Introduce getPrefixEndToken to avoid too big context in messages.

tests/compiler/dart2js/message_span_test.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.
+
+import 'package:async_helper/async_helper.dart';
+import 'package:compiler/src/commandline_options.dart';
+import 'package:compiler/src/diagnostics/messages.dart';
+import 'package:compiler/src/io/source_file.dart';
+import 'package:expect/expect.dart';
+import 'memory_compiler.dart';
+import 'memory_source_file_helper.dart';
+
+const List<Test> TESTS = const <Test>[
+  const Test('''
+class A { A(b); }
+class B extends A {
+  a() {}
+
+  lot() {}
+
+  of() {}
+
+  var members;
+}
+main() => B();''',
+  const {
+    MessageKind.NO_MATCHING_CONSTRUCTOR_FOR_IMPLICIT: '''
+class B extends A {
+^^^^^^^^^^^^^^^^^^^'''}),

[ahe, 2016/02/04 11:32:33]

I suggest this becomes:

class B extends A {
^^^^^^^^^^^^^^^^^

[Johnni Winther, 2016/02/05 09:14:20]

Done.

+
+  const Test('''
+class A { A(b); }
+class B
+    extends A {
+  a() {}
+
+  lot() {}
+
+  of() {}
+
+  var members;
+}
+main() => B();''',
+  const {
+    MessageKind.NO_MATCHING_CONSTRUCTOR_FOR_IMPLICIT: '''
+class B
+    extends A {
+'''}),
+
+  const Test('''
+void foo(int a) {
+  // a
+  // non-empty
+  // body
+}
+main() => foo('');''',
+  const {
+    MessageKind.THIS_IS_THE_METHOD: '''
+void foo(int a) {
+^^^^^^^^^^^^^^^'''}),
+
+  const Test('''
+void foo(int a,
+         int b) {
+  // a
+  // non-empty
+  // body
+}
+main() => foo('', 0);''',
+  const {
+    MessageKind.THIS_IS_THE_METHOD: '''
+void foo(int a,
+         int b) {
+'''}),
+
+  const Test('''
+class A {
+  int foo() {
+    // a
+    // non-empty
+    // body
+  }
+}
+class B extends A {
+  int get foo {
+    // a
+    // non-empty
+    // body
+    return 0;
+  }
+}
+main() => new B();''',
+  const {
+    MessageKind.CANNOT_OVERRIDE_METHOD_WITH_GETTER: '''
+  int get foo {
+  ^^^^^^^^^^^''',
+    MessageKind.CANNOT_OVERRIDE_METHOD_WITH_GETTER_CONT: '''
+  int foo() {
+  ^^^^^^^^^'''}),
+];
+
+class Test {
+  final String code;
+  final Map<MessageKind, String> kindToSpan;
+
+  const Test(this.code, this.kindToSpan);
+}
+
+const String MARKER = '---marker---';
+
+main() {
+  asyncTest(() async {
+    var cachedCompiler;
+    for (Test test in TESTS) {
+      DiagnosticCollector collector = new DiagnosticCollector();
+      CompilationResult result = await runCompiler(
+          memorySourceFiles: {'main.dart': test.code},
+          options: [Flags.analyzeOnly],
+          diagnosticHandler: collector,
+          cachedCompiler: cachedCompiler);
+      cachedCompiler = result.compiler;
+      MemorySourceFileProvider provider = cachedCompiler.provider;
+      Map<MessageKind, String> kindToSpan =
+          new Map<MessageKind, String>.from(test.kindToSpan);
+      for (CollectedMessage message in collector.messages) {
+        String expectedSpanText = kindToSpan[message.messageKind];
+        if (expectedSpanText != null) {
+          SourceFile sourceFile = provider.getSourceFile(message.uri);
+          String locationMessage =
+              sourceFile.getLocationMessage(MARKER, message.begin, message.end);
+          // Remove `filename:line:column:` and message.
+          String strippedLocationMessage = locationMessage.substring(
+              locationMessage.indexOf(MARKER) + MARKER.length + 1);
+          Expect.equals(expectedSpanText, strippedLocationMessage,
+              "Unexpected span for ${message.messageKind} in\n${test.code}"
+              "\nExpected:${expectedSpanText.codeUnits}"
+              "\nActual  :${strippedLocationMessage.codeUnits}");
+          kindToSpan.remove(message.messageKind);
+        }
+      }
+      kindToSpan.forEach((MessageKind kind, _) {
+        Expect.fail("Missing message kin $kind in\n${test.code}");
+      });
+    }
+  });
+}