Inconsistent behavior in FileType comparisons on Windows

[mikerooni]

The PartialEq/Eq implementation of FileType on Windows is currently comparing more than just the actual file type. It seems to be using all file attributes for the comparison instead.

Steps to reproduce:

1. Create two files, e.g. a.txt and b.txt
2. Using Windows Explorer:
   • Right click -> Properties -> open the "Advanced" file attributes dialog
   • Enable "Allow this file to have contents indexed in addition to file properties" for only one of these files, but not the other

The following test will now fail:

let type_a = fs::metadata("a.txt").unwrap().file_type();
let type_b = fs::metadata("b.txt").unwrap().file_type();
assert_eq!(type_a, type_b);

Expected behavior:

I would expect the comparison between two FileTypes to only compare the actual file TYPE (e.g. file, dir, symlink, any platform-specific extensions), but not file attributes.

Another issue in this case is that it isn't obvious why the comparison fails, because FileType's Debug implementation only shows is_file, is_dir, and is_symlink:

assertion `left == right` failed
  left: FileType { is_file: true, is_dir: false, is_symlink: false, .. }
 right: FileType { is_file: true, is_dir: false, is_symlink: false, .. }

I'm not sure whether this is something that can be easily fixed - I'd argue it should be considered an actual bug occurring in an edge case, but fixing it would technically introduce a breaking change.

rustc --version --verbose:

rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: x86_64-pc-windows-msvc
release: 1.85.0
LLVM version: 19.1.7

[Kyuuhachi]

When this was brought up on Discord, I also noticed that impl From<c::WIN32_FIND_DATAW> for FileAttr checks for FILE_ATTRIBUTE_REPARSE_POINT, but DirEntry::file_type does not, and thus reads reserved data.

rust/library/std/src/sys/fs/windows.rs

Lines 1068 to 1073 in 259fdb5

	reparse_tag: if wfd.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
	// reserved unless this is a reparse point
	wfd.dwReserved0
	} else {
	0
	},

rust/library/std/src/sys/fs/windows.rs

Lines 177 to 180 in 259fdb5

	Ok(FileType::new(
	self.data.dwFileAttributes,
	/* reparse_tag = */ self.data.dwReserved0,
	))

[ChrisDenton]

When this was brought up on Discord, I also noticed that impl From<c::WIN32_FIND_DATAW> for FileAttr checks for FILE_ATTRIBUTE_REPARSE_POINT, but DirEntry::file_type does not, and thus reads reserved data.

While not ideal, that part is technically "fine" because dwReserved0 must be initialised (because WIN32_FIND_DATAW is stored by value, so must be fully initialised). And FileType does not use reparse_tag unless the file attributes contain FILE_ATTRIBUTE_REPARSE_POINT. So it may store a nonsense value but it doesn't affect behaviour as far as I can tell.

[Kyuuhachi]

Except for equality. I haven't tested, but I think the FileType returned from a DirEntry and from a Metadata might not compare equal, even for the same file.

[ChrisDenton]

I submitted a fix (see above) that only compares the relevant information, so let's see what the libs-api team says.