Fix crash: JSTypeAliasDeclaration passed to GetTypeOfDeclaration during CJS declaration emit

[Copilot]

When a @typedef and a module.exports.Property = value assignment share the same symbol name, TypeScript merges both into symbol.Declarations — one JSTypeAliasDeclaration (type) and one BinaryExpression (value). During declaration emit, the "first-in-wins" fallback in serializeTypeForDeclaration searched for any declaration with a non-nil Type(), which matched the JSTypeAliasDeclaration. Calling GetTypeOfDeclaration on it panicked since it only handles inferrable (value) nodes.

Repro:

// local-lib/ModuleGraphConnection.js
/** @typedef {typeof T} T */
const T = Symbol();
module.exports = class ModuleGraphConnection {};
module.exports.T = T;  // ← 'T' symbol now has both JSTypeAliasDeclaration and BinaryExpression

// repro.js
/** @typedef {import('./local-lib/ModuleGraphConnection')} ImportedType */
/** @type {ImportedType} */
module.exports = class Repro {};

tsc --allowJs --emitDeclarationOnly --declaration repro.js → panic

Changes

• internal/checker/nodebuilderimpl.go: Guard the fallback declaration search with ast.HasInferredType(d) so only inferrable (value) declarations are candidates for GetTypeOfDeclaration, filtering out JSTypeAliasDeclaration and any other non-inferrable kinds.
• testdata/tests/cases/compiler/jsTypedefMergedWithModuleExportProperty.ts: Regression test covering this exact pattern.

• Fixes TypeScript 7.0 Can't compile webpack #4607

[Copilot]

Pull request overview

Prevents a CJS declaration-emit panic caused by merged type and value declarations.

Changes:

• Restricts fallback type inference to inferrable declarations.
• Adds regression coverage and compiler baselines.

Show a summary per file

File	Description
internal/checker/nodebuilderimpl.go	Filters unsafe fallback declarations.
testdata/tests/cases/compiler/jsTypedefMergedWithModuleExportProperty.ts	Adds the crash regression case.
testdata/baselines/reference/compiler/jsTypedefMergedWithModuleExportProperty.types	Records inferred types.
testdata/baselines/reference/compiler/jsTypedefMergedWithModuleExportProperty.symbols	Records merged symbols.
testdata/baselines/reference/compiler/jsTypedefMergedWithModuleExportProperty.js	Records JS and declaration output.
testdata/baselines/reference/compiler/jsTypedefMergedWithModuleExportProperty.errors.txt	Records expected diagnostics.

Review details

• Files reviewed: 6/6 changed files
• Comments generated: 0
• Review effort level: Medium

[weswigham]

@copilot IMO, this is a bug in hasTypeAnnotation - likely because of it relying solely on .Type() which is overbroad - it shouldn't be returning true for typedefs or similar constructs. Fix it at the root instead of patching it just here. Use getEffectiveTypeAnnotationNode in strada as a reference (even though we don't need the JSDoc lookup parts anymore) - it bails on type aliases for this reason.

[Copilot]

@copilot IMO, this is a bug in hasTypeAnnotation - likely because of it relying solely on .Type() which is overbroad - it shouldn't be returning true for typedefs or similar constructs. Fix it...

Fixed in commit fb16199. hasTypeAnnotation now explicitly excludes TypeAliasDeclaration and JSTypeAliasDeclaration, mirroring the if (isTypeAliasDeclaration(node)) return undefined bail-out in getEffectiveTypeAnnotationNode. The call site reverts to the plain hasTypeAnnotation predicate — no &&ast.HasInferredType(d) needed since the only non-value declarations that have .Type() set are the type alias kinds we now filter in the function itself.