analyzer strong mode: infer final field from initializer if super getters are dynamic

pkg/analyzer/lib/src/task/strong_mode.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.
 
 library analyzer.src.task.strong_mode;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
@@ skipping 276 matching lines @@
       if (overriddenGetters.isNotEmpty && _onlyGetters(overriddenGetters)) {
         newType = _computeReturnType(overriddenGetters);
         List<ExecutableElement> overriddenSetters = inheritanceManager
             .lookupOverrides(
                 fieldElement.enclosingElement, fieldElement.name + '=');
         if (!_isCompatible(newType, overriddenSetters)) {
           newType = null;
         }
       }
       //
-      // Then, if none was found, infer the type from the initialization
-      // expression.
+      // If there is no overridden getter or if the overridden getter's type is
+      // dynamic, then we can infer the type from the initialization expression
+      // without breaking subtype rules. We could potentially infer a consistent
+      // return type even if the overridden getter's type was not dynamic, but
+      // choose not to for simplicity. The field is required to be final to
+      // prevent choosing a type that is inconsistent with assignments we cannot
+      // analyze.
       //
-      if (newType == null) {
+      if (newType == null || newType.isDynamic) {
         if (fieldElement.initializer != null &&
             (fieldElement.isFinal || overriddenGetters.isEmpty)) {
           newType = fieldElement.initializer.returnType;
         }
       }
       if (newType == null || newType.isBottom) {
         newType = typeProvider.dynamicType;
       }
       (fieldElement as FieldElementImpl).type = newType;
       setReturnType(fieldElement.getter, newType);
@@ skipping 161 matching lines @@
         results.add(element);
       }
     }
   }
 }
 
 /**
  * A class of exception that is not used anywhere else.
  */
 class _CycleException implements Exception {}