[META] Pain Point Tracker

[Stebalien]

This is where I'm going to keep a list of known pain points with tempfile v3 that can't be fixed without breaking changes. I don't know if we'll ever have a v4, but if we do, we can revisit everything on this list:

• TempDir implements AsRef<Path> making it easy to accidentally drop it.
• A file name prefix can contain a slash. May be fixable in a minor version with a warning?
• Temporary directories are created with the default mode unlike temporary files which are created with 0o600. Ideally temporary directories would use restrictive permissions by default.
• The builder has two lifetime parameters making it awkward to add additional fields with new lifetime parameters. Ideally, it would just have a single lifetime and we'd rely on subtyping.
• Take shared advisory locks on all named temporary files to prevent temporary file cleaners from deleting them. This could break some things so we have to be careful, but taking a shared lock is probably reasonable? Possibly only do this if the parent directory is +t (sticky)?

[marcospb19]

I'd expect the #59 fix to require a major version update, it's not obvious to users whether that's a bug or intended behavior, so that should be assumed as breaking IMHO.

EDIT: that is, if the fix is to make that function panic.

[Stebalien]

Closing in favor of #327 where I'll be tracking all 4.0 changes.