Don't allow overlapping source directories.

sdk/lib/_internal/pub/test/barback/fails_on_overlapping_directories_test.dart

Index: sdk/lib/_internal/pub/test/barback/fails_on_overlapping_directories_test.dart
diff --git a/sdk/lib/_internal/pub/test/barback/fails_on_overlapping_directories_test.dart b/sdk/lib/_internal/pub/test/barback/fails_on_overlapping_directories_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..8e98b86759580fa06de4e8e24db245555e59a5e7
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/barback/fails_on_overlapping_directories_test.dart
@@ -0,0 +1,52 @@
+// 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.
+
+import 'package:path/path.dart' as path;
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../lib/src/exit_codes.dart' as exit_codes;
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  initConfig();
+
+  setUp(() {
+    d.dir(appPath, [
+      d.appPubspec(),
+      d.dir("web", [
+        d.dir("sub1", [
+          d.file("file.txt", "contents"),
+          d.dir("sub2", [
+            d.file("file.txt", "contents")
+          ]),
+          d.dir("sub3", [
+            d.file("file.txt", "contents")
+          ])
+        ])
+      ])
+    ]).create();
+  });
+
+  var webSub1 = path.join("web", "sub1");
+  var webSub1Sub2 = path.join("web", "sub1", "sub2");
+  var webSub1Sub3 = path.join("web", "sub1", "sub3");
+
+  pubBuildAndServeShouldFail("if a superdirectory follows a subdirectory",
+      args: [webSub1Sub2, webSub1],
+      error: 'Directories "$webSub1Sub2" and "$webSub1" cannot overlap.',
+      exitCode: exit_codes.USAGE);
+
+  pubBuildAndServeShouldFail("if a subdirectory follows a superdirectory",
+      args: [webSub1, webSub1Sub2],
+      error: 'Directories "$webSub1" and "$webSub1Sub2" cannot overlap.',
+      exitCode: exit_codes.USAGE);
+
+  pubBuildAndServeShouldFail("if multiple directories overlap",
+      args: [webSub1, webSub1Sub2, webSub1Sub3],
+      error: 'Directories "$webSub1", "$webSub1Sub2" and "$webSub1Sub3" '
+             'cannot overlap.',
+      exitCode: exit_codes.USAGE);
+}