Provide type coverage metrics

Search Terms

• type coverage
• flow coverage

Suggestion

I'd love it if TypeScript had a tool to capture type coverage metrics, similar to Flow's Type Coverage feature. That coverage data could be used by IDEs (again, currently supported by Flow) to highlight gaps in type coverage. Basically, it should tell us which parts of our code are being evaluated as any.
Assuming it would work like Flow's feature, this could be a separate tsc option or separate cli command. Theirs works for single files and also offers a batch-coverage command for checking directories / whole projects, etc.

Use Cases

• The Type Coverage metric could be used much like test coverage info, helping us to identify gaps in our typing (particularly unexpected gaps caused by insufficient type definitions from library code).

Examples

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

まず、issue にリンクされている Flow Type Coverage と batch-coverage のドキュメントを確認し、次に TypeScript の tsc オプションまたは CLI コマンドで同等のメトリクスを公開できる方法を調査します。完了条件は、個々のファイル、およびディレクトリまたはプロジェクト全体のカバレッジについて、コードのどの部分が any として評価されるかを、IDE で利用可能なデータとともに報告することです。