[isolatedDeclarations] Should imported JSON files be emitted when "resolveJsonModules", "emitDeclarationOnly", and "isolatedDeclarations" are all enabled?

🔍 Search Terms

json, resolvejsonmodules, isolateddeclarations, emit, declarations, import, emitDeclarationOnly

✅ Viability Checklist

• 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, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Emit/transpile JSON files when the aforementioned compile options are enabled

📃 Motivating Example

The primary purpose of isolated declarations is to be able to emit declarations for a project without needing to typecheck it and one of the main motivators for that is being able to start typechecking downstream projects, e.g. in a composite build, without waiting for typecheck.

It might be fair to say then that it would be good for downstream projects to be able to start typechecking without waiting for their dependees to transpile code. Even with isolated declarations, this is not possible at the moment, because types may depend on JSON files when resolveJsonModules is enabled, and JSON files are only emitted/copied when JS transpilation is enabled, i.e. "emitDeclarationOnly": false.

💻 Use Cases

Being able to typecheck a composite project in parallel where sub-projects are configured with

    "isolatedDeclarations": true,
    "emitDeclarationOnly": true,
    "resolveJsonModule": true,