AST: Introduce a new LookUpConformanceInSignature functor

For now, it "cheats" and performs the lookup in the module
declaring the protocol. This will change shortly.

Author: slavapestov

include/swift/AST/Type.h

@@ -125,6 +125,20 @@ class MakeAbstractConformanceForGenericType {
              ProtocolType *conformedProtocol) const;
 };
 
+/// Functor class suitable for use as a \c LookupConformanceFn that fetches
+/// conformances from a generic signature.
+class LookUpConformanceInSignature {
+  const GenericSignature &Sig;
+public:
+  LookUpConformanceInSignature(const GenericSignature &Sig)
+    : Sig(Sig) {}
+  
+  Optional<ProtocolConformanceRef>
+  operator()(CanType dependentType,
+             Type conformingReplacementType,
+             ProtocolType *conformedProtocol) const;
+};
+  
 /// Flags that can be passed when substituting into a type.
 enum class SubstFlags {
   /// If a type cannot be produced because some member type is

lib/AST/Type.cpp

@@ -2961,8 +2961,8 @@ LookUpConformanceInModule::operator()(CanType dependentType,
     return ProtocolConformanceRef(conformedProtocol->getDecl());
 
   return M->lookupConformance(conformingReplacementType,
-                  conformedProtocol->getDecl(),
-                  conformingReplacementType->getASTContext().getLazyResolver());
+                              conformedProtocol->getDecl(),
+                              M->getASTContext().getLazyResolver());
 }
 
 Optional<ProtocolConformanceRef>
@@ -2982,6 +2982,21 @@ MakeAbstractConformanceForGenericType::operator()(CanType dependentType,
   return ProtocolConformanceRef(conformedProtocol->getDecl());
 }
 
+Optional<ProtocolConformanceRef>
+LookUpConformanceInSignature::operator()(CanType dependentType,
+                                         Type conformingReplacementType,
+                                         ProtocolType *conformedProtocol) const {
+  // FIXME: Actually implement this properly.
+  auto *M = conformedProtocol->getDecl()->getParentModule();
+
+  if (conformingReplacementType->isTypeParameter())
+    return ProtocolConformanceRef(conformedProtocol->getDecl());
+
+  return M->lookupConformance(conformingReplacementType,
+                              conformedProtocol->getDecl(),
+                              M->getASTContext().getLazyResolver());
+}
+
 Type DependentMemberType::substBaseType(ModuleDecl *module,
                                         Type substBase,
                                         LazyResolver *resolver) {