Fix a bug with the printing of optional typealiases.

Author: rjmccall

lib/AST/ASTPrinter.cpp

@@ -3529,24 +3529,7 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
       return;
     }
 
-    bool isSimple = T->hasSimpleTypeRepr();
-    if (!isSimple && T->is<OpaqueTypeArchetypeType>()) {
-      auto opaqueTy = T->castTo<OpaqueTypeArchetypeType>();
-      switch (Options.OpaqueReturnTypePrinting) {
-      case PrintOptions::OpaqueReturnTypePrintingMode::StableReference:
-      case PrintOptions::OpaqueReturnTypePrintingMode::Description:
-        isSimple = true;
-        break;
-      case PrintOptions::OpaqueReturnTypePrintingMode::WithOpaqueKeyword:
-        isSimple = false;
-        break;
-      case PrintOptions::OpaqueReturnTypePrintingMode::WithoutOpaqueKeyword: {
-        isSimple = opaqueTy->getExistentialType()->hasSimpleTypeRepr();
-        break;
-      }
-      }
-    }
-
+    bool isSimple = isSimpleUnderPrintOptions(T);
     if (isSimple) {
       visit(T);
     } else {
@@ -3556,6 +3539,28 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
     }
   }
 
+  /// Determinee whether the given type has a simple representation
+  /// under the current print options.
+  bool isSimpleUnderPrintOptions(Type T) {
+    if (auto typealias = dyn_cast<TypeAliasType>(T.getPointer())) {
+      if (shouldDesugarTypeAliasType(typealias))
+        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 false;
+      case PrintOptions::OpaqueReturnTypePrintingMode::WithoutOpaqueKeyword:
+        return isSimpleUnderPrintOptions(opaque->getExistentialType());
+      }
+      llvm_unreachable("bad opaque-return-type printing mode");
+    }
+    return T->hasSimpleTypeRepr();
+  }
+
   template <typename T>
   void printModuleContext(T *Ty) {
     FileUnit *File = cast<FileUnit>(Ty->getDecl()->getModuleScopeContext());
@@ -3693,8 +3698,12 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
     Printer << BUILTIN_TYPE_NAME_SILTOKEN;
   }
 
+  bool shouldDesugarTypeAliasType(TypeAliasType *T) {
+    return Options.PrintForSIL || Options.PrintTypeAliasUnderlyingType;
+  }
+
   void visitTypeAliasType(TypeAliasType *T) {
-    if (Options.PrintForSIL || Options.PrintTypeAliasUnderlyingType) {
+    if (shouldDesugarTypeAliasType(T)) {
       visit(T->getSinglyDesugaredType());
       return;
     }