GH-127236: pathname2url(): generate RFC 1738 URL for absolute POSIX path

[barneygale]

When handed an absolute Windows path such as C:\foo or \\server\share, the urllib.request.pathname2url() function returns a URL with an authority section, such as ///C:/foo or //server/share (or before GH-126205, ////server/share). Only the file: prefix is omitted.

But when handed an absolute POSIX path such as /etc/hosts, or a Windows path of the same form (rooted but lacking a drive), the function returns a URL without an authority section, such as /etc/hosts.

This patch corrects the discrepancy by adding a // prefix before drive-less, rooted paths when generating URLs.

See #127125 for a related clarification to the docs.

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📚 Documentation preview 📚: https://cpython-previews--127194.org.readthedocs.build/

• Issue: urllib.request.pathname2url(): generate RFC 1738 URLs where possible #127236

[serhiy-storchaka]

LGTM, but could you somewhere make a difference between adding // for path starting with / and // more explicit? It is necessary in the latter case, but cosmetic in the former case.

If RFC 8089 support will become more widespread and browsers and other programs will start normalizing the file: URI to a single flash, this change can be reverted, but the case with double slash should still be handled specially.

[barneygale]

Thanks v much Serhiy - I've adjusted the code comment to explain the difference between / and //-prefixed paths.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86-64 MacOS Intel NoGIL 3.x has failed when building commit 5bb059f.

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/#/builders/1258/builds/3419) and take a look at the build logs.
4. Check if the failure is related to this commit (5bb059f) 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/#/builders/1258/builds/3419

Failed tests:

• test_threading

Failed subtests:

• test_start_new_thread_failed - test.test_threading.ThreadTests.test_start_new_thread_failed
• test_dump_traceback_threads - test.test_faulthandler.FaultHandlerTests.test_dump_traceback_threads

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/ec2-user/buildbot/buildarea/3.x.itamaro-macos-intel-aws.nogil/build/Lib/test/test_threading.py", line 1205, in test_start_new_thread_failed
    self.assertEqual(out, b'ok')
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^
AssertionError: b"skip\nshouldn't be printed" != b'ok'


Traceback (most recent call last):
  File "/Users/ec2-user/buildbot/buildarea/3.x.itamaro-macos-intel-aws.nogil/build/Lib/test/test_faulthandler.py", line 596, in test_dump_traceback_threads
    self.check_dump_traceback_threads(None)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/Users/ec2-user/buildbot/buildarea/3.x.itamaro-macos-intel-aws.nogil/build/Lib/test/test_faulthandler.py", line 592, in check_dump_traceback_threads
    self.assertRegex(output, regex)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
AssertionError: Regex didn't match: '^Thread 0x[0-9a-f]+ \\(most recent call first\\):\n(?:  File ".*threading.py", line [0-9]+ in [_a-z]+\n){1,3}  File "<string>", line (?:22|23) in run\n  File ".*threading.py", line [0-9]+ in _bootstrap_inner\n  File ".*threading.py", line [0-9]+ in _bootstrap\n\nCurrent thread 0x[0-9a-f]+ \\(most recent call first\\):\n  File "<string>", line 10 in dump\n  File "<string>", line 28 in <module>$' not found in 'Thread 0x000070000d520000 (most recent call first):\n  File "/Users/ec2-user/buildbot/buildarea/3.x.itamaro-macos-intel-aws.nogil/build/Lib/threading.py"'