[compiler] Repro for false positive mutation of a value derived from props (#35139)
Repro from the compiler WG (Thanks Cody!) of a case where the compiler incorrectly thinks a value is mutable. --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/facebook/react/pull/35139). * #35140 * __->__ #35139
Joseph Savona committed
Nov 14, 2025 at 12:14 UTC
dbf2538355c288c984a58f4d417aff2396924882
2 files changed
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compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/new-mutability/error.todo-repro-destructure-from-prop-with-default-value.expect.md
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+
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+## Input
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+
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+```javascript
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+export function useFormatRelativeTime(opts = {}) {
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+ const {timeZone, minimal} = opts;
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+ const format = useCallback(function formatWithUnit() {}, [minimal]);
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+ // We record `{timeZone}` as capturing timeZone into the object,
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+ // then assume that dateTimeFormat() mutates that object,
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+ // which in turn can mutate timeZone and the object it came from,
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+ // which means that the value `minimal` is derived from can change.
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+ //
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+ // The bug is that we shouldn't be recording a Capture effect given
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+ // that `opts` is known maybe-frozen. If we correctly recorded
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+ // an ImmutableCapture, this wouldn't be mistaken as mutating
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+ // opts/minimal
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+ dateTimeFormat({timeZone});
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+ return format;
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+}
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+
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+```
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+
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+
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+## Error
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+
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+```
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+Found 1 error:
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+
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+Compilation Skipped: Existing memoization could not be preserved
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+
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+React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This dependency may be mutated later, which could cause the value to change unexpectedly.
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+
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+error.todo-repro-destructure-from-prop-with-default-value.ts:3:60
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+ 1 | export function useFormatRelativeTime(opts = {}) {
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+ 2 | const {timeZone, minimal} = opts;
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+> 3 | const format = useCallback(function formatWithUnit() {}, [minimal]);
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+ | ^^^^^^^ This dependency may be modified later
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+ 4 | // We record `{timeZone}` as capturing timeZone into the object,
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+ 5 | // then assume that dateTimeFormat() mutates that object,
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+ 6 | // which in turn can mutate timeZone and the object it came from,
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+```
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+
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+
\ No newline at end of file
compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/new-mutability/error.todo-repro-destructure-from-prop-with-default-value.js
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+export function useFormatRelativeTime(opts = {}) {
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+ const {timeZone, minimal} = opts;
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+ const format = useCallback(function formatWithUnit() {}, [minimal]);
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+ // We record `{timeZone}` as capturing timeZone into the object,
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+ // then assume that dateTimeFormat() mutates that object,
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+ // which in turn can mutate timeZone and the object it came from,
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+ // which means that the value `minimal` is derived from can change.
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+ //
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+ // The bug is that we shouldn't be recording a Capture effect given
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+ // that `opts` is known maybe-frozen. If we correctly recorded
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+ // an ImmutableCapture, this wouldn't be mistaken as mutating
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+ // opts/minimal
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+ dateTimeFormat({timeZone});
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+ return format;
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+}