Infer type of extract index expressions.

pkg/analyzer/test/src/summary/resynthesize_ast_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.
 
 library analyzer.test.src.summary.resynthesize_ast_test;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/generated/engine.dart'
@@ skipping 191 matching lines @@
   void test_downwardsInferenceYieldYieldStar() {
     super.test_downwardsInferenceYieldYieldStar();
   }
 
   @override
   @failingTest
   void test_genericMethods_inferJSBuiltin() {
     super.test_genericMethods_inferJSBuiltin();
   }
 
+  void test_infer_extractIndex_custom() {
+    var unit = checkFile('''
+class A {
+  String operator [](_) => null;
+}
+var a = new A();
+var b = a[0];
+  ''');
+    expect(unit.topLevelVariables[1].type.toString(), 'String');
+  }
+
+  void test_infer_extractIndex_fromList() {
+    var unit = checkFile('''
+var a = <int>[1, 2, 3];
+var b = a[0];
+  ''');
+    expect(unit.topLevelVariables[1].type.toString(), 'int');
+  }
+
+  void test_infer_extractIndex_fromMap() {
+    var unit = checkFile('''
+var a = <int, double>{};
+var b = a[0];
+  ''');
+    expect(unit.topLevelVariables[1].type.toString(), 'double');
+  }
+
   void test_infer_extractProperty_getter() {
     checkFile(r'''
 var a = 1.isEven;
 var b = 2.isNaN;
 var c = 3.foo;
 var d = foo.bar;
   ''');
   }
 
   void test_infer_extractProperty_method() {
@@ skipping 333 matching lines @@
     }
 
     UnlinkedUnit definingUnit = _getUnlinkedUnit(librarySource);
     LinkedLibraryBuilder linkedLibrary =
         prelink(definingUnit, getPart, getImport);
     linkedLibrary.dependencies.skip(1).forEach((LinkedDependency d) {
       _serializeLibrary(resolveRelativeUri(d.uri));
     });
   }
 }