FileSystemEnumerable has some issues when the item gets deleted during enumeration on Linux

[tmds]

On Windows, all information of the FileSystemEntry is retrieved as part of the enumeration syscall.
On Unix, some of the properties are retrieved by making additional stat calls.
This means the Unix implementation needs to handle the case where the item may be deleted after it was reported by the readdir syscall, and before the stat syscall was made to get the additional properties.
For Windows compatibility, the Unix implementation does not throw for errors on the stat call.

These are some issues with the implementation:

• continueOnError should be used on all calls that retrieve info FileStatus to avoid the exception getting thrown.
• When the item no longer exists, Attributes should return a value based on the information of the dirent_t. The FileAttributesAreExpected and DirectoryAttributesAreExpected that check for this have a bug which causes them to report a false positive due to performing a stat call when checking to remove FileAttributes.Hidden.
• The FileStatus gets reused across the enumeration. GetLength is missing a check to ensure the status is initialized that can cause information from the previous entry to leak into the next when the latter can not be initialized.

cc @carlossanlop

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Issue Details

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On Windows, all information of the FileSystemEntry is retrieved as part of the enumeration syscall.
On Unix, some of the properties are retrieved by making additional stat calls.
This means the Unix implementation needs to handle the case where the item may be deleted after it was reported by the readdir syscall, and before the stat syscall was made to get the additional properties.
For Windows compatibility, the Unix implementation does not throw for errors on the stat call.

These are some issues with the implementation:

• continueOnError should be used on all calls that retrieve info FileStatus to avoid the exception getting thrown.
• When the item no longer exists, Attributes should return a value based on the information of the dirent_t. The FileAttributesAreExpected and DirectoryAttributesAreExpected that check for this have a bug which causes them to report a false positive due to performing a stat call when checking to remove FileAttributes.Hidden.
• The FileStatus gets reused across the enumeration. GetLength is missing a check to ensure the status is initialized that can cause information from the previous entry to leak into the next when the latter can not be initialized.

cc @carlossanlop

Author:	tmds
Assignees:	-
Labels:	area-System.IO, untriaged
Milestone:	-

[adamsitnik]

Fixed by #60214