Avoid redundant computation of enclosingElement in _getElementReferenceId

pkg/analyzer/lib/src/summary/summarize_elements.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 serialization.elements;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
@@ skipping 998 matching lines @@
       deferredLinkedTypes
           .add(() => serializeTypeRef(type, context, linked: true, slot: slot));
     }
     return slot;
   }
 
   int _getElementReferenceId(Element element, {bool linked: false}) {
     return referenceMap.putIfAbsent(element, () {
       LibraryElement dependentLibrary = librarySerializer.libraryElement;
       int unit = 0;
+      Element enclosingElement;
       if (element != null) {
-        Element enclosingElement = element.enclosingElement;
+        enclosingElement = element.enclosingElement;
         if (enclosingElement is CompilationUnitElement) {
           dependentLibrary = enclosingElement.library;
           unit = dependentLibrary.units.indexOf(enclosingElement);
           assert(unit != -1);
         }
       }
       ReferenceKind kind = _getReferenceKind(element);
       String name = element == null ? 'void' : element.name;
       int index;
       LinkedReferenceBuilder linkedReference;
       if (linked) {
         linkedReference =
             new LinkedReferenceBuilder(kind: kind, unit: unit, name: name);
-        Element enclosing = element?.enclosingElement;
-        if (enclosing != null && enclosing is! CompilationUnitElement) {
+        if (enclosingElement != null &&
+            enclosingElement is! CompilationUnitElement) {
           linkedReference.containingReference =
-              _getElementReferenceId(enclosing, linked: linked);
-          if (enclosing is ClassElement) {
-            linkedReference.numTypeParameters = enclosing.typeParameters.length;
-          } else if (enclosing is ExecutableElement) {
+              _getElementReferenceId(enclosingElement, linked: linked);
+          if (enclosingElement is ClassElement) {
+            linkedReference.numTypeParameters =
+                enclosingElement.typeParameters.length;
+          } else if (enclosingElement is ExecutableElement) {
             if (element is FunctionElement) {
-              assert(enclosing.functions.contains(element));
-              linkedReference.localIndex = enclosing.functions.indexOf(element);
+              assert(enclosingElement.functions.contains(element));
+              linkedReference.localIndex =
+                  enclosingElement.functions.indexOf(element);
             } else if (element is LocalVariableElement) {
-              assert(enclosing.localVariables.contains(element));
+              assert(enclosingElement.localVariables.contains(element));
               linkedReference.localIndex =
-                  enclosing.localVariables.indexOf(element);
+                  enclosingElement.localVariables.indexOf(element);
             } else {
               throw new StateError(
                   'Unexpected enclosed element type: ${element.runtimeType}');
             }
-          } else if (enclosing is VariableElement) {
-            assert(identical(enclosing.initializer, element));
+          } else if (enclosingElement is VariableElement) {
+            assert(identical(enclosingElement.initializer, element));
           } else {
             throw new StateError(
-                'Unexpected enclosing element type: ${enclosing.runtimeType}');
+                'Unexpected enclosing element type: ${enclosingElement.runtimeType}');
           }
         }
         index = linkedReferences.length;
         linkedReferences.add(linkedReference);
       } else {
         assert(unlinkedReferences.length == linkedReferences.length);
         int prefixReference = 0;
         Element enclosing = element?.enclosingElement;
         if (enclosing == null || enclosing is CompilationUnitElement) {
           // Figure out a prefix that may be used to refer to the given element.
@@ skipping 358 matching lines @@
       exportNames.add(new LinkedExportNameBuilder(
           name: name,
           dependency: serializeDependency(dependentLibrary),
           unit: unit,
           kind: kind));
     }
     pb.exportNames = exportNames;
     return pb;
   }
 }