[swift-dev] How should NSArray<void(^)(void)>* be imported?

[Jacob Bandes-Storch]

I'm interested in fixing a pet peeve of mine:
https://bugs.swift.org/browse/SR-772

The failing assertion is in Array._forceBridgeFromObjectiveC, namely
Swift._isBridgedToObjectiveC(Element.self). Element is plain ol "() -> ()",
but probably should be @convention(block) since it was imported from
void(^)(void).

I've started tracing through the importer, and I found that
`adjustTypeForConcreteImport` is enforcing
FunctionTypeRepresentation::Swift because the ImportKind is BridgedValue —
this is hardcoded in the call to importType for the type parameters to
NSArray (and NSDictionary and NSSet) in
SwiftTypeConverter::VisitObjCObjectPointerType.

Are the Foundation collection classes only temporarily special-cased here,
until Obj-C generics are generally supported? Is someone working on this in
the near future?

If this worked correctly, would we expect to see "var executionBlocks:
[@convention(block) () -> ()]" ? If so, would this be best achieved by
passing a different ImportKind, possibly introducing a new ImportKind, or
some other solution?

I'm guessing that it doesn't make sense for () -> () to be
_ObjectiveCBridgeable, but either way I'm not sure where the
_isBridgedToObjectiveC implementation for blocks would come from.

Bumblingly,
Jacob
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