clarify that calling fs::remove_dir_all on a file is an error

[lolbinarycat]

Location

https://doc.rust-lang.org/stable/std/fs/fn.remove_dir_all.html

Summary

Add to the errors section "if the passed path is a regular file, this function returns NotADirectory". This clarifies that it is not the same operation as rm -r, and also specifies which error will be returned in this case.

[jieyouxu]

This is actually mentioned already as

Additionally, [remove_dir_all] will also fail if the path is not a directory.

EDIT: wait I'm dumb, I just added that locally 💀

Though I do want to slightly reformat the caveats to make it easier to spot on a quick glance.

[jieyouxu]

Oh wait, this line exists on nightly std docs but not yet stable, which is why I'm so confused. It is indeed present already at https://doc.rust-lang.org/nightly/std/fs/fn.remove_dir_all.html.

I'm going to close this as the core request "documenting it will fail on not-a-directory" is satisfied, I'll send a follow-up to slightly reformat the error docs.