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.

[draperunner]

FYI, this works:

tsc --noEmit --emitDeclarationOnly false

[aryzing]

@SamB seems reasonable, although to retain the general idea that CLI flags generally override configured behavior, cli flags should always override code emit settings from config, and noEmit should only override emit requests at the same level

For example, the noEmit flag overrides other flags that request code be emitted, and noEmit key in config overrides other keys in config that request code to be emitted. However, flags requesting code to be emitted will override noEmit key in config.

Pseudo-code for logic:

if (noEmit_flag) {
  do not emit anything
} else if (noEmit_flag && emitSomething_flag) {
  do not emit anything
} else if (noEmit_key && emitSomething_flag) {
  emit what was requested, cli flags always override 
} else if (noEmit_key && emitSomething_key) {
  do not emit anything
}