fix(cursor): cursor count with collation fix

When a collation set is applied to a cursor,
the count method reflects this and returns
the correct value.

Fixes NODE-1369

lib/collection.js

@@ -13,6 +13,7 @@ const toError = require('./utils').toError;
 const normalizeHintField = require('./utils').normalizeHintField;
 const handleCallback = require('./utils').handleCallback;
 const decorateCommand = require('./utils').decorateCommand;
+const decorateWithCollation = require('./utils').decorateWithCollation;
 const formattedOrderClause = require('./utils').formattedOrderClause;
 const ReadPreference = require('mongodb-core').ReadPreference;
 const CommandCursor = require('./command_cursor');
@@ -2279,17 +2280,6 @@ var findAndRemove = function(self, query, sort, options, callback) {
   self.findAndModify(query, sort, null, options, callback);
 };
 
-function decorateWithCollation(command, self, options) {
-  // Do we support collation 3.4 and higher
-  var capabilities = self.s.topology.capabilities();
-  // Do we support write concerns 3.4 and higher
-  if (capabilities && capabilities.commandsTakeCollation) {
-    if (options.collation && typeof options.collation === 'object') {
-      command.collation = options.collation;
-    }
-  }
-}
-
 function decorateWithReadConcern(command, self, options) {
   let readConcern = Object.assign({}, command.readConcern || {});
   if (self.s.readConcern) {

lib/cursor.js

@@ -5,6 +5,7 @@ const f = require('util').format;
 const deprecate = require('util').deprecate;
 const formattedOrderClause = require('./utils').formattedOrderClause;
 const handleCallback = require('./utils').handleCallback;
+const decorateWithCollation = require('./utils').decorateWithCollation;
 const ReadPreference = require('mongodb-core').ReadPreference;
 const MongoError = require('mongodb-core').MongoError;
 const Readable = require('stream').Readable;
@@ -1013,6 +1014,9 @@ var count = function(self, applySkipLimit, opts, callback) {
     command.hint = self.s.cmd.hint;
   }
 
+  // Apply a collation if set
+  decorateWithCollation(command, self, self.s.cmd);
+
   if (typeof opts.maxTimeMS === 'number') {
     command.maxTimeMS = opts.maxTimeMS;
   } else if (self.s.cmd && typeof self.s.cmd.maxTimeMS === 'number') {

lib/utils.js

@@ -533,6 +533,30 @@ function isPromiseLike(maybePromise) {
   return maybePromise && typeof maybePromise.then === 'function';
 }
 
+/**
+ * Applies collation to a given command.
+ *
+ * @param {object} [command] the command on which to apply collation
+ * @param {(Cursor|Collection)} [target] target of command
+ * @param {object} [options] options containing collation settings
+ */
+function decorateWithCollation(command, target, options) {
+  const topology = target.s && target.s.topology;
+
+  if (!topology) {
+    throw new TypeError('parameter "target" is missing a topology');
+  }
+
+  // Do we support collation 3.4 and higher
+  const capabilities = target.s.topology.capabilities();
+  // Do we support write concerns 3.4 and higher
+  if (capabilities && capabilities.commandsTakeCollation) {
+    if (options.collation && typeof options.collation === 'object') {
+      command.collation = options.collation;
+    }
+  }
+}
+
 module.exports = {
   filterOptions,
   mergeOptions,
@@ -554,5 +578,6 @@ module.exports = {
   executeOperation,
   applyWriteConcern,
   convertReadPreference,
-  isPromiseLike
+  isPromiseLike,
+  decorateWithCollation
 };

test/functional/collations_tests.js

@@ -3,6 +3,7 @@ var test = require('./shared').assert;
 var setupDatabase = require('./shared').setupDatabase;
 var co = require('co');
 var mock = require('mongodb-mock-server');
+const expect = require('chai').expect;
 
 var defaultFields = {
   ismaster: true,
@@ -1102,6 +1103,33 @@ describe('Collation', function() {
     }
   });
 
+  it('cursor count method should return the correct number when used with collation set', {
+    metadata: { requires: { mongodb: '>=3.4.0' } },
+    test: function(done) {
+      const configuration = this.configuration;
+      const client = configuration.newClient({ w: 1 }, { poolSize: 1, auto_reconnect: false });
+
+      client.connect(function(err, client) {
+        const db = client.db(configuration.db);
+        const docs = [{ _id: 0, name: 'foo' }, { _id: 1, name: 'Foo' }];
+        const collation = { locale: 'en_US', strength: 2 };
+        let collection, cursor;
+        const close = e => cursor.close(() => client.close(() => done(e)));
+
+        Promise.resolve()
+          .then(() => db.createCollection('cursor_collation_count'))
+          .then(() => (collection = db.collection('cursor_collation_count')))
+          .then(() => collection.insertMany(docs))
+          .then(() => collection.find({ name: 'foo' }).collation(collation))
+          .then(_cursor => (cursor = _cursor))
+          .then(() => cursor.count())
+          .then(val => expect(val).to.equal(2))
+          .then(() => close())
+          .catch(e => close(e));
+      });
+    }
+  });
+
   /******************************************************************************
   .___        __                              __  .__
   |   | _____/  |_  ____   ________________ _/  |_|__| ____   ____
@@ -1125,7 +1153,13 @@ describe('Collation', function() {
         var col = db.collection('collation_test');
         // Create collation index
         col.createIndexes(
-          [{ key: { a: 1 }, collation: { locale: 'nn' }, name: 'collation_test' }],
+          [
+            {
+              key: { a: 1 },
+              collation: { locale: 'nn' },
+              name: 'collation_test'
+            }
+          ],
           function(err) {
             test.equal(null, err);