Allow comments in .swift-format

[antigluten]

Enable allowsJSON5 on the JSONDecoder. With this change, the decoder can now parse JSON5-formatted data.

Resolves #1011.

[allevato]

Unfortunately it looks like allowsJSON5 wasn't added to Foundation on Linux until the 6.0 toolchain (so I'm assuming it came with the swift-foundation changeover). I suspect this would be true for other non-Apple platforms as well, like Android. (On macOS, it's available since 12.0, which swift-format's deployment target is already above.)

We'll need to guard this property (and the test) appropriately. For conciseness, we could use canImport(Darwin) as an indicator that we're on an Apple platform and canImport(FoundationEssentials) to make sure we have a compatible Foundation on other platforms, so something like #if canImport(Darwin) || canImport(FoundationEssentials) ought to be fine, I think.

@ahoppen Do you think that's ok or would you prefer a more explicit check involving something like the compiler version on non-Apple OSes?

[ahoppen]

I would prefer to check for a compiler version on non-Darwin OSs because that’s something that’s easier to remove in the future. It’s easy to tell that #if compiler(>=6) will always evaluate to true if we no longer support building swift-format using a Swift 5 compiler. But for #if canImport(FoundationEssentials) is a bit harder to determine if that’s always true because you need to remember when FoundationEssentials was introduced.

[antigluten]

Hi @allevato @ahoppen, added checking for compiler version.

[allevato]

You'll need to wrap the rest of the body in an #else here, too, otherwise it will still try to compile the code below in the compiler(<6) case (since it's just unguarded code right now).

[antigluten]

✅ Fixed

[allevato]

Thank you!