swift-format breaks Package.swift by moving an import above the `// swift-tools-version:` comment

[dabrahams]

When I ran swift-format over my project, it turned this

// swift-tools-version:5.7
import Foundation
import PackageDescription

Into this:

import Foundation
// swift-tools-version:5.7
import PackageDescription

Which results in this error:

error: 'hylo': package 'package.swift' is using Swift tools version 3.1.0 which is no longer supported; consider using '// swift-tools-version: 5.9' to specify the current tools version

[allevato]

I can't imagine why it would think that comment should be glued to the other import, but in addition to fixing that, we should probably carve out a special case for // swift-tools-version:... comments to always keep them at the top of the file.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://126948395