[GSB] Make requirement-signature computation more robust for nested protocols.

Add all of the generic parameters from outer contexts as well. This only
occurs in ill-formed code, but maintains a GenericSignatureBuilder
invariant that it knows about all of the generic parameters in play.

Author: DougGregor

lib/AST/GenericSignatureBuilder.cpp

@@ -7491,6 +7491,17 @@ GenericSignature *GenericSignatureBuilder::computeGenericSignature(
   return sig;
 }
 
+/// Add all of the generic parameters from the given parameter list (and it's
+/// outer generic parameter lists) to the given generic signature builder.
+static void addAllGenericParams(GenericSignatureBuilder &builder,
+                                GenericParamList *genericParams) {
+  if (!genericParams) return;
+
+  addAllGenericParams(builder, genericParams->getOuterParameters());
+  for (auto gp : *genericParams)
+    builder.addGenericParameter(gp);
+}
+
 GenericSignature *GenericSignatureBuilder::computeRequirementSignature(
                                                      ProtocolDecl *proto) {
   GenericSignatureBuilder builder(proto->getASTContext());
@@ -7501,12 +7512,12 @@ GenericSignature *GenericSignatureBuilder::computeRequirementSignature(
       lazyResolver->resolveDeclSignature(proto);
   }
 
-  // Add the 'self' parameter.
-  auto selfType =
-    proto->getSelfInterfaceType()->castTo<GenericTypeParamType>();
-  builder.addGenericParameter(selfType);
+  // Add all of the generic parameters.
+  addAllGenericParams(builder, proto->getGenericParams());
 
   // Add the conformance of 'self' to the protocol.
+  auto selfType =
+    proto->getSelfInterfaceType()->castTo<GenericTypeParamType>();
   auto requirement =
     Requirement(RequirementKind::Conformance, selfType,
                 proto->getDeclaredInterfaceType());