dirstate.walk: use the file foldmap to normalize Computing the set of directories in the dirstate is expensive. It turns out that it isn't necessary for operations like 'hg status' at all. Why? Consider the file 'foo/bar' on disk, which is represented in the dirstate as 'FOO/BAR'. On 'hg status', we'd walk down the directory tree, coming across 'foo' first. Before: we'd normalize 'foo' to 'FOO', then add 'FOO' to our visited stack. We'd then visit 'FOO', finding the file 'bar'. We'd normalize 'FOO/bar' to 'FOO/BAR', then add it to the results dict. After: we wouldn't normalize 'foo' at all. We'd add it to our visited stack, then visit 'foo', finding the file 'bar'. We'd normalize 'foo/bar' to 'FOO/BAR', then add it to the results dict. So whether we normalize intermediate directories or not actually makes no difference in most cases. The only case where normalization matters at all is if a file is replaced with a directory with the same case-folded name. In that case we can do a relatively cheap file normalization instead and still get away with not computing the set of directories. This is a nice boost in status performance. On OS X with case-insensitive HFS+, for a large repo with over 200,000 files, this brings down 'hg status' from 4.00 seconds to 3.62.