It's decent and getting better. I'm using Swift for computer graphics projects on Linux and it's working great and it's quite pleasant to use. Currently it's

It's decent and getting better. I'm using Swift for computer graphics projects on Linux and it's working great and it's quite pleasant to use. Currently it's only officially supported on macOS and Ubuntu, but the next major release (5.3) will add official support for Windows and more linux distros. Tooling still has a ways to go. XCode is still the best way to write Swift, but, SublimeText, vim and VSCode are usable with Swift thanks to LSP support.