copies: choose target directory based on longest match If one side of a merge renames `dir1/` to `dir2/` and the subdirectory `dir1/subdir1/` to `dir2/subdir2/`, and the other side of the merge adds a file in `dir1/subdir1/`, we should clearly move that into `dir2/subdir2/`. We already detect the directories correctly before this patch, but we iterate over them in arbitrary order. That results in the new file sometimes ending up in `dir2/subdir1/` instead. This patch fixes it by iterating over the source directories by visiting subdirectories first. That's achieved by simply iterating over them in reverse lexicographical order. Without the fix, the test case still passes on Python 2 but fails on Python 3. It depends on the iteration order of the dict. I did not look into how it's built up and why it behaved differently before the fix. I could probably have gotten it to fail on Python 2 as well by choosing different directory names. Differential Revision: https://phab.mercurial-scm.org/D10115