Fix use of .. in dep-info-basedir

[Gnurfos]

Summary

This allows setting, in .cargo/config's dep-info-basedir, some relative path that goes above the crate's directory.

Motivation

In a setup like this:

repo_root
├── Makefile
├── some_c_things
│   └── foo.c
└── rust_things
    ├── Cargo.toml
    └─── src
        └── lib.rs

If you want the generated .d files to be includable directly in the Makefile (without post-processing), you need them to mention paths relative to the root, like:

rust_things/target/....: rust_things/src/lib.rs

Implementation

For this you need to have relative paths with parent directories (in this case ..) in dep-info-basedir, which does not work without the change in this PR (due to render_filename doing only strip_prefix, while the basedir still contains literal ..s).

Let me know if this change is acceptable. Another implementation could be to canonicalize in ConfigRelativePath::resolve_path instead, especially since that struct outputs absolute paths. But that would have it access the filesystem, while it currently doesn't.

[rust-highfive]

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

Please see the contribution instructions for more information.

[Gnurfos]

Hi, @ehuss , I'm having trouble getting this to work for Windows, due to canonicalize there converting to an "extended path", while I need to support non-existing files (as per the pre-existing test) which cannot be canonicalized.
Is it problematic if my changes are made unix-only ? (the behaviour of canonicalize might change in the future)

[ehuss]

Using fs::canonicalize is generally problematic and we try to avoid it as much as possible. It does need to support Windows, so you'll need to find some way around that. Maybe something like normalize_path could be used?

[Gnurfos]

Thanks, I got it to work with normalize_path. It's not great that it doesn't follow symlinks, but I suppose it will fit most people's use cases. Better to have it work on Windows and use a centralized function

[ehuss]

Thanks!

@bors r+

[bors]

📌 Commit e5ff81b has been approved by ehuss

[bors]

⌛ Testing commit e5ff81b with merge 9fa2bba...

[bors]

☀️ Test successful - checks-actions
Approved by: ehuss
Pushing 9fa2bba to master...