Improve Dart master index selectivity.

pkg/analysis_services/lib/src/index/store/codec.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 services.src.index.store.codec;
 
 import 'dart:collection';
 
+import 'package:analysis_services/index/index.dart';
+import 'package:analysis_services/src/index/store/collection.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
-import 'package:analysis_services/src/index/store/collection.dart';
-import 'package:analysis_services/index/index.dart';
 
 
 /**
  * A helper that encodes/decodes [AnalysisContext]s from/to integers.
  */
 class ContextCodec {
   /**
    * A table mapping contexts to their unique indices.
    */
   Map<AnalysisContext, int> _contextToIndex =
@@ skipping 80 matching lines @@
     List<int> path = _getLocationPath(element);
     int index = _pathToIndex[path];
     if (index == null) {
       index = _indexToPath.length;
       _pathToIndex[path] = index;
       _indexToPath.add(path);
     }
     return index;
   }
 
+  /**
+   * Returns an integer that corresponds to an approximated location of the given {@link Element}.
+   */
+  int encodeHash(Element element) {
+    List<int> path = _getLocationPathLimited(element);
+    int index = _pathToIndex[path];
+    if (index == null) {
+      index = _indexToPath.length;
+      _pathToIndex[path] = index;
+      _indexToPath.add(path);
+    }
+    return index;
+  }
+
   List<String> _getLocationComponents(List<int> path) {
     int length = path.length;
     List<String> components = new List<String>();
     for (int i = 0; i < length; i++) {
       int componentId = path[i];
       String component = _stringCodec.decode(componentId);
       if (i < length - 1 && path[i + 1] < 0) {
         component += '@${(-path[i + 1])}';
         i++;
       }
@@ skipping 22 matching lines @@
     } else {
       List<int> path = new List<int>.filled(length, 0);
       for (int i = 0; i < length; i++) {
         String component = components[i];
         path[i] = _stringCodec.encode(component);
       }
       return path;
     }
   }
 
+  /**
+   * Returns an approximation of the given {@link Element}'s location.
+   */
+  List<int> _getLocationPathLimited(Element element) {
+    List<String> components = element.location.components;
+    int length = components.length;
+    String firstComponent = components[0];
+    String lastComponent = components[length - 1];
+    firstComponent = firstComponent.substring(1);
+    lastComponent = _substringBeforeAt(lastComponent);
+    int firstId = _stringCodec.encode(firstComponent);
+    int lastId = _stringCodec.encode(lastComponent);
+    return <int>[firstId, lastId];
+  }
+
   bool _hasLocalOffset(List<String> components) {
     for (String component in components) {
       if (component.indexOf('@') != -1) {
         return true;
       }
     }
     return false;
   }
+
+  String _substringBeforeAt(String str) {
+    int atOffset = str.indexOf('@');
+    if (atOffset != -1) {
+      str = str.substring(0, atOffset);
+    }
+    return str;
+  }
 }
 
 
 /**
  * A helper that encodes/decodes [Relationship]s to/from integers.
  */
 class RelationshipCodec {
   final StringCodec _stringCodec;
 
   RelationshipCodec(this._stringCodec);
@@ skipping 35 matching lines @@
   int encode(String name) {
     int index = nameToIndex[name];
     if (index == null) {
       index = _indexToName.length;
       nameToIndex[name] = index;
       _indexToName.add(name);
     }
     return index;
   }
 }