It looks like the only thing that fails is the linkage computation
for the dynamic replacement key of class methods. Even though
methods have hidden linkage to prevent them from being directly
referenced from outside a resilient module, we need to ensure
the dynamic replacement key is visible.
Fixes <rdar://problem/58457716>.
getDirectlyInheritedNominalTypeDecls looks for inherited protocols in two places: the actual inheritance clause of a declaration and the trailing where clause. This works fine for normal declarations, but deserialized protocols that have Self constraints have no trailing where clause and appear to have no super-protocol bounds. This means clients can potentially disagree about the structure of the protocol, and any symbols derived from it.
The test case demonstrates this problem directly: We build a hollowed-out SwiftUI preview provider then try to dynamically replace a requirement in a Self-constrained protocol extension. The SwiftUI module sees the where clause, but when we go to deserialize the module in the "Preview" the protocol extension sees the wrong inheritance bounds and mis-mangles the call to Self.view(for:ofType).
The fix is to ask the requirement signature for Self requirements that would normally appear on a trailing where clause.
Resolves rdar://57150777
