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…member JSXTag::parse built the dotted name of a tag like <a.b.c> by allocating name.len() + 1 + member.len() bytes in the AST arena and copying the accumulated prefix for every member. The arena is only reset after the parse, so a tag with n members held ~n^2 bytes: a 92 KB source left the process at 2.1 GB RSS and 131 KB was OOM-killed. Count the length while parsing the chain and join the name once at the end, reading the members back off the E::Dot chain that was just built.
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Included review availability: Your plan provides up to 10 included reviews per hour; 1 remains after this review. WalkthroughThe JSX parser defers qualified member-name allocation until parsing completes. Regression tests cover name output, whitespace, closing-tag validation, and memory use for deep member chains. ChangesJSX member-tag parsing
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to The member-tag allocation change preserves parsing behavior while bounding memory use for deep JSX member chains. No merge-blocking risk remains. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Status: ready for review. Reproduced on 1.4.2 and on a debug build of main with the ledger script: The regression test ( CI: the new test passes on every lane. The one red job (debian 13 x64-asan) fails only in |
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The fixed parser finishes in under a second on a debug build. Also measure with memoryFootprint on macOS, like the sibling memory tests.
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Inline comments:
In `@test/js/bun/transpiler/transpiler-jsx-member-tag-oom.test.ts`:
- Around line 48-52: Update the assertions in the JSX member-tag OOM test to
validate stdout and stderr first, then assert exitCode separately with
expect(exitCode).toBe(0) as the final assertion.
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src/js_parser/parser.rstest/js/bun/transpiler/transpiler-jsx-member-tag-oom.test.ts
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LGTM — thanks for dropping the per-test timeout.
What was reviewed:
- Traced the back-fill in
JSXTag::parse:dot.name.slice()returns the same bytes summed intoname_len, soendlands exactly atname.len()and thedebug_assertholds; the zero-member path is unchanged. - Correctness test covers the joined output and both mismatch-error shapes, so the only consumer of
name(open/close tag comparison + error text) is exercised. - New file follows the existing
transpiler-*-oom.test.tsconvention alongside two siblings; the 150 MB RSS bound is ~7× headroom over ASAN's post-fix delta and ~7× below the pre-fix growth.
Extended reasoning...
Overview
The PR fixes an O(n²) arena-memory blowup in JSXTag::parse (src/js_parser/parser.rs). The old loop re-allocated and copied the full accumulated dotted-name prefix into the AST bump arena once per .member; the arena only resets after the parse, so all n prefixes stayed live. The fix sums the joined length during the loop, then makes a single arena allocation and fills it back-to-front by walking the E::Dot chain that was just built. A new test file adds a correctness check (joined name renders right, mismatched closing tags still error with the correct message) and a spawned-subprocess memory test asserting RSS growth stays under 150 MB for 16×8000-member tags.
Security risks
None. This is a parser-internal memory optimization; the joined name is only used to compare opening/closing JSX tags and to format the mismatch error. No new input surface, no untrusted-length arithmetic beyond summing byte lengths of identifiers the lexer already produced. The single allocation is exactly name_len bytes and every copy_from_slice is bounded by the walked slices; the debug_assert_eq!(end, name.len()) and the correctness test guard the invariant.
Level of scrutiny
Medium — it touches the JS parser, but the change is ~20 lines, mechanical (sum-then-allocate-once replacing reallocate-per-iteration), and the sole consumer of the produced string is covered by the new correctness test. I read the surrounding function to confirm E::Dot.name is populated from the same member bytes whose lengths are summed, so the back-fill cannot underflow or leave gaps. The zero-member case (name_len == name.len()) skips the new block entirely, preserving prior behavior.
Other factors
The one nit from my prior review (per-test 60_000 timeout, forbidden by test/CLAUDE.md) was removed in the follow-up commit. The new test file matches the local convention set by transpiler-enum-concat-chain-oom.test.ts and transpiler-comma-chain-oom.test.ts (one fuzz-derived OOM finding per file), so the "add to existing file" default doesn't apply here. The RSS threshold isn't branched on isASAN/isDebug, but per the PR's measurements the post-fix delta is under 10 MB even under ASAN and the pre-fix delta is ~1 GB, so 150 MB gives comfortable margin in both directions without needing a branch. PR description states the broader transpiler/bundler JSX suites were run.
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Problem
x = <a.b.b.b… />) uses ~n^2 bytes of AST arena. A 92 KB source leaves the process at 2.1 GB RSS, and 131 KB is OOM-killed at a 3 GB cap (fuzz ledger: JSX member-expression tag quadratic arena allocation).JSXTag::parse(src/js_parser/parser.rs:819) allocatedname.len() + 1 + member.len()arena bytes for every.memberand copied the whole accumulated name into it. The arena is only reset after the parse, so all n prefixes stay live.Fix
E::Dotchain that the loop just built.<Foo.Bar>still does exactly one allocation.test/js/bun/transpiler/transpiler-jsx-member-tag-oom.test.ts(16 tags x 8000 members: 1.07 GB RSS growth on 1.4.2, 6 to 9 MB with this change). Alsotest/bundler/transpiler/transpiler.test.js,jsx-production.test.ts,jsx-deep-nesting-stack-overflow.test.tsandtest/bundler/esbuild/ts.test.ts.Background
JSXTag::parsehandles<Foo.Bar.Baz ...>. It builds anE::IdentifierforFooand wraps it in oneE::Dotper member.</Foo.Bar.Baz>can be checked against the opening tag.Notes
transformSync("x=<a" + ".b".repeat(n) + "/>"), one process): before, n = 4096 / 8192 / 16384 / 24000 took 10 / 28 / 106 / 240 ms and left 47 / 103 / 317 / 629 MB RSS. After: 2 / 2 / 3 / 2 ms and 34 / 38 / 41 / 42 MB.Maximum call stack size exceeded. That is the visit/print recursion limit on a 16k-deep member chain and is the same forx = a.b.b.b…without JSX. It is not part of this change.scanImportsrather thantransformSyncbecause debug builds hit the printer's recursion limit at a chain depth of about 1000, and the quadratic needs a deep chain to show clearly. Both go through the sameJSXTag::parse.no test proof · iteration 0 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/bun/transpiler/transpiler-jsx-member-tag-oom.test.ts