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…de frame when every frame is inside bun: or node: modules
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Status: ready for review. Head 143f017. This PR now also carries #38335 (GitHub Actions annotation and code frame caret) and #38356 (excerpt the picked frame, not frame 0), which changed the same frame-selection logic. Both are closed in its favor. See the PR description for the combined change. Reproduced on bun 1.4.3 and on main with: bun -e 'try { require("node:stream").Readable.from(42) } catch (e) { console.error(e) }'
bun -e 'try { new (require("ws").WebSocketServer)({}) } catch (e) { console.error(e) }'
bun -e 'new (require("node:worker_threads").Worker)("/nope.mjs").on("error", console.error)'
bun -e 'new (require("node:vm").Script)("[].reduce((a, b) => a)", { filename: "/virtual/r.js" }).runInThisContext({ displayErrors: false })'
printf '[].reduce((a, b) => a);\n' > reduce.js && GITHUB_ACTIONS=true bun reduce.jsThe first two print bundled Fail-before / pass-after: |
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Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to Error reporting now attributes frames and annotations to user code while avoiding builtin source previews. The covered behavior is ready to merge with no identified current risk. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Inline comments:
In `@src/jsc/VirtualMachine.rs`:
- Around line 5840-5841: Update the source URL predicate near frames[top] so
node:vm is excluded from the node: prefix match, preserving fallback source
collection for that URL while retaining the existing behavior for other node:
URLs. Add a regression test covering hidden Bun stack frames with node:vm and
verifying the documented source excerpt remains available.
In `@test/js/bun/util/inspect-error.test.js`:
- Line 465: Update the codeFrameLines filter to recognize both numbered
code-frame lines and the “- |” form emitted for invalid top-frame positions,
while preserving the existing newline splitting and filtering behavior.
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src/jsc/VirtualMachine.rstest/js/bun/util/inspect-error.test.js
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LGTM — narrow, well-placed guard on the two collect_source_lines fallbacks.
What was reviewed:
- Traced
topselection atVirtualMachine.rs:5807-5827:top_frame_is_bun_modulecan only be true when no user frame was found (frame 0 stays abun:/node:URL), so eval/new Function/node:vmand user-frame-under-builtin cases keep their excerpt;hide_bun_stackframes = falseshort-circuits it soBUN_SHOW_BUN_STACKFRAMES=1is unchanged. frames[top]access is guarded by theframes.is_empty()early return above.- Tests follow harness conventions (
await using,Promise.allon pipes, content asserted before exit code,describe.concurrent) and assert the strongest invariant — zeroN |lines plus a positive content check.
Extended reasoning...
Overview
The PR gates the two exception.collect_source_lines(...) fallback calls in remap_zig_exception (src/jsc/VirtualMachine.rs) behind a new top_frame_is_bun_module predicate. The predicate is true only when hide_bun_stackframes is on (the default) and the frame chosen for the source excerpt has a bun: or node: URL — which, given the frame-selection loop just above, only happens when every frame is a builtin and top fell through to 0. Two subprocess tests are appended to test/js/bun/util/inspect-error.test.js exercising node:worker_threads errors whose stacks contain only builtin frames.
Security risks
None. This is display-only logic in the error printer; it narrows when a source-code excerpt is emitted. No parsing of untrusted input, no allocation changes, no auth/crypto/permissions surface.
Level of scrutiny
Low-to-moderate. The change is a two-site boolean guard in a well-understood code path, deliberately narrower than the existing top_frame_is_builtin flag so eval/new Function/[source: frames keep their excerpt. I verified the interaction with the top selection loop: when a user frame exists it becomes top and its URL cannot match the prefix; when hide_bun_stackframes is off the predicate is trivially false. The frames.is_empty() early return above makes the frames[top] index safe. The four-line comment is load-bearing "why" (naming the JSC source-provider fallback as the mechanism), not narration.
Other factors
Tests are placed in the existing inspect-error.test.js, use bunExe()/bunEnv with -e, await using on the spawned process, drain all three pipes concurrently, assert output before exit code, and assert codeFrameLines(stdout) is exactly [] alongside a positive content match — a non-vacuous check that would fail on the unfixed build per the PR's USE_SYSTEM_BUN=1 claim. No CODEOWNERS entries cover the changed paths, and there are no outstanding third-party reviews on the timeline.
…ode frame, and skip the source-line fallback when every frame is a builtin The frame picker and the caret picker classified bun's modules by the bun: and node: URL prefixes only, so a throw from an internal:* module (stream validation, for example) excerpted the bundled internal source instead of the caller's line. When every frame is a builtin, the collect_source_lines fallback still excerpted frame 0's JSC source, which is the bundled module text. One helper now classifies bun:, node: and internal: URLs for all three sites, and the fallback is skipped when no user frame exists.
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Updated 9:16 PM PT - Sep 8th, 2026
❌ @robobun, your commit 143f017 has 1 failures in 🧪 To try this PR locally: bunx bun-pr 41862That installs a local version of the PR into your bun-41862 --bun |
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Code review found no new issues
No new issues were found in this update; 2 findings from earlier reviews are still open above.
Still open from earlier reviews (2):
- 🔴
src/jsc/VirtualMachine.rs:5922—Gating collect_source_lines on !top_frame_is_builtin is wider than the PR's stated intent: that flag is also set when e… - Also unresolved: 1 minor or pre-existing.
…odule, not on every frame being a builtin collect_source_lines excerpts frame 0's JSC source. Gating it on top_frame_is_builtin also dropped the excerpt of user code that has no source URL and no user frame below it (eval called directly by a timer), which the base build prints. Gate on frame 0 naming a bun:/node:/internal: module instead, and add a test for the eval case.
robobun
changed the title
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Revision summary (head 7fd25c0):
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LGTM — the latest push replaces the wide !top_frame_is_builtin gate with the narrow first_frame_is_bun_module check on frames[0] and adds the eval-via-timer test proving anonymous user code keeps its excerpt, which resolves the regression I flagged earlier.
What was reviewed: frames[0] is guarded by the frames.is_empty() early return above; the new flag reads only bun:/node:/internal: prefixes so empty/native/[source: URLs still fall through to collect_source_lines; both fallback call sites are gated identically; the third is_bun_module_url call site at ~6310 gains internal: consistently. The pre-existing thirdparty-specifier gap noted inline is unchanged but not a regression.
Extended reasoning...
Overview
The PR stops Bun's error printer from excerpting bundled builtin source when every stack frame lives inside a bun:/node:/internal: module. It extracts the two-clause prefix check into is_bun_module_url (adding internal:), applies it at all three parallel sites in remap_zig_exception and the exception printer, and introduces a first_frame_is_bun_module flag that gates both collect_source_lines fallbacks. Four subprocess tests cover the caller-frame case, two all-builtin-frames cases, and a positive control for anonymous user code.
Security risks
None. This is presentation-only logic in the error inspector — it decides whether to print a source excerpt above an error message. No untrusted input parsing, no allocation, no auth/crypto/permission surface. The only indexing added (frames[0]) is already guarded by an is_empty() early return three lines above.
Level of scrutiny
Low-to-moderate. The change is ~15 net Rust lines in a well-understood cosmetic path plus ~95 lines of tests. My earlier 🔴 finding (gating on the wider top_frame_is_builtin flag would drop excerpts for eval/new Function/node:vm code with no user frame below) was directly addressed in commit 7fd25c0: the gate now checks only is_bun_module_url(&frames[0].source_url) — the narrow condition matching exactly what collect_source_lines reads — and a new test (setTimeout(eval, 0, ...)) locks that in. The helper extraction hits every sibling site the diff touched, satisfying the "fix the whole class" rule for this diff's scope.
Other factors
Tests follow harness conventions (bunExe()/bunEnv, describe.concurrent, concurrent pipe drain, stderr/stdout asserted before exitCode, added to the existing inspect-error.test.js). No human CHANGES_REQUESTED reviews are outstanding; open bot threads are advisory. The remaining 🟣 inline note about thirdparty/ specifiers lacking a prefix is pre-existing behavior and non-blocking.
…uiltin-source-preview
…ret and the GitHub annotation, and excerpt the picked frame The code frame picker in remap_zig_exception, the caret in print_error_instance_body and print_github_annotation each had their own idea of which frames belong to the user. They now share ZigStackFrame::has_user_source() (false for bun:, node:, internal:, empty, native, unknown, [unknown] and [source:...] URLs), so all three attribute the error to the same frame: the first one whose source the user can open. collect_source_lines() takes the index of that frame and excerpts it instead of frame 0, so a node:vm script, eval or new Function source that calls into a builtin shows its own line. When the picked frame is itself one of bun's bundled modules (no user frame exists), no excerpt is collected, as before. Folds #38335 and #38356 into this branch together with their tests.
…lag, not only the URL prefix
ZigStackFrame gets an is_builtin flag that populateStackFrameMetadata
sets from the code block (bun's bundled modules are builtin executables
too, and nested functions inherit it). has_user_source() and the
excerpt gate use it, so a frame inside a src/js/thirdparty module that
runs under a bare name (ws, undici, node-fetch) is no longer taken for
the user's: new (require("ws").WebSocketServer)({}) now excerpts the
caller instead of six lines of bundled ws source. The URL prefixes stay
for frames parsed back out of an error.stack string, which carry no
code block. The field takes the padding byte before
jsc_stack_frame_index, so the struct size is unchanged.
remap_zig_exception's local is_unknown_source() moves onto
ZigStackFrame next to the other predicate.
…ts assert the builtin frame is on top The caret, vm and annotation tests now also check that the builtin's frame is listed above the user's, so they cannot pass without exercising the frame pick if the builtin ever stops showing up as a frame.
robobun
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Both concerns I raised earlier are now addressed — the excerpt gate is the narrower frames[top].is_builtin_code() (so URL-less eval/new Function keeps its excerpt, covered by the new "still excerpts user code that has no source URL" test), and bare-named thirdparty modules like ws are now caught by the is_builtin flag from unlinkedCodeBlock()->isBuiltinFunction() rather than a URL-prefix list. I found no further issues; given the mirrored FFI struct change and the frame-selection refactor across three consumers, a maintainer glance at the error-printer interaction is still worthwhile.
What was reviewed
- FFI layout:
is_builtinsits in the padding byte beforejsc_stack_frame_index;static_assert/assert_ffi_layout!(72/8) match on both sides, and the bake dev-server literal and both default constructors are updated. top as u8:frames_lenisu8on both sides sotopcannot exceed 255.- The removed
OnlySourceLinesper-frame loop only rewrote positions theOnlyPositionpass had already stored; the single-frame lookup keeps the samereferenced_source_providerref semantics.
Extended reasoning...
Overview
This PR fixes error-printer attribution when the top stack frame is a JSC builtin or a bundled Bun module: the code-frame excerpt, its caret column, and the GitHub Actions ::error annotation now come from the first user-source frame instead of frame 0. It adds an is_builtin bool to the FFI-mirrored ZigStackFrame (set from unlinkedCodeBlock()->isBuiltinFunction() in C++), consolidates three open-coded URL-prefix heuristics into is_builtin_code()/is_unknown_source()/has_user_source() on the Rust side, and threads a frame_index: u8 through ZigException__collectSourceLines/populateStackTrace(OnlySourceLines) so the excerpt is read from the frame Rust selected. New tests span bun-test.test.ts, stack.test.ts, inspect-error.test.js, and vm.test.ts.
Prior findings addressed
My two earlier findings are resolved by code changes, not just thread resolution. The first (gating on the wide !top_frame_is_builtin suppressed excerpts for anonymous eval/new Function) is fixed by introducing top_frame_is_builtin_code = hide_bun_stackframes && frames[top].is_builtin_code(), which is false for URL-less user code since is_builtin is false and no prefix matches — verified by the new eval-via-timer test in inspect-error.test.js. The second (bare-named thirdparty modules like ws slipped past URL-prefix checks) is fixed structurally: is_builtin is set from JSC's own builtin-executable flag, which is true for all src/js/ bundled modules regardless of their source URL — verified by the new WebSocketServer({}) test.
Security risks
None. This is diagnostic-output formatting and stack-frame selection; no untrusted input reaches allocation, filesystem, or network paths. The frame_index is bounds-checked in C++ (>= trace.frames_len early-returns) and top is bounded by frames_len: u8, so the as u8 narrowing cannot truncate.
Level of scrutiny
Medium-high. The FFI struct field addition is guarded by matching size/align asserts on both sides and lands in an existing padding byte, so field offsets are unchanged. The OnlySourceLines loop removal is sound: the discarded per-frame populateStackFramePosition calls with null buffers only rewrote positions already computed in the OnlyPosition pass, and nothing consumed the rewrites. The referenced_source_provider ref is still taken at most once per call and released in ZigException::deinit. Still, this reshapes control flow across a Rust/C++ boundary in the error printer and consolidates three PRs' worth of frame-selection logic — a maintainer familiar with remap_zig_exception should confirm the interaction with the sourcemap path and hide_bun_stackframes = false.
Other factors
Test coverage is thorough and hits both sides of each guard (fresh error vs. after .stack was read; JS builtin vs. node: module vs. bare-named ws vs. internal:; excerpt present vs. suppressed vs. no-location annotation). Tests follow harness conventions (bunExe()/bunEnv, -e for single-file, concurrent Promise.all on pipes, output asserted before exit code, test.each for matrices). No outstanding third-party CHANGES_REQUESTED; coderabbitai threads were resolved by a non-author. Exit reason dry_streak.
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Problem
Readable.from(42)prints19 | throw @makeErrorWithCode(112, ...)frominternal:streams/fromas the code frame.new (require("ws").WebSocketServer)({})prints bundledwssource.[].reduce((a, b) => a)insideevalprints theArray.prototype.reducesource. UnderGITHUB_ACTIONS=true,[].reduce(...)inx.jsprints::error file=,line=1,col=11, with the caret at the builtin's column.src/jsc/VirtualMachine.rskept its own URL list for "not the user's frame".remap_zig_exceptionmissedinternal:and bare-named modules. The caret loop skipped onlybun:andnode:.print_github_annotationtookframes[0].collect_source_lines(ZigException.cpp) excerpted frame 0 whatever frame was picked.Fix
ZigStackFramegets anis_builtinflag, set from JSC'sisBuiltinFunction()on the frame's code block. One predicate,has_user_source()(not builtin, nobun:/node:/internal:URL, no empty,native,unknownor[source:...]placeholder), serves all three consumers.ZigException__collectSourceLinestakes the index of the picked frame and excerpts it. When that frame is builtin code (no user frame exists), nothing is excerpted.wsslipped past a URL-prefix list) led to theis_builtinflag.inspect-error.test.js,vm.test.ts,bun-test.test.ts,stack.test.tsfail on 1.4.3 (17 of 18, one is a guard) and pass here.Background
name: messageabove theat ...list.remap_zig_exceptionpicks its frame and re-reads the file when bun transpiled it. Otherwisecollect_source_linescuts lines out of the frame'sJSC::SourceProvider.src/jsmodules are builtin executables to JSC, nested functions included. Their URL isnode:*,bun:*,internal:*, or a bare name (ws).error.stackhave no code block and spell builtins asnative/unknown.Notes
bun-test.test.tsandstack.test.tstests), error printer: excerpt the frame picked for the code frame, not frame 0, for sources without a source map #38356 (excerpt the picked frame instead of frame 0, theZigException.cppchange and thevm.test.tstests), and the first revision of this PR (theinternal:prefix and the all-builtin fallback,inspect-error.test.js). GitHub Actions annotation and code frame caret: use the first frame that has a file, not a builtin frame on top #38335 and error printer: excerpt the frame picked for the code frame, not frame 0, for sources without a source map #38356 are closed in favor of this one.preview_frame()predicate for the excerpt and the caret, and a frame index into a rewrittencollectSourceLines. It does not coverinternal:/ bare-named modules or the annotation. The two PRs conflict textually inVirtualMachine.rs,ZigException.{rs,cpp}andheaders-handwritten.h; on top of worker errors: carry the parse error's location to the parent; let parse/resolve diagnostics cross structured clone #38324 this PR reduces to the predicate (withis_builtin), the annotation pick and the excerpt gate. Whichever lands second, I will do that rebase.::error file=native,...andfile=unknown,line=1,col=1onceerror.stackwas read,file=node%3Aevents,line=59,col=31foremitter.emit("error")with no listener, and six numbered lines ofnode:worker_threads#onErroraboveerror: Cannot find modulefornew Worker("/nope.mjs").on("error", ...). With no user frame at all the annotation is::error title=...without a location. URL-less user code (evalcalled directly by a timer) keeps its excerpt: it is not builtin code.node:vmscript with the defaultdisplayErrors: trueis unchanged: node:vm materializeserr.stackfirst, so the printer works from parsed frames and prints no code frame before or after.emitter.emit("error")) now shows the user's line. Before, the excerpt was skipped whenever frame 0 was a bun module. The excerpt now followstop, and is skipped only whentopitself is builtin code.is_builtintakes the padding byte beforejsc_stack_frame_indexon both sides of the FFI struct, so its size and the offsets of the other fields are unchanged.OnlySourceLinesloop also re-ranpopulateStackFramePositionon every other frame with null buffers. That only rewrote positions with the values theOnlyPositionpass had stored, and nothing read them, so the loop is gone with theis_topparameter. The source provider ref taken for the excerpt is still one per call, released inZigException::deinit.BUN_SHOW_BUN_STACKFRAMES=1(hide_bun_stackframes = false) keeps the old frame choice for the code frame and the caret. The annotation is not gated on it: an emptyfile=is wrong either way. GitHub attaches an::error file=F,...annotation toFonly whenFis a file in the checkout.inspect.test.js,reportError.test.ts,capture-stack-trace.test.js,worker_threads.test.ts,vm-sourceUrl.test.ts,test/js/bun/sourcemap/,23022-stack-trace-iterator.test.ts,test-test.test.ts,test/cli/inspect/inspect.test.ts, all ofbun-test.test.ts.node:vmcolumnOffset); after both land, the printer's frame loop only decides whether a caret is drawn. bun test: emit one anchored GitHub Actions annotation per failed test #41876 (one annotation per failed test) also changes theprint_github_annotationframe pick, to skipnode_modules; the two compose and whichever lands second has a few-line rebase in that block. error printer: don't invent a 1:1 position for frames parsed out of error.stack without one #38328 and error printer: keep parsing error.stack past frames without a function name #38308 change how anerror.stackstring is parsed back into frames.evalcode (for examplesetTimeout(eval, 0, "[].reduce((a, b) => a)")) now prints no excerpt where main printed the builtin's text; neither is the eval'd line. Aftererror.stackwas read, a bare-named module frame (ws) has no code block and no URL prefix to go by, so it is treated as user code, as on main.ZigStackFramenow has astatic_assert/assert_ffi_layout!pair (72 bytes, align 8) likeResolvedSourceandErrorableString.no test proof · iteration 4 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/vm/vm.test.ts, test/cli/test/bun-test.test.ts