Fix TS4053 when public method return type uses imported type alias for unexported symbol

[Copilot]

• Created test case declarationEmitTypeAliasCannotBeNamed.ts reproducing the TS4053 issue
• Reverted incorrect fix that caused regressions in submodule tests (declarationEmitUsingTypeAlias1, transformNestedGeneratorsWithTry, chained, enums, importClause_namedImports)
• Removed spurious .diff files for submodule baselines
• Test baselines now correctly show the TS4053 error (documenting the bug)

The previous fix attempted to resolve type aliases in getContainersOfSymbol and getAliasForSymbolInContainer, but this had unintended side effects on how symbols are resolved globally, causing regressions in Bluebird↔Promise resolution, enum member symbols, and import clause symbols. A correct fix will need a more targeted approach.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>TS4053 happens when public class method adopts imported type from library</issue_title>
<issue_description>## Steps to reproduce

1. Start a plain new project
   a. "@typescript/native-preview": "^7.0.0-dev.20260225.1"
   b. "typescript": "6.0.0-beta"
2. Run npx tsgo --init to get the default tsconfig.
3. Add a src/lib.ts & src/main.ts. Run npx tsc --noEmit & npx tsgo --noEmit to see the difference.

// lib.ts
interface Base { }

export type ExportBase = Base;

// main.ts
import type { ExportBase } from './lib.js'

interface Clonable<T> {
    clone(): Clonable<T>
}

export default class C {
    async method(res: Clonable<{ key: ExportBase }>) {
        if (Math.random() > 0.5) {
            res.clone();
        } else {
            return res.clone();
        }
    };
}

Behavior with typescript@6.0

No error.

Behavior with tsgo

src/main.ts:8:11 - error TS4053: Return type of public method from exported class has or is using name 'Base' from external module "package-directory/src/lib" but cannot be named.

8 async method(res: Clonable<{ key: ExportBase }>) {

Found 1 error in src/main.ts:8

---

I did find myself a few workarounds.

1. Add back or remove all return on all the branches in method(); but this could be impractical for a large codebase.
2. Export Base together with ExportBase; but it requires (hacky) package patching when it comes to 3rd party dependencies..

Also note that the error goes away if ExportBase is NOT purely an alias of Base. In other words, the below typing will actually pass tsc & tsgo typechecking.

- export type ExportBase = Base;
+ export type ExportBase = Base & { extra: number; };
```</issue_description>

<agent_instructions>Create a test for this case FIRST. COMMIT THAT with accepted baselines. Then, work on the issue.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes TS4053 happens when public class method adopts imported type from library #2911

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[jakebailey]

@copilot This is the wrong fix. See all the failing tests and newly added diffs.