From 412d56f81ae4396bdf0b39aec69cc4da1f7d7984 Mon Sep 17 00:00:00 2001
From: Seth Brenith <seth.brenith@microsoft.com>
Date: Fri, 17 Apr 2020 09:36:36 -0700
Subject: [PATCH] [torque] Require "extends" clause for class declarations

Currently it's possible to hit an internal compiler error by declaring a
non-extern class that doesn't extend anything. It's not very meanigful
for a class to not extend from anything, so the parser should enforce
this requirement.

Change-Id: I38064f87345d28ce84521261bbfd33d9b1c71334
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2153847
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67212}
---
 src/torque/ast.h            | 5 ++---
 src/torque/torque-parser.cc | 7 +++----
 src/torque/type-visitor.cc  | 5 +----
 3 files changed, 6 insertions(+), 11 deletions(-)

diff --git a/src/torque/ast.h b/src/torque/ast.h
index 93e0622aee..d05338923f 100644
--- a/src/torque/ast.h
+++ b/src/torque/ast.h
@@ -1175,8 +1175,7 @@ struct ClassBody : AstNode {
 struct ClassDeclaration : TypeDeclaration {
   DEFINE_AST_NODE_LEAF_BOILERPLATE(ClassDeclaration)
   ClassDeclaration(SourcePosition pos, Identifier* name, ClassFlags flags,
-                   base::Optional<TypeExpression*> super,
-                   base::Optional<std::string> generates,
+                   TypeExpression* super, base::Optional<std::string> generates,
                    std::vector<Declaration*> methods,
                    std::vector<ClassFieldExpression> fields,
                    InstanceTypeConstraints instance_type_constraints)
@@ -1188,7 +1187,7 @@ struct ClassDeclaration : TypeDeclaration {
         fields(std::move(fields)),
         instance_type_constraints(std::move(instance_type_constraints)) {}
   ClassFlags flags;
-  base::Optional<TypeExpression*> super;
+  TypeExpression* super;
   base::Optional<std::string> generates;
   std::vector<Declaration*> methods;
   std::vector<ClassFieldExpression> fields;
diff --git a/src/torque/torque-parser.cc b/src/torque/torque-parser.cc
index 1713af0b70..aced93e79d 100644
--- a/src/torque/torque-parser.cc
+++ b/src/torque/torque-parser.cc
@@ -906,8 +906,8 @@ base::Optional<ParseResult> MakeClassDeclaration(
   if (!IsValidTypeName(name->value)) {
     NamingConventionError("Type", name, "UpperCamelCase");
   }
-  auto extends = child_results->NextAs<base::Optional<TypeExpression*>>();
-  if (extends && !BasicTypeExpression::DynamicCast(*extends)) {
+  auto extends = child_results->NextAs<TypeExpression*>();
+  if (!BasicTypeExpression::DynamicCast(extends)) {
     ReportError("Expected type name in extends clause.");
   }
   auto generates = child_results->NextAs<base::Optional<std::string>>();
@@ -2358,8 +2358,7 @@ struct TorqueGrammar : Grammar {
             &externalString, Token(";")},
            AsSingletonVector<Declaration*, MakeExternConstDeclaration>()),
       Rule({annotations, CheckIf(Token("extern")), CheckIf(Token("transient")),
-            OneOf({"class", "shape"}), &name,
-            Optional<TypeExpression*>(Sequence({Token("extends"), &type})),
+            OneOf({"class", "shape"}), &name, Token("extends"), &type,
             Optional<std::string>(
                 Sequence({Token("generates"), &externalString})),
             &optionalClassBody},
diff --git a/src/torque/type-visitor.cc b/src/torque/type-visitor.cc
index 10ed87d247..fc1adb19f6 100644
--- a/src/torque/type-visitor.cc
+++ b/src/torque/type-visitor.cc
@@ -247,7 +247,7 @@ const ClassType* TypeVisitor::ComputeType(
   ClassFlags flags = decl->flags;
   bool is_shape = flags & ClassFlag::kIsShape;
   std::string generates = decl->name->value;
-  const Type* super_type = TypeVisitor::ComputeType(*decl->super);
+  const Type* super_type = TypeVisitor::ComputeType(decl->super);
   if (is_shape) {
     if (!(flags & ClassFlag::kExtern)) {
       ReportError("Shapes must be extern, add \"extern\" to the declaration.");
@@ -266,9 +266,6 @@ const ClassType* TypeVisitor::ComputeType(
     // support for type-checks on the C++ side.
     generates = super_class->name();
   }
-  if (!decl->super) {
-    ReportError("Extern class must extend another type.");
-  }
   if (super_type != TypeOracle::GetStrongTaggedType()) {
     const ClassType* super_class = ClassType::DynamicCast(super_type);
     if (!super_class) {