zig init: allow specifying project path

[fel1x-developer]

This PR allows zig init to initialize project when path is specified.

Usage:

$ zig init # path not provided, initialize in the current directory
$ zig init foo # create dir named foo if it does not exists, then initialize under ./foo
$ zig init foo/bar # create dir tree foo/bar if it does not exists, then initialize under ./foo/bar

When specified path already exists as non-dir, the cli throws fatal()

Closes: #24290

[thep1geon]

I need to preface this with the fact that I am not involved in any development of Zig in any way. I am looking at this PR from the perspective of just a programmer.

Just by looking over your changes, I wonder if it be more readable to make the 'path' variable an optional u8 slice instead of relying on a separate 'path_specified' boolean variable and the u8 slice for the path? My thought process here is that it is less separate variables to have to be thinking about, and the path is either preset and valid or null and not specified.

Further more, looking over the code to make the directory, if one was provided, I believe you should return an error if the directory already exists. By not returning an error, the user would assume nothing went wrong and the project correctly initialized in the directory they specified. I suppose you could implement further logic to check if the directory is empty and still initialize the project, but I'm not sure about that one.

Just some food for thought.

[linusg]

This will fail before the first assignment because path starts as an empty slice. Did you test these changes?

[fel1x-developer]

Sorry I have a problem with building zig on my computer so I couldn't test it. I'll convert this to a draft and request reviews once the problem is resolved.

[siarie]

I think it's better to be an error instead. Someone might not want to accidentally writing any Zig files in their existing directory