node:vm: report compileFunction body lines relative to lineOffset when it is 0 - #38240
node:vm: report compileFunction body lines relative to lineOffset when it is 0#38240robobun wants to merge 9 commits into
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…n it is 0
compileFunction compiled the body as line 2 of a "(function () {\n<body>\n})"
program and started the program one line early to compensate. JSC clamps a
SourceCode's first line to 1, so with the default lineOffset of 0 the
compensation was lost and every runtime position in the function (stack
frames, call sites, the vm error header) was reported one line too high.
Compile the body on the same line as the wrapper instead, so body line N is
physical line N of the program for every lineOffset. Columns on body line 1
now include the wrapper text; the part of columnOffset beyond it is still
applied (previously columnOffset was dropped entirely). The wrapper's length
is recorded on the NodeVMScriptFetcher so handleException can keep showing
the user's own first line, with the caret in the right place, when such a
function throws inside a vm run.
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Updated 7:05 AM PT - Aug 14th, 2026
❌ @robobun, your commit 5d4c0f5 has some failures in 🧪 To try this PR locally: bunx bun-pr 38240That installs a local version of the PR into your bun-38240 --bun |
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Status: reproduced on bun 1.4.0 and main ( Review: the wrapper bookkeeping is keyed to the wrapper program's own CI: on the current head every lane that has run is green (177 jobs on the previous build, the same set on this one). The only non-green item is the darwin 14 aarch64 test lane, which has not been getting an agent (it expired unrun on the previous build and is still queued on this one); the build's only annotation is two unrelated retried flakes ( |
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Note on the The two layouts are exact in complementary cases, so the layout could be chosen per call instead of globally:
What is left inexact is Cost of the refinement: |
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Heads-up on an overlap: #38248 fixes negative The two compose either way: this PR's layout plus #38248's formatter also yields N + lineOffset for negative offsets, and both PRs' compileFunction tests stay green with either layout. The only textual conflicts are the |
…vider eval() and new Function() inside the body create providers that inherit the function's SourceOrigin, and with it the NodeVMScriptFetcher, but contain no wrapper. Record the wrapper program's SourceID next to the prefix length so handleException only strips the prefix from frames in that provider, and apply the strip to the extracted first line rather than to the whole source so the physical line numbering never shifts.
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Inline comments:
In `@src/jsc/bindings/NodeVM.cpp`:
- Around line 397-401: Normalize a leading hashbang in the body to a line
comment before constructing the wrapper in both compileFunction paths, including
the parameterized path, so the wrapped source no longer places “#!” after the
physical offset zero. Update the relevant NodeVM compilation logic around
tryMakeString and add regression coverage for no-parameter and parameterized
vm.compileFunction calls containing a leading hashbang.
- Around line 197-202: Update the runtime stack-frame line calculation
associated with SourceCode creation so negative lineOffset values are reapplied,
matching decorateParseErrorStack() and producing lineOffset plus bodyLine rather
than JSC’s clamped physical line. Add runtime coverage for negative offsets
while preserving existing behavior for non-negative offsets.
In `@test/js/node/test/parallel/test-vm-basic.js`:
- Around line 134-141: Remove the Bun-specific typeof Bun branches and related
source/stack expectations from the vendored test in the assertions around
vm.compileFunction and the affected later cases. Restore upstream
Node-compatible expectations, and keep Bun-specific coverage in
test/js/node/vm/vm.test.ts instead.
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📒 Files selected for processing (4)
src/jsc/bindings/NodeVM.cppsrc/jsc/bindings/NodeVMScriptFetcher.htest/js/node/test/parallel/test-vm-basic.jstest/js/node/vm/vm.test.ts
With the body on the wrapper's line, JSC's columns for that line count the wrapper text, and Bun's error printer showed the wrapper glued to the user's first line. Record, next to the wrapper length, how far those columns exceed the columns Node reports (the wrapper net of columnOffset), take it off in the two places Bun derives frame positions from JSC (the error.stack formatter and getAdjustedPositionForBytecode, which feeds call sites and the error printer), and skip the wrapper text when the printer excerpts that line. Line 1 positions now match the same code on any other line plus columnOffset, for every consumer, so the vendored test-vm-basic.js expectations become the plain columns.
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Correction to my note above after reading the current revision here (7443cf5) more carefully: the two do not compose "either way". #38248 adds a line bias at readout ( |
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Problem
vm.compileFunction()function are one line too high unlesslineOffsetis at least 1.vm.compileFunction('throw new Error("x")', [], { filename: "cf.js" })()reportscf.js:2, Node reportscf.js:1.lineOffset: 0is the default, so this affects every caller that does not pass an offset. WithlineOffset: 5both report line 6.error.stackframes,Error.prepareStackTracecall sites, frames of functions nested in the body, the source excerpt Bun prints for an uncaught error, and the<file>:<line>header node:vm prepends when such a function throws inside a vm script. Compile-time SyntaxErrors were already right (they come from a separate parse of the bare body).columnOffsetwas ignored entirely: it landed on the wrapper's line instead of the body's first line.constructAnonymousFunction(src/jsc/bindings/NodeVM.cpp) compiles(function () {\n<body>\n}), so the body is line 2 of what JSC parses, and compensates by starting the program one line early (lineOffset - 1).JSC::SourceCodeclamps its first line to 1 (vendor/WebKit/Source/JavaScriptCore/parser/SourceCode.h,std::max(firstLine, 1)), so forlineOffset <= 0the compensation is discarded and the wrapper line is reported as part of the body.Fix
stringifyAnonymousFunctionnow emits(function (<params>) {<body>\n}): the body starts on the wrapper's own line, so body line N is physical line N of the program and is reported aslineOffset + Nfor everylineOffset, with nothing to compensate. This is the only layout JSC can report correctly: a position is alwaysfirst line of the executable (>= 1) + line terminators before it, so a body preceded by a newline can never report as line 1, and JSC has no line bias (overrideLineNumberpins one constant line for a whole function).constructAnonymousFunctionrecords on the function'sNodeVMScriptFetcher, keyed by the wrapper program'sSourceID, the wrapper's length and the amount by which JSC's columns on that line exceed Node's (columnOffsetis split: the part beyond the wrapper is given to JSC as the program's start column, since a start column cannot be negative; the recorded amount covers the rest). Keying bySourceIDmatters becauseeval()/new Function()inside the body inherit the fetcher through theSourceOriginbut contain no wrapper; for them, and forvm.Scriptsources, every query below returns 0 and nothing changes.formatStackTrace(the defaulterror.stacktext) andgetAdjustedPositionForBytecode(call sites and the uncaught-error printer). The printer (ZigException.cpp) additionally skips the wrapper text when it excerpts the first line, and node:vm's ownhandleExceptionheader does the same, so the excerpt, the caret and the frame agree. Net effect: a statement on body line 1 reports exactly the column it reports on any other line, pluscolumnOffset, which is Node's rule; only JSC's usual choice of column within a statement still differs from V8's (the(of a call rather thannew), as it does everywhere else in Bun.SourceOrigin.fn.toString()is nowfunction () {<body>\n}(wasfunction () {\n<body>\n}, the text V8 synthesizes), and a body whose first line is an Annex B-->comment no longer compiles, since that comment form is only recognized at the start of a line.cachedDatafrom earlier versions is rejected as with any change to the compiled text; produce/consume within one version still round-trips, including across different offsets.#!was already rejected (any wrapper puts it past offset 0; node:vm: accept a hashbang line at the start of a compileFunction body #38245 fixes that separately), and negativelineOffsetvalues are still clamped by JSC for runtime frames exactly as forvm.Script(compileFunction used to report N + 1 there and now reports N).test/js/node/test/parallel/test-vm-basic.jsalready carried Bun-gated expectations for these four frames (pinning the off-by-one line and the wrapper-free columns of the old layout); they are updated to the Node lines with the same columns as before, and thetoString()assertion gets a gated expectation. The Node branches are untouched and the file still passes under Node v26.test/js/node/vm/vm.test.ts, six newcompileFunction()tests: lines forlineOffsetunset/0/1/7 with params and nested functions; call-site lines; first-line columns against the same statement on line 2 (plain, params,columnOffset3 and 100, nested arrow); call-site columns; the uncaught-error excerpt compared with the excerptvm.Scriptprints for the same text (spawned, also withlineOffset); and the vm header for line 1, params,columnOffset, line 2,lineOffset, and direct/indirectevalin the body, compared with the headervm.Scriptproduces. All six fail on the released binary (line 2 instead of 1, offset dropped, excerpt and header labeled:2) and pass with the fix.test/js/node/vm/, all 95test/js/node/test/parallel/test-vm-*.jsplus the 3 sequential ones, the error-relatedtest-repl-*tests, the stack-trace and error-printing suites touched by the generic changes (inspect-error,reportError,bun/test/stack,v8/capture-stack-trace, the stack-trace regression tests; the twoinspect-errorminified-file failures reproduce without this diff), and the compileFunction tests underBUN_JSC_validateExceptionChecks=1.stringifyAnonymousFunctioncall), node:vm: accept a hashbang line at the start of a compileFunction body #38245 (hashbang rewrite inside it), node:vm: report compileFunction body errors as SyntaxErrors and reject bodies that close the function #38239 (body syntax errors; replaces the pre-parse above this diff and works in body offsets, using the same stringify out-param this PR uses as the wrapper length) and error printer: fix the code frame lines above errors thrown from vm/eval sources #38244 (rewrites the excerpt loop inZigException.cpp; the wrapper skip becomes one clamp of the line start inside itslineText). All compose with this change; whichever lands later re-applies a few lines.Background
vm.compileFunction(body, params, options)returns a function whose source isbody; V8 compiles the body directly, so its positions are exact. Bun has no such JSC entry point and compiles a program containing one function expression that wraps the body, then returns that function.lineOffset/columnOffsetsay where the body sits in a larger file; Node addslineOffsetto every line andcolumnOffsetto the first line's columns only.JSC::SourceCodeis a range of aSourceProvider(the text) plus the one-based line and column the range starts at. A reported position is that line plus the line terminators before the position; on the first line the start column is added too. Nested functions derive theirSourceCodefrom the enclosing one, so the layout fix is picked up by every consumer, while anything about the first line's columns has to be applied where positions are read out.formatStackTrace(FormatStackTraceForJS.cpp) builds the defaulterror.stacktext fromStackFrame::computeLineAndColumn(), andgetAdjustedPositionForBytecode(ErrorStackFrame.cpp) builds theZigStackFramePositionused byprepareStackTracecall sites and by the uncaught-error printer, which also uses its byte offset to excerpt the source line (ZigException.cpp).NodeVMScriptFetcheris the per-compilation object node:vm attaches to a source'sSourceOrigin(it already carries the dynamic import callback); every frame of the compiled program reaches it through its code block's provider. JSC copies the caller'sSourceOriginonto the sources it creates foreval()andnew Function(), which is why the fetcher has to check the provider'sSourceID(JSC's process-unique id per provider) before answering.handleExceptionimplements Node'sDecorateErrorStack: when an error escapesrunInContextand friends it prepends<url>:<line>, the top frame's source line and a caret; the top frame can be a compileFunction function called by the script.Before/after (node v26 for comparison)
An earlier revision of this PR left the first line's columns including the wrapper text (reporting 1:30 above) and only corrected node:vm's own header; review of the printer output showed the wrapper text leaking into uncaught-error excerpts, which is what led to recording the column amount and applying it where positions are read out.
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