FileSystemEntry.Attributes property is not correct on Unix

[iSazonov]

Description

Comes from PowerShell/PowerShell#12834 where custom file enumerator is replaced with .Net FileSystemEnumerator.

Expectation is that:

1. FileSystemEntry.Attributes property works the same as FileSystemInfo.Attributes property for Hidden (and perhaps ReadOnly) flags.
2. For Extended Unix flags and Windows Reparse points we need new property FileSystemInfo.ExtendedAttributes.

It turns out the first has a simplified implementation

runtime/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEntry.Unix.cs

Lines 69 to 84 in bd6cbe3

	entry._status = default;
	FileStatus.Initialize(ref entry._status, isDirectory);
	FileAttributes attributes = default;
	if (isSymlink)
	attributes |= FileAttributes.ReparsePoint;
	if (isDirectory)
	attributes |= FileAttributes.Directory;
	if (directoryEntry.Name[0] == '.')
	attributes |= FileAttributes.Hidden;
	if (attributes == default)
	attributes = FileAttributes.Normal;
	entry._initialAttributes = attributes;
	return attributes;

than the second

runtime/src/libraries/System.IO.FileSystem/src/System/IO/FileStatus.Unix.cs

Lines 76 to 91 in bd6cbe3

	FileAttributes attributes = default;
	if (IsReadOnly(path))
	attributes |= FileAttributes.ReadOnly;
	if ((_fileStatus.Mode & Interop.Sys.FileTypes.S_IFMT) == Interop.Sys.FileTypes.S_IFLNK)
	attributes |= FileAttributes.ReparsePoint;
	if (_isDirectory)
	attributes |= FileAttributes.Directory;
	// If the filename starts with a period or has UF_HIDDEN flag set, it's hidden.
	if (fileName.Length > 0 && (fileName[0] == '.' || (_fileStatus.UserFlags & (uint)Interop.Sys.UserFlags.UF_HIDDEN) == (uint)Interop.Sys.UserFlags.UF_HIDDEN))
	attributes |= FileAttributes.Hidden;
	return attributes != default ? attributes : FileAttributes.Normal;

Also CHFLAGS works only on BSD-like systems (MacOS, FreeBSD) but not on Linux. So expectation is that assigning Hidden flag on Linux throws PlatformNotSupportedException - it was very amazing to discover that some PowerShell tests are passed on Linux but really Hidden flag does not work.

[danmoseley]

Was this just an oversight in dotnet/corefx#34560

[iSazonov]

@davidkaya @danmosemsft @JeremyKuhne Could you please look the issue? I'd be happy to get the fix for PowerShell.

[JeremyKuhne]

@danmosemsft Yes, this looks like an oversight. We should add a comment in both places pointing out the connection if we can't share the code.

@iSazonov I'm no longer on the libraries team, but this should clearly be consistent between the two. @carlossanlop will have to decide the best course of action on throwing. If we can be confident on checking that it isn't supported than throwing seems reasonable to me at first glance.

[iSazonov]

If the fix is "to throw" the issue should be fixed in 5.0 milestone - later it will be a breaking change.

[carlossanlop]

@iSazonov I marked it for 5.0. Would you have a chance to work on this in the next few days? If not, @jozkee or I can take over when we get some bandwidth.

[iSazonov]

@carlossanlop I have not possibility to develop on Unix :-(

[danmoseley]

@iSazonov even with WSL 2 ? 😃

[iSazonov]

@danmosemsft I would like, but my laptop is against 😃

[carlossanlop]

@iSazonov can you take a look at the PR, please?

[iSazonov]

@carlossanlop Can we re-open the issue?

[billwert]

@daxian-dbw hit this when trying to move Powershell to RC1. Here's the test we should ensure works well when we address this for 6.0:

Measure-Command { TabExpansion2 -inputScript "Invoke-Web" -cursorColumn "Invoke-Web".Length }

In WSL2 if that takes more than a couple hundred milliseconds, there's a problem. (In .NET 5 RC1 it is ~2.5 seconds due to all the stating.)

[iSazonov]

Priority:3

I wonder how you weight this:

1. There is two code paths which contradict each other
2. There is a clear performance issue
3. Finally, it's just bad design, even wrong

[jeffhandley]

@iSazonov Thanks for the comment and feedback. The priority is based on our overall themes and the relative priority of fixing this issue compared to completing other items that the team is committing to for 6.0.0. Even with Priority:3, our project plan includes time to work on this issue during the 6.0.0 release cycle.

[iSazonov]

@jeffhandley Thanks for clarify! I am trying to speed up PowerShell Core file operation and I hope we get this in the PowerShell milestone. So I have many concerns about .Net file API design and performance. Feel free to ping me when will your team start this work.

[jeffhandley]

@iSazonov What timing would enable you to utilize this fix in the PowerShell milestone you're targeting?

[iSazonov]

@jeffhandley MSFT PowerShell team said they want to stop big changes before summer and then work only on bugs and stability.

[iSazonov]

I added in the OP that is right design should be - "For Extended Unix flags and Windows Reparse points we need new property FileSystemInfo.ExtendedAttributes."

Update: It should be File Flags. Extended Attributes is another conception.