Elide namespace imports used only by type-only export aliases

[Copilot]

A namespace import was preserved when its only use was a type-only export import alias. This caused tsgo to emit runtime imports that TypeScript elides.

• Alias reference tracking

  • Avoid marking a namespace import as value-referenced from the module reference of an import = alias.
  • Preserve existing value alias behavior through the existing deferred import = reference path.

• Regression coverage

  • Added a compiler emit test for:

import * as ns from "./a";

export import A = ns.A;

which now emits:

export {};

[jakebailey]

@copilot Why does the old compiler not need this?

[Copilot]

The old compiler normally does not reach this case for checked TS emit: it records references during checking with specific hints (the import = declaration is marked via ReferenceHint.ExportImportEquals), rather than treating the RHS qualified name as an emitted expression. Its recursive markLinkedReferences fallback is mainly for noCheck/unchecked emit, where this pattern also preserves the import. tsgo currently relies on the recursive pass for normal import elision, so the RHS ns.A was visited and incorrectly marked ns as a value reference unless we skip import-equals module references here.

[Copilot]

The old compiler normally does not reach this case for checked TS emit: it records references during checking with specific hints (the import = declaration is marked via ReferenceHint.ExportImportEquals), rather than treating the RHS qualified name as an emitted expression. Its recursive markLinkedReferences fallback is mainly for noCheck/unchecked emit, where this pattern also preserves the import. tsgo currently relies on the recursive pass for normal import elision, so the RHS ns.A was visited and incorrectly marked ns as a value reference unless we skip import-equals module references here.