Throw TypeError instead of CastError for type coercions.

lib/src/compiler/code_generator.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 531 matching lines @@
       }
 
       // A no-op in JavaScript.
       return jsFrom;
     }
 
     var type = _emitType(to,
         nameType: options.nameTypeTests || options.hoistTypeTests,
         hoistType: options.hoistTypeTests);
     if (_inAngularTemplate) return jsFrom;
-    return js.call('dart.as(#, #)', [jsFrom, type]);
+    if (isReifiedCoercion(node)) {
+      return js.call('dart.check(#, #)', [jsFrom, type]);
+    } else {
+      return js.call('dart.as(#, #)', [jsFrom, type]);
+    }
+  }
+
+  bool isReifiedCoercion(AstNode node) {
+    // TODO(sra): Find a better way to recognize reified coercion, since we
+    // can't set the isSynthetic attribute.
+    return (node is AsExpression) && (node.asOperator.offset == 0);
   }
 
   @override
   visitIsExpression(IsExpression node) {
     // Generate `is` as `dart.is` or `typeof` depending on the RHS type.
     JS.Expression result;
     var type = node.type.type;
     var lhs = _visit(node.expression);
     var typeofName = _jsTypeofName(type);
     if (typeofName != null) {
@@ skipping 3832 matching lines @@
     }
     if (node is BinaryExpression) {
       JS.Expression shortCircuit(String code) {
         return finish(js.call(code,
             [_visitTest(node.leftOperand), _visitTest(node.rightOperand)]));
       }
       var op = node.operator.type.lexeme;
       if (op == '&&') return shortCircuit('# && #');
       if (op == '||') return shortCircuit('# || #');
     }
-    // Offset 0 from start of file is syntactically impossible for normal code.
-    // TODO(sra): Find a better way to recognize reified coercion, since we
-    // can't set the isSynthetic attribute.
-    if (node is AsExpression && node.asOperator.offset == 0) {
-      assert(node.staticType == types.boolType);
-      return js.call('dart.test(#)', _visit(node.expression));
+    if (isReifiedCoercion(node)) {
+      AsExpression asNode = node;
+      assert(asNode.staticType == types.boolType);
+      return js.call('dart.test(#)', _visit(asNode.expression));
     }
     JS.Expression result = _visit(node);
     if (isNullable(node)) result = js.call('dart.test(#)', result);
     return result;
   }
 
   /// Like [_emitMemberName], but for declaration sites.
   ///
   /// Unlike call sites, we always have an element available, so we can use it
   /// directly rather than computing the relevant options for [_emitMemberName].
@@ skipping 243 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';