Add a few more tests.

tests/language/covariant_test.dart

 // Copyright (c) 2017, 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.
 
 // Test that `covariant` can be parsed (and ignored) by
 // dart2js and the VM.
 // This test only checks for non-strong mode behavior.
 //
 // Generally, `covariant` should be ignored, when it is used in the right
 // places.
 
 import 'package:expect/expect.dart';
 
 // Top level field may not have a covariant.
 // Would be considered a minor (acceptable) bug, if it was accepted here too.
 covariant  /// 00: compile-time error
 int x0;
 
+covariant int covariant;  /// 00b: compile-time error
+
+int covariant;  /// 00c: ok
+
 // Getters may never have `covariant`. (Neither on the top-level nor as members)
 covariant  /// 01: compile-time error
 int get x1 => 499;
 
 // Top level setters may not have a covariant.
 // Would be considered a minor (acceptable) bug, if it was accepted here too.
 void set x2(
     covariant /// 02: compile-time error
     int val) {}
 
@@ skipping 12 matching lines @@
     int
     covariant /// 05: compile-time error
     val) {}
 
 
 // Same without types.
 
 // Since `covariant` is a built-in identifier, it is not allowed here.
 covariant x6;  /// 06: compile-time error
 
+covariant covariant;  /// 06b: compile-time error
+
 // Getters may never have `covariant`.
 covariant  /// 07: compile-time error
 get x7 => 499;
 
 // Top level setters may not have a covariant.
 // Would be considered a minor (acceptable) bug, if it was accepted here too.
 void set x8(
     covariant /// 08: compile-time error
     val) {}
 
@@ skipping 44 matching lines @@
 // `Covariant` must be in front of modifiers.
 int f17(
     final
     covariant /// 17: compile-time error
     int
     x) => 499;
 
 // On its own, `covariant` is just a parameter name.
 int f18(covariant) => covariant;
 
+covariant;  /// 19: compile-time error
+
 // All of the above as statics in a class.
 class A {
   // Static fields may not have a covariant.
   // Would be considered a minor (acceptable) bug, if it was accepted here too.
   static
   covariant  /// 20: compile-time error
   int x20;
 
+  static covariant int covariant  /// 20b: compile-time error
+
+  static int covariant;  /// 20c: ok
+
   // Getters may never have `covariant`.
   static
   covariant  /// 21: compile-time error
   int get x21 => 499;
 
   // Getters may never have `covariant`.
   covariant  /// 21b: compile-time error
   static
   int get x21b => 499;
 
@@ skipping 14 matching lines @@
   covariant  /// 24: compile-time error
   get x24 => 499;
 
   static void set x25(
     int
     covariant /// 25: compile-time error
     val) {}
 
   // Since `covariant` is a built-in identifier, it is not allowed here.
   static covariant x26; /// 26: compile-time error
+  static covariant covariant; /// 26b: compile-time error
 
   // Getters may never have `covariant`.
   static
   covariant  /// 27: compile-time error
   get x27 => 499;
 
   covariant  /// 27b: compile-time error
   static
   get x27b => 499;
 
@@ skipping 59 matching lines @@
 
   // `Covariant` must be in front of modifiers.
   static int f37(
       final
       covariant /// 37: compile-time error
       int
       x) => 499;
 
   // `Covariant` on its own is just a parameter name.
   static int f38(covariant) => covariant;
+
+  static covariant;  /// 39: compile-time error
+
 }
 
 // All of the above as instance members in a class.
 class B {
-  covariant int x40;
+  covariant  /// 40: ok
+  int x40;
+
+  covariant int covariant;  /// 40b: ok
+
+  int covariant;            /// 40c: ok
 
   // Getters may never have `covariant`.
   covariant  /// 41: compile-time error
   int get x41 => 499;
 
-  void set x42(covariant int val) {}
+  void set x42(
+      covariant  /// 42: ok
+      int val) {}
 
   // `covariant` in the wrong position.
   int
   covariant  /// 43: compile-time error
   x43;
 
   // `covariant` in the wrong position.
   int
   covariant  /// 44: compile-time error
   get x44 => 499;
 
   void set x45(
     int
     covariant /// 45: compile-time error
     val) {}
 
   // Since `covariant` is a built-in identifier, it is not allowed here.
   covariant x46; /// 46: compile-time error
+  covariant covariant; /// 46b: compile-time error
 
   // Getters may never have `covariant`.
   covariant  /// 47: compile-time error
   get x47 => 499;
 
-  void set x48(covariant val) {}
+  void set x48(
+      covariant  /// 48: ok
+      val) {}
 
   // If there is no type, then `covariant` is simply the parameter name:
   void set x49(covariant) {}
 
   // Covariant won't work on return types.
   covariant  /// 50: compile-time error
   int f50() => 499;
 
   // Covariant won't work as a return type.
   covariant  /// 51: compile-time error
   f51() => 499;
 
-  int f52(covariant int x) => 499;
+  int f52(
+      covariant  /// 52: ok
+      int x) => 499;
 
   // `Covariant` must be in front of the types.
   int f53(
       int
       covariant /// 53: compile-time error
       x) => 499;
 
-  int f54(covariant final x) => 499;
+  int f54(
+      covariant  /// 54: ok
+      final x) => 499;
 
   // `Covariant` must be in front of modifiers.
   int f55(
       final
       covariant /// 55: compile-time error
       x) => 499;
 
-  int f56(covariant final int x) => 499;
+  int f56(
+      covariant  /// 56: ok
+      final int x) => 499;
 
   // `Covariant` must be in front of modifiers.
   int f57(
       final
       covariant /// 57: compile-time error
       int
       x) => 499;
 
   // `Covariant` on its own is just a parameter name.
   int f58(covariant) => covariant;
+
+  covariant;  /// 59: compile-time error
 }
 
 void use(x) {}
 
 main() {
   x0 = 0;
+  covariant = 0;  /// 00b: continued
+  covariant = 0;  /// 00c: continued
   use(x1);
   x2 = 499;
   use(x3);
   use(x4);
   x5 = 42;
   x6 = 0; /// 06: continued
+  covariant = 0; /// 06b: continued
   use(x7);
   x8 = 11;
   x9 = 12;
   use(f10());
   use(f11());
   use(f12(2));
   use(f13(3));
   use(f14(3));
   use(f15(3));
   use(f16(3));
   use(f17(3));
   Expect.equals(123, f18(123));
+  use(covariant);  /// 19: continued
 
   A.x20 = 0;
+  A.covariant = 0;  /// 20b: continued
+  A.covariant = 0;  /// 20c: continued
   use(A.x21);
   use(A.x21b);
   A.x22 = 499;
   use(A.x23);
   use(A.x24);
   A.x25 = 42;
   A.x26 = 0; /// 26: continued
+  A.covariant = 0; /// 26b: continued
   use(A.x27);
   use(A.x27b);
   A.x28 = 11;
   A.x29 = 12;
   use(A.f30());
   use(A.f31());
   use(A.f31b());
   use(A.f32(2));
   use(A.f33(3));
   use(A.f34(3));
   use(A.f35(3));
   use(A.f36(3));
   use(A.f37(3));
   Expect.equals(1234, A.f38(1234));
+  use(A.covariant);  /// 39: continued
 
   var b = new B();
   b.x40 = 0;
+  b.covariant = 0;  /// 40b: continued
+  b.covariant = 0;  /// 40c: continued
   use(b.x41);
   b.x42 = 499;
   use(b.x43);
   use(b.x44);
   b.x45 = 42;
   b.x46 = 0; /// 46: continued
+  b.covariant = 0; /// 46b: continued
   use(b.x47);
   b.x48 = 11;
   b.x49 = 12;
   use(b.f50());
   use(b.f51());
   use(b.f52(2));
   use(b.f53(2));
   use(b.f54(3));
   use(b.f55(3));
   use(b.f56(3));
   use(b.f57(3));
   Expect.equals(12345, b.f58(12345));
+  use(B.covariant);  /// 59: continued
 }