[compiler] Distingush optional/extraneous deps #35204
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In ValidateExhaustiveDependencies, I previously changed to allow extraneous dependencies as long as they were non-reactive. Here we make that more precise, and distinguish between values that are definitely referenced in the memo function but optional as dependencies vs values that are not even referenced in the memo function. The latter now error as extraneous even if they're non-reactive. This also turned up a case where constant-folded primitives could show up as false positives of the latter category, so now we track manual deps which quality for constant folding and don't error on them.
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josephsavona
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Nov 25, 2025
| if ($[0] === Symbol.for("react.memo_cache_sentinel")) { | ||
| Component = Stringify; | ||
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|
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| Component; |
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looks like an existing bug where DCE isn't cleaning this up
mofeiZ
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Nov 25, 2025
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| const isOptionalDependency = | ||
| !reactive.has(inferredDependency.identifier.id) && | ||
| (isStableType(inferredDependency.identifier) || | ||
| isPrimitiveType(inferredDependency.identifier)); | ||
| if (hasMatchingManualDependency || isOptionalDependency) { | ||
| continue; |
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Nice, this switches us back to special casing non-reactive deps allowed by exhaustive-deps rule.
This code should now bail out (right)?
hook useHook() {
const obj = {};
return useMemo(() => obj, []);
}
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tested in a follow-up
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| /* | ||
| * Constant primitives can get constant-folded, which means we won't | ||
| * see a LoadLocal for the value within the memo function. | ||
| */ |
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makes sense, thanks for the explanation
mofeiZ
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Nov 25, 2025
| const x = useMemo(() => { | ||
| return [state]; | ||
| // error: `setState` is a stable type, but not actually referenced | ||
| }, [state, setState]); |
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Makes sense! Could we add something like this as a fixture?
// error.fixture
hook useHook() {
const obj = {};
return useMemo(() => obj, []);
}
// error.fixture2
hook useHook() {
// here, obj goes unmemoized
const obj = {};
useHook();
obj.x = 4;
return useMemo(() => obj, []);
}
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In ValidateExhaustiveDependencies, I previously changed to allow extraneous dependencies as long as they were non-reactive. Here we make that more precise, and distinguish between values that are definitely referenced in the memo function but optional as dependencies vs values that are not even referenced in the memo function. The latter now error as extraneous even if they're non-reactive. This also turned up a case where constant-folded primitives could show up as false positives of the latter category, so now we track manual deps which quality for constant folding and don't error on them.
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