Implement checked mode for const constructors.

lib/compiler/implementation/compile_time_constants.dart

 // Copyright (c) 2012, 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.
 
 /**
  * The [ConstantHandler] keeps track of compile-time constants,
  * initializations of global and static fields, and default values of
  * optional parameters.
  */
 class ConstantHandler extends CompilerTask {
@@ skipping 624 matching lines @@
     if (Elements.isLocal(element)) {
       Constant constant = definitions[element];
       if (constant === null) {
         compiler.internalError("Local variable without value", node: send);
       }
       return constant;
     }
     return super.visitSend(send);
   }
 
+  void potentiallyCheckType(Node node, Element element, Constant constant) {
+    if (compiler.enableTypeAssertions) {
+      DartType elementType = element.computeType(compiler);
+      DartType constantType = constant.computeType(compiler);
+      // TODO(ngeoffray): Handle type parameters.
+      if (elementType.element.isTypeVariable()) return;
+      if (!constantSystem.isSubtype(compiler, constantType, elementType)) {
+        MessageKind kind = MessageKind.NOT_ASSIGNABLE;
+        compiler.reportError(node, new CompileTimeConstantError(
+            kind, [elementType, constantType]));
+      }
+    }
+  }
+
+  void updateFieldValue(Node node, Element element, Constant constant) {
+    potentiallyCheckType(node, element, constant);
+    fieldValues[element] = constant;
+  }
+
   /**
    * Given the arguments (a list of constants) assigns them to the parameters,
    * updating the definitions map. If the constructor has field-initializer
    * parameters (like [:this.x:]), also updates the [fieldValues] map.
    */
   void assignArgumentsToParameters(List<Constant> arguments) {
     // Assign arguments to parameters.
     FunctionSignature parameters = constructor.computeSignature(compiler);
     int index = 0;
     parameters.forEachParameter((Element parameter) {
       Constant argument = arguments[index++];
+      Node node = parameter.parseNode(compiler);
+      potentiallyCheckType(node, parameter, argument);
       definitions[parameter] = argument;
       if (parameter.kind == ElementKind.FIELD_PARAMETER) {
         FieldParameterElement fieldParameterElement = parameter;
-        fieldValues[fieldParameterElement.fieldElement] = argument;
+        updateFieldValue(node, fieldParameterElement.fieldElement, argument);
       }
     });
   }
 
   void evaluateSuperOrRedirectSend(Selector selector,
                                    Link<Node> arguments,
                                    FunctionElement targetConstructor) {
     List<Constant> compiledArguments =
         evaluateArgumentsToConstructor(selector, arguments, targetConstructor);
 
     ConstructorEvaluator evaluator = new ConstructorEvaluator(
         targetConstructor, constantSystem, compiler);
     evaluator.evaluateConstructorFieldValues(compiledArguments);
     // Copy over the fieldValues from the super/redirect-constructor.
+    // No need to go through [updateFieldValue] because the
+    // assignments have already been checked in checked mode.
     evaluator.fieldValues.forEach((key, value) => fieldValues[key] = value);
   }
 
   /**
    * Runs through the initializers of the given [constructor] and updates
    * the [fieldValues] map.
    */
   void evaluateConstructorInitializers() {
     FunctionExpression functionNode = constructor.parseNode(compiler);
     NodeList initializerList = functionNode.initializers;
@@ skipping 12 matching lines @@
           Selector selector = elements.getSelector(call);
           Link<Node> arguments = call.arguments;
           evaluateSuperOrRedirectSend(selector, arguments, targetConstructor);
           foundSuperOrRedirect = true;
         } else {
           // A field initializer.
           SendSet init = link.head;
           Link<Node> initArguments = init.arguments;
           assert(!initArguments.isEmpty() && initArguments.tail.isEmpty());
           Constant fieldValue = evaluate(initArguments.head);
-          fieldValues[elements[init]] = fieldValue;
+          updateFieldValue(init, elements[init], fieldValue);
         }
       }
     }
 
     if (!foundSuperOrRedirect) {
       // No super initializer found. Try to find the default constructor if
       // the class is not Object.
       ClassElement enclosingClass = constructor.getEnclosingClass();
       ClassElement superClass = enclosingClass.superclass;
       if (enclosingClass != compiler.objectClass) {
@@ skipping 37 matching lines @@
       Constant fieldValue = fieldValues[field];
       if (fieldValue === null) {
         // Use the default value.
         fieldValue = compiler.compileConstant(field);
       }
       jsNewArguments.add(fieldValue);
     });
     return jsNewArguments;
   }
 }