Could you provide an example of why this is useful / what possibilities this unblocks please?

Also, why transpileOnly specific? (Unless I've misunderstood your PR it's not catering for non-transpile)

And, would the change you are suggesting change the usage for other people already relying on custom transformers? Would this be a breaking change?

Could you provide an example of why this is useful / what possibilities this unblocks please?

Yes, I want to write a typescript transformer plugin like https://github.com/emotion-js/emotion/tree/master/packages/babel-plugin-emotion#sourcemap, and I must inject source-map into output results. Before I do such things, I must access the rawPath of source files.

Also, why transpileOnly specific?

in non-transpile situation, rawPath could get by typescript itself

would the change you are suggesting change the usage for other people already relying on custom transformers? Would this be a breaking change?

Maybe. It would change the value of node.getSourceFile().fileName in custom transformers. from xx.ts to /Users/aaa/bbb/ccc/xx.ts.
But as I know, most of custom transformers are not relying on this value. (only filename is too simply, you can do so little things with it)

Before I do such things, I must access the rawPath of source files.

Cool

in non-transpile situation, rawPath could get by typescript itself

Sorry I don't follow your meaning here. Could you expand on this please?

let me explain it in this way.
if you write a custom transformer, and using it with transpileOnly: true and transpileOnly : false flags.
in transpileOnly: true situation, the value of node.getSourceFile().fileName is xxx.ts
in transpileOnly: false situation, the value of node.getSourceFile().fileName is /Users/aaa/bbb/ccc/xxx.ts, this value is correct for me now, and it was provided by TypeScript (typescript.Program resolve this path and provide it to custom transformer)

Ah I see! So this will align the behaviour of transpileOnly: true and transpileOnly: false, is that right?

If that's the case I kind of consider this a bugfix and I think we should take it.

So this will align the behaviour of transpileOnly: true and transpileOnly: false, is that right?

Yes, right

Could you update the package.json to 5.1.1 and put an entry in the changelog please?

updated

@johnnyreilly

Thanks - quite busy right now but I'll try to put a release out soon.

thank you😁

Shipped with https://github.com/TypeStrong/ts-loader/releases/tag/v5.1.1