[api-extractor] Unable to analyze the export "Seq" when bundling immutable v5

Start with API Extractor's ExportAnalyzer._getExportOfAstModule and reproduce the failure using immutable@5.1.5, TypeScript 5.7.3, and the entry declaration described in the issue. Compare how Seq and its nested namespaces are resolved against immutable@4.x; done means the bundled .d.ts rollup succeeds and inlines immutable's declarations without the internal export-analysis error.

Summary

@microsoft/api-extractor crashes with an internal error when immutable (v5) is listed in bundledPackages. The crash happens during analysis of the Seq export and is reproducible against an unmodified immutable@5.1.5 install.

This blocks distributing a self-contained .d.ts rollup for any consumer that re-exports types from immutable v5. The same project bundled immutable@4.x without issue, so the regression is on the Immutable v5 declaration shape.

Repro steps

1. npm i immutable@5.1.5 @microsoft/api-extractor@7.58.7 typescript@5.7.3

2. Create an entry .d.ts that re-exports something from immutable, e.g.:

   import type { List } from 'immutable'
   export declare function getList(): List<string>
   
   

3. In api-extractor.json set "bundledPackages": ["immutable"].

4. Run api-extractor run --local --diagnostics.

Expected result: API Extractor inlines Immutable's declarations into the rollup, as it does for immutable@4.x.

Actual result:

ERROR: Internal Error: Unable to analyze the export "Seq" in node_modules/immutable/dist/immutable.d.ts

You have encountered a software defect. Please consider reporting the issue to the maintainers of this application.
Error: API Extractor failed with exit code 1

Details

The Immutable v5 declaration uses the same overall shape as v4 (declare namespace Immutable { … } export = Immutable; export as namespace Immutable;), but Seq and its nested namespaces (Seq.Keyed, Seq.Indexed, Seq.Set) are declared in a way that ExportAnalyzer._getExportOfAstModule can't resolve.

Workaround we ended up using: remove immutable from bundledPackages, let API Extractor emit import … from 'immutable', then post-process the rollup with a small script that inlines the namespace and rewrites the renamed imports (Immutable_2, Map_3, Set_2, …) to local aliases of the inlined namespace. Happy to share if it helps reproduce.

Related to (but distinct from) #2220, #1972, #5507, #5694. Those all surface the same generic "Unable to analyze the export" error from different triggers.

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