Add support for assert statements with messages to the analyzer.

pkg/analyzer/test/generated/parser_test.dart

 // Copyright (c) 2014, 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 engine.parser_test;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/error.dart';
@@ skipping 5140 matching lines @@
     ArgumentList argumentList = parse4("parseArgumentList", "(x: x, y: y)");
     NodeList<Expression> arguments = argumentList.arguments;
     expect(arguments, hasLength(2));
   }
 
   void test_parseAssertStatement() {
     AssertStatement statement = parse4("parseAssertStatement", "assert (x);");
     expect(statement.assertKeyword, isNotNull);
     expect(statement.leftParenthesis, isNotNull);
     expect(statement.condition, isNotNull);
+    expect(statement.comma, isNull);
+    expect(statement.message, isNull);
     expect(statement.rightParenthesis, isNotNull);
     expect(statement.semicolon, isNotNull);
   }
+
+  void test_parseAssertStatement_messageLowPrecedence() {
+    // Using a throw expression as an assert message would be silly in
+    // practice, but it's the lowest precedence expression type, so verifying
+    // that it works should give us high confidence that other expression types
+    // will work as well.
+    AssertStatement statement =
+        parse4('parseAssertStatement', 'assert (x, throw "foo");');
+    expect(statement.assertKeyword, isNotNull);
+    expect(statement.leftParenthesis, isNotNull);
+    expect(statement.condition, isNotNull);
+    expect(statement.comma, isNotNull);
+    expect(statement.message, isNotNull);
+    expect(statement.rightParenthesis, isNotNull);
+    expect(statement.semicolon, isNotNull);
+  }
+
+  void test_parseAssertStatement_messageString() {
+    AssertStatement statement =
+        parse4('parseAssertStatement', 'assert (x, "foo");');
+    expect(statement.assertKeyword, isNotNull);
+    expect(statement.leftParenthesis, isNotNull);
+    expect(statement.condition, isNotNull);
+    expect(statement.comma, isNotNull);
+    expect(statement.message, isNotNull);
+    expect(statement.rightParenthesis, isNotNull);
+    expect(statement.semicolon, isNotNull);
+  }
 
   void test_parseAssignableExpression_expression_args_dot() {
     PropertyAccess propertyAccess =
         parse("parseAssignableExpression", <Object>[false], "(x)(y).z");
     FunctionExpressionInvocation invocation =
         propertyAccess.target as FunctionExpressionInvocation;
     expect(invocation.function, isNotNull);
     expect(invocation.typeArguments, isNull);
     ArgumentList argumentList = invocation.argumentList;
     expect(argumentList, isNotNull);
@@ skipping 5943 matching lines @@
         new Scanner(null, new CharSequenceReader(source), listener);
     Token tokenStream = scanner.tokenize();
     //
     // Parse the source.
     //
     Parser parser = new Parser(null, listener);
     return invokeParserMethodImpl(
         parser, methodName, <Object>[tokenStream], tokenStream) as Token;
   }
 }