fix #27259, implement covariance checking for strong mode and DDC

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, 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.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
@@ skipping 6497 matching lines @@
     }
     FunctionType expectedClosureType = mayByFunctionType as FunctionType;
     // If the expectedClosureType is not more specific than the static type,
     // return.
     DartType staticClosureType =
         resolutionMap.elementDeclaredByFunctionExpression(closure)?.type;
     if (staticClosureType != null &&
         !FunctionTypeImpl.relate(
             expectedClosureType,
             staticClosureType,
-            (DartType t, DartType s, _, __) =>
-                (t as TypeImpl).isMoreSpecificThan(s),
+            (s, t) => true,
             new TypeSystemImpl(typeProvider).instantiateToBounds,
-            returnRelation: (s, t) => true)) {
+            parameterRelation: (t, s) =>
+                (t.type as TypeImpl).isMoreSpecificThan(s.type))) {
       return;
     }
     // set propagated type for the closure
     if (!strongMode) {
       closure.propagatedType = expectedClosureType;
     }
     // set inferred types for parameters
     NodeList<FormalParameter> parameters = closure.parameters.parameters;
     List<ParameterElement> expectedParameters = expectedClosureType.parameters;
     for (int i = 0;
@@ skipping 4126 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }