[Mariana Castro (maricastroc)]

Fixes #64706

Problem

A type parameter and a parameter with the same name (<value>(value: value)) share one symbol. When declaration emit reuses existing type nodes and renames a shadowed inner type parameter (for example to value_1), the identifier rewriter in nodecopy.go only checked whether the symbol had TypeParameter flags. So references that need the value meaning were renamed too:

• type predicate and assertion targets (value is ..., asserts value, asserts value is ...)
• typeof value and typeof value.member
• computed property names ({ [value]: number })

This produced declarations that don't compile (TS1225, TS2693), or, when another parameter was already named value_1, declarations that compile but refer to the wrong parameter.

Fix

attachSymbolToLeftmostIdentifier now receives the meaning of the reference and only uses typeParameterToName when the symbol is a type parameter in that meaning. The type parameter accessibility shortcut in trackExistingEntityName uses the same check, so value references to the shared symbol go through the normal accessibility check.

Before:

export declare function predicate<value>(value: value): <value_1>(value: value_1) => value_1 is value_1 & string;
export declare function capturedQuery<value>(value: value): <value_1>(value: value_1, value_1: number) => typeof value_1;

After:

export declare function predicate<value>(value: value): <value_1>(value: value_1) => value is value_1 & string;
export declare function capturedQuery<value>(value: value): <value_1>(value: value_1, value_1: number) => typeof value;

Tests

declarationEmitShadowedTypeParameterSharesParameterName.ts covers type predicates, both assertion forms, typeof in return and parameter types, qualified typeof, computed property names, the cases where another parameter is already named value_1, nested functions, arrow functions, object methods, and a local typeof that refers to a different symbol. Thanks Jason Kuhrt (@jasonkuhrt) for the extra cases in the issue.

I also checked the emitted declarations with a consumer (skipLibCheck: false): it type-checks, and the predicates, assertions and typeof return types act on the first parameter, as in the source.

npx hereby validate passes.

This PR was prepared with AI assistance (Claude Code).

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

The narrowly scoped checks preserve value references while retaining type-parameter renaming, and the regression baselines cover the reported failure modes.

No open issues 🎉

What changed in this PR

Fixes #64706 in the native TypeScript compiler by preserving value-reference names when declaration emit renames shadowed type parameters.

Changes:

• Makes identifier rewriting and accessibility checks respect whether a reference uses the type or value meaning.
• Adds regression coverage for predicates, assertions, type queries, computed properties, and parameter-name collisions.
• Records expected declaration output, types, and symbol bindings.

File	Description
tsc/​internal/​checker/​nodecopy.go	Restricts type-parameter renaming to references with the appropriate meaning.
tsc/​testdata/​tests/​cases/​compiler/​declarationEmitShadowedTypeParameterSharesParameterName.ts	Adds regression cases for shared type/value names.
tsc/​testdata/​baselines/​reference/​compiler/​declarationEmitShadowedTypeParameterSharesParameterName.types	Records expected types with preserved value references.
tsc/​testdata/​baselines/​reference/​compiler/​declarationEmitShadowedTypeParameterSharesParameterName.symbols	Records symbol bindings for the regression cases.
tsc/​testdata/​baselines/​reference/​compiler/​declarationEmitShadowedTypeParameterSharesParameterName.js	Records JavaScript and corrected declaration output.

_{Review effort: Balanced}