Compiletest should set `RUST_SAVE_ANALYSIS_CONFIG` for `run-pass` tests

[jyn514]

#96777 was necessary because a test used both -Zsave-analysis and run-pass. That generated an untracked save-analysis-temp file in the root directory. That behavior is not great - we shouldn't do that even if the test is marked run-pass. We can avoid it by passing --out-dir config.build_base in compiletest:

rust/src/tools/compiletest/src/runtest.rs

Lines 1895 to 1907 in fee75fb

	match output_file {
	TargetLocation::ThisFile(path) => {
	rustc.arg("-o").arg(path);
	}
	TargetLocation::ThisDirectory(path) => {
	if is_rustdoc {
	// `rustdoc` uses `-o` for the output directory.
	rustc.arg("-o").arg(path);
	} else {
	rustc.arg("--out-dir").arg(path);
	}
	}
	}

We should also investigate why this wasn't caught by CI - it makes the source directory read only, which should have prevented this being merged.

@rustbot label +E-easy +A-testsuite +E-mentor

[jyn514]

We should also investigate why this wasn't caught by CI - it makes the source directory read only, which should have prevented this being merged.

I think it might run x.py from a working directory other than the source root.

[kingdido999]

@rustbot claim

[lionellloh]

@kingdido999 are you still working on it?

[lionellloh]

@rustbot claim

[lionellloh]

Hey @jyn514, thanks for offering to mentor!

Some questions -

What is the difference between check-pass and run-pass?

That generated an untracked save-analysis-temp file in the root directory.

What is the best way to repro this?

[jyn514]

@lionellloh "the difference between cargo check and cargo run" - the first just runs rustc --emit metadata while the second actually generates a binary and runs it. The reason it causes trouble here is because save-analysis uses --out-dir to determine where to put the generated JSON file, and defaults to the working directory if it isn't passed.

What is the best way to repro this?

Change any existing UI test with -Z save-analysis and check-pass to be run-pass instead.

[lionellloh]

@jyn514

Qq regarding dev efficiency:
I managed to repro the issue by running ./x.py test src/test/ui/const-generics/const-argument-non-static-lifetime.rs and changing check-pass to be run-pass.

The command ran for 10 minutes. I deleted the save-analysis-temp folder after the repro, made my patch and tried to run again. I realised the tests were ignored this time. I deleted the build folder so that the tests may not be ignored, but it seems like that causes the test to run for a pretty long time again. I wonder if that is avoidable?

One more n00b qn:
I am a little curious how // [full] run-pass is parsed. They seem like comments to me. Why does changing it change anything?

[jyn514]

@lionellloh touch src/test/ui/const-generics/const-argument-non-static-lifetime.rs should work and be quite fast.

[jyn514]

I think there's also a force-rerun flag or something like that.