Fix resetting of failed locale lookup when successfully resolving loc…

…ale in composite message lookup

pkgs/intl/lib/message_lookup_by_library.dart

@@ -75,8 +75,8 @@ class CompositeMessageLookup implements MessageLookup {
     if (newLocale != null) {
       availableMessages[localeName] = newLocale;
       availableMessages[canonical] = newLocale;
-      // If there was already a failed lookup for [newLocale], null the cache.
-      if (_lastLocale == newLocale) {
+      // If there was already a failed lookup for [localeName], null the cache.
+      if (_lastLocale == localeName) {
         _lastLocale = null;
         _lastLookup = null;
       }

pkgs/intl/test/message_lookup_by_library.dart

@@ -0,0 +1,31 @@
+// 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.
+
+library message_lookup_by_library_test;
+
+import 'package:intl/message_lookup_by_library.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('Resolves message successfully after unsuccessful lookup', () {
+    final CompositeMessageLookup lookup = CompositeMessageLookup();
+    final lookupMessage = lookup.lookupMessage('Hello', 'pt', 'greeting', null, null);
+    expect(lookupMessage, 'Hello');
+
+    lookup.addLocale('pt', (locale) => TestMessageLookupByLibrary('pt', {'greeting': () => 'Bom dia'}));
+
+    final lookupMessage2 = lookup.lookupMessage('Hello', 'pt', 'greeting', null, null);
+    expect(lookupMessage2, 'Bom dia');
+  });
+}
+
+class TestMessageLookupByLibrary extends MessageLookupByLibrary {
+  @override
+  final Map<String, dynamic> messages;
+
+  @override
+  final String localeName;
+
+  TestMessageLookupByLibrary(this.localeName, this.messages);
+}