Compute API signatures of files.

pkg/front_end/test/src/incremental/file_state_test.dart

Index: pkg/front_end/test/src/incremental/file_state_test.dart
diff --git a/pkg/front_end/test/src/incremental/file_state_test.dart b/pkg/front_end/test/src/incremental/file_state_test.dart
index affeb0e2aa4f717aa13b8a45b353b0ec68fca3cf..2a4b6546954d61702341ef497598a502364650ba 100644
--- a/pkg/front_end/test/src/incremental/file_state_test.dart
+++ b/pkg/front_end/test/src/incremental/file_state_test.dart
@@ -2,6 +2,8 @@
 // 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 'dart:async';
+
 import 'package:front_end/memory_file_system.dart';
 import 'package:front_end/src/fasta/translate_uri.dart';
 import 'package:front_end/src/incremental/file_state.dart';
@@ -29,7 +31,110 @@ class FileSystemStateTest {
     uriTranslator.dartLibraries.addAll(dartLibraries);
     _coreUri = Uri.parse('dart:core');
     expect(_coreUri, isNotNull);
-    fsState = new FileSystemState(fileSystem, uriTranslator);
+    fsState = new FileSystemState(fileSystem, uriTranslator, <int>[]);
+  }
+
+  test_apiSignature() async {
+    var path = '/a.dart';
+    var uri = writeFile(path, '');
+    FileState file = await fsState.getFile(uri);
+
+    List<int> lastSignature = file.apiSignature;
+
+    /// Assert that the given [newCode] has the same API signature as
+    /// the last computed.
+    Future<Null> assertSameSignature(String newCode) async {
+      writeFile(path, newCode);
+      await file.refresh();
+      List<int> newSignature = file.apiSignature;
+      expect(newSignature, lastSignature);
+    }
+
+    /// Assert that the given [newCode] does not have the same API signature as
+    /// the last computed, and update the last signature to the new one.
+    Future<Null> assertNotSameSignature(String newCode) async {
+      writeFile(path, newCode);
+      await file.refresh();
+      List<int> newSignature = file.apiSignature;
+      expect(newSignature, isNot(lastSignature));
+      lastSignature = newSignature;
+    }
+
+    await assertNotSameSignature('''
+var v = 1;
+foo() {
+  print(2);
+}
+bar() {
+  print(3);
+}
+baz() => 4;
+''');
+
+    // [S] Add comments.
+    await assertSameSignature('''
+var v = 1; // comment
+/// comment 1
+/// comment 2
+foo() {
+  print(2);
+}
+bar() {
+  print(3);
+}
+/**
+ *  Comment
+ */
+baz() => 4;
+''');
+
+    // [S] Remove comments.
+    await assertSameSignature('''
+var v = 1;
+foo() {
+  print(2);
+}
+bar() {
+  print(3);
+}
+baz() => 4;
+''');
+
+    // [NS] Change the top-level variable initializer.
+    await assertNotSameSignature('''
+var v = 11;
+foo() {
+  print(2);
+}
+bar() {
+  print(3);
+}
+baz() => 4;
+''');
+
+    // [S] Change in a block function body.
+    await assertSameSignature('''
+var v = 11;
+foo() {
+  print(22);
+}
+bar() {
+  print(33);
+}
+baz() => 4;
+''');
+
+    // [NS] Change in an expression function body.
+    await assertNotSameSignature('''
+var v = 11;
+foo() {
+  print(22);
+}
+bar() {
+  print(33);
+}
+baz() => 44;
+''');
   }
 
   test_getFile() async {