Migrate test suite to use run-pass stdout/stderr testing

[Mark-Simulacrum]

Where possible, we should prefer to use the functionality added by #63825 instead of std::process and the like. At least one such test is known, but it's possible more can be found.

[Mark-Simulacrum]

I'll try to get mentoring instructions up for the actual move but the first step here is to look for all run-pass tests (// run-pass in src/test/ui I believe) and verify we're ignoring cloudabi, emscripten, and sgx in all of them. This is pretty annoying to do manually I suspect but I'd recommend comparing the results of rg -o ignore-\w+ src/test/ui and rg -c run-pass src/test/ui (exact commands may need to differ)

[RalfJung]

verify we're ignoring cloudabi, emscripten, and sgx in all of them

It does not at all seem like we do:

$ rg run-pass src/test/ui | wc -l
3200
$ rg ignore-cloudabi src/test/ui | wc -l
82

[RalfJung]

I think that file changed in #63825 was ignored just because it uses process -- but just running the test seems to work fine on those platforms. I suppose CI has some way to cross-run them and compiletest uses that?

It does not use process any more so probably it can be unignored.

[Mark-Simulacrum]

Ah, so the comment is just misleading in that this is not "no processes" but rather no "std::process"?

[RalfJung]

That's how I initially read that comment, and I still do, yes.

[Mark-Simulacrum]

Aha, okay, then probably just misread on my part. Closing since we probably don't actually want to do anything here.

[RalfJung]

Well I think we want to remove those ignore from the test that got changed in #63825.