IDE: Fix a usage of lookupVisibleMemberDecls() to not pass in an existential type

It's better to use the 'Self' archetype here.

Author: slavapestov

lib/IDE/CodeCompletion.cpp

@@ -4177,13 +4177,12 @@ class CompletionOverrideLookup : public swift::VisibleDeclConsumer {
     }
   }
 
-  void addDesignatedInitializers(Type CurrTy) {
+  void addDesignatedInitializers(NominalTypeDecl *NTD) {
     if (hasFuncIntroducer || hasVarIntroducer || hasTypealiasIntroducer ||
         hasOverridabilityModifier)
       return;
 
-    assert(CurrTy);
-    const auto *CD = dyn_cast_or_null<ClassDecl>(CurrTy->getAnyNominal());
+    const auto *CD = dyn_cast<ClassDecl>(NTD);
     if (!CD)
       return;
     if (!CD->hasSuperclass())
@@ -4200,14 +4199,12 @@ class CompletionOverrideLookup : public swift::VisibleDeclConsumer {
     }
   }
 
-  void addAssociatedTypes(Type CurrTy) {
+  void addAssociatedTypes(NominalTypeDecl *NTD) {
     if (!hasTypealiasIntroducer &&
         (hasFuncIntroducer || hasVarIntroducer || hasInitializerModifier ||
          hasOverride || hasOverridabilityModifier))
       return;
 
-    NominalTypeDecl *NTD = CurrTy->getAnyNominal();
-
     for (auto Conformance : NTD->getAllConformances()) {
       auto Proto = Conformance->getProtocol();
       if (!Proto->isAccessibleFrom(CurrDeclContext))
@@ -4233,13 +4230,14 @@ class CompletionOverrideLookup : public swift::VisibleDeclConsumer {
     if (isa<ProtocolDecl>(CurrDeclContext))
       return;
 
-    Type CurrTy = CurrDeclContext->getDeclaredTypeInContext();
+    Type CurrTy = CurrDeclContext->getSelfTypeInContext();
+    auto *NTD = CurrDeclContext->getSelfNominalTypeDecl();
     if (CurrTy && !CurrTy->is<ErrorType>()) {
       lookupVisibleMemberDecls(*this, CurrTy, CurrDeclContext,
                                TypeResolver,
                                /*includeInstanceMembers=*/false);
-      addDesignatedInitializers(CurrTy);
-      addAssociatedTypes(CurrTy);
+      addDesignatedInitializers(NTD);
+      addAssociatedTypes(NTD);
     }
   }
 };