[Timur Vural (timurzvural)]

Fixes #65106

Summary

Under the flag --isolatedDeclarations, native tsc reported the wrong diagnostics when a function return expression involved the return of an entity name:

For "return x", TS9039 private name was the actual error, vs. the expected "TS9007 add return type".
For "return this.x", TS9013 expression was the actual error, vs. the expected TS9008 add return type.

There were two related port mistakes:

1. diagnostics.go — The entity-in-type-node error is the diagnostic for an entity name used inside a type when that name isn’t safely usable for declaration emit. Strada only emits the entity-in-type-node error when (isPartOfTypeNode(node) \|\| isTypeQueryNode(node.parent)) && (isEntityName(node) \|\| isEntityNameExpression(node)). Go checked IsTypeQueryNode(node) and it had an unconditional entity-name branch, so value-position identifiers hit TS9039.

2. typeFromSingleReturnExpression — Unlike typeFromVariable / typeFromProperty (and Strada's failed result for bare identifiers), a bare PseudoTypeInferred from return x / return this.x was kept as the return pseudotype, so inference fallback looked at the expression. The update treats bare Inferred (no ErrorNodes) as a failure and falls through to Inferred(fn), relying on the signature of the function fn.

Testing plan

• go -C ./tsc test -run='TestLocal/isolatedDeclaration' ./internal/testrunner
• New isolatedDeclarationsReturnEntityName baselines show TS9007/TS9008
• Verified against issue reproduction: native diagnostics now match classic 6.0.3

[Ryan Cavanaugh (RyanCavanaugh)]

Please wash the AI smell off these code comments

[Copilot]

🟢 Approval recommended

No active review issues are reported for the changes aligning isolated-declaration return diagnostics with classic TypeScript.

No open issues 🎉

What changed in this PR

Fixes #65106 by aligning native TypeScript’s --isolatedDeclarations diagnostics with classic TypeScript for return x and return this.x, reporting missing return-type annotations instead of private-name or expression errors.

Changes:

• Restricts private-name diagnostics to entity names in type positions.
• Falls back to signature-level diagnostics when return-expression inference fails without specific error nodes.
• Adds regression coverage and baselines for TS9007 and TS9008.

File	Description
tsc/​testdata/​tests/​cases/​compiler/​isolatedDeclarationsReturnEntityName.ts	Adds function and method return regression cases.
tsc/​testdata/​baselines/​reference/​compiler/​isolatedDeclarationsReturnEntityName.types	Records expected inferred types.
tsc/​testdata/​baselines/​reference/​compiler/​isolatedDeclarationsReturnEntityName.symbols	Records expected symbol bindings.
tsc/​testdata/​baselines/​reference/​compiler/​isolatedDeclarationsReturnEntityName.js	Records expected JavaScript output.
tsc/​testdata/​baselines/​reference/​compiler/​isolatedDeclarationsReturnEntityName.errors.txt	Records TS9007/TS9008 and return-annotation guidance.
tsc/​internal/​transformers/​declarations/​diagnostics.go	Corrects type-position and parent type-query checks.
tsc/​internal/​pseudochecker/​lookup.go	Routes unsupported return inference to signature-level diagnostics.

_{Review effort: Balanced}

[Timur Vural (timurzvural)]

Removed the explanatory comments from lookup.go and diagnostics.go — the logic-only changes remain.

[Timur Vural (timurzvural)]

Removed all comments from tsc/internal/pseudochecker/lookup.go and tsc/internal/transformers/declarations/diagnostics.go (40480ab).