Reordering @preconcurrency imports should be suppressed even if they're in #if conditions

[saagarjha]

@preconcurrency imports need to come before future modules that also export them (without @preconcurrency). swift-format avoids reordering these, except if they are behind compiler guards. In particular:

#if canImport(Glibc)
@preconcurrency import Glibc
#endif
import Foundation

When formatting, swift-format will move Foundation first:

import Foundation

#if canImport(Glibc)
@preconcurrency import Glibc
#endif

This breaks the effect of @preconcurrency, so we shouldn't do this transformation.

[ahoppen]

Synced to Apple’s issue tracker as rdar://136999610

[ahoppen]

I don’t think the order of imports should matter for anything. Would you mind also filing an issue to https://github.com/swiftlang/swift/issues/new/choose with an example where the import order does matter?

[saagarjha]

Ok, filed as swiftlang/swift#76842