fix(transformer): hoist lowered async declarations#22770
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Pull request overview
This PR fixes semantic scope mismatches in async-to-generator lowering by registering emitted plain function declarations in the same scope a rebuilt semantic tree would use under sloppy-mode Annex B hoisting.
Changes:
- Adds scope selection logic for lowered async function declarations.
- Moves original lowered function bindings to the appropriate hoist scope when needed.
- Updates the Test262 semantic snapshot to reflect newly passing cases.
Reviewed changes
Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
crates/oxc_transformer/src/es2017/async_to_generator.rs |
Adds helper logic to choose binding scopes for lowered function declarations and generated helper declarations. |
tasks/coverage/snapshots/semantic_test262.snap |
Updates semantic coverage results after resolving related binding mismatches. |
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Fixes semantic scope mismatches when async function declarations are lowered inside sloppy block scopes.
Before this change, `async_to_generator` kept the original async function binding, and the generated helper binding, in the current block scope. After transform those declarations are no longer async:
```js
with (obj) {
async function ref() {}
}
```
becomes roughly:
```js
with (obj) {
function ref() {
return _ref.apply(this, arguments);
}
function _ref() {
_ref = babelHelpers.asyncToGenerator(function* () {});
return _ref.apply(this, arguments);
}
}
```
A fresh semantic rebuild treats those lowered plain function declarations with Annex B hoisting rules, so in sloppy block scopes their bindings can belong to the enclosing var scope instead of the block scope. The transformed semantic tree was still using the pre-lowered block placement, which caused rebuild mismatches in Test262 coverage.
This PR makes `async_to_generator` choose the same binding scope that a rebuilt semantic tree would use for the emitted plain function declarations, while preserving the existing behavior for TypeScript, strict mode, var scopes, and cases where the hoist scope already has a binding.
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camc314
added a commit
that referenced
this pull request
Jul 3, 2026
Fixes semantic scope mismatches when async function declarations are lowered inside sloppy block scopes.
Before this change, `async_to_generator` kept the original async function binding, and the generated helper binding, in the current block scope. After transform those declarations are no longer async:
```js
with (obj) {
async function ref() {}
}
```
becomes roughly:
```js
with (obj) {
function ref() {
return _ref.apply(this, arguments);
}
function _ref() {
_ref = babelHelpers.asyncToGenerator(function* () {});
return _ref.apply(this, arguments);
}
}
```
A fresh semantic rebuild treats those lowered plain function declarations with Annex B hoisting rules, so in sloppy block scopes their bindings can belong to the enclosing var scope instead of the block scope. The transformed semantic tree was still using the pre-lowered block placement, which caused rebuild mismatches in Test262 coverage.
This PR makes `async_to_generator` choose the same binding scope that a rebuilt semantic tree would use for the emitted plain function declarations, while preserving the existing behavior for TypeScript, strict mode, var scopes, and cases where the hoist scope already has a binding.
camc314
added a commit
that referenced
this pull request
Jul 3, 2026
Fixes semantic scope mismatches when async function declarations are lowered inside sloppy block scopes.
Before this change, `async_to_generator` kept the original async function binding, and the generated helper binding, in the current block scope. After transform those declarations are no longer async:
```js
with (obj) {
async function ref() {}
}
```
becomes roughly:
```js
with (obj) {
function ref() {
return _ref.apply(this, arguments);
}
function _ref() {
_ref = babelHelpers.asyncToGenerator(function* () {});
return _ref.apply(this, arguments);
}
}
```
A fresh semantic rebuild treats those lowered plain function declarations with Annex B hoisting rules, so in sloppy block scopes their bindings can belong to the enclosing var scope instead of the block scope. The transformed semantic tree was still using the pre-lowered block placement, which caused rebuild mismatches in Test262 coverage.
This PR makes `async_to_generator` choose the same binding scope that a rebuilt semantic tree would use for the emitted plain function declarations, while preserving the existing behavior for TypeScript, strict mode, var scopes, and cases where the hoist scope already has a binding.
Boshen
added a commit
that referenced
this pull request
Jul 6, 2026
### 🚀 Features - 260425f semantic/examples: Include unresolved references (#24214) (camc314) - 2d9b0b3 minifier: Fold boolean-literal ternary branches in value contexts (#24110) (Dunqing) - 61fbf10 ast: Implement `ReplaceWith` on all AST types (#24013) (overlookmotel) - 7db7a29 allocator: Add `ReplaceWith` trait (#24012) (overlookmotel) - 4eb074e mangler: Add `reserved` option for names that must not be mangled (#24041) (Dunqing) - 2e62012 data_structures: Add `StringExt` trait (#24006) (overlookmotel) - 60e7160 minifier: Drop side-effect-free IIFEs whose result is unused (#23967) (Dunqing) - 26dd9e2 ast: Add method to widen inherited enum ref to parent ref (#23961) (overlookmotel) ### 🐛 Bug Fixes - e8b50ee transformer: Clean up semantics for stripped TypeScript syntax (#24180) (camc314) - d966d0b react_compiler: Remove clippy allows (#24168) (Boshen) - 854ef8d react_compiler: Compile generic functions instead of over-bailing on type-param hoisting (#24158) (Boshen) - 093586c react_compiler: Align memoization cache-slot allocation with Babel (#24157) (Boshen) - 09c8f59 react_compiler: Normalize snapshot fixture paths (#24142) (camc314) - f13df97 react_compiler: Drop stray empty statement from catch bindings (#24133) (Boshen) - cb2a505 react_compiler: Codegen destructuring reassignment targets (#24131) (Boshen) - b82c394 react_compiler: Propagate codegen invariants instead of emitting empty bodies (#24128) (Boshen) - 5771982 react_compiler: Render unchanged programs as source in fixture snapshots (#24129) (Boshen) - 4b16e1a transformer/async-to-generator: Preserve direct eval scope flags (#24136) (camc314) - 4e9194f react_compiler: Lower `delete obj.prop` to Property/ComputedDelete (#24123) (Boshen) - 0b25582 ast: Type binding node `typeAnnotation` as `TSTypeAnnotation | null` (#23113) (Boshen) - 018c0e5 transformer: Hoist lowered async declarations (#22770) (camc314) - 652fbaf mangler: Keep names of destructured exported bindings (#24036) (Dunqing) - e274415 minifier: Don't drop global calls that throw despite pure arguments (#23917) (Dunqing) - 59abb30 minifier: Only merge string literals in `try_fold_add` when the inner operator is `+` (#23622) (Jerry Zhao) ### ⚡ Performance - c5ca77b transformer: Avoid cloning refresh options (#24191) (camc314) - bf1a151 react_compiler: Compile out debug printers (#24184) (Boshen) - abb44a0 transformer: Build fixed object-rest arguments (#24190) (camc314) - a4db731 isolated_declarations: Use `ReplaceWith` instead of `TakeIn` (#24016) (overlookmotel) - ff10855 transformer: Use `ReplaceWith` instead of `TakeIn` (#24015) (overlookmotel) - bd49aff ecmascript: Avoid heap-allocating Math.min/max/imul operands (#23941) (Lawrence Lin) - e4b708b react_compiler: Skip compiled files before prefilters (#24171) (Boshen) - c59f2fe rust: Return impl ExactSizeIterator from slice-backed accessors (#24144) (Boshen) - 5d6d04a codegen: SWAR-skip boring byte runs in sourcemap line/column scan (#24023) (Boshen) - a55e0be traverse: Reduce string operations in `get_var_name_from_node` (#24007) (overlookmotel) - e6d48e1 transformer/nullish_coalescing: Move cold path into separate function (#23989) (overlookmotel) - c4e35b5 transformer/object_rest_spread: Pre-allocate capacity in `Vec` (#23988) (overlookmotel) - 527b8e5 transformer/decorators: Narrow type earlier (#23987) (overlookmotel) ### 📚 Documentation - 30d17f5 allocator: Clarify docs for `TakeIn::take_in_box` (#24093) (overlookmotel) - 675e6a8 ast: Correct doc comment for `PrivateFieldExpression` (#24008) (overlookmotel) - e4c30e6 minifier: Explain what `dce` mode means (#23994) (Dunqing) - 37cbf88 ast_macros: Document fields of `StructDetails` (#23959) (overlookmotel) - 4de3e54 ast: Correct doc comment (#23948) (overlookmotel) Co-authored-by: Boshen <[email protected]>
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Fixes semantic scope mismatches when async function declarations are lowered inside sloppy block scopes.
Before this change,
async_to_generatorkept the original async function binding, and the generated helper binding, in the current block scope. After transform those declarations are no longer async:becomes roughly:
A fresh semantic rebuild treats those lowered plain function declarations with Annex B hoisting rules, so in sloppy block scopes their bindings can belong to the enclosing var scope instead of the block scope. The transformed semantic tree was still using the pre-lowered block placement, which caused rebuild mismatches in Test262 coverage.
This PR makes
async_to_generatorchoose the same binding scope that a rebuilt semantic tree would use for the emitted plain function declarations, while preserving the existing behavior for TypeScript, strict mode, var scopes, and cases where the hoist scope already has a binding.