fix part of #25200, reject non-generic function subtype of generic function

pkg/analyzer/test/src/task/strong/checker_test.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 /// General type checking tests
 library analyzer.test.src.task.strong.checker_test;
 
 import 'package:unittest/unittest.dart';
@@ skipping 1143 matching lines @@
 
       class A {
         void bar() => null;
         void foo() => bar; // allowed
       }
    ''');
     });
 
     test('uninferred closure', () {
       checkFile('''
-      typedef num Num2Num(num x);
-      void main() {
-        Num2Num g = /*info:INFERRED_TYPE_CLOSURE,severe:STATIC_TYPE_ERROR*/(int x) { return x; };
-        print(g(42));
-      }
-    ''');
+        typedef num Num2Num(num x);
+        void main() {
+          Num2Num g = /*info:INFERRED_TYPE_CLOSURE,severe:STATIC_TYPE_ERROR*/(int x) { return x; };
+          print(g(42));
+        }
+      ''');
+    });
+
+    test('subtype of universal type', () {
+      checkFile('''
+        void main() {
+          nonGenericFn(x) => null;
+          {
+            /*=R*/ f/*<P, R>*/(/*=P*/ p) => null;
+            /*=T*/ g/*<S, T>*/(/*=S*/ s) => null;
+
+            var local = f;
+            local = g; // valid
+
+            // Non-generic function cannot subtype a generic one.
+            local = /*severe:STATIC_TYPE_ERROR*/(x) => null;
+            local = /*severe:STATIC_TYPE_ERROR*/nonGenericFn;
+          }
+          {
+            Iterable/*<R>*/ f/*<P, R>*/(List/*<P>*/ p) => null;
+            List/*<T>*/ g/*<S, T>*/(Iterable/*<S>*/ s) => null;
+
+            var local = f;
+            local = g; // valid
+
+            var local2 = g;
+            local = local2;
+            local2 = /*severe:STATIC_TYPE_ERROR*/f;
+            local2 = /*warning:DOWN_CAST_COMPOSITE*/local;
+
+            // Non-generic function cannot subtype a generic one.
+            local = /*severe:STATIC_TYPE_ERROR*/(x) => null;
+            local = /*severe:STATIC_TYPE_ERROR*/nonGenericFn;
+          }
+        }
+      ''');
     });
   });
 
   test('Relaxed casts', () {
     checkFile('''
 
       class A {}
 
       class L<T> {}
       class M<T> extends L<T> {}
@@ skipping 1410 matching lines @@
               }
 
               class M2 {
                   m(B a) {}
               }
 
               // Here we want to report both, because the error location is
               // different.
               // TODO(sigmund): should we merge these as well?
               class T1 extends Object
-                  with /*severe:INVALID_METHOD_OVERRIDE*/M1
-                  with /*severe:INVALID_METHOD_OVERRIDE*/M2
+                  with /*severe:INVALID_METHOD_OVERRIDE*/M1,
+                  /*severe:INVALID_METHOD_OVERRIDE*/M2
                   implements I1 {
               }
            ''');
     });
 
     test('base type and mixin override same method in interface', () {
       checkFile('''
               class A {}
               class B {}
 
@@ skipping 147 matching lines @@
 
         baz1() sync* { yield* (/*info:DYNAMIC_CAST*/x); }
         Iterable baz2() sync* { yield* (/*info:DYNAMIC_CAST*/x); }
         Iterable<int> baz3() sync* { yield* (/*warning:DOWN_CAST_COMPOSITE*/x); }
         Iterable<int> baz4() sync* { yield* new Iterable<int>(); }
         Iterable<int> baz5() sync* { yield* (/*info:INFERRED_TYPE_ALLOCATION*/new Iterable()); }
     ''');
     });
   });
 }