Add ElementInfo.id check fr null to debug flakiness on bots.

pkg/analyzer/lib/src/summary/index_unit.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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/summary/format.dart';
@@ skipping 84 matching lines @@
    */
   _ElementInfo _getElementInfo(Element element) {
     return _elementMap.putIfAbsent(element, () {
       CompilationUnitElement unitElement = getUnitElement(element);
       int unitId = _getUnitElementId(unitElement);
       int offset = element.nameOffset;
       if (element is LibraryElement || element is CompilationUnitElement) {
         offset = 0;
       }
       IndexSyntheticElementKind kind = getIndexElementKind(element);
-      return new _ElementInfo(unitId, offset, kind);
+      return new _ElementInfo(element, unitId, offset, kind);
     });
   }
 
   /**
    * Add information about [str] to [_strings] if necessary, and return the
    * location in this array representing [str].
    */
   int _getStringId(String str) {
     return _stringMap.putIfAbsent(str, () {
       int id = _strings.length;
@@ skipping 70 matching lines @@
   final int offset;
 
   _DefinedNameInfo(this.nameId, this.kind, this.offset);
 }
 
 /**
  * Information about an element referenced in index.
  */
 class _ElementInfo {
   /**
+   * TODO(scheglov) remove after fixing build flakiness on bots
+   */
+  final Element element;
+
+  /**
    * The identifier of the [CompilationUnitElement] containing this element.
    */
   final int unitId;
 
   /**
    * The name offset of the element.
    */
   final int offset;
 
   /**
    * The kind of the element.
    */
   final IndexSyntheticElementKind kind;
 
   /**
    * The unique id of the element.  It is set after indexing of the whole
    * package is done and we are assembling the full package index.
    */
   int id;
 
-  _ElementInfo(this.unitId, this.offset, this.kind);
+  _ElementInfo(this.element, this.unitId, this.offset, this.kind);
 }
 
 /**
  * Visits a resolved AST and adds relationships into [_UnitIndexAssembler].
  */
 class _IndexContributor extends GeneralizingAstVisitor {
   final _UnitIndexAssembler assembler;
 
   _IndexContributor(this.assembler);
 
@@ skipping 353 matching lines @@
       relations.add(new _RelationInfo(elementInfo, kind, offset, length));
     } on StateError {}
   }
 
   /**
    * Assemble a new [UnitIndexBuilder] using the information gathered
    * by [addRelation] and [defineName].
    */
   UnitIndexBuilder assemble() {
     relations.sort((a, b) {
+      if (a.elementInfo.id == null) {
+        throw new StateError('No id for ${a.elementInfo.element}, '
+            'location= ${a.elementInfo.element?.location}');
+      }
       return a.elementInfo.id - b.elementInfo.id;
     });
     definedNames.sort((a, b) {
       return a.nameId - b.nameId;
     });
     return new UnitIndexBuilder(
         definedNames: definedNames.map((n) => n.nameId).toList(),
         definedNameKinds: definedNames.map((n) => n.kind).toList(),
         definedNameOffsets: definedNames.map((n) => n.offset).toList(),
         elements: relations.map((r) => r.elementInfo.id).toList(),
         kinds: relations.map((r) => r.kind).toList(),
         locationOffsets: relations.map((r) => r.offset).toList(),
         locationLengths: relations.map((r) => r.length).toList(),
         libraryUri: pkg._getUriId(unitElement.library.source.uri),
         unitUri: pkg._getUriId(unitElement.source.uri));
   }
 
   void defineName(String name, IndexNameKind kind, int offset) {
     int nameId = pkg._getStringId(name);
     definedNames.add(new _DefinedNameInfo(nameId, kind, offset));
   }
 }