In Swift 3, an Objective-C type like SomeClass <SomeProtocol> is
imported as SomeClass. The protocol qualification is erased unless
the class bound is 'id' or 'Class'.
Importing such types as class-constrained existentials is a source
breaking change, so the new behavior is only enabled in Swift 4
mode.
Furthermore as a transitional step the staging flag
-enable-experimental-subclass-existentials has to be passed in
also. The flag will soon be removed.
Most of the time, "generics" means "cannot be exposed to Objective-C"
and certainly "cannot be exposed in the generated header", but there
is one exception: imported Objective-C parameterized types, and their
extensions. We were previously dropping this on the floor and printing
`Foo</* BarType */>` in the generated header, which is nonsense.
https://bugs.swift.org/browse/SR-3480
More specifically, don't try to emit a definition for them. Just fall
through to what we do for forward-declarations...which also needed some
fixing, to make sure we don't use a Swift typealias as its underlying
type but never import the underlying type.
https://bugs.swift.org/browse/SR-2352
When bridging values via the ObjectiveCBridgeable protocol,
SILGen has to look up conformances directly, behind the
type checker's back.
To make sure the ObjectiveCBridgeable conformance is forced,
Sema calls useObjectiveCBridgeableConformances() in the right
places.
However, another conformance we may also need when bridging
is the Hashable conformance for a Set or Dictionary's key type.
Make sure we force these too, because otherwise when bridging
a nil literal nothing needs them in Sema.
Fixes <rdar://problem/27470505>.
Now that ObjC types can be generic, we need to satisfy the type system by plumbing pseudogeneric parameters through func-to-block invocation thunks. Fixes rdar://problem/26524763.
We were failing to bridge Array<T> parameters in the signatures of Objective-C generics when their NSArray<T> * type in ObjC depended on generic parameters. This partially fixes rdar://problem/26371959, though IRGen still needs a fix to get us all the way through (which @rjmccall is working on).
(@DougGregor did all the work here, I'm just testing and committing.)
The fix for methods to lower the dynamic method type from the substituted AST type of the expression also needed to be applied to the optional chaining, subscript, and property paths.
This also exposed a problem in the Clang importer, where imported subscript accessors would get the unbound generic context type as their Self parameter type instead of the type with the correct generic parameters. Fix this by renaming the all-too-convenient ParamDecl::createSelf factory to `createUnboundSelf`, and introduce a new `createSelf` that uses the bound generic type.
Fixes rdar://problem/26447758.
Though the generic type information isn't present, it isn't necessary if we're just invoking other operations from Objective-C. This should allow an extension to use the generic class's own API to some degree, as it would if defined on the nongeneric form.
