resolver: keep forward slashes when imports target is a package specifier

[robobun]

Repro

Per the reporter on Windows (also reproduced on main):

// packages/app/package.json
{
  "imports": { "#res": "@myproject/resolver" }
}

// packages/resolver/package.json
{
  "name": "@myproject/resolver",
  "main": "./index.cjs",
  "exports": { ".": "./index.mjs" }
}

import { type } from '#res';   // Node: 'esm (from exports)'
                                // Bun (Windows): 'cjs (from main)'

Linux/macOS output the expected ESM value; Windows falls back to the legacy main field.

Cause

In src/resolver/package_json.rs resolve_target, the branch that handles an imports target which is itself a bare package specifier (not ./…, ../…, /…) joins [target, subpath] via resolve_path::platform::Auto and hands the joined string back to package-resolve for a second pass.

platform::Auto is platform::Windows on Windows, so the join calls normalize_string_node_t::<u8, Windows> which rewrites / to \. The scoped package name @myproject/resolver becomes @myproject\resolver; that no longer matches anything in node_modules and the resolver falls back to legacy main-field lookup, producing the CJS file.

Per the Node.js packages spec, values inside imports and exports are URL-like specifiers that always use forward slashes — they are not OS-specific filesystem paths and must not be normalized to backslashes. The Zig reference (package_json.zig:1782) uses .auto here too; the Rust port inherited the bug.

Fix

Use platform::Posix for this one join so the scoped-package / is preserved. The other two platform::Auto joins in the same function operate on [package_url, str] / [package_url, str, subpath], where the result IS a real filesystem path — Windows normalization there is correct and stays as-is.

Test

Added describe.if(isWindows)("#30839 - imports entry pointing at a scoped package", …) in test/js/bun/resolve/resolve.test.ts that mirrors the reporter's setup: a workspace with @myproject/resolver dual-built (main=cjs, exports=mjs) and an imports entry mapping #res to the scoped name. Asserts that running bun test.mjs outputs the ESM value.

The test is Windows-only because on Linux/macOS platform::Auto is already platform::Posix and this join is a no-op for forward-slash input; the misbehavior only surfaces when the join's platform is Windows. That matches the existing test.if(isWindows) regression pattern in the repo (e.g. test/regression/issue/23292.test.ts).

Verification

• Linux: bun bd test test/js/bun/resolve/resolve.test.ts — 37 pass, 2 skip (including the new Windows-only case), 0 fail.
• Reproduction script from the issue, run against build/debug/bun-debug on Linux, prints Resolved type: esm (from exports) both before and after the fix (expected — Linux isn't affected).

Fixes #30839

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: 72b48e72-1018-4790-81a8-fd5bfa05e9dd

📥 Commits

Reviewing files that changed from the base of the PR and between 314d044 and 8de894f.

📒 Files selected for processing (12)

• src/crash_handler/lib.rs
• src/errno/lib.rs
• src/perf/tracy.rs
• src/resolver/package_json.rs
• src/runtime/cli/Arguments.rs
• src/runtime/cli/run_command.rs
• src/runtime/cli/upgrade_command.rs
• src/runtime/jsc_hooks.rs
• src/runtime/webview/ChromeProcess.rs
• src/spawn/process.rs
• src/spawn_sys/spawn_process.rs
• test/js/bun/resolve/resolve.test.ts

---

Walkthrough

This PR fixes scoped package imports resolution on Windows by switching path joining from platform-aware to Posix semantics, preserving forward slashes required for URL-like package specifiers. Supporting formatting refactors standardize multi-line platform configuration attributes across crash handling, runtime startup, process spawning, and system monitoring modules.

Changes

Windows scoped package imports fix and platform configuration cleanup

Layer / File(s)	Summary
Scoped package imports resolution for #30839 src/resolver/package_json.rs, test/js/bun/resolve/resolve.test.ts	Imports resolution for package-specifier-like targets now uses Posix path joining to preserve forward slashes on Windows, preventing fallback to main fields. Regression test validates exports resolution via scoped package imports on Windows with junction symlinks.
Crash handler and error diagnostics platform configuration src/crash_handler/lib.rs, src/errno/lib.rs	Platform-specific conditionals for crash handler initialization, error reporting, and error number mapping tests are reformatted from single-line to multi-line #[cfg(...)] form while maintaining identical supported target OS sets.
Performance monitoring platform detection src/perf/tracy.rs	Tracy profiler's dlsym path initialization platform condition is reformatted into multi-line form, preserving conditional logic for target OS selection.
Runtime startup and optimization link sections src/runtime/cli/Arguments.rs, src/runtime/cli/run_command.rs, src/runtime/cli/upgrade_command.rs	Startup table and cold-path function link section attributes are reformatted from single-line to multi-line #[cfg_attr(...)] form, maintaining Linux/Android-specific .rodata.startup and .text.unlikely placement.
File operations and temp path handling src/runtime/jsc_hooks.rs	Embedded file temp path construction is reformatted into clearer multi-line expressions without semantic change to filename or directory resolution.
Webview and developer tools platform configuration src/runtime/webview/ChromeProcess.rs	Playwright cache fallback and dev tools port detection conditionals are reformatted into multi-line form, preserving platform-specific paths for Linux/Android and cross-platform support.
Process spawning and lifecycle platform handling src/spawn/process.rs, src/spawn_sys/spawn_process.rs	POSIX process spawning logic and orphan handling predicates are reformatted into multi-line conditionals, maintaining platform predicates for Linux, Android, and macOS with adjusted label warning suppression scope.

Possibly related PRs

• oven-sh/bun#30720: Introduces or refactors the resolve_embedded_file_to_buf helper in src/runtime/jsc_hooks.rs that this PR reformats.
• oven-sh/bun#30735: Functionally adjusts the same Android/Linux-compat platform gates in crash handler, perf/tracy, runtime/cli, and runtime/webview modules that this PR reformats for consistency.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main fix: using Posix path joining to preserve forward slashes in imports targets that are package specifiers.
Description check	✅ Passed	The description comprehensively covers the repro, cause analysis, fix explanation, test verification, and links to issue #30839, following the template sections.
Linked Issues check	✅ Passed	The PR directly addresses the core requirement from #30839: using platform::Posix instead of platform::Auto when joining imports/exports specifiers to preserve forward slashes on Windows.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the Windows resolver bug: the primary fix in package_json.rs, supporting cfg reformatting across multiple files for code consistency, and a Windows-only regression test.

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---

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[robobun]

^{Updated 2:57 PM PT - May 15th, 2026}

❌ @robobun, your commit cdd4869 has 1 failures in Build #54936 (All Failures):

• test/js/node/http/node-http-backpressure.test.ts - SIGKILL on 🐧 25.04 aarch64

---

🧪   To try this PR locally:

bunx bun-pr 30845

That installs a local version of the PR into your bun-30845 executable, so you can run:

bun-30845 --bun

[claude]

LGTM — one-word resolver fix (Auto → Posix) with a targeted Windows regression test; the other 10 files are pure cargo fmt output from autofix.ci with no semantic change.

Extended reasoning...

Overview

The substantive change is a single identifier in src/resolver/package_json.rs (resolve_target): the path join for an imports target that is itself a bare package specifier now uses platform::Posix instead of platform::Auto. A Windows-only regression test is added to test/js/bun/resolve/resolve.test.ts. The remaining 10 files (crash_handler, errno, perf/tracy, runtime/cli/*, jsc_hooks, webview/ChromeProcess, spawn/*) are exclusively whitespace — #[cfg(...)] / #[cfg_attr(...)] attributes reflowed from single-line to multi-line form by the autofix.ci cargo fmt --all commit (8de894f), which follows the recently-merged #30682 that switched the format workflow to cargo fmt. I checked each hunk; none alter the predicate set or any token other than whitespace.

Security risks

None. The change narrows path normalization for a URL-like package specifier (per the Node.js packages spec, imports/exports values are always forward-slash). It does not touch filesystem-path joins (the two adjacent platform::Auto joins on package_url are correctly left as-is), auth, crypto, permissions, or any user-input parsing surface.

Level of scrutiny

Low. The logic delta is one word with a clear, well-argued PORT NOTE comment and PR description tying it to the Node spec and the original Zig line. On non-Windows targets platform::Auto already equals platform::Posix, so the change is a no-op everywhere except the broken Windows path it fixes. The new test mirrors the reporter's setup exactly and uses the established describe.if(isWindows) pattern. The autofix-applied formatting churn is mechanical and verifiably semantics-preserving.

Other factors

The robobun build failures cited are for commit b1d7b4d (pre-autofix) on the build-rust step across several targets; given the autofix commit that followed is purely cargo fmt output, those were format-check failures now resolved by 8de894f. No human reviewer comments are outstanding, no CODEOWNERS gating, and the bug-hunting system found nothing.

[craftingmod]

x bun-30845 test
bun test v1.3.14-canary.1 (8de894fec)

packages\main\bun\index.test.ts:
✓ Resolve 'resolver' module directly [1.45ms]
✓ Resolve 'resolver' module from subpath import [0.09ms]
✓ Resolve 'exporter' module directly [0.71ms]
✓ Resolve 'exporter' module from subpath import [0.08ms]

It works 👀

Test repo: https://github.com/craftingmod/bun-subpath-import-slash

[claude]

LGTM — one-line Posix-join fix for #30839 plus a Windows regression test; the other 10 files are pure cargo fmt reflows from autofix.ci.

Extended reasoning...

Overview

The substantive change is a single token swap in src/resolver/package_json.rs (platform::Auto → platform::Posix) inside the resolve_target branch that handles an imports target which is itself a bare package specifier (gated by internal && !./ && !../ && !/, returning Status::PackageResolve). A Windows-only regression test is added to test/js/bun/resolve/resolve.test.ts. The remaining 10 files (crash_handler, errno, tracy, Arguments.rs, run_command.rs, upgrade_command.rs, jsc_hooks.rs, ChromeProcess.rs, spawn/process.rs, spawn_sys/spawn_process.rs) are byte-for-byte semantic no-ops: #[cfg(...)]/#[cfg_attr(...)] attributes reflowed from single-line to multi-line by the [autofix.ci] apply automated fixes commit, following the recent switch of the format workflow to cargo fmt --all.

Security risks

None. No input parsing, auth, crypto, or privilege boundaries are touched. The resolver change only affects which path-separator style is used when concatenating a bare specifier with a subpath before re-entering package resolution; it cannot introduce traversal because the result is fed back into the package resolver (not opened as a filesystem path), and the ../ / / prefixes are already excluded by the surrounding guards.

Level of scrutiny

Low. The fix is one line whose correctness follows directly from the Node.js packages spec (imports/exports targets are URL-like, always /). On Linux/macOS Auto == Posix, so behavior is identical there; on Windows it now preserves the scoped-package / instead of normalizing to \. The PR description's analysis matches the code, the sibling PATTERN arm already builds a forward-slash specifier via string replace (no platform join), and the issue reporter independently confirmed the fix works on Windows. The formatting hunks require no review beyond confirming they are whitespace-only, which they are.

Other factors

A targeted Windows regression test is included and follows existing repo patterns (describe.if(isWindows), tempDir, junction symlink for the workspace link). CodeRabbit found nothing actionable, the bug-hunter system found no bugs, and there are no outstanding human review comments.

[robobun]

CI diff is green: all Windows lanes pass (the target of this fix), all macOS lanes pass, all Rust/C++ build lanes pass. The overall buildkite/bun is marked failing because of one flaky shard — shard 15 of 20 on :ubuntu: 25.04 aarch64 - test-bun exited with code 2 (test failure).

This change is in src/resolver/package_json.rs and swaps platform::Auto for platform::Posix in a single path-join. On Linux/macOS platform::Auto is already platform::Posix, so the change is a compile-time no-op on every non-Windows target — it cannot cause a Linux test failure. (The earlier attempt had darwin-14-aarch64 Expired — runner expiration, also unrelated; I used my single retrigger on that one.)

Stopping here per the CI-flake rule (one re-roll max). Needs a maintainer to re-run the flaky lane or merge.