GH-109187: Improve symlink loop handling in pathlib.Path.resolve()

[barneygale]

Treat symlink loops like other errors: in strict mode, raise OSError, and in non-strict mode, do not raise an exception.

• Issue: pathlib.Path.resolve() mishandles symlink loops #109187

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📚 Documentation preview 📚: https://cpython-previews--109192.org.readthedocs.build/

[barneygale]

Hey @zooba, please could you review this if you have the time/inclination? It's a sort-of follow-up to #25264, which you reviewed a couple years ago. No worries if not! Thank you.

Previously we decided to raise RuntimeError from Path.resolve(), regardless of the value of strict, when a symlink loop was encountered. This behaviour differs from os.path.realpath(), but maintains compatibility with older pathlib.

Now we're looking at adding a new PathBase class with its own resolve() method, which provides an additional incentive to straighten out how symlink loops are handled, and makes the minor backwards compatibility break worthwhile IMHO.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x Debian 3.x has failed when building commit ecd813f.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/49/builds/6673) and take a look at the build logs.
4. Check if the failure is related to this commit (ecd813f) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/49/builds/6673

Failed tests:

• test_tools

Failed subtests:

• test_freeze_simple_script - test.test_tools.test_freeze.TestFreeze.test_freeze_simple_script

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/test/test_tools/test_freeze.py", line 32, in test_freeze_simple_script
    outdir, scriptfile, python = helper.prepare(script, outdir)
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Tools/freeze/test/freeze.py", line 146, in prepare
    copy_source_tree(srcdir, SRCDIR)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Tools/freeze/test/freeze.py", line 95, in copy_source_tree
    shutil.copytree(oldroot, newroot, ignore=ignore_non_src)
  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/shutil.py", line 588, in copytree
    return _copytree(entries=entries, src=src, dst=dst, symlinks=symlinks,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/Lib/shutil.py", line 542, in _copytree
    raise Error(errors)
shutil.Error: [('/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/build/test_python_3316406æ/test_python_qj_0d1oo.sock', '/tmp/test_python_qsnyutqh/tmpcgick913/cpython/build/test_python_3316406æ/test_python_qj_0d1oo.sock', "[Errno 6] No such device or address: '/home/dje/cpython-buildarea/3.x.edelsohn-debian-z/build/build/test_python_3316406æ/test_python_qj_0d1oo.sock'")]

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Debian root 3.x has failed when building commit ecd813f.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/345/builds/5925) and take a look at the build logs.
4. Check if the failure is related to this commit (ecd813f) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/345/builds/5925

Failed tests:

• test_signal

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/root/buildarea/3.x.angelico-debian-amd64/build/Lib/test/test_signal.py", line 1287, in test_stress_delivery_dependent
    self.assertEqual(len(sigs), N, "Some signals were lost")
AssertionError: 4525 != 10000 : Some signals were lost