Handle missing imports/exports/parts.

tests/compiler/dart2js/import_test.dart

+// Copyright (c) 2013, 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.
+
+// Test that the compiler can handle imports when package root has not been set.
+
+library dart2js.test.import;
+
+import 'package:expect/expect.dart';
+import 'memory_compiler.dart';
+
+const MEMORY_SOURCE_FILES = const {
+  'main.dart': '''
+
+library main;
+
+import 'dart:bar';

[ahe, 2013/08/06 15:01:00]

The comment on line 5 implies that you meant package:bar here. I think it makes
sense to test for both.

However, given names as pub and barback, perhaps you'd better not assume that a
library named "dart:bar" or "package:bar" will never exist.

[Johnni Winther, 2013/08/19 08:05:19]

Done.

+export 'foo.dart';
+
+part 'bar.dart';
+
+main() {
+  int i = "";
+}
+''',
+};
+
+testMissingImports() {
+  var collector = new DiagnosticCollector();
+  var compiler = compilerFor(MEMORY_SOURCE_FILES, diagnosticHandler: collector);
+  compiler.run(Uri.parse('memory:main.dart'));
+  Expect.equals(3, collector.errors.length);
+  Expect.equals(1, collector.warnings.length);  
+}
+
+testMissingMain() {
+  var collector = new DiagnosticCollector();
+  var compiler = compilerFor({}, diagnosticHandler: collector);
+  compiler.run(Uri.parse('memory:missing.dart'));
+  Expect.equals(1, collector.errors.length);
+  Expect.equals(0, collector.warnings.length);  
+}
+
+void main() {
+  testMissingImports();
+  testMissingMain();
+}