Type check untyped == calls specially.

lib/type_checker.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 library kernel.type_checker;
 
 import 'ast.dart';
 import 'class_hierarchy.dart';
 import 'core_types.dart';
 import 'type_algebra.dart';
 import 'type_environment.dart';
@@ skipping 443 matching lines @@
       }
     }
     return instantiation.substituteType(function.returnType);
   }
 
   @override
   DartType visitMethodInvocation(MethodInvocation node) {
     var target = node.interfaceTarget;
     if (target == null) {
       var receiver = visitExpression(node.receiver);
-      return (node.name.name == 'call' && receiver is FunctionType)
-          ? handleFunctionCall(node, receiver, node.arguments)
-          : handleDynamicCall(receiver, node.arguments);
+      if (node.name.name == '==') {
+        visitExpression(node.arguments.positional.single);
+        return environment.boolType;

[ahe, 2016/11/01 16:52:24]

I don't see how you know that you can return bool here. How do you know that the
argument is null or the receiver is null?

[asgerf, 2016/11/01 17:07:33]

In strong mode (which is what we are checking), operator== must return bool
because it overrides Object.==

+      }
+      if (node.name.name == 'call' && receiver is FunctionType) {
+        return handleFunctionCall(node, receiver, node.arguments);
+      }
+      return handleDynamicCall(receiver, node.arguments);
     } else if (environment.isOverloadedArithmeticOperator(target)) {
       assert(node.arguments.positional.length == 1);
       var receiver = visitExpression(node.receiver);
       var argument = visitExpression(node.arguments.positional[0]);
       return environment.getTypeOfOverloadedArithmetic(receiver, argument);
     } else {
       return handleCall(node.arguments, target.function,
           receiver: getReceiverType(node, node.receiver, node.interfaceTarget));
     }
   }
@@ skipping 318 matching lines @@
   }
 
   @override
   visitLocalInitializer(LocalInitializer node) {
     visitVariableDeclaration(node.variable);
   }
 
   @override
   visitInvalidInitializer(InvalidInitializer node) {}
 }