bootstrap: Simplify absolute path handling

[Zalathar]

The existing code takes a command-line argument (that might not even be a path), glues it to the repository path, makes it absolute relative to the working directory, then tries to strip the repository path off again.

That all seems needlessly complicated.

The new approach is much simpler: If an argument is an absolute path that exists, try to strip the repository path from it, or otherwise change nothing. That should hopefully give the same results in every useful case.

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Relevant earlier PRs:

• Support absolute source paths in bootstrap #126782
• Allow running x <cmd> <path> from a different directory #146774

r? Kobzol (who last modified this code), or bootstrap

[rustbot]

Kobzol is not on the review rotation at the moment.
They may take a while to respond.

[Zalathar]

I believe this simpler implementation handles all the useful cases imagined by the previous PRs, but I could use a second opinion in case there's something I overlooked.

Specifically:

• Paths relative to the repository root, and arguments that aren't physical paths, should both continue to work regardless of working directory.
• Absolute paths to files/directories in the repository root should be correctly stripped. Any other absolute path is passed-through as-is, and will likely lead to failure (as expected).

[Kobzol]

This is indeed easier, thanks!

One thing that has changed though is that non-existing absolute paths no longer panic. I think that would be nice to keep, otherwise the path might get "too far" in bootstrap, and fail somewhere where the error message might be much less understandable.

View changes since this review

[Zalathar]

One thing that has changed though is that non-existing absolute paths no longer panic. I think that would be nice to keep, otherwise the path might get "too far" in bootstrap, and fail somewhere where the error message might be much less understandable.

Hmm yeah, it might be worth being more defensive here.

[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.

[Zalathar]

I added a check and early-exit for absolute paths that weren't resolved (diff).

[Kobzol]

Ok. The error can still a bit misleading in theory, but hopefully people will understand what it means. Thank you!

@bors r+ rollup

[rust-bors]

📌 Commit b531faf has been approved by Kobzol

It is now in the queue for this repository.

[Zalathar]

Ok. The error can still a bit misleading in theory, but hopefully people will understand what it means.

I agree that the error isn't great (which is why I tried to improve it), but in the end I didn't want the cleanup itself to get derailed by the harder problem of emitting good error messages. So for now I'll settle for not-worse. 😅