[AST] Add ErrorType originator for PlaceholderType

Author: hamishknight

include/swift/AST/Types.h

@@ -7734,8 +7734,8 @@ class PlaceholderType : public TypeBase {
   // NOTE: If you add a new Type-based originator, you'll need to update the
   // recursive property logic in PlaceholderType::get.
   using Originator =
-      llvm::PointerUnion<TypeVariableType *, DependentMemberType *, VarDecl *,
-                         ErrorExpr *, TypeRepr *>;
+      llvm::PointerUnion<TypeVariableType *, DependentMemberType *, ErrorType *,
+                         VarDecl *, ErrorExpr *, TypeRepr *>;
 
   Originator O;
 

lib/AST/ASTContext.cpp

@@ -3675,6 +3675,9 @@ Type PlaceholderType::get(ASTContext &ctx, Originator originator) {
     if (auto *depTy = originator.dyn_cast<DependentMemberType *>())
       return depTy->getRecursiveProperties();
 
+    if (auto *errTy = originator.dyn_cast<ErrorType *>())
+      return errTy->getRecursiveProperties();
+
     return RecursiveTypeProperties();
   }();
   auto arena = getArena(originatorProps);

lib/AST/ASTDumper.cpp

@@ -6077,6 +6077,8 @@ namespace {
                             Label::optional("originating_var"), DeclColor);
       } else if (isa<ErrorExpr *>(originator)) {
         printFlag("error_expr");
+      } else if (auto *errTy = originator.dyn_cast<ErrorType *>()) {
+        printRec(errTy, Label::always("error_type"));
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         printRec(DMT, Label::always("dependent_member_type"));
       } else if (isa<TypeRepr *>(originator)) {

lib/AST/ASTPrinter.cpp

@@ -6146,6 +6146,8 @@ class TypePrinter : public TypeVisitor<TypePrinter, void, NonRecursivePrintOptio
         Printer << VD->getName();
       } else if (isa<ErrorExpr *>(originator)) {
         Printer << "error_expr";
+      } else if (auto *errTy = originator.dyn_cast<ErrorType *>()) {
+        visit(errTy);
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         visit(DMT);
       } else if (isa<TypeRepr *>(originator)) {