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…nt does not converge This is #42807, squashed. The next commit depends on it. 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.
…row.ref}` in a callback
ValidateNoRefAccessInRender had two additions that upstream does not have.
Both made it reject components that babel-plugin-react-compiler compiles.
It seeded the captured places of every nested function from their types.
For a ref that is a new ref id on each visit, and the fixpoint visits
every nested function again on each pass. The pass pairs the write in
`if (ref.current == null) { ref.current = x }` with the guard through the
ref id, so on the second pass the guard no longer matched and the read of
`ref.current` was reported. One function that captures the ref, anywhere
in the component, was enough.
It also collected the side map of temporaries for nested functions. There
a property load became an alias of its object. `row.ref` in
`rows.map(row => <li ref={row.ref} />)` made `row` a ref, and the next
pass took `row.ref` for a ref value. `ref.size` in an event handler
turned `ref` into a ref value for the whole component.
Remove both. A nested function shares the environment of its parent, so a
captured ref already has its type when the function is visited, and a
function above the declaration of the ref gets it on the next pass.
The two blocks also reported a ref error in some functions that return
themselves, and that error ended the fixpoint of such a function on its
first pass. Without the error the fixpoint does not converge, as in
upstream, so this change needs the previous commit to stop there.
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Status: fix pushed (a702d06), waiting for CI. The first commit is #42807, squashed. This change needs it (see Background). How to reproduce (bun 1.4.3, release build): // c.jsx
import { useRef, useEffect } from "react";
export function Lazy(props) {
const ref = useRef(null);
if (ref.current === null) {
ref.current = new Map();
}
useEffect(() => {
ref.current.set("a", props.x);
}, [props.x]);
return <div>{props.x}</div>;
}
export function List(p) {
return <ul>{p.items.map(i => <li key={i.id} ref={i.ref}>{i.label}</li>)}</ul>;
}bun build c.jsx --react-compiler --target=browser --external '*' | grep -c '_c('
The test is |
Contributor
WalkthroughThe compiler validation now scopes temporary sidemap collection to the current function and propagates invariant diagnostics from nested validation. Bundler tests cover lazy ref initialization, nested-function convergence, termination, output preservation, and compiler-runtime exclusion. ChangesReact Compiler validation
Suggested reviewers: Priority: ⬇️ Low Merge Risk: 🔵 Low · up to The compiler change has no supported production defect, but its termination regression test can fail prematurely or miss the intended assertions. Set the explicit timeout before merging. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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In `@test/bundler/transpiler/react-compiler.test.ts`:
- Around line 3757-3787: Set the explicit per-test timeout for the test.each
registration covering “react-compiler compile time is not exponential for a
function that returns itself” to 30 seconds, passing it as the third argument
after the callback so it exceeds the child process timeout.
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Problem
bun build --react-compilerskips a component that hasif (ref.current == null) { ref.current = x }and a function that capturesref, for example an effect. It also skipsrows.map(row => <li ref={row.ref} />). The error isCannot access refs during render. babel-plugin-react-compiler compiles both.ValidateNoRefAccessInRenderseeds the captured places of each nested function (validate_no_ref_access_in_render.rs:599). The ref gets a new id on each visit, so on fixpoint pass two the guard no longer matches it.row.refmakesrowa ref, and the next pass takesrow.reffor a ref value.Fix
test/bundler/transpiler/react-compiler.test.ts(a new case of 25 components and two new rows, stock bun fails them),react-compiler-fixtures.test.ts,bundler_jsx.test.ts.Background
ref.currentduring render. Each pass of its fixpoint visits the nested functions again, with one shared environment.useRefvalue gets a ref id.ref.current == nullbecomes a guard with that id, and the guarded block can write once to that ref.LoadLocal,StoreLocalor property load share the environment entry of its source.Notes
Repro.
bun build c.jsx --react-compiler --target=browser --external "*"has no_c(in the output. babel-plugin-react-compiler 1.0.0 emits_c(6)and_c(4). The function can be before, inside or after the guard. Without the function,Lazycompiles.How the id changes.
ref_type_of_typereturnsRef { ref_id: next_ref_id() }.Env::setjoins it with the entry of the ref, and the join of twoRefs with different ids makes a third id.Ref == Refignores ids, sochangedstays false. On pass two,ref.currentis aRefValuewith the new id. The join with theRefValueof pass one (old id) givesRefValue { loc: None, ref_id: None }.== nullthen makes noGuard, andvalidate_no_ref_value_accessreports the read.How the side map leaks. With the recursion,
$b = PropertyLoad $a.refin a nested function maps$bto the entry ofrow. The type of$bis a ref (it goes to a JSXrefattribute), so the entry ofrowbecomesRef. On the next pass a property load on aRefis aRefValue, and the JSX attribute reports it.ref.sizein an event handler does the same toreffor the whole component, which then fails at<div ref={ref}>, atuseCustom(ref)or at the guard. A function above the declaration of the ref reads it withLoadContext, which gets no type, so the side map does not skipref.currentthere. Upstream collects the side map for the outermost function only.Why the seeding is not needed. The comment on the block names callbacks passed to
useStateanduseReducer, and IIFEs. These fixtures pass without it:error.invalid-access-ref-in-state-initializer,error.invalid-access-ref-in-reducer-init,error.invalid-access-ref-in-reducer,error.invalid-ref-in-callback-invoked-during-render,error.invalid-aliased-ref-in-callback-invoked-during-render-. A captured place has the identifier of the outer function (EnterSSA maps it), soLoadLocalin the nested function finds theRefentry. When the function is above the declaration, the first pass sees no type, theStoreContextof the ref setschanged, and the second pass visits the function again.Why #42807 is in this PR. Both blocks reported a false ref error in
ffor shapes like the one below. The fixpoint of a function returns after the first pass that has an error, sofnever reached the passes where its type (it returns itself) stops converging, and the component compiled. Without the false error these are the same asconst f = () => ffor the pass: it does not converge, upstream throwsRef type environment did not convergeand skips the component, and the port runs 10^depth passes until #42807 stops it. #42807 is open and green. Its branch is on a commit of main that needs clang 21, which my build machine no longer has, so this branch has it as one squashed commit with the same diff. If it merges first, that commit drops out of this PR in the rebase.The 16 are
Found missing memoization dependenciesfrom another validation. main has the same 16. The hook above takes 9 ms on main, does not finish in 200 s with this change alone, and takes 0.2 s with this PR (skipped, as upstream). The two new rows offunctionsThatReturnThemselvespin this.Differential check. Generators made components from: ref source (
useRef,forwardRefparameter, destructured prop), body of the function (returns the ref, reads, writes, alias, destructure, another property, nested functions, object method, phi of two refs, async), position (before, inside, after the guard, above theuseRef), use (JSX handler, call in render,useEffect,useState,useMemo,useCallback, custom hook, global function, JSX child) and guard form or other use of the ref. I compared_c(n)for each component with babel-plugin-react-compiler 1.0.0 and 0.0.0-experimental-a1856f3-20260507.Every difference is a component that upstream compiles and Bun skips. No component compiles in Bun and not upstream, before or after. With 1.0.0 as the reference, 40 and 34 components of the first two sets differ, because 1.0.0 does not have the effect-based check of call arguments yet. I rendered the components that change from skipped to compiled with a fake React that counts reads and writes of
.currentduring render. In the first two sets none does more than guard reads and one write to an empty ref.What upstream accepts that it should not. This PR does not change these, but Bun now accepts them where main skipped some of them by accident.
if (ref.current != null) { ref.current = x }compiles upstream. main accepts it without a function that captures the ref, and skipped it with one.NotEqualThenWritein the new test pins it.changedflag that its parent shares, so the parent can stop before a ref read has moved up a chain of callers. Withconst a = () => b(); const b = () => c(); const c = () => d(); const d = () => ref.current; const v = a();upstream compiles the component. Of the 360 generated chains, upstream compiles 44 whose last function reads or writes the ref and whose first runs in render (caller declared first, 3 or more long). main skips 6 of the 44, this PR none. The TypeScript original has the same flag. I did not change it here: the port follows upstream, and a fix belongs there first.What upstream rejects that it should not. Bun matches these too.
<input ref={props.inputRef} />at the top level of a component: the side map makespropsa ref ([Compiler Bug]: false positive ref access in render error when props contain both arefand avalueand both are accessed react/react#34342, Bug: eslint-react-hooks false positives on refs rule react/react#34775). This PR stops the same effect inside nested functions only, where upstream does not have it.useRefthat captures the ref, with the lazy initialization in the component body. The ref is then a context variable, and its loads have no type.if (ref.current == null) { ref.current = () => x }. The store of a function value joins aStructurewith theRefand makes a new id.Found, not changed. Upstream f1f7ed2ac2 changed the join of a non-
RefValuewith aRefValueto keep theRefValue(location and id). The port still has the older arm. A sync brings it.Suites.
react-compiler.test.ts79 pass.react-compiler-fixtures.test.ts3,293 pass and 320 skip, the same as main. The runner skips the upstream fixtures for the lazy initialization (allow-ref-initialization*,error.ref-initialization-*) because they are Flow files, so the new case has their shapes, each next to a function that captures the ref.bundler_jsx.test.ts57 pass. With the source of the first commit only, the new case and the two new rows fail and the tests of #42807 pass.Self-review. Self-reviewed: 7 concerns raised, 6 addressed. The review of the first version found that it made some builds hang without #42807, that the title and the test left out the
ref={row.ref}family, that "real ref access still reports" was too strong, that the fixture line overstated the coverage, and that the upstream-shared skips and over-acceptances were not listed. All of these are addressed above. Not done: it also asked to report the two over-acceptances to facebook/react.Other open PRs in this file. #43530 (nested types become
Rc) and #43559 (nested types in a table): the hunks do not overlap, and #43530 names this bug as the cause of its remaining N^3 case. #43230 adds a stack check at the top ofcollect_temporaries_sidemap, next to the lines this PR changes. That function no longer recurses, so the check there can go when the two meet.[human-review] gate passed · iteration 0 · 2 files touched
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