io::walk_dir could have a more detailed return value, to avoid extra stat calls

[huonw]

When calling walk_dir one often wishes to handle files and directories differently, the walk_dir call knows this internally (it calls .is_dir and readdir etc.) but this is not passed on to the users, and so users are forced to call .is_dir etc. themselves.

Maybe walk_dir could return a Iterator<DirEntry>, with (as a bikeshedable suggestion)

struct DirEntry {
    pub path: Path,
    pub stat: FileStat
}

(Inspired by http://legacy.python.org/dev/peps/pep-0471/ , which shows dramatic performance improvements with changes similar to this.)

[huonw]

cc #16237

cc @alexcrichton

[alexcrichton]

Interesting! We should definitely keep this in mind when stabilizing the walk_dir function. It sounds like this would be great to implement.

[aturon]

cc me

[alexcrichton]

This is now implemented.