fix(transformer/typescript): remove unused import equals declaration

[Dunqing]

close: #16628

[Dunqing]

• fix(transformer/typescript): remove unused import equals declaration #16776 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #16776 will not alter performance

_{Comparing 12-12-fix_transformer_typescript_remove_unused_import_equals_declaration (42b4e46) with main (73da317)}

Summary

✅ 38 untouched
⏩ 7 skipped¹

Footnotes

1. 7 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. ↩

[Copilot]

Pull request overview

This PR attempts to fix the removal of unused TypeScript import equals declarations by marking their references as type references before transformation. The implementation moves the reference marking logic from the declaration removal phase to an earlier enter_program phase and processes import chains in reverse order to handle dependencies correctly.

Key changes:

• Adds mark_unused_import_equals_references_as_type method that processes import equals declarations before transformation
• Processes imports in reverse order to correctly handle chains where one import references another
• Removes inline reference marking code from transform_ts_import_equals

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
crates/oxc_transformer/src/typescript/module.rs	Adds enter_program hook and two new helper methods for marking unused import equals references; removes inline reference marking from transformation logic
crates/oxc_transformer/src/typescript/mod.rs	Calls module.enter_program to mark unused import references before transformation
tasks/transform_conformance/tests/.../remove-unused-import-equals/input.ts	Test case with used/unused import chains and namespace with unused imports
tasks/transform_conformance/tests/.../remove-unused-import-equals/output.js	Expected output showing only used imports transformed and unused ones removed
tasks/transform_conformance/snapshots/oxc.snap.md	Test snapshot showing semantic mismatches indicating the test doesn't fully pass yet

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[charliecreates]

The new unused import = pre-pass is directionally good, but it currently only scans top-level statements and misses nested import = declarations inside namespaces/modules, which is a correctness issue (and likely related to the new snapshot mismatches). Additionally, moving reference-flag mutation to enter_program introduces ordering assumptions about when semantic references are finalized. Finally, the strict debug_assert_eq!(..., ReferenceFlags::Read) makes the transformer fragile to future semantic-flag changes.

Additional notes (1)

• Maintainability | crates/oxc_transformer/src/typescript/mod.rs:81-85
  The new pre-pass marks module-reference identifiers as Type only when the binding has all-type references. This assumes that get_resolved_references(decl.id.symbol_id()) is fully populated and stable at enter_program time.

If any later traversal phase can create additional value references to that symbol (e.g., via desugaring, namespace transforms, or other TS passes that synthesize identifiers), this pre-pass can incorrectly flip a Read to Type too early, potentially causing an actually-used value import to be treated as type-only downstream.

Given you now call this at enter_program, it’s worth asserting/ensuring that no subsequent pass introduces new value references to TSImportEqualsDeclaration bindings (or that such passes run before this marking).

Summary of changes

What changed

• TypeScript transformer traversal order: TypeScriptModule::enter_program is now invoked from TypeScript::enter_program (crates/oxc_transformer/src/typescript/mod.rs).
• Refactor of unused import = handling: moved the logic that re-flags module-reference identifiers from Read → Type out of transform_ts_import_equals and into a dedicated pre-pass:
  • Added TypeScriptModule::enter_program which calls mark_unused_import_equals_references_as_type.
  • Implemented reverse-order scanning of top-level statements to correctly handle chained import x = y.z relationships.
• Conformance coverage: added a new fixture remove-unused-import-equals and updated snapshot counts/results.

Files touched:

• crates/oxc_transformer/src/typescript/mod.rs
• crates/oxc_transformer/src/typescript/module.rs
• tasks/transform_conformance/snapshots/oxc.snap.md
• tasks/transform_conformance/tests/.../remove-unused-import-equals/{input.ts,output.js}