Update path remapping

[jsgf]

This is an update of PR #38348 to fix issue #38322. It allows arbitrary numbers of mappings, and attempts to handle relative remap paths to work as expected on relative source paths.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @eddyb (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[eddyb]

r? @michaelwoerister

[michaelwoerister]

Thanks for the PR! This looks like a step in the right direction (multiple remappings, better handling of relative paths) but here are some things to note:

• We have not actually reached an agreement on what the command line interface should look like in the other PR.
• It's not clear whether we should do path remapping in absolute/canonical space. I'd like to but GCC doesn't seem to do that.
• I think we should have a clear specification of the remapping logic and a test suite that makes sure we actually implement it correctly. The currently code is already pretty inconsistent.

I'll try to make some progress clarifying the actual logic in the original issue (#38322) soonish.

[jsgf]

@michaelwoerister Thanks - the main reason for posting this is to try and kick things along a bit. This is an issue I've started running into, so I'd like to see it resolved.

[bors]

☔ The latest upstream changes (presumably #39563) made this pull request unmergeable. Please resolve the merge conflicts.

[jsgf]

Superseded by #41419