On Windows, null byte added to user from `FileManager.default.homeDirectoryForCurrentUser`, resulting in infinite looping in `DirectoryEnumerator`

[ahoppen]

import Foundation

// Prints file:///C:/Users/alex%00/
// Notice the null byte after the user
print(FileManager.default.homeDirectoryForCurrentUser) 

// Same here
print(URL(fileURLWithPath: ("~" as NSString).expandingTildeInPath))

// Prints 
// file:///C:/Users/alex%00/alex/
// file:///C:/Users/alex%00/alex/alex/
// file:///C:/Users/alex%00/alex/alex/alex/
// file:///C:/Users/alex%00/alex/alex/alex/alex/
// file:///C:/Users/alex%00/alex/alex/alex/alex/alex/
// .. continues forever
let enumerator = FileManager.default.enumerator(at: FileManager.default.homeDirectoryForCurrentUser, includingPropertiesForKeys: nil)
while let url = enumerator?.nextObject() as? URL {
  print("\(url)\r\n")
}

[ahoppen]

This issue caused sourcekit-lsp to hang on launch. I’m working around it in swiftlang/sourcekit-lsp#1596 by manually removing the null byte.

[parkera]

Presumably this is on Swift 6.0?

[jrflat]

I think we might need

return withUnsafeTemporaryAllocation(of: WCHAR.self, capacity: Int(dwcchSize)) {
    var dwcchSize: DWORD = DWORD($0.count)
    guard GetUserProfileDirectoryW(hToken, $0.baseAddress, &dwcchSize) else {
        fatalError("unable to query user profile directory")
    }
--    return String(decoding: $0, as: UTF16.self)
++    return String(decodingCString: $0.baseAddress!, as: UTF16.self)
}

I can test to see if that's the case