Restrict `@immutable` checks to instance fields

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 762 matching lines @@
           }
         }
         if (element.supertype != null) {
           return isOrInheritsImmutable(element.supertype.element, visited);
         }
       }
       return false;
     }
 
     /**
-     * Return `true` if the given class [element] defines a non-final field.
+     * Return `true` if the given class [element] defines a non-final instance
+     * field.
      */
-    bool hasNonFinalField(ClassElement element) {
+    bool hasNonFinalInstanceField(ClassElement element) {
       for (FieldElement field in element.fields) {
-        if (!field.isSynthetic && !field.isFinal) {
+        if (!field.isSynthetic && !field.isFinal && !field.isStatic) {
           return true;
         }
       }
       return false;
     }
 
     /**
      * Return `true` if the given class [element] defines or inherits a
      * non-final field.
      */
-    bool hasOrInheritsNonFinalField(
+    bool hasOrInheritsNonFinalInstanceField(
         ClassElement element, HashSet<ClassElement> visited) {
       if (visited.add(element)) {
-        if (hasNonFinalField(element)) {
+        if (hasNonFinalInstanceField(element)) {
           return true;
         }
         for (InterfaceType mixin in element.mixins) {
-          if (hasNonFinalField(mixin.element)) {
+          if (hasNonFinalInstanceField(mixin.element)) {
             return true;
           }
         }
         if (element.supertype != null) {
-          return hasOrInheritsNonFinalField(element.supertype.element, visited);
+          return hasOrInheritsNonFinalInstanceField(element.supertype.element, visited);
         }
       }
       return false;
     }
 
     ClassElement element = node.element;
     if (isOrInheritsImmutable(element, new HashSet<ClassElement>()) &&
-        hasOrInheritsNonFinalField(element, new HashSet<ClassElement>())) {
+        hasOrInheritsNonFinalInstanceField(element, new HashSet<ClassElement>())) {
       _errorReporter.reportErrorForNode(HintCode.MUST_BE_IMMUTABLE, node.name);
     }
   }
 
   /**
    * This verifies that the passed left hand side and right hand side represent a valid assignment.
    *
    * This method corresponds to ErrorVerifier.checkForInvalidAssignment.
    *
    * @param lhs the left hand side expression
@@ skipping 10095 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }