[SourceKit] SourceKit support for opaque result types

[rintaro]

Initial implementation for SourceKit support for "opaque result types"

• libSyntax: Grammer and parser change
• Syntax highlighting, Cursor Info, Indexing
• Code completion for some keyword
• Conformance completion using opaque result types

rdar://problem/49997412

[rintaro]

@swift-ci Please smoke test

[slavapestov]

Can an opaque type have a superclass and one conformance? CC @jckarter

[jckarter]

Yes, an opaque type can have any combination of constraints.

[slavapestov]

What about T->getSuperclass()?

Maybe this should be generalized to get all the constraints from T->getBoundSignature() instead?

[rintaro]

Will fix.

[slavapestov]

Is there a more direct way to turn an opaque type into an existential, @jckarter ?

[jckarter]

I added ArchetypeType::getExistentialType() in #24166.

[rintaro]

@jckarter Thanks! I'll modify ASTPrinter to use that too.

[slavapestov]

What if getInherited() has multiple entries?

[rintaro]

  associatedtype Aaaa: Collection, Comparable

Thanks! I didn't know this is accepted by the compiler.

[slavapestov]

In fact the inheritance clause doesn’t contain all the information you need. I would suggest asking the protocol’s generic signature instead.

Eg, protoDecl->getGenericSignature()->getConformsTo(assocDecl->getDeclaredInterfaceType())

You should also check for a superclass and layout constraint, so you can print ‘some SomeClass’ or ‘some AnyObject & P’, etc.

[slavapestov]

I'm not sure what this function is doing. Are you printing protocol requirements and extension methods that return associated types as returning an opaque type?

[rintaro]

Yes, for example:

protocol P {
  associatedtype Assoc: Collection
  func foo() -> Assoc
}
protocol C: P {
  func /* Complete here. */
}

We wan't to complete foo() as func foo() -> some Collection { <#code#> }