GH-73435: Add pathlib.PurePath.full_match()

[barneygale]

In #101398 we added support for the recursive wildcard ** in pathlib.PurePath.match(). This should allow arbitrary prefix and suffix matching, like p.match('foo/**') or p.match('**/foo'), but there's a problem: for relative patterns only, match() implicitly inserts a ** token on the left hand side, causing all patterns to match from the right. As a result, it's impossible to match relative patterns from the left: PurePath('foo/bar').match('bar/**') is true!

This PR reverts the changes to match(), and instead adds a new full_match() method that:

• Allows empty patterns
• Supports the recursive wildcard **
• Matches the entire path when given a relative pattern

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• Issue: Support recursive wildcards in pathlib.PurePath.match() #73435

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📚 Documentation preview 📚: https://cpython-previews--114350.org.readthedocs.build/en/114350/library/pathlib.html#pathlib.PurePath.globmatch

[zooba]

Does the problem extend beyond "** is allowed to match nothing"? Or can we change the existing algorithm to require that a trailing ** has to match at least one segment?

Presumably .match("foo\\*") has to find something after foo\, so would be a better version of "foo\\**" anyway, but I can't imagine anyone being happy that "foo\\**" matches "foo\\" - you wouldn't specify the ** if you didn't want something to be found there.

[barneygale]

** matching nothing is quite normal I think - it's what glob.glob(), pathlib.Path.glob(), zsh, and IIRC bash do. If you want at least one segment after foo/, you can spell that with foo/**/*.

[barneygale]

e.g. zsh man page:

A pathname component of the form '(foo/)#' matches a path consisting of zero or more directories matching the pattern foo.

As a shorthand, '**/' is equivalent to '(*/)#'; note that this therefore matches files in the current directory as well as subdirectories. Thus:

ls (*/)#bar

or

ls **/bar

does a recursive directory search for files named 'bar' (potentially including the file 'bar' in the current directory).

[zooba]

Okay, I definitely like having full in the name somewhere then. It's still a match, and the parallel is fullmatch is way more helpful than to glob (which would just raise questions about "how does match do its matching then?")

[zooba]

LGTM

[barneygale]

Thanks for the reviews, both.