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 ? 😃