[compiler] Don't outline functions that reference unbound module-local names#36539
[compiler] Don't outline functions that reference unbound module-local names#36539tejasupmanyu wants to merge 1 commit into
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…l names
When the outermost function being compiled is itself nested inside
another function (e.g. a factory or HOC, as in `infer` compilation
mode), `HIRBuilder` resolves identifiers relative to
`parentFunction.scope.parent`, which is the enclosing function's scope
rather than the program scope. References to the enclosing function's
locals are therefore tagged as `ModuleLocal` and surface in the
outlining pass as `LoadGlobal` instructions with `context.length === 0`,
making the inner function look outlineable.
Hoisting such a function to module scope would leave the captured name
undefined at runtime. Repro from the linked issue:
function makeCounter(initialValue) {
const counter = {value: initialValue};
const Counter = () => {
const getCount = () => counter.value; // hoisted; `counter` undef
return <div>{getCount()}</div>;
};
return Counter;
}
This change skips outlining for any `FunctionExpression` whose body
contains a `LoadGlobal(ModuleLocal)` for a name that does not actually
resolve at the program scope.
Fixes facebook#34901
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Summary
When the outermost function being compiled is nested inside another function (factory/HOC,
infermode),HIRBuilderresolves identifiers againstparentFunction.scope.parent— the enclosing function's scope, not the program scope. The enclosing scope's locals are mis-tagged asModuleLocal, andoutlineFunctionsseescontext.length === 0and hoists the inner closure to module scope, where the captured name is undefined at runtime.This PR adds a guard in
outlineFunctions: a function is not outlined if its body contains aLoadGlobal(ModuleLocal)whose name does not resolve at the program scope.Fixes #34901
Alternative considered
A more principled fix is to correct the misclassification in
HIRBuilder.resolveIdentifier/isContextIdentifierby usingscope.getProgramParent()instead ofscope.parent. That change alone is semantically correct but exposes a deeper structural gap: the compiler's capture machinery (gatherCapturedContext,captureScopes) only walks scopes up toparentFunction.scope, so factory-scope variables get no value-kind initialization andInferMutationAliasingEffectsinvariant-fails. Closing that gap requires extending capture collection up to (but excluding) the program scope and gathering captures for the outermost function as well — a substantially larger change with wide effects on how nested functions are lowered. Worth doing in a follow-up; out of scope for this fix.Test plan
factory-function-component-captures-outer-scope.js. Eval output renders<div>42</div>, confirminggetCountstays inline.yarn workspace babel-plugin-react-compiler lintclean.Supersedes #36538 (closed; force-push diverged history, GitHub wouldn't reopen).