Allow '--noEmit' to override 'emitDeclarationOnly' from config.

Search Terms

• TS5053
• emitDeclarationOnly

Suggestion

Using "emitDeclarationOnly": true in your tsconfig.json prevents you to do typechecking only runs as running tsc --noEmit will throw the following error.

error TS5053: Option 'emitDeclarationOnly' cannot be specified with option 'noEmit'.

And the CLI does not look like to have any flag to bypass the error (eg. something like --noEmitDeclarationOnly).

I don't see a reason why a noEmit cli flag would not take precedence over the emitDeclarationOnly from the tsconfig.

Use Cases

With a project with a tsconfig.json set with emitDeclarationOnly and using another compiler like babel to produce the built javascript code, you want to be able to both:

• Compile declaration files (running tsc)
• Perform typechecking as a test stage (eg. travis) (running tsc --noEmit). Especially since you do not use TypeScript to compile (so a build could pass with typings errors).

Examples

https://github.com/mgcrea/node-influx-syslog

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.

Start at the compiler-option validation that reports TS5053 and trace how command-line noEmit is merged with tsconfig emitDeclarationOnly. Add coverage for the requested precedence and verify both declaration emission and noEmit type-checking paths; done means tsc --noEmit accepts the configuration while normal tsc behavior remains intact.