fix #26992, inference failures are now an error

pkg/analyzer/lib/src/generated/error.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.error;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart' show AstNode;
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 5951 matching lines @@
   static const StrongModeCode DYNAMIC_CAST = const StrongModeCode(
       ErrorType.HINT, 'DYNAMIC_CAST', _implicitCastMessage);
 
   static const StrongModeCode ASSIGNMENT_CAST = const StrongModeCode(
       ErrorType.HINT, 'ASSIGNMENT_CAST', _implicitCastMessage);
 
   static const StrongModeCode INVALID_PARAMETER_DECLARATION =
       const StrongModeCode(ErrorType.COMPILE_TIME_ERROR,
           'INVALID_PARAMETER_DECLARATION', _typeCheckMessage);
 
+  static const StrongModeCode COULD_NOT_INFER = const StrongModeCode(
+      ErrorType.COMPILE_TIME_ERROR,
+      'COULD_NOT_INFER',
+      "Could not infer type parameter {0}, {1} must be of type {2}.");
+
   static const StrongModeCode INFERRED_TYPE = const StrongModeCode(
       ErrorType.HINT, 'INFERRED_TYPE', _inferredTypeMessage);
 
   static const StrongModeCode INFERRED_TYPE_LITERAL = const StrongModeCode(
       ErrorType.HINT, 'INFERRED_TYPE_LITERAL', _inferredTypeMessage);
 
   static const StrongModeCode INFERRED_TYPE_ALLOCATION = const StrongModeCode(
       ErrorType.HINT, 'INFERRED_TYPE_ALLOCATION', _inferredTypeMessage);
 
   static const StrongModeCode INFERRED_TYPE_CLOSURE = const StrongModeCode(
@@ skipping 153 matching lines @@
    * Initialize a newly created error code to have the given [name].
    */
   const TodoCode(String name) : super(name, "{0}");
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.INFO;
 
   @override
   ErrorType get type => ErrorType.TODO;
 }