Copying a symlink always fails on Windows

[jakepetroules]

Consider the following code:

let fm = FileManager()
do {
    try fm.createFile(atPath: "test", contents: nil)
    try fm.linkItem(atPath: "test", toPath: "test2")
    precondition(!fm.fileExists(atPath: "test3"))
    try fm.copyItem(atPath: "test2", toPath: "test3")
} catch {
    print("\(error)")
    exit(EXIT_FAILURE)
}

Running this will produce the following filesystem contents:

E:\symlinktest>dir
 ...

 Directory of E:\symlinktest

...
08/12/2024  02:16 PM                 0 test
08/12/2024  02:16 PM    <SYMLINK>      test2 [test]
08/12/2024  02:16 PM                 0 test3
...

AND will throw this error from copyItem:

CocoaError(code: FoundationEssentials.CocoaError.Code(rawValue: 516), userInfo: ["NSFilePath": AnyHashable("test2"), "NSUnderlyingError": AnyHashable(FoundationEssentials.Win32Error(code: 183))])

Somehow, copyItem ALWAYS fails with ERROR_ALREADY_EXISTS when copying a symlink, even though the destination definitely did not exist prior to the call.

Swift version 6.0-dev (LLVM 31f0cdc6d5ff8a6, Swift aa0786cc7b3190c)
Microsoft Windows [Version 10.0.22631.3958]

[jakepetroules]

This also appears to be a regression as I don't recall observing this fail with the July snapshot of Swift 6 (but is failing with the August 7 snapshot)

[jakepetroules]

Also reproduces with the copyItem call replaced with the same Win32 APIs that swift-foundation is calling internally:

var ExtendedParameters: COPYFILE2_EXTENDED_PARAMETERS = .init()
ExtendedParameters.dwSize = DWORD(MemoryLayout<COPYFILE2_EXTENDED_PARAMETERS>.size)
ExtendedParameters.dwCopyFlags = DWORD(COPY_FILE_FAIL_IF_EXISTS | COPY_FILE_COPY_SYMLINK | COPY_FILE_NO_BUFFERING | COPY_FILE_OPEN_AND_COPY_REPARSE_POINT)

"test2".withCString(encodedAs: UTF16.self) { pwszSource in
    "test3".withCString(encodedAs: UTF16.self) { pwszDestination in
        let x: HRESULT = CopyFile2(pwszSource, pwszDestination, &ExtendedParameters)
        print(UInt32(bitPattern: x))
    }
}

This returns HRESULT 0x80070050 (The file exists)

So I suspect the dwCopyFlags might be invalid. Some potentially relevant docs: https://learn.microsoft.com/en-us/windows/win32/fileio/symbolic-link-effects-on-file-systems-functions

@compnerd Any idea what might be wrong here?