Normalize .. and . in diagnostic file paths

[arferreira]

Fixes #51349

Lexically normalize . and .. in file paths when rendering diagnostics, so errors show foo.rs instead of sub/../foo.rs. Normalization is scoped to the new FileNameDisplayPreference::Diagnostics variant used by SourceMap::filename_for_diagnostics; file!(), debuginfo, and remapped/local/short paths are unchanged.

Uses the unstable Path::normalize_lexically, canonicalize is avoided because it turns relative paths absolute, which broke the previous attempt in #83345. Paths that normalize_lexically rejects (leading escapes, net-negative ..) fall back to the raw path and don't occur in practice for the diagnostic paths this PR targets. Compiletest gains a $DIR/.. substitution so existing .stderr files that referenced auxiliary paths above $DIR keep matching.

Previous attempt was #68654.

r? @estebank

[rustbot]

Some changes occurred in src/tools/compiletest

cc @jieyouxu

[Urgau]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[estebank]

My only concern with lexical normalization is that it doesn't hit the disk and one can craft a volume where ./foo/../bar.rs doesn't map to ./bar.rs. That seems convoluted though.

Could we add support for --verbose to print the path without normalization?

View changes since the review

[ChrisDenton]

If it's desirable, it would be possible to use something like same_file to test if both paths resolve to the same underlying file.

[arferreira]

I don't think we can hit the disk here, these paths don't need to exist locally. --verbose should cover the cases where you'd want the raw path anyway.

[ChrisDenton]

I would note that normalize_lexically is still very much a new API and there's currently some debate as to how it should be shaped. However, it should always be possible to do what's needed here so I'm not too concerned. I'm just bringing up that it may require a bit of churn.