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Data::write_format printed Location.line_text in full and indented the caret by column - 1. A location keeps the whole line for an error in the last 80 bytes of it, and a CSS location always keeps the whole line, so a syntax error at the end of a 400 KB one-line file printed 800 KB. write_format now prints at most 120 bytes of the line around the caret and indents the caret by what it printed. line_text and column do not change.
The redaction marks a secret by the key in front of it. A cut 40 bytes before the caret can drop that key and print the secret.
WalkthroughThe diagnostic formatter now limits ordinary source excerpts to 120 bytes, preserves caret positions across UTF-8 and UTF-16 boundaries, skips whitespace-only lines, and keeps redacted values fully masked. Tests cover JavaScript, CSS, package configuration, and install diagnostics. ChangesDiagnostic excerpt formatting
Suggested reviewers: Priority: ➖ Normal Merge Risk: 🔵 Low · up to Mid-line diagnostics can display the caret at the excerpt edge instead of beneath the error. This is localized but should be corrected before merge. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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StatusReproduced on 1.4.3-canary.1+b52d51348 (Linux x64): node -e 'process.stdout.write("var a = [" + "1,".repeat(200000) + "]; var b = (;")' > long-end.js
bun long-end.js 2>&1 | wc -cThe release build prints 800,159 bytes of stderr. This branch prints 352. The description has the same check for a mid-line error, a one-line CSS file and a one-line
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline nit, I traced the index arithmetic in excerpt_around_column (src/ast/lib.rs) and ruled out a few things: the saturating_sub(40) + max_len sum cannot overflow when max_len is usize::MAX, since the line_text.len() <= max_len early return takes that path first; the lo -= 1 / hi += 1 snapping cannot underflow or run past visible because is_on_char_boundary returns true at 0 and at len; and lo <= caret <= hi holds on every branch, so both visible[lo..hi] and visible[lo..caret] are in range. The reordered left/right trim is behavior-preserving since the left-trim set is a subset of the right-trim set. I did not have a debug build to run the new tests; the PR states a merge-order dependency on #41658 that a maintainer will need to sequence.
Extended reasoning...
The Rust change is about 60 lines confined to the diagnostic printer; I read excerpt_around_column, advance_utf16_columns, is_on_char_boundary, CodepointIterator::next, and the unchanged Location::init_or_null_impl window logic to check that the printer's assumptions about line_text and column match the producers. The arithmetic is bounded on every branch, including invalid UTF-8 (each edge moves at most 3 bytes) and a column past the end of the text (clamped via min(visible.len())). The test expectations for the 2-byte, 4-byte, and CSS € cases were checked by hand against the byte offsets and they line up. The remaining reasons not to approve outright are the user-visible output change (a mid-line excerpt with no leading marker, which is a design call) and the stated merge-ordering dependency on another PR, both of which need a maintainer's judgment rather than further bug hunting.
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Updated 11:35 AM PT - Sep 18th, 2026
✅ @robobun, your commit 4add19d2da0ded6a4665eaf5f7051cf03dffae26 passed in 🧪 To try this PR locally: bunx bun-pr 43313That installs a local version of the PR into your bun-43313 --bun |
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I re-reviewed this after the latest pushes and didn't find any bugs; the earlier exit-code nit is addressed by printedExcerpts now returning exitCode with every new test asserting it. Because this changes the shape of every CLI diagnostic excerpt (new 120/40-byte cut) and the PR states it must be rebased onto #41658, which edits the same statement, a human look at the ordering and the chosen constants would still be worthwhile.
What was reviewed:
excerpt_around_column/advance_utf16_columnsinsrc/ast/lib.rs: window and caret arithmetic for the short-line, long-line, trailing-whitespace, and column-past-end cases —lo/hicannot leave0..=visible.len()sinceis_on_char_boundaryreturns true at 0 and atlen, andcaretis clamped before slicing, so invalid/truncated UTF-8 cannot index out of bounds.- Redaction path:
redact_sensitive_informationforcesmax_len = usize::MAX, so thetoken =key stays visible to the masker; the new bunfig test covers a value 143 bytes past the key. - Byte-search lint: only
bun_core::trim_*,is_on_char_boundary, andCodepointIteratorare used; no deniedstdsearch primitives.
Extended reasoning...
Overview
The PR changes Data::write_format in src/ast/lib.rs so that the N | <line> / ^ excerpt for a diagnostic prints at most MAX_EXCERPT_LEN (120) bytes of line_text, starting EXCERPT_LEN_BEFORE_CARET (40) bytes before the caret or earlier when the line ends first. Two helpers were added: advance_utf16_columns walks a byte slice with bun_core::strings::CodepointIterator counting UTF-16 units (astral code points count as 2) and returns the byte offset reached, and excerpt_around_column slices the window, snaps both ends to UTF-8 char boundaries via is_on_char_boundary, right-trims it, and recomputes the caret column as the UTF-16 width of the printed bytes before the caret. Messages flagged redact_sensitive_information (bunfig.toml, .npmrc) bypass the cut. Location.line_text and column themselves are unchanged, so BuildMessage.position and the dev-server overlay are not affected. Tests: 17 new cases in test/js/bun/transpiler/parse-error-column.test.ts (build/run/CSS/install, UTF-8 2-byte and 4-byte boundaries, trailing whitespace on short and long lines, note-plus-error on one line) and one new bunfig redaction test in test/cli/install/redacted-config-logs.test.ts.
Security risks
The only security-adjacent surface is the credential-redaction path. The change explicitly disables the cut when redact_sensitive_information is set, so the key that identifies a secret cannot be sliced off before the masker sees it; the new test spawns bun install with a long token value both with NO_COLOR and FORCE_COLOR and asserts the raw value appears in neither stdout nor stderr. On the memory-safety side, I traced the index arithmetic: lo starts at hi.saturating_sub(max_len) and only decrements while is_on_char_boundary is false, which is never true at index 0; hi is capped at visible.len() and only increments while not on a boundary, which is never true at len; caret is .min(visible.len()) before visible[lo..caret], and caret >= lo holds by construction. CodepointIterator may report a width that overruns the buffer on a truncated trailing sequence, but the resulting offset is only used after clamping, so no out-of-bounds slice is reachable from malformed input. The pre-existing expect("int cast") remains guarded by location.column > 0.
Level of scrutiny
Moderate. The code is small and self-contained but is the shared output path for every diagnostic Bun prints, and it introduces a user-visible format change (long lines are now truncated). The bug-hunting run exited on dry_streak with zero findings, and my own reading of the boundary cases agrees. What remains is a judgment call, not a correctness question: the 120/40 constants, whether cutting at the printer rather than at Location creation is the right layer, and the author's own statement that #41658 must land first and that this PR needs a rebase because both edit the same statement. Those are decisions a maintainer should make, so a human look is warranted even though no defect was found.
Other factors
The one item raised in the prior review (the excerpt tests discarded proc.exited) was addressed in commit e8f7683: printedExcerpts now returns exitCode and every test asserts toBe(1) after the output expectations. Tests use Buffer.alloc fills, tempDir, test.concurrent, and drain all pipes concurrently, matching harness conventions; the reported ASAN timings (hundreds of ms per case) keep the file within budget. No CODEOWNERS rule covers the changed files, and the timeline shows no outstanding CHANGES_REQUESTED review from a third party. The existing CLI caret stays under the token... test had its expected offsets updated from 154 to 123 to match the new cut, which is consistent with the intended behavior rather than a weakened assertion.
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Two notes for the maintainer who looks at the open points from the review.
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Inline comments:
In `@src/ast/lib.rs`:
- Around line 983-985: Adjust the caret column in Data::write_format after
trimming the line prefix by subtracting the removed prefix’s UTF-16 width before
calling excerpt_around_column, while preserving correct behavior for full-line
excerpts. Strengthen the middle-error test to assert the exact caret position
rather than only checking its bounds.
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src/ast/lib.rstest/cli/install/redacted-config-logs.test.tstest/js/bun/transpiler/parse-error-column.test.ts
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Problem
Data::write_format(src/ast/lib.rs:980) printsLocation.line_textin full and indents the caret bycolumn - 1.Location::init_or_null_impl(src/ast/lib.rs:808) keeps the whole line for an error in its last 80 bytes.ErrorLocation::to_location(src/css/error.rs:185) always keeps it.Fix
write_formatprints at most 120 bytes ofline_text, from 40 bytes before the caret, or earlier when the line ends first. The caret indent is the width of the printed bytes before it.redact_sensitive_information(bunfig.toml,.npmrc) prints its line whole. The redaction knows a secret by the key in front of it, and a cut can drop that key.line_textandcolumndo not change, so the dev server overlay andBuildMessage.positionsee no change.test/js/bun/transpiler/parse-error-column.test.ts(17 new tests, 14 fail on the release build), one new test intest/cli/install/redacted-config-logs.test.ts.Background
Locationcarries a copy of its line's text, taken when the diagnostic is created.write_formatdrawsN | <text>and a^under it.columncounts UTF-16 code units from the start of the whole line.line_textstarts, so the caret can point at the token. This PR only bounds that caret line. Both PRs change the same statement, so this one needs a rebase after it.Notes
Repro:
Bytes of stderr:
long-start.jslong-mid.jslong-end.js@importafter 20,000 rules,bun buildpackage.json, 80 KB, cut short,bun installWhy 120 and 40:
init_or_null_implalready uses these numbers for a mid-line error (src/ast/lib.rs:809-810: 40 bytes before the error, 80 after). With the same numbers in the printer, an excerpt has the same size wherever the error is in the line.Not covered:
Expected ";" but found "<token>"echoes the found token whole, so a 100 KB identifier still prints 100 KB. The table and thestderr.lengthassertions in the tests use short tokens.Location.line_textstill holds the whole line for an error in the last 80 bytes and for every CSS error. To cut it at creation, each reader ofline_textmust first learn where the excerpt starts. The review on logger: indent the caret relative to the windowed line excerpt #41658 asked for that, and bake: align the error overlay underline with a windowed line excerpt #37872 does it for the dev server overlay.long-mid.jsthe caret sits at the end of the excerpt, not under the token. It was 200,000 columns to the right of it before. logger: indent the caret relative to the windowed line excerpt #41658 places it.init_or_null_implalready drops the key in front of a secret for a mid-line error inbunfig.toml. This PR does not change that cut. It only makes sure the new cut in the printer does not do the same.Merge with #41658, checked on a local merge of both branches (30 tests in
parse-error-column.test.ts, thebun-lock.test.tscaret test andredacted-config-logs.test.tspass):column - 1 - location.line_text_start_column.filland oneprintedExcerptshelper in the test file.for an error in its middleassertscaret: 4 + 40.CLI caret stays under the token for an error at the end of a long lineasserts the last 120 bytes:"1 | " + fill(119, "a") + "]",caret: 4 + 119.Behaviour at the edges, checked by hand on the debug build:
line_textputs the caret right after the text.0xF0bytes) stays bounded, because each end of the excerpt moves by at most 3 bytes.The existing test
CLI caret stays under the token for an error at the end of a long lineasserted that the whole 151-byte line is printed (token: 154). It now asserts the last 120 bytes (token: 123). The caret is still under the token.Self-reviewed: 4 concerns raised, 3 addressed. Addressed: the cut came before the redaction and printed part of a
bunfig.tomltoken (fixed, test added). The unbounded message line is now stated above. The merge with #41658 is checked and described above. Not done: the review asked to base this branch on #41658. That branch is 249 commits behind main, with another Rust toolchain and WebKit build, so this PR targets main and states the order.Suites run with the debug build:
test/js/bun/transpiler/parse-error-column.test.ts(23 pass),test/cli/install/redacted-config-logs.test.ts(17 pass),test/cli/install/bun-lock.test.ts(40 pass),test/cli/install/bun-install.test.ts -t "should report error on invalid format"(4 pass),test/regression/issue/03830.test.ts,23649.test.ts,jsx-template-string-crash.test.ts,12782.test.ts,11793.test.ts.[human-review] gate passed · iteration 1 · 3 files touched
fails on main (without fix)
passes on PR (with fix)
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