Transformers with transpileOnly

[thetutlage]

I have read the readme file and it does mention that the transformers are not supported with the transpileOnly mode.

I do see that the source code is using ts.transpileModule which does support custom transformers. So my question is mainly to understand the reasoning behind not allowing transformers, when the underlying API of typescript allows it?

[cspotcode]

Git blame offers some context.

https://github.com/TypeStrong/ts-node/blame/master/src/index.ts#L789
#879

Transformers get access to the typechecker, which isn't available in transpileOnly mode.

If you want to use transformers in transpileOnly mode, I recommend using ttypescript via our compiler option. This will let you configure transformers via your tsconfig file.

ttypescript is a drop-in replacement for typescript with comprehensive transformer support. ts-node supports using alternative compilers.

https://github.com/cevek/ttypescript/tree/master/packages/ttypescript

[thetutlage]

Transformers get access to the typechecker

Yup, but there are other transformers as well. For example: A transformer to process path aliases and can be done in transpile only mode as well.

If you want to use transformers in transpileOnly mode, I recommend using ttypescript via our compiler option. This will let you configure transformers via your tsconfig file.

Yes, but don't want to use that.

The main question was, if transpileModule from compiler API accept the transfomers (with whatever limited capability), then why we cannot pass those transformers to typescript vs deciding to remove them all together

[cspotcode]

Looking at our source code again, it looks like transformers actually are supported in transpileOnly mode. The README's not super-clear, but it says that you cannot pass a factory function to our transformers option, but you can pass an object.

[thetutlage]

The code right now only accepts the compilerOptions and not the transformers. https://github.com/TypeStrong/ts-node/blob/master/src/index.ts#L492-L494

Whereas the options Typescript accepts are following.

interface TranspileOptions {
  compilerOptions?: CompilerOptions;
  fileName?: string;
  reportDiagnostics?: boolean;
  moduleName?: string;
  renamedDependencies?: MapLike<string>;
  transformers?: CustomTransformers;
}

[cspotcode]

This is what I'm looking at:

Which matches the type signature in our README.

[thetutlage]

If types are working doesn't mean the runtime code is also working. The source code reference I shared with you clearly shows that transformers are not passed to the transpileModule method.

Check this out

[cspotcode]

In that case, marked as "bug" and "help wanted." We'll accept a pull request that fixes it.

[thetutlage]

Sure, I will do a PR. Just wanted to understand, if we both expect it to work. Thanks 😄

[cspotcode]

This is (finally) published in v9.0.0: https://github.com/TypeStrong/ts-node/releases/tag/v9.0.0