Disable PlaceholderType parsing

Author: Jumhyn

lib/Parse/ParseType.cpp

@@ -151,7 +151,6 @@ LayoutConstraint Parser::parseLayoutConstraint(Identifier LayoutConstraintID) {
 ///     type-simple '!'
 ///     type-collection
 ///     type-array
-///     '_'
 ParserResult<TypeRepr> Parser::parseTypeSimple(Diag<> MessageID) {
   ParserResult<TypeRepr> ty;
 
@@ -183,9 +182,6 @@ ParserResult<TypeRepr> Parser::parseTypeSimple(Diag<> MessageID) {
     ty = parseTypeCollection();
     break;
   }
-  case tok::kw__:
-    ty = makeParserResult(new (Context) PlaceholderTypeRepr(consumeToken()));
-    break;
   case tok::kw_protocol:
     if (startsWithLess(peekToken())) {
       ty = parseOldStyleProtocolComposition();
@@ -1443,9 +1439,6 @@ bool Parser::canParseType() {
     if (!consumeIf(tok::r_square))
       return false;
     break;
-  case tok::kw__:
-      consumeToken();
-    break;
 
 
   default:

lib/Sema/PreCheckExpr.cpp

@@ -1476,12 +1476,8 @@ TypeExpr *PreCheckExpression::simplifyTypeExpr(Expr *E) {
     return simplifyNestedTypeExpr(UDE);
   }
 
-  // Fold '_' into a placeholder type.
-  if (auto *DAE = dyn_cast<DiscardAssignmentExpr>(E)) {
-    auto *placeholderRepr =
-        new (getASTContext()) PlaceholderTypeRepr(DAE->getLoc());
-    return new (getASTContext()) TypeExpr(placeholderRepr);
-  }
+  // TODO: Fold DiscardAssignmentExpr into a placeholder type here once parsing
+  // them is supported.
 
   // Fold T? into an optional type when T is a TypeExpr.
   if (isa<OptionalEvaluationExpr>(E) || isa<BindOptionalExpr>(E)) {
@@ -1688,8 +1684,6 @@ TypeExpr *PreCheckExpression::simplifyTypeExpr(Expr *E) {
         return nullptr;
       if (auto *TyE = dyn_cast<TypeExpr>(E))
         return TyE->getTypeRepr();
-      if (auto *DAE = dyn_cast<DiscardAssignmentExpr>(E))
-        return new (getASTContext()) PlaceholderTypeRepr(DAE->getLoc());
       if (auto *TE = dyn_cast<TupleExpr>(E))
         if (TE->getNumElements() == 0)
           return TupleTypeRepr::createEmpty(ctx, TE->getSourceRange());

lib/Sema/TypeCheckType.cpp

@@ -711,6 +711,8 @@ static Type applyGenericArguments(Type type, TypeResolution resolution,
       if (!options.is(TypeResolverContext::TypeAliasDecl)) {
         // If the resolution object carries an opener, attempt to open
         // the unbound generic type.
+        // TODO: We should be able to just open the generic arguments as N
+        // different PlaceholderTypes.
         if (const auto openerFn = resolution.getUnboundTypeOpener())
           if (const auto boundTy = openerFn(unboundTy))
             return boundTy;