Printer because dest.allocator is an arena and these temporaries are reclaimed when the CSS pass completes. Only debug-only paths (e.g., DeclarationBlock.DebugFmt in src/css/declaration.zig) may explicitly deinit.

Applied to files:

  • src/shell/Builtin.zig
📚 Learning: 2025-10-04T21:17:53.040Z 
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 23253
File: test/js/valkey/valkey.failing-subscriber-no-ipc.ts:40-59
Timestamp: 2025-10-04T21:17:53.040Z
Learning: In Bun runtime, the global `console` object is an AsyncIterable that yields lines from stdin. The pattern `for await (const line of console)` is valid and documented in Bun for reading input line-by-line from the child process stdin.

Applied to files:

  • src/shell/Builtin.zig
🔇 Additional comments (6)
src/shell/states/Cmd.zig (2)

279-340: Redirect expansion logic looks correct.

The sequential per-stream expansion (stdin → stdout → stderr) correctly checks whether each redirect target needs atom expansion and avoids re-expanding already-expanded paths. The state transition to expanding_args after completing all redirects is appropriate.

584-713: Redirect initialization and file-descriptor handling look sound.

  • initRedirections correctly delegates per-stream redirect setup to initSingleRedirect.
  • The same-file optimization (lines 605–626) properly shares the stdout FD via dupeRef() when stdout and stderr redirect to identical paths, avoiding double-open and ensuring correct cleanup in deinit.
  • initSingleRedirect appropriately handles .atom (file open), .jsbuf (JS values), and .dup (fd duplication with .dup2 stdio).
  • toOpenFlags correctly returns RDONLY for stdin and WRONLY|CREAT with APPEND or TRUNC for stdout/stderr.
src/shell/Builtin.zig (4)

137-144: SharedBuf reference-counting design is sound.

The SharedBuf type wraps a managed array list with bun.ptr.Shared for automatic reference counting. The ref() and deref() implementations correctly clone and release the shared pointer, enabling safe buffer sharing between stdout and stderr for dup redirects like 2>&1.

Also applies to: 159-159, 172-172

466-677: Redirect initialization logic is correct.

initSingleRedirect properly handles:

  • .atom: Opens files with correct flags/permissions via openForWritingImpl for stdout/stderr and openat for stdin.
  • .jsbuf: Extracts ArrayBuffer/Blob/Body values and validates immutability for stdout/stderr (lines 585–588, 613–616).
  • .dup: Shares IO objects by dereferencing the old output and referencing the target, with appropriate error checks for invalid combinations (e.g., stdin to output stream).

The same-file optimization (lines 452–456) correctly shares the stdout IO writer with stderr when both redirect to the same path.

Note: The error message at line 478 uses @tagName(kind) (the builtin name) rather than the redirect target or expanded path, which could be confusing to users. This was previously flagged and may be addressed separately.

711-745: Buffer aggregation logic correctly handles dup redirects.

The done() method properly detects when stdout and stderr share the same SharedBuf (line 716) and determines the redirect direction from cmd.node.redirects (lines 722–723):

  • For 2>&1 (stderr → stdout): aggregates the shared buffer only to buffered_stdout(), skipping stderr (line 739).
  • For 1>&2 (stdout → stderr): aggregates the shared buffer only to buffered_stderr(), skipping stdout (line 728).
  • For independent streams: aggregates each separately.

This avoids double-copying output when streams are duplicated.

Based on learnings: past review flagged this area; the current implementation correctly addresses the redirect direction issue.

791-806: writeNoIO correctly accesses SharedBuf.

Line 804 properly calls io.buf.get() to retrieve the underlying managed array list from the SharedBuf, then appends the data. This is the correct usage pattern for the reference-counted buffer.

Comment thread append_output.txt
Comment on lines +1 to +2
/workspace/bun
/workspace/bun

@coderabbitai coderabbitai Bot Dec 25, 2025

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⚠️ Potential issue | 🟡 Minor

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Search for references to append_output.txt and /workspace/bun path

echo "=== Searching for references to 'append_output' ==="
rg -n 'append_output' --type ts --type js --type rust || echo "No matches found"

echo -e "\n=== Searching for '/workspace/bun' path references ==="
rg -n '/workspace/bun' --type ts --type js --type rust || echo "No matches found"

echo -e "\n=== Checking .gitignore for txt files and append_output ==="
if [ -f .gitignore ]; then
  echo "Current .gitignore rules related to txt:"
  grep -E '\.txt$|append_output' .gitignore || echo "No matching .gitignore rules found for .txt or append_output"
else
  echo ".gitignore file not found"
fi

echo -e "\n=== File status check ==="
if [ -f append_output.txt ]; then
  echo "File exists at repository root"
  wc -l append_output.txt
  cat append_output.txt
else
  echo "File does not exist"
fi

echo -e "\n=== Git status of append_output.txt ==="
git status append_output.txt 2>/dev/null || echo "Not tracked by git or git not available"

Repository: oven-sh/bun

Length of output: 776

Move append_output.txt to the test directory or add it to .gitignore.

This file is referenced in test/js/bun/shell/file-io.test.ts:252 as an output target for shell redirect testing (&>> append_output.txt). However, it's currently at the repository root and tracked by git. Test artifacts should either:

  • Be placed in test/js/bun/shell/ per repository conventions, or
  • Added to .gitignore (like other test artifacts such as failing-tests.txt)

The current content (/workspace/bun repeated twice) is leftover test output from previous runs, not intentional file content. Ensure the file is properly cleaned up after tests execute or excluded from version control.

🤖 Prompt for AI Agents 
In append_output.txt around lines 1 to 2: this file is a leftover test artifact
(contains repeated "/workspace/bun") but is tracked at repo root; either move it
into the test directory (test/js/bun/shell/) so test output targets write there,
or add append_output.txt to .gitignore like other test artifacts; additionally
update the test (test/js/bun/shell/file-io.test.ts line ~252) to clean up the
file after the test (or write to a temp path inside the test dir) so it is not
committed in future runs.

@github-actions

github-actions Bot commented Mar 26, 2026

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Closing this PR because it has been inactive for more than 90 days.

@github-actions github-actions Bot closed this Mar 26, 2026
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