[armadavalor]

Fixes #5166

cp -r W:/ dest on Windows failed with 'W:/id.dat' and 'W:/id.dat' are the same file.

A filesystem root has no parent, so Context::new leaves root_parent as None, and get_local_to_root_parent then returned the absolute source path unchanged. Entry::new does target.join(descendant), and joining an absolute path (or one with a drive prefix) discards target, so every entry was mapped onto itself. With W:/* it worked because the glob gives root_parent = Some(..).

The None arm now drops the Prefix and RootDir components, so the entries are placed relative to the target (dest/id.dat, dest/sub/x.txt). This is not Windows-specific logic: cp -r / dest goes through the same path, so I added a portable unit test as well as a Windows one.

Testing:

• unit tests in copydir.rs (one portable, one cfg(windows))
• manual, on Windows: subst Q: <dir> then cp -r Q:/ dest and cp -r Q:\ dest — before: the "same file" error, after: dest/id.dat, dest/sub/x.txt
• cargo test --features cp --test tests test_cp:: gives the same result before and after the change (136 passed, 41 failed); all 41 are tests that create symlinks, which need a privilege this Windows machine lacks.

I did not add an integration test in tests/by-util/test_cp.rs, since reproducing the bug needs a drive root (subst/mounted volume), which isn't reliably available in CI. Happy to add one if you have a preferred approach.

I have not verified the Unix side (cp -r / dest) by running it.

🤖 Generated with Claude Code

[sylvestre]

could you please import std::path::Component? it would fit on one line