[`mod_util`] Iterate over a `Mod`'s folder

[redruin1]

Mod has get_file, which is great for getting the contents of a particular named file. However, certain processes (localization + migrations) are filename agnostic - meaning that their location in some folder indicates their function instead of their filename. In these cases, it would be much nicer to give a folder and return a iterator containing all of the files/folders inside of it (probably alphabetically). Essentially, this would be a fs::read_dir equivalent:

let some_mod: Mod = ...;

let english_locale = some_mod.read_dir("locale/en")?;
for filename in english_locale {
    let data = mod.get_file(filename)?;

    // ...
}

This should be pretty easy to implement, so I'm willing to contribute a PR if you don't have any complaints.

[fgardt]

sure that'd be a great addition

I think in terms of order it should either be the regular lexicographic or natural order, but I'm not entirely sure what the game uses here. I'll try and figure out what would be the correct approach (maybe even both get used) and will update here.

In any case: please feel free to give an implementation a shot.

Mod::read_dir(impl AsRef<Path>) -> ??? to mimic std APIs seems good.
But I think having a function that would also only get files in a folder with a given extension could also be nice like Mod::get_files(impl AsRef<Path>, Option<&OsStr>) -> ???, whats your take on that?
(Could also be named Mod::read_dir_with_extension(....) I guess?)

[redruin1]

I think the Mod interface would behave as similarly to the standard filesystem stuff as possible, since ideally a Mod should just be a generic wrapper around a directory or a zip file. It would be nice, for example, if the iterator returned result objects that had the same kind of is_dir()/is_file()/etc. convenience methods that you would expect from regular filesystems. I was actually originally hoping to have Mod::read_dir(...) return an iterator of fs::DirEntry objects to make it truly opaque, but it doesn't seem like this is possible.

For now, the prototype version I wrote simply returns a Vec<String> of filenames that can be loaded with Mod::get_file().

To your second point: a Mod::get_files(...) function could definitely work, although my first impression is that you could simply use filter with read_dir to compose the set of files that you're looking for:

let mod: Mod = ...;

let cfg_files = mod.read_dir("locale/en")?.filter(|&x| x.ends_with(".cfg"));
for cfg_file in cfg_files {
    let data = mod.read_file(cfg_file)?;
    // ...
}

This would also benefit from the utility functions is_dir()/etc as well, as you could use it to filter based on file type/metadata/etc.

Perhaps there's a implementation reason as to why Mod::get_files(...) would be better, but I'm not sure that it would be much clearer/more concise than the code above..

[redruin1]

Implemented in #234.