Check root archetypes in a few more places.

This makes more code agnostic to the presence of NestedArchetypeType.

Author: DougGregor

lib/AST/ASTPrinter.cpp

@@ -4841,17 +4841,19 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
         return isSimpleUnderPrintOptions(typealias->getSinglyDesugaredType());
     } else if (auto opaque =
                  dyn_cast<OpaqueTypeArchetypeType>(T.getPointer())) {
-      switch (Options.OpaqueReturnTypePrinting) {
-      case PrintOptions::OpaqueReturnTypePrintingMode::StableReference:
-      case PrintOptions::OpaqueReturnTypePrintingMode::Description:
-        return true;
-      case PrintOptions::OpaqueReturnTypePrintingMode::WithOpaqueKeyword:
-        return opaque->getDecl()->hasExplicitGenericParams();
-      case PrintOptions::OpaqueReturnTypePrintingMode::WithoutOpaqueKeyword:
-        return opaque->getDecl()->hasExplicitGenericParams() ||
-            isSimpleUnderPrintOptions(opaque->getExistentialType());
+      if (opaque->isRoot()) {
+        switch (Options.OpaqueReturnTypePrinting) {
+        case PrintOptions::OpaqueReturnTypePrintingMode::StableReference:
+        case PrintOptions::OpaqueReturnTypePrintingMode::Description:
+          return true;
+        case PrintOptions::OpaqueReturnTypePrintingMode::WithOpaqueKeyword:
+          return opaque->getDecl()->hasExplicitGenericParams();
+        case PrintOptions::OpaqueReturnTypePrintingMode::WithoutOpaqueKeyword:
+          return opaque->getDecl()->hasExplicitGenericParams() ||
+              isSimpleUnderPrintOptions(opaque->getExistentialType());
+        }
+        llvm_unreachable("bad opaque-return-type printing mode");
       }
-      llvm_unreachable("bad opaque-return-type printing mode");
     } else if (auto existential = dyn_cast<ExistentialType>(T.getPointer())) {
       if (!Options.PrintExplicitAny)
         return isSimpleUnderPrintOptions(existential->getConstraintType());

lib/AST/DiagnosticEngine.cpp

@@ -709,7 +709,9 @@ static void formatDiagnosticArgument(StringRef Modifier,
       type = type->getWithoutSyntaxSugar();
     }
 
-    if (needsQualification && isa<OpaqueTypeArchetypeType>(type.getPointer())) {
+    if (needsQualification &&
+        isa<OpaqueTypeArchetypeType>(type.getPointer()) &&
+        cast<ArchetypeType>(type.getPointer())->isRoot()) {
       auto opaqueTypeDecl = type->castTo<OpaqueTypeArchetypeType>()->getDecl();
 
       llvm::SmallString<256> NamingDeclText;

lib/AST/GenericEnvironment.cpp

@@ -340,7 +340,7 @@ GenericEnvironment::getOrCreateArchetypeFromInterfaceType(Type depType) {
     result = NestedArchetypeType::getNew(ctx, depMemTy,
                                          requirements.protos, superclass,
                                          requirements.layout, this);
-  } else if (genericParam->isTypeSequence()) {
+  } else if (requirements.anchor->getRootGenericParam()->isTypeSequence()) {
     result = SequenceArchetypeType::get(ctx, this, requirements.anchor,
                                         requirements.protos, superclass,
                                         requirements.layout);

lib/IDE/CodeCompletion.cpp

@@ -2442,7 +2442,8 @@ class CompletionLookup final : public swift::VisibleDeclConsumer {
       // and not both.
       if (auto *archetypeType = t->getAs<ArchetypeType>()) {
         // Don't erase opaque archetype.
-        if (isa<OpaqueTypeArchetypeType>(archetypeType))
+        if (isa<OpaqueTypeArchetypeType>(archetypeType) &&
+            archetypeType->isRoot())
           return t;
 
         auto protos = archetypeType->getConformsTo();