When looking for worksapce root, don't step over CARGO_HOME

[matklad]

See the description of the problem in #4764 (comment).

The gist is that if you invoke cargo inside CARGO_HOME, which is inside a workspace, Cargo should not think that it is inside workspace.

This is the function where I think the fix should be applied:

cargo/src/cargo/core/workspace.rs

Line 311 in 806e487

fn find_root(&mut self, manifest_path: &Path)

Relevant tests are here: https://github.com/rust-lang/cargo/blob/806e487c0e3b6af6203ef8bebf5d6f49faf8909d/tests/workspaces.rs

[nox]

AFAIK, the value that holds CARGO_HOME reachable from that code is self.config.home(), but that returns a Filesystem and there is no way to inspect the inner PathBuf from that. Should I implement PartialEq<Path> for Filesystem?

[alexcrichton]

Yes it should be fine to implement PartialEq for that type, the Filesystem newtype is basically just preventing access when unlocked to help prevent synchronization bugs.

[nox]

@alexcrichton Will do that then.

As for the test, I guess we should make Cargo itself put a dependency in a custom CARGO_PATH, and for that to happen it needs to be a git dependency with a repository specified as a path. The dependency should then have a build script that invokes $CARGO metadata with CARGO_MANIFEST_PATH. I've looked at the existing tests and that should be pretty straightforward to do.

[alexcrichton]

Each test already has its own CARGO_HOME I believe, so it'd be fine to just throw a crate in there and build it. I believe you can use the Package helper used throughout to do this.