Eliminate OpaqueTypeArchetypeType::getOrdinal(), which shouldn't be used

It only made sense on the root, and clients that care can look at the
interface type.

Author: DougGregor

include/swift/AST/Types.h

@@ -5567,15 +5567,6 @@ class OpaqueTypeArchetypeType final : public ArchetypeType,
     return T->getKind() == TypeKind::OpaqueTypeArchetype;
   }
 
-  /// Get the ordinal of the type within the declaration's opaque signature.
-  ///
-  /// If a method declared its return type as:
-  ///
-  ///   func foo() -> (some P, some Q)
-  ///
-  /// then the underlying type of `some P` would be ordinal 0, and `some Q` would be ordinal 1.
-  unsigned getOrdinal() const;
-  
 private:
   OpaqueTypeArchetypeType(GenericEnvironment *environment,
                           RecursiveTypeProperties properties,

lib/AST/ASTDumper.cpp

@@ -3722,6 +3722,7 @@ namespace {
                               StringRef label) {
       printCommon(label, className);
       printField("address", static_cast<void *>(T));
+      printRec("interface_type", T->getInterfaceType());
       printFlag(T->requiresClass(), "class");
       if (auto layout = T->getLayoutConstraint()) {
         OS << " layout=";
@@ -3731,6 +3732,7 @@ namespace {
         printField("conforms_to", proto->printRef());
       if (auto superclass = T->getSuperclass())
         printRec("superclass", superclass);
+
     }
 
     void visitPrimaryArchetypeType(PrimaryArchetypeType *T, StringRef label) {
@@ -3755,7 +3757,6 @@ namespace {
                                       StringRef label) {
       printArchetypeCommon(T, "opaque_type", label);
       printField("decl", T->getDecl()->getNamingDecl()->printRef());
-      printField("ordinal", T->getOrdinal());
       if (!T->getSubstitutions().empty()) {
         OS << '\n';
         SmallPtrSet<const ProtocolConformance *, 4> Dumped;

lib/AST/ASTPrinter.cpp

@@ -5893,6 +5893,12 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
   }
 
   void visitOpenedArchetypeType(OpenedArchetypeType *T) {
+    if (auto parent = T->getParent()) {
+      visitParentType(parent);
+      printArchetypeCommon(T, getAbstractTypeParamDecl(T));
+      return;
+    }
+
     if (Options.PrintForSIL)
       Printer << "@opened(\"" << T->getOpenedExistentialID() << "\") ";
     visit(T->getOpenedExistentialType());
@@ -5940,10 +5946,17 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
   }
 
   void visitOpaqueTypeArchetypeType(OpaqueTypeArchetypeType *T) {
+    if (auto parent = T->getParent()) {
+      visitParentType(parent);
+      printArchetypeCommon(T, getAbstractTypeParamDecl(T));
+      return;
+    }
+
     // Try to print a named opaque type.
     auto printNamedOpaque = [&] {
-      if (auto genericParam =
-              T->getDecl()->getExplicitGenericParam(T->getOrdinal())) {
+      unsigned ordinal =
+          T->getInterfaceType()->castTo<GenericTypeParamType>()->getIndex();
+      if (auto genericParam = T->getDecl()->getExplicitGenericParam(ordinal)) {
         visit(genericParam->getDeclaredInterfaceType());
         return true;
       }

lib/AST/Type.cpp

@@ -3302,10 +3302,6 @@ OpaqueTypeArchetypeType::OpaqueTypeArchetypeType(
 {
 }
 
-unsigned OpaqueTypeArchetypeType::getOrdinal() const {
-  return getInterfaceType()->castTo<GenericTypeParamType>()->getIndex();
-}
-
 SequenceArchetypeType::SequenceArchetypeType(
     const ASTContext &Ctx, GenericEnvironment *GenericEnv, Type InterfaceType,
     ArrayRef<ProtocolDecl *> ConformsTo, Type Superclass,