gh-117587: Add C implementation of os.path.abspath

[nineteendo]

Benchmark

posixpath.py by @eryksun:

absolute, with "/a" repeated
len   speedup
100   1.521x
500   1.157x
1000  1.128x
2000  1.068x
4000  1.019x

relative 'a', with cwd length
len     speedup
93+2    1.861x
548+2   1.729x
1003+2  1.881x
2043+2  1.556x
4058+2  1.548x

ntpath.py

script

::speedup-posixpath.abspath.bat
@echo off
echo 10 chars && call main\python -m timeit -s "import os" "os.path.abspath('a/' * 5)" && call speedup-posixpath.abspath\python -m timeit -s "import os" "os.path.abspath('a/' * 5)"
echo 100 chars && call main\python -m timeit -s "import os" "os.path.abspath('a/' * 50)" && call speedup-posixpath.abspath\python -m timeit -s "import os" "os.path.abspath('a/' * 50)"
echo 1000 chars && call main\python -m timeit -s "import os" "os.path.abspath('a/' * 500)" && call speedup-posixpath.abspath\python -m timeit -s "import os" "os.path.abspath('a/' * 500)"

10 chars
500000 loops, best of 5: 635 nsec per loop # before
500000 loops, best of 5: 517 nsec per loop # after
# -> 1.23x faster
100 chars
200000 loops, best of 5: 1.53 usec per loop # before
200000 loops, best of 5: 1.23 usec per loop # after
# -> 1.24x faster
1000 chars
50000 loops, best of 5: 9.87 usec per loop # before
50000 loops, best of 5: 7.73 usec per loop # after
# -> 1.28x faster

• Issue: Speedup posixpath.abspath() for relative paths #117587

[nineteendo]

The same approach doesn't work on Window, because ntpath.join() is much slower than nt._getfullpathname():

PS C:\Users\wanne\cpython> python -m timeit -s "import nt" "nt._getfullpathname('.')"; python -m timeit -s "import os" "os.path.join(r'C:\Users\wanne\cpython', '')"
1000000 loops, best of 5: 286 nsec per loop # _getfullpathname
200000 loops, best of 5: 1.41 usec per loop # join

[nineteendo]

Preferably, abspath() should not be naively implemented by simply joining a relative path with the working directory. It doesn't work for drive-relative paths. That's a long-standing bug in the generic implementation ntpath._abspath_fallback().

I didn't even get that far in the testing process. I already knew it wasn't going to work.
I did notice this while trying to eliminate normpath() from the current implementation.

[bedevere-app]

Thanks for making the requested changes!

@erlend-aasland: please review the changes made to this pull request.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[nineteendo]

erlend-aasland, I have made the requested changes; please review again.

[bedevere-app]

Thanks for making the requested changes!

@erlend-aasland: please review the changes made to this pull request.

[picnixz]

Some nitpicks