bpo-37412: pythoninfo: add Windows long paths

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On Windows, test.pythoninfo now checks if support for long paths is
enabled using ntdll.RtlAreLongPathsEnabled() function.

Co-Authored-By: Eryk Sun eryksun@gmail.com

https://bugs.python.org/issue37412

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The code comes from @eryksun, so I added him as a co-author:
#14424 (comment)

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@eryksun: Would you mind to review this change?

I tested it manually on my Windows VM:

windows.long_paths_enabled: True

Maybe it was the Python installer who proposed me to enable this Windows feature, I don't recall.

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• AppVeyor: windows.long_paths_enabled: False
• Azure Pipelines, win32: windows.long_paths_enabled: True
• Azure Pipelines, win64: windows.long_paths_enabled: True

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Oh, there is also a RtlIsLongPathAwareProcessByManifest() function which may be interesting to check:
https://stackoverflow.com/questions/40983329/are-long-path-behavior-per-app-can-be-enable-via-the-manifest

I updated my PR to also call this function. Result on my Windows 10 VM:

sys.windowsversion: sys.getwindowsversion(major=10, minor=0, build=17763, platform=2, service_pack='')
windows.RtlAreLongPathsEnabled: True
windows.RtlIsLongPathAwareProcessByManifest: <function not available>

Oh, RtlIsLongPathAwareProcessByManifest is not function not available in ntdll on my VM? :-(

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Results on AppVeyor:

platform.platform: Windows-10-10.0.14393-SP0
sys.windowsversion: sys.getwindowsversion(major=10, minor=0, build=14393, platform=2, service_pack='')
windows.RtlAreLongPathsEnabled: False
windows.RtlIsLongPathAwareProcessByManifest: True

Results on Azure Pipeline, win32 and win64 (same values):

sys.windowsversion: sys.getwindowsversion(major=10, minor=0, build=14393, platform=2, service_pack='')
windows.RtlAreLongPathsEnabled: True
windows.RtlIsLongPathAwareProcessByManifest: True

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RtlIsLongPathAwareProcessByManifest may be interesting when I will backport this change to old Python versions. I'm trying to keep the pythoninfo.py code the same in all branches.

[eryksun]

RtlIsLongPathAwareProcessByManifest may be interesting when I will backport this change to old Python versions. I'm trying to keep the pythoninfo.py code the same in all branches.

I wouldn't worry about RtlIsLongPathAwareProcessByManifest. It only exists in older versions of Windows 10, and IIRC it's called only once at process startup. I'm pretty sure that RtlIsLongPathAwareProcessByManifest was removed because the scope of the long-path policy is the Windows base API, not the NT API. Thus the initial configuration should be, and now is, implemented completely in kernelbase.dll, using private functions.

KernelbasePostInit evaluates whether long paths are enabled, and if so it sets the IsLongPathAwareProcess flag in the Process Environment Block (PEB). This flag value is what RtlAreLongPathsEnabled checks.

KernelbasePostInit first calls BasepIsProcessLongPathAwareByPolicy to check the "LongPathsEnabled" registry value. If the policy is enabled, it calls BasepIsProcessLongPathAwareByGlobalOverride to check the "LPGO" registry value, which is a relatively new feature that globally overrides the application manifest. (I would recommend against setting this value.) If the global override isn't set, it calls BasepIsProcessLongPathAwareByManifest, which calls RtlQueryActivationContextApplicationSettings to check whether "longPathAware" is enabled in the application manifest. If so, it sets the IsLongPathAwareProcess flag in the PEB.

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I wouldn't worry about RtlIsLongPathAwareProcessByManifest

Ok ok. Anyway, this info can be retrieved indirectly from the Python version. I rebased my PR and squashed commits.

@eryksun: Would you mind to review the updated PR?

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I merged my PR. Thanks @eryksun for reviews!