fix(transformer/es2018/for-await): hoist for-await generated bindings#22355
Merged
Conversation
Contributor
There was a problem hiding this comment.
Pull request overview
Fixes incorrect scoping of generated var bindings produced by the for await (...) transform so that they are hoisted into the correct “var/hoist” scope (function or program), eliminating semantic binding/symbol-scope mismatches in coverage runs.
Changes:
- Generate the internal
stepbinding inctx.current_hoist_scope_id()instead of the current (potentially block) scope. - Generate the internal iterator bookkeeping bindings (
_iterator,_step,_didIteratorError, etc.) inctx.current_hoist_scope_id()to matchvarhoisting semantics. - Update semantic coverage snapshots to reflect the resolved mismatches (improved “Positive Passed” counts).
Reviewed changes
Copilot reviewed 1 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| crates/oxc_transformer/src/es2018/async_generator_functions/for_await.rs | Hoists for-await transform-generated var bindings into the correct hoist scope to match JS var semantics. |
| tasks/coverage/snapshots/semantic_test262.snap | Snapshot update showing removal of prior for-await binding/scope mismatches and improved pass count. |
| tasks/coverage/snapshots/semantic_babel.snap | Snapshot update showing removal of a prior for-await-related binding/scope mismatch and improved pass count. |
Merging this PR will not alter performance
Comparing 
Footnotes
|
Contributor
Author
Merge activity
|
…#22355) `for await` lowering emits several temporary bindings as `var`, but the transformer was registering those generated symbols in the current block scope instead of the nearest hoist scope. For example, this input: ```js async function* f(iter) { { for await (const value of iter) { value; } } } ``` is lowered into code shaped like this: ```js async function* f(iter) { { var _iteratorAbruptCompletion = false; var _didIteratorError = false; var _iteratorError; try { for ( var _iterator = _asyncIterator(iter), _step; // ^^^^^^^^^ ^^^^^ // These are `var` declarations, so semantically they belong to // the function/hoist scope, not the inner block scope. _iteratorAbruptCompletion = !(_step = await _iterator.next()).done; _iteratorAbruptCompletion = false ) { const value = _step.value; value; } } catch (err) { _didIteratorError = true; _iteratorError = err; } } } ``` Before this PR, the AST transform generated the right JavaScript, but its semantic metadata recorded `_iterator`, `_step`, `_didIteratorError`, `_iteratorError`, and `_iteratorAbruptCompletion` in the current block scope: That made the transformed semantic data disagree with semantic data rebuilt from the emitted AST.
38e1470 to
67ab1c9
Compare
overlookmotel
added a commit
that referenced
this pull request
May 15, 2026
### 🚀 Features - bc91a17 codegen: Expose `Codegen::with_source_type` method (#22432) (camc314) ### 🐛 Bug Fixes - 5ac7e79 minifier: Drop unused-var-init pure IIFEs and preserve annotation for downstream (#22349) (Dunqing) - 4ab57eb allocator: Fixed-size allocators use `VirtualAlloc` on Windows (#22124) (overlookmotel) - 66d77eb allocator: Fix segfault on Linux MUSL with fixed-size allocators (#22388) (overlookmotel) - b8fbc1f transformer/object-rest-spread: Correct scope id when moving bindings (#22419) (camc314) - 18edc2c codegen: Keep `Object.defineProperty` property name as plain string in minify (#22400) (Dunqing) - dda33de transformer/explicit-resource-management: Align lexical binding scopes (#22320) (camc314) - 8e79de8 transformer: Preserve for-await statement bodies (#22361) (camc314) - 0cba210 transformer/class: Replace `new.target` in static blocks (#22360) (camc314) - 67ab1c9 transformer/es2018/for-await: Hoist for-await generated bindings (#22355) (camc314) - c3ceb4a transformer/object-rest-spread: Use hoisted scope for `for-of` temp refs (#22347) (camc314) ### ⚡ Performance - 73a9043 allocator/bitset: Avoid temp heap `String` allocation (#22403) (camc314) - 8b2f4f9 transformer/object-rest-spread: Collect `Vec<SymbolId` over `Vec<BindingIdentifier>` (#22418) (camc314) - 83679ea parser: Split TriviaBuilder::handle_token hot/cold paths (#22415) (Boshen) - 2c7d781 codegen: Inline identifier-name accessors (#22411) (Boshen) - 618bc76 diagnostics: Inline `OxcDiagnosticInner` to avoid heap allocation (#22406) (Boshen) - 0b4e158 parser: Reserve cap `2` for sequence expressions vec (#22374) (camc314) - 5f3bdd0 codegen: Add `#[inline]` to `code`, `code_len` (#22373) (camc314) Co-authored-by: overlookmotel <557937+overlookmotel@users.noreply.github.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
for awaitlowering emits several temporary bindings asvar, but the transformer was registering those generated symbols in the current block scope instead of the nearest hoist scope.For example, this input:
is lowered into code shaped like this:
Before this PR, the AST transform generated the right JavaScript, but its semantic metadata recorded
_iterator,_step,_didIteratorError,_iteratorError, and_iteratorAbruptCompletionin the current block scope:That made the transformed semantic data disagree with semantic data rebuilt from the emitted AST.