Type check all files when emitting a file under -out

[JsonFreeman]

Since it is necessary to type check a source file before you emit it, it is necessary to type check all files before emitting -out.

Thanks @vladima for your help on this fix. It fixes #2061.

[CyrusNajmabadi]

nice catch. I'm wondering if there's a way to make this less error prone (though nothing is coming to mind). To some extent, what is weird is a model where a source file is passed at all to emit when you have -out. I mean, what does it mean to say "emit foo.ts" or "emit bar.ts" when you have "--out"? There's no effective difference, and it probably makes more sense for this to not be supported, or for the caller to have to say "emit all". (i'm just speaking out loud. i don't have an actual proposal).

[vladima]

👍

[CyrusNajmabadi]

Ok. So the managed side already distinguishes the idea between asking to get the emit output whne you have --out or not. So i think a better solution would be to make it an error to ask for emit output for a single file when you have --out. Instead, if you have --out, you just call getEmitResult with no source file specified. If you want the emit output for a single file, and you don't have --out, then you cna ask for it, and it should work.

Of course, this would be a breaking change. So we'd need to do this through some sort of getEmitOutput2 API .

[JsonFreeman]

@CyrusNajmabadi Looking at the logic in emitFiles that decides which files to emit, the choice of whether or not a file is specified does not correspond one-to-one with whether the compiler options include -out. The most salient example is -out with external modules. You can have -out, but call getEmitOutput on an external module, and it will only emit that module. That seems like a meaningful behavior, and the most obvious way to signify it is by passing a source file. Another example (less interesting) is if you getEmitOutput for a declaration file when -out is specified, which actually does not emit anything. This one doesn't matter as much because callers can just not call getEmitOutput for a declaration file. In fact, I could see making it an error to call getEmitOutput on a declaration file. But I think for the external module case, passing a source file to getEmitOutput is the best way to emit it.

[CyrusNajmabadi]

Ah true. So your approach makes a ton of sense, and is a very nice, lightweight way to get non-broken behavior. 👍

[CyrusNajmabadi]

Note: this shoudl be something we should be able to make a fourslash test for. Just a simple case with two files, with appropriate options set, and we ask for getEmitOutput for one file and get the wrong result.

[JsonFreeman]

It does have a fourslash test. It's part of the review.

[CyrusNajmabadi]

Yes. I am blind.