Add exists method on Dir

[aurelj]

This is pretty useful to be able to check for the existence of a file without having to actually open it.

[MabezDev]

is_dir: Option<bool> in the API feels a bit weird, I don't think it's needed.

IIRC, if is_dir is None, find_entry will return the entry whether it's a file or a dir. Could you check this, and also add a test case?

[aurelj]

Yes, indeed, if is_dir is None, find_entry will return the entry whether it's a file or a dir.

I understand why is_dir: Option<bool> feels weird in the API.
It may be clearer to have instead 3 separate functions in the API:

pub async fn exists(&self, mut path: &str) -> Result<bool, Error<IO::Error>>;
pub async fn file_exists(&self, mut path: &str) -> Result<bool, Error<IO::Error>>;
pub async fn dir_exists(&self, mut path: &str) -> Result<bool, Error<IO::Error>>;

(each one would only call a non-public function with a is_dir parameter)

Does it feel like a better API to you ?

Oh, and yes, I will add some tests.

[MabezDev]

LGTM, thanks!