Replace use of str(pathlib.Path(...)) in codebase

[freakboy3742]

Describe the bug

Brett Cannon tweeted this recently:

Python tip: anytime you accept a path that could be a path-like object (e.g. pathlib), never rely on its string repr; always use os.fsdecode(), os.fsencode(), or os.fspath() depending on what you want; None is probably not an acceptable path for your needs 😉. https://twitter.com/brettsky/status/1404521184008413184

This is something we do extensively in the Briefcase codebase... but I guess we shouldn't.

To Reproduce

Not sure - seeking clarification from Brett.

[papalotis]

I can try working on it

[freakboy3742]

After further conversation with Brett, we might not be as badly affected as I initially thought.

I originally thought this would manifest as filesystem encoding problems; but it turns out it's "objects that have an str() representation but aren't paths" that are the problem - most notably, None.

We don't (or shouldn't) have any places where a None can turn up as a path - so this won't affect us too badly.

However, there are a lot of test cases where we included explicit calls to str() for compatibility with Python 3.5; and there will be a couple of places in the codebase where we're calling str() but should be calling os.fsdecode().

@papalotis You're welcome to take a look at this is you want! The task will be to audit everywhere in the codebase that we're currently explicitly invoking str(); If the argument is a pathlib object, update the code. This will involve either:

1. Removing the str() call entirely (because it was introduced for Python 3.5 compatibility)
2. Replacing the use of str() with os.fsdecode().

The slightly harder audit will be to look for all implicit invocations of str(), caused when a pathlib object is being passed to an f-string/str.format() call. It might make sense to do this as part of converting all the str.format() calls with their equivalent f-strings.

[iamzili]

@papalotis Hi, are you working on this issue? If not I would like to take it.

[freakboy3742]

@zili55 Based on the lack of response from @papalotis, I'd say the ticket is yours! If you've got any questions, ask away, either here or in Discord.

[mullera3]

I would like to try working on it @freakboy3742

[freakboy3742]

@mullera3 @zili55 is already working on this issue; they have been communicating with me on details outside this ticket. If you're interested in contributing to a different ticket, check out the first timers only tickets in our repo for some ideas.

[mullera3]

Okay thank you! @freakboy3742

[iamzili]

@freakboy3742 this issue can be closed, right?

[freakboy3742]

Yes - this was corrected by #599.