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…nt does not converge The pass runs a fixpoint of at most 10 passes for each function. When the fixpoint of a nested function does not converge, the TypeScript original throws an invariant, which ends each enclosing fixpoint too. The port recorded the failure as a ref read by that function and continued with the shared `changed` flag still set, so each enclosing function ran all 10 of its passes as well: 10^depth passes. A function that returns itself (`const f = () => f`) has a type that contains itself, so the fixpoint of the function around it never converges. Two arrows around it took 93 seconds and three did not finish. `p.a ? [f] : f` doubles the type on each pass, so one arrow around it used memory without bound. Propagate the invariant out of the nested call, as the throw does.
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Status: fix pushed, review comments addressed (fee3ac8), waiting for CI. How to reproduce (bun 1.4.3, release build): // two.jsx
export default function App(p) {
const outer = () => () => { const f = () => f; return f; };
return <div onClick={outer}>{p.a}</div>;
}time bun build --react-compiler --target=browser --external '*' two.jsx
The tests in |
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Included review availability: Your plan provides up to 10 included reviews per hour; 1 remains after this review. WalkthroughNested validation now propagates invariant diagnostics from non-converging analyses and returns ChangesReact Compiler fixpoint handling
Suggested reviewers: Priority: ➖ Normal Merge Risk: ⚪ Minimal · up to Nested non-converging functions now terminate promptly while preserving successful validation behavior, with no actionable merge-blocking risk identified. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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In `@test/bundler/transpiler/react-compiler.test.ts`:
- Around line 2970-2971: Replace the manual
Object.entries(functionsThatReturnThemselves) loop with a describe.each()-based
parameterized suite, preserving each input name in the generated test title and
keeping the existing test body behavior unchanged.
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src/react_compiler/validation/validate_no_ref_access_in_render.rstest/bundler/transpiler/react-compiler.test.ts
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I reviewed this PR and didn't find any bugs. The short-circuit on ErrorCategory::Invariant correctly mirrors the upstream throw, and the tests follow the harness conventions closely. Because this deliberately diverges from the direct port and changes user-visible output — NestedReturnsItself / NestedReturnsItselfOrRefReader compiled on main and are now left un-transformed — a human familiar with the React compiler port should confirm that trade-off.
What was reviewed:
- The new early return in
validate_no_ref_access_in_render_impl:errors.appendmoves the invariant diagnostic up so the enclosing loop's!errors.is_empty()guard exits on its next check, andRefAccessType::Nonematches the existing non-convergence return. - Checked that
ErrorCategory::Invariantin this pass is only produced by the "did not converge" diagnostic, so the filter doesn't catch unrelated inner errors. - The
itBundledbehavioral test and the two hang-guard tests: pipes drained viaPromise.all,signalCodeasserted null,Buffer.alloc(len, fill)used for the arrow chain, stderr/stdout asserted beforeexitCode, and the 20 s kill-switch is commented per the repo rule.
Extended reasoning...
Overview
The PR fixes an exponential-time / unbounded-memory blowup in Bun's React Compiler port. ValidateNoRefAccessInRender runs a bounded 10-pass fixpoint per function; when a nested function's fixpoint fails to converge (e.g. const f = () => f), upstream babel-plugin-react-compiler throws, terminating every enclosing fixpoint. The Rust port recorded the error and continued with the shared changed flag still set, so each enclosing function also ran all 10 passes (10^depth), and a branching self-type doubled per pass. The fix adds an 11-line early return after the recursive FunctionExpression/ObjectMethod call: if any inner error is ErrorCategory::Invariant, move those errors into the parent's list and return RefAccessType::None. Three tests are added to test/bundler/transpiler/react-compiler.test.ts: one itBundled behavioral test asserting which components are skipped vs compiled via a fake react/compiler-runtime that records _c(n) sizes, and two spawned hang-guard tests with a 20 s SIGKILL kill-switch.
Security risks
None. This is an internal compiler validation pass that only decides whether a component gets memoization transforms applied; it does not touch auth, crypto, filesystem, or network. No untrusted-input parsing is added — the input is already-lowered HIR. The added code paths cannot allocate unboundedly (they short-circuit earlier than before).
Level of scrutiny
Medium. The Rust change is tiny and mechanically simple, and the only place ErrorCategory::Invariant is emitted in this file is the "Ref type environment did not converge" diagnostic, so the .any() filter is precisely scoped. The comment satisfies the REVIEW.md rule that ported-code divergences must be justified against the reference implementation. What raises this above auto-approve is the acknowledged behavior change: two component shapes that main compiles (on an unfinished validation, per the PR) are now left un-transformed to match Babel. That's almost certainly correct, but it's a user-visible output change in a code transformer and the PR itself flags it as a deliberate deviation from the straight port — a human owner of src/react_compiler/ should sign off on it.
Other factors
Test quality is high and follows the repo's conventions: itBundled for the bundler behavioral assertion, tempDir/bunExe()/bunEnv for the spawned tests, Buffer.alloc(n, fill) instead of .repeat, concurrent draining of stdout/stderr/exited, signalCode === null asserted so a regression that hangs fails the test rather than reporting a killed process as pass, stderr asserted before exit code, and the 20 s literal timeout carries the required "why no observable signal exists" comment. The new tests sit alongside an existing "compile time is not exponential in the function nesting depth" test in the same file, matching its shape. No CODEOWNERS entry covers src/react_compiler/. Exit reason was dry_streak and no findings were reported.
Keep them serial. When a test times out, bun test kills the process the test spawned only if the tests run one at a time. With test.concurrent an unfixed build left both children running.
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Updated 7:37 AM PT - Sep 15th, 2026
✅ @robobun, your commit fee3ac83cfe635f38a9bf793e6a8f08d3d6dd55c passed in 🧪 To try this PR locally: bunx bun-pr 42807That installs a local version of the PR into your bun-42807 --bun |
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Review follow-up:
For a maintainer: the one thing to confirm is the behaviour change in the second Fix bullet of the description. |
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Problem
bun build --react-compilerhangs when a component nests a function that returns itself.const outer = () => () => { const f = () => f; return f; }takes 93 s on 1.4.3. One more arrow does not finish. Babel needs 0.3 s.ValidateNoRefAccessInRenderruns a fixpoint of at most 10 passes per function, and the one around such anfnever converges. The TypeScript original throws there (ValidateNoRefAccessInRender.ts:832), which ends each enclosing fixpoint. The port records a ref read and continues with the sharedchangedflag set, so each enclosing function runs all 10 passes too: 10^depth passes.Fix
validate_no_ref_access_in_render.rs, markedNot in upstream).changedafter a nested fixpoint failed, and the component compiles on an unfinished validation. It is now left as written, as Babel leaves it.test/bundler/transpiler/react-compiler.test.ts(NestedFunctionThatDoesNotConvergeand two timing tests fail on 1.4.3). Alsoreact-compiler-fixtures.test.ts.Background
ref.currentduring render. A rejected component stays as written, with no message.const f = () => fcontains itself and grows on every pass.fdirectly in its body, a component is still skipped (Ref type environment did not converge), as upstream. This PR keeps that.Notes
Timings (
bun build --react-compiler --target=browser --external '*', one component):outer() => { const f = () => f; return f; }() => { const f = () => (p.a ? [f] : f); return f; }Outcomes. I ran about 45 inputs through main, this PR, and
babel-plugin-react-compiler@1.0.0: a function that returns itself, itself ornull, an array of itself, an arrow that calls it, two functions that return each other, loop-carried variants, each of those nested, and each combined with a ref read during render. With this PR every input gives the result Babel gives. Two groups differ from main:NestedReturnsItselfandNestedReturnsItselfOrRefReaderin the new test compile on main (_c(2),_c(5)) and are now skipped. Babel skips both. On main the fixpoint ofouterfails, the port recordsread_ref_effect: truefor it, and the fixpoint of the next sibling closure resets thechangedflag that all fixpoints share, so the top level looks converged.Not in this PR.
const a = p.a ? [f] : f; return p.b ? [a] : () => a) grow it exponentially inside the 10 passes of the top level: 30 s on 1.4.3. Babel runs node out of memory on the three-layer form, so that is upstream behaviour.const f = () => fcompile needs a bounded type, which upstream does not have. An earlier version of this branch had a depth-limited second run for that. It changes no result in the 1,806 upstream fixtures and no one reported the skip, so it does not belong in a file that is a direct port. It fits better as an upstream change.changedflag is the same in the TypeScript original. This PR does not touch it.Related limits seen on the way (separate upstream limits, same on Babel):
function f() { return f; }stops atTodo: [PruneHoistedContexts] Rewrite hoisted function referencesonce the ref validation is off, andconst f = function g() { return g; }stops at[InferMutationAliasingEffects] Expected value kind to be initialized.[human-review] gate passed · iteration 0 · 2 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 1 passed · 0 rejected · iteration 0
evidence per changed file