Mine returns "swift", which I think means it's returning garbage.

Interesting. I ran into another garbage NSString/String problem with URL at the same time. I didn't think they were the same thing because this consistently returns "testing" for me, whereas that one seems like it's just reading random bytes from the heap. I'll create a new issue for that and link it here.

Anyway, I also tested this issue in Objective-C (using the macOS 10.12 SDK) and wasn't able to reproduce it.

@import Foundation;

int main() {
  NSString *s = [[NSURL fileURLWithPath: @""] lastPathComponent];
  NSLog(@"%lu", (unsigned long)s.length);
  // Logs "0"
}

The possibly related issue is SR-2591.

Oops, never mind — I think this returns the lastPathComponent of the current working directory. URL(fileURLWithPath: "") might be the root cause here. That call produces this: {{ URL = "./ – ile:///Users/field-thompson/dev/testing/" }} . I think that's the wrong way to display the URL and it's a little surprising seeing as it's a change in behavior, but it's correct according to the doc comment, so I'll close this bug.

Aha, we're treating it as a relative URL. I still think we should attempt to do the same thing as NSURL, though. @phausler?