fixes #27586, prefer context type in generic inference

pkg/analyzer/lib/src/summary/link.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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 2581 matching lines @@
     TypeSystem ts = linker.typeSystem;
     if (rawMethodType != null) {
       if (rawMethodType.typeFormals.isNotEmpty && typeArguments.isNotEmpty) {
         Element methodElement = rawMethodType.element;
         if (methodElement is TypeParameterizedElement &&
             methodElement.typeParameters.length == typeArguments.length) {
           return rawMethodType.instantiate(typeArguments);
         }
       } else if (rawMethodType.typeFormals.isNotEmpty &&
           ts is StrongTypeSystemImpl) {
-        List<DartType> paramTypes = <DartType>[];
+        List<ParameterElement> params = <ParameterElement>[];
         List<DartType> argTypes = <DartType>[];
         // Add positional parameter and argument types.
         for (int i = 0; i < numPositional; i++) {
           ParameterElement parameter = rawMethodType.parameters[i];
           if (parameter != null) {
-            paramTypes.add(parameter.type);
+            params.add(parameter);
             argTypes.add(positionalArgTypes[i]);
           }
         }
         // Prepare named argument types map.
         Map<String, DartType> namedArgTypes = <String, DartType>{};
         for (int i = 0; i < numNamed; i++) {
           String name = namedArgNames[i];
           DartType type = namedArgTypeList[i];
           namedArgTypes[name] = type;
         }
         // Add named parameter and argument types.
-        Map<String, DartType> namedParameterTypes =
-            rawMethodType.namedParameterTypes;
+        Map<String, ParameterElement> namedParameters = new Map.fromIterable(
+            rawMethodType.parameters
+                .where((p) => p.parameterKind == ParameterKind.NAMED),
+            key: (p) => p.name);
         namedArgTypes.forEach((String name, DartType argType) {
-          DartType parameterType = namedParameterTypes[name];
-          if (parameterType != null) {
-            paramTypes.add(parameterType);
+          ParameterElement parameter = namedParameters[name];
+          if (parameter != null) {
+            params.add(parameter);
             argTypes.add(argType);
           }
         });
         // Perform inference.
-        FunctionType inferred = ts.inferGenericFunctionCall(rawMethodType,
-            paramTypes, argTypes, rawMethodType.returnType, null);
+        FunctionType inferred = ts.inferGenericFunctionOrType(
+            rawMethodType, params, argTypes, null);
         return inferred;
       }
     }
     // Not a generic function type, use the raw type.
     return rawMethodType;
   }
 
   DartType _leastUpperBound(DartType s, DartType t) {
     return linker.typeSystem.getLeastUpperBound(s, t);
   }
@@ skipping 2541 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }