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fix(semantic): report redeclaration error for import bindings conflicting with value declarations#19068

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fix/import-value-redeclaration
Feb 6, 2026
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fix(semantic): report redeclaration error for import bindings conflicting with value declarations#19068
graphite-app[bot] merged 1 commit intomainfrom
fix/import-value-redeclaration

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@Boshen Boshen commented Feb 6, 2026

Summary

  • In JavaScript modules, import { Foo } from './foo.js'; var Foo; (and let, const, class, function) should report "Identifier 'Foo' has already been declared" per the ES spec
  • The existing excludes-based conflict detection in the binder doesn't catch this because Import is not in the Value bitset
  • Added a checker function that runs at Program leave, scanning root scope bindings for symbols with both Import and a value flag, and reports a redeclaration error
  • TypeScript is excluded since it has its own declaration merging rules

Closes #15961

🤖 Generated with Claude Code

@Boshen Boshen requested a review from Dunqing as a code owner February 6, 2026 14:41
Copilot AI review requested due to automatic review settings February 6, 2026 14:41
@github-actions github-actions bot added A-semantic Area - Semantic C-bug Category - Bug labels Feb 6, 2026
@Boshen Boshen added the 0-merge Merge with Graphite Merge Queue label Feb 6, 2026
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Boshen commented Feb 6, 2026 •
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Pull request overview

This PR fixes a JavaScript module early-error case where an import binding conflicts with a top-level value declaration (e.g. import { Foo } ...; var/let/const/class/function Foo ...), ensuring a redeclaration error is reported per the ECMAScript spec. It also updates coverage exclusions/snapshots and adds an integration test for the new behavior.

Changes:

  • Add a program-level semantic check to detect import + value redeclarations in JS modules (excluding TypeScript mode).
  • Add integration tests covering import conflicts with var/let/const/class/function.
  • Update TypeScript coverage exclusions and regenerate related snapshot summaries.

Reviewed changes

Copilot reviewed 3 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file
File Description
tasks/coverage/src/typescript/constants.rs Excludes an additional TS test case that differs from OXC behavior.
tasks/coverage/snapshots/transformer_typescript.snap Snapshot count updates after test exclusion.
tasks/coverage/snapshots/semantic_typescript.snap Snapshot count updates after test exclusion.
tasks/coverage/snapshots/parser_typescript.snap Snapshot count updates after test exclusion.
tasks/coverage/snapshots/formatter_typescript.snap Snapshot count updates after test exclusion.
tasks/coverage/snapshots/estree_typescript.snap Snapshot count updates after test exclusion.
tasks/coverage/snapshots/codegen_typescript.snap Snapshot count updates after test exclusion.
crates/oxc_semantic/tests/integration/symbols.rs Adds integration coverage for import/value redeclaration errors (and TS non-error expectation).
crates/oxc_semantic/src/checker/mod.rs Wires the new JS checker into the Program-level checks.
crates/oxc_semantic/src/checker/javascript.rs Implements the import/value redeclaration scan over root-scope bindings.

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codspeed-hq bot commented Feb 6, 2026

CodSpeed Performance Report

Merging this PR will not alter performance

Comparing fix/import-value-redeclaration (1948a59) with main (f7f4015)

Summary

✅ 47 untouched benchmarks
⏩ 3 skipped benchmarks1

Footnotes

  1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

@Boshen
fix(semantic): report redeclaration error for import bindings conflic…
f32ea19 
…ting with value declarations (#19068)

## Summary

- In JavaScript modules, `import { Foo } from './foo.js'; var Foo;` (and `let`, `const`, `class`, `function`) should report `"Identifier 'Foo' has already been declared"` per the [ES spec](https://tc39.es/ecma262/#sec-imports-static-semantics-early-errors)
- The existing excludes-based conflict detection in the binder doesn't catch this because `Import` is not in the `Value` bitset
- Added a checker function that runs at `Program` leave, scanning root scope bindings for symbols with both `Import` and a value flag, and reports a redeclaration error
- TypeScript is excluded since it has its own declaration merging rules

Closes #15961

🤖 Generated with [Claude Code](https://claude.com/claude-code)
@graphite-app graphite-app bot force-pushed the fix/import-value-redeclaration branch from 1948a59 to f32ea19 Compare February 6, 2026 15:03
@graphite-app graphite-app bot merged commit f32ea19 into main Feb 6, 2026
21 checks passed
@graphite-app graphite-app bot deleted the fix/import-value-redeclaration branch February 6, 2026 15:10
@graphite-app graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Feb 6, 2026
This was referenced Feb 9, 2026
Closed
Merged
camc314 added a commit that referenced this pull request Feb 10, 2026
@Boshen @camc314
release(crates): oxc v0.113.0 (#19210)
acdb40e 
### 💥 BREAKING CHANGES

- 2bf7293 mangler: [**BREAKING**] Enable `top_level` by default for
modules and commonjs (#18278) (sapphi-red)
- 48b0542 span: [**BREAKING**] SourceType::ts should set module to
unambigious (#18873) (Boshen)

### 🚀 Features

- 500d071 minifier: Local traverse ctx and generated minifier traverse
(#19106) (Boshen)
- 142a1be parser: Detect binary files with TS1490 error (#19047)
(Boshen)
- e316857 allocator/bitset: Add `Ones` iterator to `BitSet` (#19027)
(sapphi-red)
- 742ad3f minifier: Default `invalid_import_side_effects` to `false`
(#18916) (sapphi-red)
- 0eff6be parser: Error JSX-like type assertions and generics in
`.mts`/`.cts` (#18910) (Boshen)
- 18320c6 span: Store file extension in `SourceType` (#18893) (Boshen)

### 🐛 Bug Fixes

- a7514e4 isolated-declarations: Preserve const context in literal type
inference (#19178) (camc314)
- 312e756 isolated-declarations: Preserve readonly literal initializers
(#19177) (camc314)
- d0ca8d0 isolated-declarations: Skip parenthesis when inferring type
(#19176) (camc314)
- 110c300 oxc_ecmascript: `+[false]` and `+[true]` should evaluate to
`NaN` (#19174) (copilot-swe-agent)
- f32ea19 semantic: Report redeclaration error for import bindings
conflicting with value declarations (#19068) (Boshen)
- 3aeba7a semantic: Report redeclaration error for `function a() {} var
a` in module mode (#19041) (Boshen)
- 35e32c6 coverage: Match Babel's options.json inheritance for test
fixtures (#19002) (Boshen)
- 463d60d semantic: Skip TS2391 for standalone computed-name class
methods (#19025) (Boshen)
- 56c086b parser: Add modifier ordering validation (TS1029) (#19024)
(Boshen)
- 6067a49 linter/jsdoc: False positive in `check-tag-names` for `@` in
email addresses and npm scopes (#19021) (Boshen)
- b13bb70 semantic/jsdoc: Inline tags like `{@link}` break jsdoc parsing
(#19019) (Boshen)
- e3609e3 regular_expression: Preserve UnicodeEscape CharacterKind in
string literals (#18998) (Boshen)
- 57917ee parser: Parse decorators on rest parameters (#18938) (Boshen)
- 487601b napi: Disable mimalloc on Windows to fix worker_threads crash
(#18923) (Boshen)
- 1f6b193 parser: Validate TypeScript import type options (#18889)
(Boshen)
- 1663184 parser: Allow conditional types in function type parameters
(#18886) (Boshen)
- 5758046 parser: Error on property access after instantiation
expression (#18887) (Boshen)
- 5eb4a94 parser: Handle `<<` as two `<` tokens in type argument
contexts (#18885) (Boshen)

### ⚡ Performance

- ed8c054 oxc_str: Add precomputed hash to Ident for fast HashMap
lookups (#19143) (Boshen)
- d4a0867 transformer_plugins: Switch ReplaceGlobalDefines from Traverse
to VisitMut (#19146) (Boshen)
- 9eb16b3 syntax: Pack ASCII identifier tables into single bitflag table
(#19088) (Boshen)
- e7595d1 mangler: Use BitSet for exported symbols set (#19023)
(sapphi-red)
- 2537924 semantic: Optimize scope resolution with fast paths and
inlining (#19029) (Boshen)
- 69a8d85 mangler: Use BitSet for keep_names symbols set (#19028)
(sapphi-red)
- f78c525 parser: Try hybrid parsing for jsx children and closing
element/fragments (#18789) (camchenry)

Co-authored-by: camc314 <[email protected]>
@Boshen Boshen mentioned this pull request Feb 10, 2026
Closed
owjs3901 pushed a commit to owjs3901/oxc that referenced this pull request Feb 11, 2026
@Boshen @camc314 @owjs3901
release(crates): oxc v0.113.0 (oxc-project#19210)
68e76fb 
### 💥 BREAKING CHANGES

- 2bf7293 mangler: [**BREAKING**] Enable `top_level` by default for
modules and commonjs (oxc-project#18278) (sapphi-red)
- 48b0542 span: [**BREAKING**] SourceType::ts should set module to
unambigious (oxc-project#18873) (Boshen)

### 🚀 Features

- 500d071 minifier: Local traverse ctx and generated minifier traverse
(oxc-project#19106) (Boshen)
- 142a1be parser: Detect binary files with TS1490 error (oxc-project#19047)
(Boshen)
- e316857 allocator/bitset: Add `Ones` iterator to `BitSet` (oxc-project#19027)
(sapphi-red)
- 742ad3f minifier: Default `invalid_import_side_effects` to `false`
(oxc-project#18916) (sapphi-red)
- 0eff6be parser: Error JSX-like type assertions and generics in
`.mts`/`.cts` (oxc-project#18910) (Boshen)
- 18320c6 span: Store file extension in `SourceType` (oxc-project#18893) (Boshen)

### 🐛 Bug Fixes

- a7514e4 isolated-declarations: Preserve const context in literal type
inference (oxc-project#19178) (camc314)
- 312e756 isolated-declarations: Preserve readonly literal initializers
(oxc-project#19177) (camc314)
- d0ca8d0 isolated-declarations: Skip parenthesis when inferring type
(oxc-project#19176) (camc314)
- 110c300 oxc_ecmascript: `+[false]` and `+[true]` should evaluate to
`NaN` (oxc-project#19174) (copilot-swe-agent)
- f32ea19 semantic: Report redeclaration error for import bindings
conflicting with value declarations (oxc-project#19068) (Boshen)
- 3aeba7a semantic: Report redeclaration error for `function a() {} var
a` in module mode (oxc-project#19041) (Boshen)
- 35e32c6 coverage: Match Babel's options.json inheritance for test
fixtures (oxc-project#19002) (Boshen)
- 463d60d semantic: Skip TS2391 for standalone computed-name class
methods (oxc-project#19025) (Boshen)
- 56c086b parser: Add modifier ordering validation (TS1029) (oxc-project#19024)
(Boshen)
- 6067a49 linter/jsdoc: False positive in `check-tag-names` for `@` in
email addresses and npm scopes (oxc-project#19021) (Boshen)
- b13bb70 semantic/jsdoc: Inline tags like `{@link}` break jsdoc parsing
(oxc-project#19019) (Boshen)
- e3609e3 regular_expression: Preserve UnicodeEscape CharacterKind in
string literals (oxc-project#18998) (Boshen)
- 57917ee parser: Parse decorators on rest parameters (oxc-project#18938) (Boshen)
- 487601b napi: Disable mimalloc on Windows to fix worker_threads crash
(oxc-project#18923) (Boshen)
- 1f6b193 parser: Validate TypeScript import type options (oxc-project#18889)
(Boshen)
- 1663184 parser: Allow conditional types in function type parameters
(oxc-project#18886) (Boshen)
- 5758046 parser: Error on property access after instantiation
expression (oxc-project#18887) (Boshen)
- 5eb4a94 parser: Handle `<<` as two `<` tokens in type argument
contexts (oxc-project#18885) (Boshen)

### ⚡ Performance

- ed8c054 oxc_str: Add precomputed hash to Ident for fast HashMap
lookups (oxc-project#19143) (Boshen)
- d4a0867 transformer_plugins: Switch ReplaceGlobalDefines from Traverse
to VisitMut (oxc-project#19146) (Boshen)
- 9eb16b3 syntax: Pack ASCII identifier tables into single bitflag table
(oxc-project#19088) (Boshen)
- e7595d1 mangler: Use BitSet for exported symbols set (oxc-project#19023)
(sapphi-red)
- 2537924 semantic: Optimize scope resolution with fast paths and
inlining (oxc-project#19029) (Boshen)
- 69a8d85 mangler: Use BitSet for keep_names symbols set (oxc-project#19028)
(sapphi-red)
- f78c525 parser: Try hybrid parsing for jsx children and closing
element/fragments (oxc-project#18789) (camchenry)

Co-authored-by: camc314 <[email protected]>
OskarLebuda pushed a commit to OskarLebuda/oxc that referenced this pull request Feb 17, 2026
@Boshen @OskarLebuda
fix(semantic): report redeclaration error for import bindings conflic…
82ee0b7 
…ting with value declarations (oxc-project#19068)

## Summary

- In JavaScript modules, `import { Foo } from './foo.js'; var Foo;` (and `let`, `const`, `class`, `function`) should report `"Identifier 'Foo' has already been declared"` per the [ES spec](https://tc39.es/ecma262/#sec-imports-static-semantics-early-errors)
- The existing excludes-based conflict detection in the binder doesn't catch this because `Import` is not in the `Value` bitset
- Added a checker function that runs at `Program` leave, scanning root scope bindings for symbols with both `Import` and a value flag, and reports a redeclaration error
- TypeScript is excluded since it has its own declaration merging rules

Closes oxc-project#15961

🤖 Generated with [Claude Code](https://claude.com/claude-code)
OskarLebuda pushed a commit to OskarLebuda/oxc that referenced this pull request Feb 17, 2026
@Boshen @camc314 @OskarLebuda
release(crates): oxc v0.113.0 (oxc-project#19210)
ea5f1e2 
### 💥 BREAKING CHANGES

- 2bf7293 mangler: [**BREAKING**] Enable `top_level` by default for
modules and commonjs (oxc-project#18278) (sapphi-red)
- 48b0542 span: [**BREAKING**] SourceType::ts should set module to
unambigious (oxc-project#18873) (Boshen)

### 🚀 Features

- 500d071 minifier: Local traverse ctx and generated minifier traverse
(oxc-project#19106) (Boshen)
- 142a1be parser: Detect binary files with TS1490 error (oxc-project#19047)
(Boshen)
- e316857 allocator/bitset: Add `Ones` iterator to `BitSet` (oxc-project#19027)
(sapphi-red)
- 742ad3f minifier: Default `invalid_import_side_effects` to `false`
(oxc-project#18916) (sapphi-red)
- 0eff6be parser: Error JSX-like type assertions and generics in
`.mts`/`.cts` (oxc-project#18910) (Boshen)
- 18320c6 span: Store file extension in `SourceType` (oxc-project#18893) (Boshen)

### 🐛 Bug Fixes

- a7514e4 isolated-declarations: Preserve const context in literal type
inference (oxc-project#19178) (camc314)
- 312e756 isolated-declarations: Preserve readonly literal initializers
(oxc-project#19177) (camc314)
- d0ca8d0 isolated-declarations: Skip parenthesis when inferring type
(oxc-project#19176) (camc314)
- 110c300 oxc_ecmascript: `+[false]` and `+[true]` should evaluate to
`NaN` (oxc-project#19174) (copilot-swe-agent)
- f32ea19 semantic: Report redeclaration error for import bindings
conflicting with value declarations (oxc-project#19068) (Boshen)
- 3aeba7a semantic: Report redeclaration error for `function a() {} var
a` in module mode (oxc-project#19041) (Boshen)
- 35e32c6 coverage: Match Babel's options.json inheritance for test
fixtures (oxc-project#19002) (Boshen)
- 463d60d semantic: Skip TS2391 for standalone computed-name class
methods (oxc-project#19025) (Boshen)
- 56c086b parser: Add modifier ordering validation (TS1029) (oxc-project#19024)
(Boshen)
- 6067a49 linter/jsdoc: False positive in `check-tag-names` for `@` in
email addresses and npm scopes (oxc-project#19021) (Boshen)
- b13bb70 semantic/jsdoc: Inline tags like `{@link}` break jsdoc parsing
(oxc-project#19019) (Boshen)
- e3609e3 regular_expression: Preserve UnicodeEscape CharacterKind in
string literals (oxc-project#18998) (Boshen)
- 57917ee parser: Parse decorators on rest parameters (oxc-project#18938) (Boshen)
- 487601b napi: Disable mimalloc on Windows to fix worker_threads crash
(oxc-project#18923) (Boshen)
- 1f6b193 parser: Validate TypeScript import type options (oxc-project#18889)
(Boshen)
- 1663184 parser: Allow conditional types in function type parameters
(oxc-project#18886) (Boshen)
- 5758046 parser: Error on property access after instantiation
expression (oxc-project#18887) (Boshen)
- 5eb4a94 parser: Handle `<<` as two `<` tokens in type argument
contexts (oxc-project#18885) (Boshen)

### ⚡ Performance

- ed8c054 oxc_str: Add precomputed hash to Ident for fast HashMap
lookups (oxc-project#19143) (Boshen)
- d4a0867 transformer_plugins: Switch ReplaceGlobalDefines from Traverse
to VisitMut (oxc-project#19146) (Boshen)
- 9eb16b3 syntax: Pack ASCII identifier tables into single bitflag table
(oxc-project#19088) (Boshen)
- e7595d1 mangler: Use BitSet for exported symbols set (oxc-project#19023)
(sapphi-red)
- 2537924 semantic: Optimize scope resolution with fast paths and
inlining (oxc-project#19029) (Boshen)
- 69a8d85 mangler: Use BitSet for keep_names symbols set (oxc-project#19028)
(sapphi-red)
- f78c525 parser: Try hybrid parsing for jsx children and closing
element/fragments (oxc-project#18789) (camchenry)

Co-authored-by: camc314 <[email protected]>
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semantic: no error happens with same identifier for imports and local variables

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