Better hints for await in non-async functions

tests/compiler/dart2js/resolver_test.dart

 // 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.
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import "package:async_helper/async_helper.dart";
 import 'dart:collection';
 
 import "package:compiler/src/resolution/resolution.dart";
@@ skipping 72 matching lines @@
     testSwitch,
     testTypeVariables,
     testToString,
     testIndexedOperator,
     testIncrementsAndDecrements,
     testOverrideHashCodeCheck,
     testSupertypeOrder,
     testConstConstructorAndNonFinalFields,
     testCantAssignMethods,
     testCantAssignFinalAndConsts,
+    testAwaitHint,
   ], (f) => f()));
 }
 
 Future testSupertypeOrder() {
   return Future.wait([
     MockCompiler.create((MockCompiler compiler) {
       compiler.parseScript("""
 class I1 {}
 class I2 {}
 class J1 extends K1 {}
@@ skipping 1160 matching lines @@
       main() => new B().m();
       class A {
         int x = 1;
       }
       class B extends A {
         m() { super.x = 2; }
       }
       ''', []);
 }
 
-
 /// Helper to test that [script] produces all the given [warnings].
 checkWarningOn(String script, List<MessageKind> warnings) {
   Expect.isTrue(warnings.length >= 0 && warnings.length <= 2);
   asyncTest(() => compileScript(script).then((compiler) {
     Expect.equals(0, compiler.errors.length);
     Expect.equals(warnings.length, compiler.warnings.length);
     for (int i = 0; i < warnings.length; i++) {
       Expect.equals(warnings[i], compiler.warnings[i].message.kind);
     }
   }));
 }
+
+testAwaitHint() {
+  check(String script, {String className, String functionName}) {
+    var prefix = className == null
+        ? "Cannot resolve 'await'"
+        : "No member named 'await' in class '$className'";
+    var where = functionName == null
+        ? 'the enclosing function' : "'$functionName'";
+    asyncTest(() => compileScript(script).then((compiler) {
+      Expect.equals(0, compiler.errors.length);
+      Expect.equals(1, compiler.warnings.length);
+      Expect.equals("$prefix.\n"
+          "Did you mean to add the 'async' marker to $where?",
+          '${compiler.warnings[0].message}');
+    }));
+  }
+  check('main() { await -3; }', functionName: 'main');
+  check('main() { () => await -3; }');
+  check('foo() => await -3; main() => foo();', functionName: 'foo');
+  check('''
+    class A {
+      m() => await - 3;
+    }
+    main() => new A().m();
+  ''', className: 'A', functionName: 'm');
+  check('''
+    class A {
+      static m() => await - 3;
+    }
+    main() => A.m();
+  ''', functionName: 'm');
+  check('''
+    class A {
+      m() => () => await - 3;
+    }
+    main() => new A().m();
+  ''', className: 'A');
+}