The --remap-path-prefix flag affects paths in dep-info files. This causes some problems witth Cargo.

Cargo uses these paths to detect if any source file has been modified. Since the common use case for --remap-path-prefix is to rewrite to some artificial path (like /rustc/$HASH which rust distributions use), this causes them to point to non-existent paths, which Cargo cannot check.

In some cases, this doesn't matter. Workspace members are built with relative paths which (usually) won't match the remap value. However, registry or vendored paths will get remapped. Cargo won't find the path, so it will always assume it needs to rebuilt, breaking it's rebuild detection.

I think dep-info paths should not be remapped. I think it keeps with the spirit of reproducible builds (the binaries aren't affected, this is just a side-channel build-system file). However, I'm not certain. I also don't know how hard this will be to implement.

Oh, and -Z binary-dep-depinfo doesn't seem to be affected by --remap-path-prefix.