Explicitly request to createGenericParamsIfMissing as it will be lazy

Computing the requirement signature created the generic params as
a side effect. Making getRequirementSignature lazy means that users
of the generic params must make sure they are created before use.

Author: xymus

lib/AST/DeclContext.cpp

@@ -90,6 +90,7 @@ GenericTypeParamType *DeclContext::getProtocolSelfType() const {
 
   GenericParamList *genericParams;
   if (auto proto = dyn_cast<ProtocolDecl>(this)) {
+    const_cast<ProtocolDecl*>(proto)->createGenericParamsIfMissing();
     genericParams = proto->getGenericParams();
   } else {
     genericParams = cast<ExtensionDecl>(this)->getGenericParams();

lib/Serialization/Serialization.cpp

@@ -3284,6 +3284,7 @@ void Serializer::writeDecl(const Decl *D) {
                                rawAccessLevel,
                                inherited);
 
+    const_cast<ProtocolDecl*>(proto)->createGenericParamsIfMissing();
     writeGenericParams(proto->getGenericParams());
     writeGenericRequirements(
       proto->getRequirementSignature(), DeclTypeAbbrCodes);