Improve Bun.stringWidth accuracy and robustness - #25447
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WalkthroughAdds a public GraphemeState for grapheme tracking, refactors UTF‑16 width computation to use it, expands zero‑width codepoint detection (including U+00AD and multiple combining/formatting ranges), improves CSI/OSC escape stripping and bulk ASCII/SIMD paths, and adds extensive string‑width tests for many Unicode/escape edge cases. Changes
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🧠 Learnings (20)📚 Learning: 2025-11-24T18:37:30.259ZApplied to files:
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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 frombun:test
Usetest.eachand data-driven tests to reduce boilerplate when testing multiple similar cases
Files:
test/js/bun/util/stringWidth.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}
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test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Usebun:testwith 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 useport: 0to get a random port
Prefer concurrent tests over sequential tests usingtest.concurrentordescribe.concurrentwhen multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, usebunExeandbunEnvfromharnessto ensure the same build of Bun is used and debug logging is silenced
Use-eflag for single-file tests when spawning Bun processes
UsetempDir()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, usePromise.withResolversto create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
UseBuffer.alloc(count, fill).toString()instead of'A'.repeat(count)to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Usedescribeblocks for grouping related tests
Always useawait usingorusingto 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
Usedescribe.each()for parameterized tests
UsetoMatchSnapshot()for snapshot testing
UsebeforeAll(),afterEach(),beforeEach()for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup inafterEach()
Files:
test/js/bun/util/stringWidth.test.ts
test/**/*.test.{ts,tsx}
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test/**/*.test.{ts,tsx}: For single-file tests in Bun test suite, prefer using-eflag overtempDir
For multi-file tests in Bun test suite, prefer usingtempDirandBun.spawn
Always useport: 0when spawning servers in tests - do not hardcode ports or use custom random port functions
UsenormalizeBunSnapshotto normalize snapshot output in tests instead of manual output comparison
Never write tests that check for no 'panic', 'uncaught exception', or similar strings in test output - that is not a valid test
UsetempDirfromharnessto create temporary directories in tests - do not usetmpdirSyncorfs.mkdtempSync
In tests, callexpect(stdout).toBe(...)beforeexpect(exitCode).toBe(0)when spawning processes for more useful error messages on failure
Do not write flaky tests - do not usesetTimeoutin tests; insteadawaitthe condition to be met since you're testing the CONDITION, not TIME PASSING
Verify your test fails withUSE_SYSTEM_BUN=1 bun test <file>and passes withbun bd test <file>- tests are not valid if they pass withUSE_SYSTEM_BUN=1
Avoid shell commands in tests - do not usefindorgrep; use Bun's Glob and built-in tools instead
Test files must end in.test.tsor.test.tsxand be created in the appropriate test folder structure
Files:
test/js/bun/util/stringWidth.test.ts
src/**/*.{cpp,zig}
📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)
src/**/*.{cpp,zig}: Usebun bdorbun run build:debugto build debug versions for C++ and Zig source files; creates debug build at./build/debug/bun-debug
Run tests usingbun bd test <test-file>with the debug build; never usebun testdirectly as it will not include your changes
Execute files usingbun bd <file> <...args>; never usebun <file>directly as it will not include your changes
Enable debug logs for specific scopes usingBUN_DEBUG_$(SCOPE)=1environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required
Files:
src/string/immutable/visible.zig
src/**/*.zig
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Use
bun.Output.scoped(.${SCOPE}, .hidden)for creating debug logs in Zig codeImplement 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@importat the bottom of the file (auto formatter will move them automatically)Be careful with memory management in Zig code - use defer for cleanup with allocators
Files:
src/string/immutable/visible.zig
**/*.zig
📄 CodeRabbit inference engine (.cursor/rules/zig-javascriptcore-classes.mdc)
**/*.zig: Expose generated bindings in Zig structs usingpub const js = JSC.Codegen.JS<ClassName>with trait conversion methods:toJS,fromJS, andfromJSDirect
Use consistent parameter nameglobalObjectinstead ofctxin Zig constructor and method implementations
Usebun.JSError!JSValuereturn type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup usingdeinit()method that releases resources, followed byfinalize()called by the GC that invokesdeinit()and frees the pointer
UseJSC.markBinding(@src())in finalize methods for debugging purposes before callingdeinit()
For methods returning cached properties in Zig, declare external C++ functions usingextern fnandcallconv(JSC.conv)calling convention
Implement getter functions with naming patternget<PropertyName>in Zig that acceptthisandglobalObjectparameters and returnJSC.JSValue
Access JavaScript CallFrame arguments usingcallFrame.argument(i), check argument count withcallFrame.argumentCount(), and getthiswithcallFrame.thisValue()
For reference-counted objects, use.deref()in finalize instead ofdestroy()to release references to other JS objects
Files:
src/string/immutable/visible.zig
🧠 Learnings (12)
📓 Common learnings
Learnt from: pfgithub
Repo: oven-sh/bun PR: 24212
File: src/cli/publish_command.zig:782-788
Timestamp: 2025-10-30T21:52:04.707Z
Learning: In the Bun codebase (oven-sh/bun), `enable_ansi_colors` flags are used to gate both ANSI color codes and Unicode box-drawing characters/emoji. This is the established pattern across the codebase.
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: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.
📚 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 `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
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/css.test.ts : Organize CSS tests in css.test.ts for tests concerning bundling bugs with CSS files
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Verify your test fails with `USE_SYSTEM_BUN=1 bun test <file>` and passes with `bun bd test <file>` - tests are not valid if they pass with `USE_SYSTEM_BUN=1`
Applied to files:
test/js/bun/util/stringWidth.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: Ensure V8 API tests compare identical C++ code output between Node.js and Bun through the test suite validation process
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-10-08T13:48:02.430Z
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 23373
File: test/js/bun/tarball/extract.test.ts:107-111
Timestamp: 2025-10-08T13:48:02.430Z
Learning: In Bun's test runner, use `expect(async () => { await ... }).toThrow()` to assert async rejections. Unlike Jest/Vitest, Bun does not require `await expect(...).rejects.toThrow()` - the async function wrapper with `.toThrow()` is the correct pattern for async error assertions in Bun tests.
Applied to files:
test/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-09-07T22:26:50.213Z
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 22478
File: test/regression/issue/22475.test.ts:0-0
Timestamp: 2025-09-07T22:26:50.213Z
Learning: The `toBeDate()` matcher is acceptable and supported in Bun's test suite - don't suggest replacing it with `toBeInstanceOf(Date)`.
Applied to files:
test/js/bun/util/stringWidth.test.ts
🔇 Additional comments (10)
test/js/bun/util/stringWidth.test.ts (4)
158-259: Comprehensive zero-width character test coverage.This test suite thoroughly covers the expanded zero-width character handling including soft hyphen, word joiner, Arabic formatting characters, Indic script combining marks, and tag characters. The tests align well with the implementation changes in
visible.zig.
360-436: Excellent emoji handling test coverage.The emoji tests comprehensively cover:
- Basic emoji (width 2)
- Flag emoji (regional indicator pairs → width 2, single → width 1)
- Skin tone modifiers
- ZWJ sequences (family, professions)
- Keycap sequences
- Variation selectors (VS15 for text, VS16 for emoji presentation)
These tests align with the
GraphemeStateimplementation.
340-358: Verify OSC sequence handling with ST terminator.The tests for OSC sequences with ST terminator (ESC ) look correct. However, ensure the implementation correctly handles the backslash character after ESC in all cases—specifically when ESC and
\are processed in different iterations of the UTF-16 width loop.#!/bin/bash # Verify the OSC test expectations match what Bun actually produces # This tests the ST terminator handling cat << 'EOF' > /tmp/osc_test.ts // Test OSC with ST terminator const str1 = "\x1b]8;;https://example.com\x1b\\link\x1b]8;;\x1b\\"; console.log("OSC with ST:", Bun.stringWidth(str1), "expected: 4"); const str2 = "\x1b]8;;url\x07link\x1b]8;;\x07"; console.log("OSC with BEL:", Bun.stringWidth(str2), "expected: 4"); // Mixed OSC and CSI const str3 = "\x1b[31m\x1b]8;;url\x07red link\x1b]8;;\x07\x1b[0m"; console.log("Mixed:", Bun.stringWidth(str3), "expected: 8"); EOF echo "Running OSC tests..." bun /tmp/osc_test.ts
642-653: The expected width of 2997 is correct for the mixed escape sequences test.The calculation accurately reflects how the stringWidth function handles pattern boundaries. When the incomplete CSI (\x1b[) at the end of each pattern meets the CSI (\x1b[31m) at the start of the next pattern, the second [ terminates the first CSI, leaving the subsequent "31m" (3 characters) visible. With 1000 pattern repetitions, there are 999 boundaries, each contributing 3 visible characters: 999 × 3 = 2997.
src/string/immutable/visible.zig (6)
11-13: Correct soft hyphen handling.Adding U+00AD (soft hyphen) as zero-width is correct—it's an invisible formatting character used for optional line breaks.
49-84: Comprehensive zero-width character coverage.The expanded ranges correctly cover:
- Lone surrogates (U+D800–U+DFFF) as zero-width
- Arabic formatting characters
- Indic script combining marks (with efficient offset calculation)
- Thai/Lao combining marks
- Combining Diacritical Marks Extended/Supplement
- Tag characters (U+E0000–U+E007F)
776-903: Well-designed GraphemeState for complex emoji width calculation.The
GraphemeStatestruct correctly handles:
- Regional indicator pairs (flags) → width 2
- Keycap sequences → width 2
- Skin tone modifiers with emoji base → width 2
- ZWJ sequences → width 2
- Variation selector logic (VS15 for text, VS16 for emoji presentation)
- Proper handling of digits/ASCII with VS16 (remain width 1)
The use of saturating addition (
+|=) at line 813 prevents overflow. The logic flow inwidth()correctly prioritizes special cases.
1018-1019: Correct final grapheme width finalization.Adding the width of the final grapheme after the loop ensures the last grapheme cluster is properly counted. This is necessary because width is accumulated on grapheme breaks, which wouldn't include the trailing grapheme.
691-694: Latin1 width scalar correctly handles soft hyphen.The updated condition correctly treats soft hyphen (0xAD) as zero-width alongside control characters.
1001-1002: Lone surrogate handling is correct.The
is_leadflag properly identifies unpaired high surrogates. It's set totruein two cases: (1) a high surrogate (0xD800–0xDBFF) with no following code unit, and (2) a high surrogate followed by a non-low-surrogate. The condition on line 1002 correctly skips these cases along with other invalid sequences (replacement.fail), treating lone surrogates as zero-width, which is consistent with the display width calculation.
| test("very long strings", () => { | ||
| const long = "a".repeat(10000); | ||
| expect(Bun.stringWidth(long)).toBe(10000); | ||
|
|
||
| const longEmoji = "😀".repeat(1000); | ||
| expect(Bun.stringWidth(longEmoji)).toBe(2000); | ||
| }); |
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🧹 Nitpick | 🔵 Trivial
Use Buffer.alloc for single-byte character repetition in stress tests.
Per coding guidelines, ''.repeat() is slow in debug JavaScriptCore builds. For single-byte ASCII characters, use Buffer.alloc instead.
test("very long strings", () => {
- const long = "a".repeat(10000);
+ const long = Buffer.alloc(10000, "a").toString();
expect(Bun.stringWidth(long)).toBe(10000);
const longEmoji = "😀".repeat(1000);
expect(Bun.stringWidth(longEmoji)).toBe(2000);
});Note: The emoji .repeat() is fine since Buffer.alloc cannot handle multi-byte characters.
🤖 Prompt for AI Agents
In test/js/bun/util/stringWidth.test.ts around lines 494 to 500, the test uses
"a".repeat(10000) which is slow in debug JSC builds; replace the single-byte
ASCII repetition with a Buffer allocation filled with 'a' of length 10000 and
convert it to a string for the test, leaving the emoji.repeat() case unchanged
since Buffer.alloc can't handle multi-byte characters.
| test("many ESC characters without valid sequences", () => { | ||
| // Many bare ESC characters - should not hang | ||
| const input = "\x1b".repeat(10000); | ||
| // Each ESC is a control character with width 0 | ||
| expect(Bun.stringWidth(input)).toBe(0); | ||
| }); |
There was a problem hiding this comment.
🧹 Nitpick | 🔵 Trivial
Use Buffer.alloc for ESC character repetition.
Similar to above, this single-byte repetition can use Buffer.alloc for better debug build performance.
test("many ESC characters without valid sequences", () => {
// Many bare ESC characters - should not hang
- const input = "\x1b".repeat(10000);
+ const input = Buffer.alloc(10000, 0x1b).toString();
// Each ESC is a control character with width 0
expect(Bun.stringWidth(input)).toBe(0);
});📝 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.
| test("many ESC characters without valid sequences", () => { | |
| // Many bare ESC characters - should not hang | |
| const input = "\x1b".repeat(10000); | |
| // Each ESC is a control character with width 0 | |
| expect(Bun.stringWidth(input)).toBe(0); | |
| }); | |
| test("many ESC characters without valid sequences", () => { | |
| // Many bare ESC characters - should not hang | |
| const input = Buffer.alloc(10000, 0x1b).toString(); | |
| // Each ESC is a control character with width 0 | |
| expect(Bun.stringWidth(input)).toBe(0); | |
| }); |
🤖 Prompt for AI Agents
In test/js/bun/util/stringWidth.test.ts around lines 512 to 517, replace the
string repetition of ESC ("\x1b".repeat(10000)) with a Buffer allocated and
filled with the ESC byte for better debug-build performance; create the input
using Buffer.alloc(10000, 0x1b) and keep the same assertion that
Bun.stringWidth(input) returns 0.
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Actionable comments posted: 4
♻️ Duplicate comments (2)
test/js/bun/util/stringWidth.test.ts (2)
497-503: UseBuffer.allocfor single-byte repetition in stress tests.Per coding guidelines,
''.repeat()is slow in debug JavaScriptCore builds. For single-byte ASCII characters, useBuffer.allocinstead.Apply this diff:
test("very long strings", () => { - const long = "a".repeat(10000); + const long = Buffer.alloc(10000, "a").toString(); expect(Bun.stringWidth(long)).toBe(10000); const longEmoji = "😀".repeat(1000); expect(Bun.stringWidth(longEmoji)).toBe(2000); });Note: The emoji
.repeat()is fine sinceBuffer.alloccannot handle multi-byte characters.Based on coding guidelines for test files.
515-520: UseBuffer.allocfor ESC character repetition.Similar to above, this single-byte repetition can use
Buffer.allocfor better debug build performance.Apply this diff:
test("many ESC characters without valid sequences", () => { // Many bare ESC characters - should not hang - const input = "\x1b".repeat(10000); + const input = Buffer.alloc(10000, 0x1b).toString(); // Each ESC is a control character with width 0 expect(Bun.stringWidth(input)).toBe(0); });Based on coding guidelines for test files.
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📓 Path-based instructions (6)
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 frombun:test
Usetest.eachand data-driven tests to reduce boilerplate when testing multiple similar cases
Files:
test/js/bun/util/stringWidth.test.ts
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}
📄 CodeRabbit inference engine (test/CLAUDE.md)
test/**/*.test.{ts,js,jsx,tsx,mjs,cjs}: Usebun:testwith 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 useport: 0to get a random port
Prefer concurrent tests over sequential tests usingtest.concurrentordescribe.concurrentwhen multiple tests spawn processes or write files, unless it's very difficult to make them concurrent
When spawning Bun processes in tests, usebunExeandbunEnvfromharnessto ensure the same build of Bun is used and debug logging is silenced
Use-eflag for single-file tests when spawning Bun processes
UsetempDir()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, usePromise.withResolversto create a promise that can be resolved or rejected from a callback
Do not set a timeout on tests. Bun already has timeouts
UseBuffer.alloc(count, fill).toString()instead of'A'.repeat(count)to create repetitive strings in tests, as ''.repeat is very slow in debug JavaScriptCore builds
Usedescribeblocks for grouping related tests
Always useawait usingorusingto 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
Usedescribe.each()for parameterized tests
UsetoMatchSnapshot()for snapshot testing
UsebeforeAll(),afterEach(),beforeEach()for setup/teardown in tests
Track resources (servers, clients) in arrays for cleanup inafterEach()
Files:
test/js/bun/util/stringWidth.test.ts
test/**/*.test.{ts,tsx}
📄 CodeRabbit inference engine (CLAUDE.md)
test/**/*.test.{ts,tsx}: For single-file tests in Bun test suite, prefer using-eflag overtempDir
For multi-file tests in Bun test suite, prefer usingtempDirandBun.spawn
Always useport: 0when spawning servers in tests - do not hardcode ports or use custom random port functions
UsenormalizeBunSnapshotto normalize snapshot output in tests instead of manual output comparison
Never write tests that check for no 'panic', 'uncaught exception', or similar strings in test output - that is not a valid test
UsetempDirfromharnessto create temporary directories in tests - do not usetmpdirSyncorfs.mkdtempSync
In tests, callexpect(stdout).toBe(...)beforeexpect(exitCode).toBe(0)when spawning processes for more useful error messages on failure
Do not write flaky tests - do not usesetTimeoutin tests; insteadawaitthe condition to be met since you're testing the CONDITION, not TIME PASSING
Verify your test fails withUSE_SYSTEM_BUN=1 bun test <file>and passes withbun bd test <file>- tests are not valid if they pass withUSE_SYSTEM_BUN=1
Avoid shell commands in tests - do not usefindorgrep; use Bun's Glob and built-in tools instead
Test files must end in.test.tsor.test.tsxand be created in the appropriate test folder structure
Files:
test/js/bun/util/stringWidth.test.ts
src/**/*.{cpp,zig}
📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)
src/**/*.{cpp,zig}: Usebun bdorbun run build:debugto build debug versions for C++ and Zig source files; creates debug build at./build/debug/bun-debug
Run tests usingbun bd test <test-file>with the debug build; never usebun testdirectly as it will not include your changes
Execute files usingbun bd <file> <...args>; never usebun <file>directly as it will not include your changes
Enable debug logs for specific scopes usingBUN_DEBUG_$(SCOPE)=1environment variable
Code generation happens automatically as part of the build process; no manual code generation commands are required
Files:
src/string/immutable/visible.zig
src/**/*.zig
📄 CodeRabbit inference engine (.cursor/rules/building-bun.mdc)
Use
bun.Output.scoped(.${SCOPE}, .hidden)for creating debug logs in Zig codeImplement 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@importat the bottom of the file (auto formatter will move them automatically)Be careful with memory management in Zig code - use defer for cleanup with allocators
Files:
src/string/immutable/visible.zig
**/*.zig
📄 CodeRabbit inference engine (.cursor/rules/zig-javascriptcore-classes.mdc)
**/*.zig: Expose generated bindings in Zig structs usingpub const js = JSC.Codegen.JS<ClassName>with trait conversion methods:toJS,fromJS, andfromJSDirect
Use consistent parameter nameglobalObjectinstead ofctxin Zig constructor and method implementations
Usebun.JSError!JSValuereturn type for Zig methods and constructors to enable proper error handling and exception propagation
Implement resource cleanup usingdeinit()method that releases resources, followed byfinalize()called by the GC that invokesdeinit()and frees the pointer
UseJSC.markBinding(@src())in finalize methods for debugging purposes before callingdeinit()
For methods returning cached properties in Zig, declare external C++ functions usingextern fnandcallconv(JSC.conv)calling convention
Implement getter functions with naming patternget<PropertyName>in Zig that acceptthisandglobalObjectparameters and returnJSC.JSValue
Access JavaScript CallFrame arguments usingcallFrame.argument(i), check argument count withcallFrame.argumentCount(), and getthiswithcallFrame.thisValue()
For reference-counted objects, use.deref()in finalize instead ofdestroy()to release references to other JS objects
Files:
src/string/immutable/visible.zig
🧠 Learnings (30)
📓 Common learnings
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: pfgithub
Repo: oven-sh/bun PR: 24212
File: src/cli/publish_command.zig:782-788
Timestamp: 2025-10-30T21:52:04.707Z
Learning: In the Bun codebase (oven-sh/bun), `enable_ansi_colors` flags are used to gate both ANSI color codes and Unicode box-drawing characters/emoji. This is the established pattern across the codebase.
📚 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:
a.jstest/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-11-06T00:58:23.965Z
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 24417
File: test/js/bun/spawn/spawn.test.ts:903-918
Timestamp: 2025-11-06T00:58:23.965Z
Learning: In Bun test files, `await using` with spawn() is appropriate for long-running processes that need guaranteed cleanup on scope exit or when explicitly testing disposal behavior. For short-lived processes that exit naturally (e.g., console.log scripts), the pattern `const proc = spawn(...); await proc.exited;` is standard and more common, as evidenced by 24 instances vs 4 `await using` instances in test/js/bun/spawn/spawn.test.ts.
Applied to files:
a.js
📚 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:
a.js
📚 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:
a.js
📚 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:
a.jstest/js/bun/util/stringWidth.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: Write JS builtins for Bun's Node.js compatibility and APIs, and run `bun bd` after changes
Applied to files:
a.js
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : For multi-file tests in Bun test suite, prefer using `tempDir` and `Bun.spawn`
Applied to files:
a.js
📚 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:
a.js
📚 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:
a.jstest/js/bun/util/stringWidth.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:
a.js
📚 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:
a.js
📚 Learning: 2025-09-02T05:33:37.517Z
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 22323
File: test/js/web/websocket/websocket-subprotocol.test.ts:74-75
Timestamp: 2025-09-02T05:33:37.517Z
Learning: In Bun's runtime, `await using` with Node.js APIs like `net.createServer()` is properly supported and should not be replaced with explicit cleanup. Bun has extended Node.js APIs with proper async dispose support.
Applied to files:
a.js
📚 Learning: 2025-09-02T06:10:17.252Z
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 22323
File: test/js/web/websocket/websocket-subprotocol-strict.test.ts:80-91
Timestamp: 2025-09-02T06:10:17.252Z
Learning: Bun's WebSocket implementation includes a terminate() method, which is available even though it's not part of the standard WebSocket API. This method can be used in Bun test files and applications for immediate WebSocket closure.
Applied to files:
a.js
📚 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 `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
Applied to files:
test/js/bun/util/stringWidth.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/css.test.ts : Organize CSS tests in css.test.ts for tests concerning bundling bugs with CSS files
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Use `normalizeBunSnapshot` to normalize snapshot output in tests instead of manual output comparison
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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 JSC intrinsics (prefixed with `$`) such as `$Array.from()`, `$isCallable()`, and `$newArrayWithSize()` for performance-critical operations
Applied to files:
test/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-09-12T18:16:50.754Z
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.
Applied to files:
test/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Verify your test fails with `USE_SYSTEM_BUN=1 bun test <file>` and passes with `bun bd test <file>` - tests are not valid if they pass with `USE_SYSTEM_BUN=1`
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-09-30T22:53:19.887Z
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.
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.test.ts
📚 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} : 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`
Applied to files:
DESIGN.md
📚 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:
DESIGN.md
📚 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:
DESIGN.md
🪛 markdownlint-cli2 (0.18.1)
DESIGN.md
15-15: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
34-34: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
73-73: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
119-119: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
158-158: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
223-223: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
223-223: Fenced code blocks should have a language specified
(MD040, fenced-code-language)
232-232: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
245-245: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
264-264: Fenced code blocks should be surrounded by blank lines
(MD031, blanks-around-fences)
🔇 Additional comments (7)
undici (1)
1-1: Clarify the necessity and scope of the submodule update.The PR objectives focus on improving
Bun.stringWidth(zero-width characters, ANSI/OSC sequences, emoji, tests), but the rationale for updating the undici submodule is not mentioned. Undici is an HTTP client library and appears unrelated to string width improvements.Please confirm:
- Is this submodule update necessary for the stringWidth changes to function correctly?
- Was this update intentional or incidental?
- If intentional, what specific change in the commit (e.g., e3fedb0...) supports the stringWidth improvements?
If this update is unrelated to the PR objectives, consider removing it or addressing it in a separate PR to keep this change focused.
src/string/immutable/visible.zig (5)
11-88: LGTM! Comprehensive zero-width character handling.The extended zero-width detection properly covers all the categories mentioned in the PR objectives:
- Soft hyphen, word joiner, invisible operators
- Lone surrogates
- Arabic formatting characters
- Indic script combining marks (clever bit-level logic for U+0900-0D4F blocks)
- Thai and Lao combining marks
- Extended and Supplement diacritical marks
- Tag characters
The Indic script logic using
cp & 0x7fis an efficient way to handle multiple Unicode blocks with similar structure.
776-927: Well-structured GraphemeState implementation.The new
GraphemeStatestruct properly encapsulates complex grapheme-cluster width logic for emoji and combining sequences. Key strengths:
- Fast path optimization for ASCII in
reset()(lines 798-809)- Comprehensive flag tracking for emoji components (keycaps, skin tones, ZWJ, variation selectors, regional indicators)
- Correct priority order in
width()method: regional indicator pairs → keycaps → single RI → skin tone modifiers → ZWJ sequences → variation selectors → fallback- Efficient use of ICU's
UCHAR_EMOJIproperty for accurate emoji detectionThe public API exposure as
visible.GraphemeStateallows reuse in other parts of the codebase.
696-744: Improved ANSI escape sequence handling.The enhanced CSI and OSC sequence stripping properly handles:
CSI sequences (lines 709-719):
- All final bytes in range 0x40-0x7E per ECMA-48, not just 'm' for colors
- Now strips cursor movement, erase, scroll, and other CSI commands
OSC sequences (lines 720-735):
- Both BEL (0x07) and ST (ESC ) terminators
- Correctly advances by 2 bytes for ST terminator (line 731)
- Handles OSC 8 hyperlinks and other OSC codes
The past review comment about ST terminator handling has been properly addressed.
929-1069: Excellent GraphemeState-based refactoring.The refactored UTF-16 width calculation properly:
Fast path optimization (lines 944-970):
- Bulk processes ASCII when not in escape sequences
- Correctly handles the last character separately in case combining marks follow
- Significant performance improvement for ASCII-heavy strings
State machine improvements:
- Separate flags for CSI (
saw_csi) and OSC (saw_osc) sequences- Proper handling of ESC ESC pattern (line 1017-1020)
- All CSI final bytes (0x40-0x7E) correctly terminate sequences
Grapheme clustering:
- Uses
GraphemeStateto accumulate codepoints within graphemes- Calls
grapheme.graphemeBreak()to determine boundaries- Properly skips invalid UTF-16 and lone surrogates (lines 1049-1051)
Final grapheme handling (lines 1066-1067):
- Correctly adds the last grapheme's width after the loop
- Essential to avoid losing the final grapheme
The refactoring maintains correctness while adding support for complex emoji sequences.
691-694: Correct soft hyphen handling in Latin1 path.The addition of soft hyphen (0xAD) to the zero-width check properly aligns the Latin1 fast path with the general zero-width detection in
isZeroWidthCodepointType. This ensures consistent behavior across all code paths.a.js (1)
1-24: Question: Is this file relevant to the PR objectives?This example file demonstrates
Bun.TerminalAPI usage but appears unrelated to the stringWidth improvements described in the PR objectives (zero-width characters, ANSI sequences, emoji handling). Was this file accidentally included?⛔ Skipped due to learnings
Learnt from: pfgithub Repo: oven-sh/bun PR: 24212 File: src/cli/publish_command.zig:782-788 Timestamp: 2025-10-30T21:52:04.707Z Learning: In the Bun codebase (oven-sh/bun), `enable_ansi_colors` flags are used to gate both ANSI color codes and Unicode box-drawing characters/emoji. This is the established pattern across the codebase.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;`.Learnt from: markovejnovic Repo: oven-sh/bun PR: 24417 File: test/js/bun/spawn/spawn.test.ts:903-918 Timestamp: 2025-11-06T00:58:23.965Z Learning: In Bun test files, `await using` with spawn() is appropriate for long-running processes that need guaranteed cleanup on scope exit or when explicitly testing disposal behavior. For short-lived processes that exit naturally (e.g., console.log scripts), the pattern `const proc = spawn(...); await proc.exited;` is standard and more common, as evidenced by 24 instances vs 4 `await using` instances in test/js/bun/spawn/spawn.test.ts.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 stderrLearnt 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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🧠 Learnings (1)
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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: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.
🔇 Additional comments (5)
src/string/immutable/visible.zig (5)
11-88: Comprehensive zero-width character handling improvements look good.The expanded coverage now includes soft hyphen, word joiner, Arabic formatting characters, Indic/Thai/Lao combining marks, extended diacritical marks, tag characters, and surrogates. The efficient bitmask logic for Indic scripts (lines 58-64) is well-designed.
Note: Treating lone surrogates (lines 49-51) as zero-width is a breaking change documented in the PR summary—typical behavior would render them as U+FFFD with width 1.
691-744: ANSI escape sequence handling significantly improved.The CSI enhancement (lines 709-719) now correctly strips all CSI sequences (cursor movement, erase, scroll, etc.) by recognizing any final byte in range 0x40-0x7E, not just SGR. The OSC sequence support (lines 720-735) properly handles both BEL and ST terminators, enabling correct width calculation for OSC 8 hyperlinks.
The soft hyphen update (line 693) maintains consistency with the expanded zero-width classification.
776-892: Clarify intended visibility of GraphemeState.The AI summary indicates "GraphemeState made publicly accessible via the visible module," but line 792 declares it as
const GraphemeStatewithout thepubkeyword. This makes it inaccessible outside thevisiblestruct.If GraphemeState is intended as a public API (e.g., for external grapheme-aware width calculations), add
pubto line 792:- const GraphemeState = struct { + pub const GraphemeState = struct {If it's intentionally private for internal use only, the implementation is correct but the AI summary should be updated.
The grapheme width calculation logic (lines 840-866) comprehensively handles regional indicator pairs, keycaps, emoji with skin tones/ZWJ, and variation selectors—well done!
920-957: Excellent fast-path optimization for bulk ASCII processing.The optimization (lines 936-957) cleverly handles common-case ASCII strings by:
- Flushing any pending grapheme from previous non-ASCII processing
- Counting all but the last ASCII character in bulk using SIMD
- Holding the last character in
grapheme_statein case a combining mark follows- Adding the final character's width at function end (line 1054)
This avoids double-counting and correctly handles combining marks that might follow ASCII characters. The condition
!exclude_ansi_colors(line 938) is correct—when excluding ANSI codes, per-character ESC detection is required, preventing the fast path.
959-1056: Main loop correctly handles escape sequences and grapheme boundaries.The OSC handling (lines 963-983) properly detects both BEL and ST terminators, and correctly waits for '' after ESC before exiting OSC mode (lines 976-979). The CSI handling (lines 984-994) recognizes all final bytes in range 0x40-0x7E. Consecutive ESC sequences (lines 1004-1007) are handled correctly by keeping
saw_1b = true.The grapheme processing (lines 1014-1024, 1041-1051) properly maintains state across codepoints and adds the final grapheme width at line 1054.
Surrogate handling note: Lines 1036-1037 skip invalid sequences and lone surrogates, treating them as zero-width. This aligns with the expanded
isZeroWidthCodepointType(lines 49-51) and is documented as a breaking change in the PR summary—most terminals would render lone surrogates as U+FFFD with width 1.
| /// Count printable ASCII characters (0x20-0x7E) in a UTF-16 slice using SIMD | ||
| fn countPrintableAscii16(input: []const u16) usize { | ||
| var total: usize = 0; | ||
| var remaining = input; | ||
|
|
||
| // Process 8 u16 values at a time using SIMD | ||
| const vec_len = 8; | ||
| while (remaining.len >= vec_len) { | ||
| const chunk: @Vector(vec_len, u16) = remaining[0..vec_len].*; | ||
| const low: @Vector(vec_len, u16) = @splat(0x20); | ||
| const high: @Vector(vec_len, u16) = @splat(0x7F); | ||
| const ge_low = chunk >= low; | ||
| const lt_high = chunk < high; | ||
| const printable = @select(bool, ge_low, lt_high, @as(@Vector(vec_len, bool), @splat(false))); | ||
| total += @popCount(@as(u8, @bitCast(printable))); | ||
| remaining = remaining[vec_len..]; | ||
| } | ||
|
|
||
| // Handle remaining elements | ||
| for (remaining) |c| { | ||
| total += @intFromBool(c >= 0x20 and c < 0x7F); | ||
| } | ||
|
|
||
| return total; | ||
| } |
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Potential issue with boolean vector bitcast.
Line 908 bitcasts @Vector(8, bool) to u8 and uses @popCount to count true values. This assumes each bool occupies exactly 1 bit, but Zig's boolean vector representation is implementation-defined and may use 1 byte per element, causing the bitcast to truncate and produce incorrect counts.
Use @reduce for a portable solution:
- const printable = @select(bool, ge_low, lt_high, @as(@Vector(vec_len, bool), @splat(false)));
- total += @popCount(@as(u8, @bitCast(printable)));
+ const printable_int = @select(u16, ge_low and lt_high,
+ @as(@Vector(vec_len, u16), @splat(1)),
+ @as(@Vector(vec_len, u16), @splat(0)));
+ total += @reduce(.Add, printable_int);This counts without relying on specific boolean vector layout.
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🧠 Learnings (1)
📓 Common learnings
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: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.
🔇 Additional comments (6)
src/string/immutable/visible.zig (6)
11-88: LGTM - Comprehensive zero-width codepoint coverage.The expanded zero-width handling correctly covers soft hyphen, word joiner, surrogates, Arabic formatting characters, Indic combining marks, Thai/Lao combining marks, extended diacritical marks, and tag characters. These additions align with the PR objectives and Unicode standards for non-displaying characters.
692-693: LGTM - Consistent soft hyphen handling.The soft hyphen (0xAD) is correctly treated as zero-width, consistent with the addition in
isZeroWidthCodepointType.
707-735: LGTM - Robust ANSI escape sequence handling.The enhanced CSI handling correctly excludes all CSI final bytes (0x40-0x7E), and the new OSC sequence support properly handles both BEL and ST terminators. The Latin-1 path correctly advances past both characters of the ST terminator (ESC ).
776-892: Excellent GraphemeState design for emoji-aware width calculation.The
GraphemeStatestructure is well-designed with efficient bit packing inPackedStateand comprehensive emoji handling. The width calculation correctly handles regional indicator pairs (flags), keycap sequences, skin tone modifiers, ZWJ sequences, and variation selectors. Using ICU'sUCHAR_EMOJIproperty ensures accurate emoji detection.The public API exposure aligns with the PR objectives and provides a solid foundation for grapheme-aware width calculations.
894-918: LGTM - Efficient SIMD optimization for ASCII counting.The
countPrintableAscii16function uses SIMD effectively to count printable ASCII characters (0x20-0x7E) in UTF-16 strings, processing 8 characters at a time with vector comparisons and popcount. This is a solid performance optimization for the bulk ASCII path.
1071-1072: LGTM - Essential final grapheme width accounting.Correctly adds the width of the final grapheme cluster after the main loop completes, ensuring complex emoji sequences at the end of the string are properly counted.
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This PR significantly improves Bun.stringWidth to handle a wider variety of Unicode characters and escape sequences correctly. ## Zero-width character handling Added support for many previously unhandled zero-width characters: - Soft hyphen (U+00AD) - Word joiner and invisible operators (U+2060-U+2064) - Lone surrogates (U+D800-U+DFFF) - Arabic formatting characters (U+0600-U+0605, U+06DD, U+070F, U+08E2) - Indic script combining marks (Devanagari through Malayalam) - Thai and Lao combining marks - Combining Diacritical Marks Extended and Supplement - Tag characters (U+E0000-U+E007F) ## ANSI escape sequence handling ### CSI sequences - Now properly handles ALL CSI final bytes (0x40-0x7E), not just 'm' - This means cursor movement (A/B/C/D), erase (J/K), scroll (S/T), and other CSI commands are now correctly excluded from width calculation ### OSC sequences - Added support for OSC sequences (ESC ] ... BEL/ST) - OSC 8 hyperlinks are now properly handled - Supports both BEL (0x07) and ST (ESC \) terminators ### ESC ESC fix - Fixed state machine bug where ESC ESC would incorrectly reset state - Now correctly handles consecutive ESC characters ## Emoji handling Added proper grapheme-aware emoji width calculation: - Flag emoji (regional indicator pairs) → width 2 - Skin tone modifiers → width 2 - ZWJ sequences (family, professions, etc.) → width 2 - Keycap sequences → width 2 - Variation selectors (VS15 for text, VS16 for emoji presentation) - Uses ICU's UCHAR_EMOJI property for accurate emoji detection ## Test coverage Added comprehensive test suite with 94 tests covering: - All zero-width character categories - All CSI final bytes - OSC sequences with various terminators - Emoji edge cases (flags, skin tones, ZWJ, keycaps, variation selectors) - East Asian width (CJK, fullwidth, halfwidth katakana) - Indic and Thai script combining marks - Fuzzer-like stress tests for robustness 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>
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src/string/immutable/visible.zig (1)
894-918: Boolean vector bitcast may have implementation-defined behavior.Line 908 bitcasts
@Vector(8, bool)tou8for@popCount. While this likely works in practice (LLVM typically packs bool vectors as i1 per element), the Zig language specification doesn't guarantee this representation.Consider using
@reducefor a more portable implementation:- const printable = @select(bool, ge_low, lt_high, @as(@Vector(vec_len, bool), @splat(false))); - total += @popCount(@as(u8, @bitCast(printable))); + const printable = ge_low and lt_high; + const ones: @Vector(vec_len, u16) = @splat(1); + const zeros: @Vector(vec_len, u16) = @splat(0); + total += @reduce(.Add, @select(u16, printable, ones, zeros));Alternatively, verify this works correctly by running the test suite on different architectures.
test/js/bun/util/stringWidth.test.ts (3)
497-503: UseBuffer.allocfor single-byte character repetition.Per coding guidelines,
''.repeat()is slow in debug JavaScriptCore builds. UseBuffer.allocfor the single-byte ASCII string.test("very long strings", () => { - const long = "a".repeat(10000); + const long = Buffer.alloc(10000, "a").toString(); expect(Bun.stringWidth(long)).toBe(10000); const longEmoji = "😀".repeat(1000); expect(Bun.stringWidth(longEmoji)).toBe(2000); });Note: The emoji
.repeat()is acceptable sinceBuffer.alloccannot handle multi-byte characters.
515-520: UseBuffer.allocfor ESC character repetition.Per coding guidelines, single-byte repetition should use
Buffer.allocfor better debug build performance.test("many ESC characters without valid sequences", () => { - const input = "\x1b".repeat(10000); + const input = Buffer.alloc(10000, 0x1b).toString(); expect(Bun.stringWidth(input)).toBe(0); });
522-535: Additional single-byte repetitions could useBuffer.alloc.Lines 524 and 532 use single-byte character repetition that would benefit from
Buffer.allocin debug builds.test("CSI without final byte (unterminated)", () => { - const input = "a\x1b[" + "9".repeat(10000) + "b"; + const input = "a\x1b[" + Buffer.alloc(10000, "9").toString() + "b"; expect(Bun.stringWidth(input)).toBeGreaterThanOrEqual(1); }); test("OSC without terminator (unterminated)", () => { - const input = "a\x1b]8;;" + "x".repeat(10000); + const input = "a\x1b]8;;" + Buffer.alloc(10000, "x").toString(); expect(Bun.stringWidth(input)).toBe(1); });
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Always useport: 0when spawning servers in tests - do not hardcode ports or use custom random port functions
UsenormalizeBunSnapshotto normalize snapshot output in tests instead of manual output comparison
Never write tests that check for no 'panic', 'uncaught exception', or similar strings in test output - that is not a valid test
UsetempDirfromharnessto create temporary directories in tests - do not usetmpdirSyncorfs.mkdtempSync
In tests, callexpect(stdout).toBe(...)beforeexpect(exitCode).toBe(0)when spawning processes for more useful error messages on failure
Do not write flaky tests - do not usesetTimeoutin tests; insteadawaitthe condition to be met since you're testing the CONDITION, not TIME PASSING
Verify your test fails withUSE_SYSTEM_BUN=1 bun test <file>and passes withbun bd test <file>- tests are not valid if they pass withUSE_SYSTEM_BUN=1
Avoid shell commands in tests - do not usefindorgrep; use Bun's Glob and built-in tools instead
Test files must end in.test.tsor.test.tsxand be created in the appropriate test folder structure
Files:
test/js/bun/util/stringWidth.test.ts
🧠 Learnings (26)
📚 Learning: 2025-10-24T10:43:09.398Z
Learnt from: fmguerreiro
Repo: oven-sh/bun PR: 23774
File: src/install/PackageManager/updatePackageJSONAndInstall.zig:548-548
Timestamp: 2025-10-24T10:43:09.398Z
Learning: In Bun's Zig codebase, the `as(usize, intCast(...))` cast pattern triggers a Zig compiler bug that causes compilation to hang indefinitely when used in complex control flow contexts (loops + short-circuit operators + optional unwrapping). Avoid this pattern and use simpler alternatives like just `intCast(...)` if type casting is necessary.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-09-04T02:04:43.094Z
Learnt from: Jarred-Sumner
Repo: oven-sh/bun PR: 22278
File: src/ast/E.zig:980-1003
Timestamp: 2025-09-04T02:04:43.094Z
Learning: In Bun's Zig codebase, `as(i32, u8_or_u16_value)` is sufficient for casting u8/u16 to i32 in comparison operations. `intCast` is not required in this context, and the current casting approach compiles successfully.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-11-10T00:57:09.173Z
Learnt from: franciscop
Repo: oven-sh/bun PR: 24514
File: src/bun.js/api/crypto/PasswordObject.zig:86-101
Timestamp: 2025-11-10T00:57:09.173Z
Learning: In Bun's Zig codebase (PasswordObject.zig), when validating the parallelism parameter for Argon2, the upper limit is set to 65535 (2^16 - 1) rather than using `std.math.maxInt(u24)` because the latter triggers Zig's truncation limit checks. The value 65535 is a practical upper bound that avoids compiler issues while being sufficient for thread parallelism use cases.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-10-15T22:03:50.832Z
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 23710
File: src/envvars.zig:135-144
Timestamp: 2025-10-15T22:03:50.832Z
Learning: In src/envvars.zig, the boolean feature flag cache uses a single atomic enum and should remain monotonic. Only the string cache (which uses two atomics: ptr and len) requires acquire/release ordering to prevent torn reads.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-10-16T21:24:52.779Z
Learnt from: markovejnovic
Repo: oven-sh/bun PR: 23710
File: src/crash_handler.zig:1415-1423
Timestamp: 2025-10-16T21:24:52.779Z
Learning: When a boolean EnvVar in src/envvars.zig is defined with a default value (e.g., `.default = false`), the `get()` method returns `bool` instead of `?bool`. This means you cannot distinguish between "environment variable not set" and "environment variable explicitly set to the default value". For opt-out scenarios where detection of explicit setting is needed (like `BUN_ENABLE_CRASH_REPORTING` on platforms where crash reporting defaults to enabled), either: (1) don't provide a default value so `get()` returns `?bool`, or (2) use the returned boolean directly instead of only checking if it's true.
Applied to files:
src/string/immutable/visible.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/string/immutable/visible.zig
📚 Learning: 2025-09-02T17:14:01.470Z
Learnt from: taylordotfish
Repo: oven-sh/bun PR: 22227
File: src/ptr/shared.zig:470-470
Timestamp: 2025-09-02T17:14:01.470Z
Learning: In Zig, regular arithmetic operations (like +=) have built-in overflow detection in debug/safe builds and will panic automatically. Atomic operations (like fetchAdd) do not have this automatic safety checking, so explicit overflow checks must be added manually. This is why NonAtomicCount doesn't need explicit overflow checks while AtomicCount does.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-09-07T14:00:36.526Z
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 22258
File: src/bun.js/test/jest.zig:63-86
Timestamp: 2025-09-07T14:00:36.526Z
Learning: In Bun's Zig codebase, the established pattern for HashMap hash functions is to truncate hash values to u32, even when the underlying hash computation produces u64. This is seen throughout the codebase, such as in src/css/rules/rules.zig where u64 hashes are stored but truncated to u32 in HashMap contexts. When implementing HashContext for HashMapUnmanaged, the hash function should return u32 to match this pattern.
Applied to files:
src/string/immutable/visible.zig
📚 Learning: 2025-11-12T04:11:52.293Z
Learnt from: cirospaciari
Repo: oven-sh/bun PR: 24622
File: src/deps/uws/us_socket_t.zig:112-113
Timestamp: 2025-11-12T04:11:52.293Z
Learning: In Bun's Zig codebase, when passing u32 values to C FFI functions that expect c_uint parameters, no explicit intCast is needed because c_uint is equivalent to u32 on Bun's target platforms and Zig allows implicit coercion between equivalent types. This pattern is used consistently throughout src/deps/uws/us_socket_t.zig in functions like setTimeout, setLongTimeout, and setKeepalive.
Applied to files:
src/string/immutable/visible.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 `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
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/css.test.ts : Organize CSS tests in css.test.ts for tests concerning bundling bugs with CSS files
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Use `normalizeBunSnapshot` to normalize snapshot output in tests instead of manual output comparison
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-10-01T21:59:54.571Z
Learnt from: taylordotfish
Repo: oven-sh/bun PR: 23169
File: src/bun.js/bindings/webcore/JSDOMConvertEnumeration.h:47-74
Timestamp: 2025-10-01T21:59:54.571Z
Learning: In the new bindings generator (bindgenv2) for `src/bun.js/bindings/webcore/JSDOMConvertEnumeration.h`, the context-aware enumeration conversion overloads intentionally use stricter validation (requiring `value.isString()` without ToString coercion), diverging from Web IDL semantics. This is a design decision documented in comments.
Applied to files:
test/js/bun/util/stringWidth.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 JSC intrinsics (prefixed with `$`) such as `$Array.from()`, `$isCallable()`, and `$newArrayWithSize()` for performance-critical operations
Applied to files:
test/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-09-12T18:16:50.754Z
Learnt from: RiskyMH
Repo: oven-sh/bun PR: 22606
File: src/glob/GlobWalker.zig:449-452
Timestamp: 2025-09-12T18:16:50.754Z
Learning: For Bun codebase: prefer using `std.fs.path.sep` over manual platform separator detection, and use `bun.strings.lastIndexOfChar` instead of `std.mem.lastIndexOfScalar` for string operations.
Applied to files:
test/js/bun/util/stringWidth.test.ts
📚 Learning: 2025-12-02T05:59:51.485Z
Learnt from: CR
Repo: oven-sh/bun PR: 0
File: CLAUDE.md:0-0
Timestamp: 2025-12-02T05:59:51.485Z
Learning: Applies to test/**/*.test.{ts,tsx} : Verify your test fails with `USE_SYSTEM_BUN=1 bun test <file>` and passes with `bun bd test <file>` - tests are not valid if they pass with `USE_SYSTEM_BUN=1`
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.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/util/stringWidth.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/util/stringWidth.test.ts
📚 Learning: 2025-09-30T22:53:19.887Z
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.
Applied to files:
test/js/bun/util/stringWidth.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/util/stringWidth.test.ts
🔇 Additional comments (6)
src/string/immutable/visible.zig (4)
11-88: LGTM - Comprehensive zero-width character coverage.The expanded zero-width handling correctly covers soft hyphen, word joiner/invisible operators, surrogates, Arabic formatting, Indic combining marks, Thai/Lao marks, and tag characters. The Indic mask logic efficiently identifies combining positions within each script block.
691-694: LGTM - Soft hyphen handling added consistently.The scalar function now correctly treats soft hyphen (0xAD) as zero-width, matching the
isZeroWidthCodepointTypeimplementation.
696-744: LGTM - Robust CSI/OSC handling.The ANSI sequence handling correctly:
- Recognizes all CSI final bytes (0x40-0x7E) per ECMA-48
- Handles both OSC terminators (BEL and ST)
- Advances correctly past the ST terminator (ESC )
868-883: The fast-path range logic is correct and does not incorrectly exclude emoji.U+2600–U+26FF (Miscellaneous Symbols) are not caught by the line 875 fast-path exclusion (
cp >= 0x2C00), as 0x2600 < 0x2C00. These emoji correctly proceed to the ICU check. Test coverage confirms this: stringWidth.test.ts (lines 402, 406) actively test ☀ (U+2600) with variation selectors and expect proper width calculations.Likely an incorrect or invalid review comment.
test/js/bun/util/stringWidth.test.ts (2)
158-259: LGTM - Comprehensive zero-width character tests.The tests thoroughly cover:
- Soft hyphen, word joiner, invisible operators
- ZWS/ZWNJ/ZWJ, directional marks, BOM
- Arabic formatting characters
- Variation selectors, tag characters, surrogates
- All combining diacritical mark ranges
- Control characters (C0, DEL, C1)
261-439: LGTM - Thorough ANSI and emoji sequence coverage.Excellent test coverage for:
- All major CSI command types and final bytes
- OSC sequences with both BEL and ST terminators
- Emoji with regional indicators, skin tones, ZWJ sequences
- Variation selector behavior (VS15 for text, VS16 for emoji presentation)
|
This seems to regress string width calculation of these strings: describe("non-ASCII in escape sequences and Indic script handling", () => {
test("OSC with non-ASCII (emoji) in URL should be invisible", () => {
// Non-ASCII characters inside OSC sequence should NOT be counted
// The emoji is part of the invisible hyperlink URL
const result = Bun.stringWidth("a\x1b]8;;https://🎉\x07b");
expect(result).toBe(2); // just "ab"
});
test("OSC with CJK in URL should be invisible", () => {
// CJK character inside OSC sequence should NOT be counted
const result = Bun.stringWidth("a\x1b]8;;https://中.com\x07b");
expect(result).toBe(2); // just "ab"
});
test("Indic Avagraha (U+093D) should have width 1", () => {
// U+093D (ऽ) is Devanagari Avagraha - a visible letter (category Lo)
// The Indic heuristic incorrectly marks it as zero-width
expect(Bun.stringWidth("\u093D")).toBe(1);
expect(Bun.stringWidth("a\u093Db")).toBe(3);
});
test("Malayalam Sign Para (U+0D4F) should have width 1", () => {
// U+0D4F (൏) is Malayalam Sign Para - a visible symbol (category So)
// The Indic heuristic incorrectly marks it as zero-width
expect(Bun.stringWidth("\u0D4F")).toBe(1);
});
test("Bengali Avagraha (U+09BD) should have width 1", () => {
// U+09BD (ঽ) is Bengali Avagraha - a visible letter (category Lo)
expect(Bun.stringWidth("\u09BD")).toBe(1);
});
test("Tamil Visarga (U+0B83) should have width 1", () => {
// U+0B83 (ஃ) is Tamil Sign Visarga - a visible letter (category Lo)
expect(Bun.stringWidth("\u0B83")).toBe(1);
});
}); |
Two fixes: 1. OSC sequence handling: Non-ASCII characters (emoji, CJK) inside OSC sequences were incorrectly counted towards visible width. Added escape sequence state checks in the non-ASCII character handling path to properly skip these characters. 2. Indic script heuristic: The zero-width detection for Indic scripts was too broad, incorrectly marking visible characters as zero-width: - Avagraha (position 0x3D in each block) is a visible letter (Lo) - Signs at position 0x03 (like Tamil Visarga) are visible - Malayalam Sign Para (0x0D4F) is a visible symbol (So) Refined the heuristic to exclude these positions. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>
3 participants
This PR significantly improves
Bun.stringWidthto handle a wider variety of Unicode characters and escape sequences correctly.Zero-width character handling
Added support for many previously unhandled zero-width characters:
ANSI escape sequence handling
CSI sequences
mOSC sequences
ESC ESC fix
ESC ESCwould incorrectly reset stateEmoji handling
Added proper grapheme-aware emoji width calculation:
UCHAR_EMOJIproperty for accurate emoji detectionTest coverage
Added comprehensive test suite with 94 tests covering:
Breaking changes
This is a behavior change -
stringWidthwill return different values for some inputs. However, the new values are more accurate representations of terminal display width:🤖 Generated with Claude Code