Fix renaming directory project using build scripts with cross-compiling.

[ehuss]

The rename-protection introduced in #4818 checks for paths with a prefix of /…/target/debug, but this does not work for paths used during cross-compiling.

This change checks for paths with the full OUT_DIR prefix, and the build/PKG/root-output file now includes that full OUT_DIR instead of /…/target/debug.

This also includes a few other changes:

• Support fixing KIND=PATH style paths.
• Support fixing paths in metadata (like cargo:root=… or cargo:include=… which are common).
• Adds a "version" value to the metadata hash to ensure that cargo doesn't get confused with the new root-output file format.

Fixes #6177

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+

Awesome, thanks for this!

[bors]

📌 Commit d1045c9 has been approved by alexcrichton

[bors]

⌛ Testing commit d1045c9 with merge 53e436d...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 53e436d to master...

[ExpHP]

So I imagine that, when mapping custom metadata, this probably only handles the path if it is at the very beginning of the value? (since searching for matches anywhere in the value would seem risky, even if it still is unlikely to generate false positives; and I also didn't notice anything performing a search in the source diff)

One could picture for instance custom metadata that looks something like this:

cargo:path=<OUTDIR>/subdir1:<OUTDIR>/subdir2

and it could be a pretty confusing footgun if this gets mapped to

cargo:path=<NEW_OUTDIR>/subdir1:<OLD_OUTDIR>/subdir2

At the same time, this mechanism alone is sufficiently powerful for people to write

cargo:outdir=<OUTDIR>

and join paths on their own, so perhaps it mostly boils down to just an issue of documentation.

[ehuss]

It replaces all occurrences throughout the line:

cargo/src/cargo/core/compiler/custom_build.rs

Lines 462 to 465 in 53e436d

	let value = value.replace(
	script_out_dir_when_generated.to_str().unwrap(),
	script_out_dir.to_str().unwrap(),
	);

The path should be relatively unique (/path/to/project/target/debug/build/$PKG-$HASH/out), so I think it should be safe. This also only applies when you have moved the target directory.