`BasicFormat` fails to add whitespace before effect specifiers

[stevapple]

Description

This happens in function/closure signature/type as well as accessor declarations.

Steps to Reproduce

let functionEffects = FunctionEffectSpecifiersSyntax(asyncSpecifier: .keyword(.async), throwsSpecifier: .keyword(.rethrows))
let typeEffects = TypeEffectSpecifiersSyntax(asyncSpecifier: .keyword(.async), throwsSpecifier: .keyword(.throws))
let accessorEffects = AccessorEffectSpecifiersSyntax(asyncSpecifier: .keyword(.async), throwsSpecifier: .keyword(.throws))

let functionSignature = FunctionSignatureSyntax(input: .init(parameterList: []), effectSpecifiers: functionEffects, output: .init(returnType: TypeSyntax("String")))
let functionType = FunctionTypeSyntax(arguments: [], effectSpecifiers: typeEffects, output: .init(returnType: TypeSyntax("String")))
let closureSignature = ClosureSignatureSyntax(input: .simpleInput([.init(name: "input")]), effectSpecifiers: typeEffects)
let accessorDecl = AccessorDeclSyntax(accessorKind: .keyword(.get), effectSpecifiers: accessorEffects)

print(functionSignature.formatted()) // ()async rethrows -> String
print(functionType.formatted())      // ()async throws -> String
print(closureSignature.formatted())  // inputasync throws in
print(accessorDecl.formatted())      // getasync throws

[ahoppen]

Tracked in Apple’s issue tracker as rdar://108076753

[ahoppen]

This should be fixed by my latest improvements to BasicFormat #1569

[stevapple]

@ahoppen It seems the fix wasn’t made into release/5.9 branch through #1576. Maybe we also want to cherry-pick #1511 to ensure the release branch works as we expected.

[ahoppen]

I just tested it and the formatting appears to be correct on release/5.9 for me. At least if I apply the test changes from #1511 locally, everything is still passing.

I don’t have strong opinions on whether to cherry-pick the test changes to release/5.9. It’s pretty unlikely that we’ll break these only on release/5.9 without also breaking them on main so the benefit of cherry-picking is marginal to me.