fix(bulk): fix error propagation in empty bulk.execute

Executing an empty bulk write is supposed to return a detailed
MongoError, but we were not properly returning the error object,
resulting in a cryptic error.

Fixes NODE-1822

Author: daprahamian

lib/bulk/ordered.js

@@ -12,6 +12,7 @@ const executeOperation = utils.executeOperation;
 const MongoWriteConcernError = require('mongodb-core').MongoWriteConcernError;
 const handleMongoWriteConcernError = require('./common').handleMongoWriteConcernError;
 const bson = common.bson;
+const isPromiseLike = require('../utils').isPromiseLike;
 
 /**
  * Add to internal list of Operations
@@ -114,6 +115,10 @@ class OrderedBulkOperation extends BulkOperationBase {
    */
   execute(_writeConcern, options, callback) {
     const ret = this.bulkExecute(_writeConcern, options, callback);
+    if (isPromiseLike(ret)) {
+      return ret;
+    }
+
     options = ret.options;
     callback = ret.callback;
 

lib/bulk/unordered.js

@@ -12,6 +12,7 @@ const executeOperation = utils.executeOperation;
 const MongoWriteConcernError = require('mongodb-core').MongoWriteConcernError;
 const handleMongoWriteConcernError = require('./common').handleMongoWriteConcernError;
 const bson = common.bson;
+const isPromiseLike = require('../utils').isPromiseLike;
 
 /**
  * Add to internal list of Operations
@@ -126,6 +127,10 @@ class UnorderedBulkOperation extends BulkOperationBase {
    */
   execute(_writeConcern, options, callback) {
     const ret = this.bulkExecute(_writeConcern, options, callback);
+    if (isPromiseLike(ret)) {
+      return ret;
+    }
+
     options = ret.options;
     callback = ret.callback;
 

test/functional/bulk_tests.js

@@ -3,6 +3,8 @@ const test = require('./shared').assert,
   setupDatabase = require('./shared').setupDatabase,
   expect = require('chai').expect;
 
+const MongoError = require('../../index').MongoError;
+
 describe('Bulk', function() {
   before(function() {
     return setupDatabase(this.configuration);
@@ -1571,4 +1573,38 @@ describe('Bulk', function() {
         });
       });
   });
+
+  function testPropagationOfBulkWriteError(bulk) {
+    return bulk.execute().then(
+      err => {
+        expect(err).to.be.an.instanceOf(MongoError);
+      },
+      err => {
+        expect(err).to.be.an.instanceOf(MongoError);
+        expect(err).to.not.be.an.instanceOf(TypeError);
+        expect(err.driver).to.equal(true);
+        expect(err.name).to.equal('MongoError');
+      }
+    );
+  }
+
+  it('should propagate the proper error from executing an empty ordered batch', function() {
+    const client = this.configuration.newClient();
+
+    return client.connect().then(() => {
+      const collection = client.db(this.configuration.db).collection('doesnt_matter');
+
+      return testPropagationOfBulkWriteError(collection.initializeOrderedBulkOp());
+    });
+  });
+
+  it('should propagate the proper error from executing an empty unordered batch', function() {
+    const client = this.configuration.newClient();
+
+    return client.connect().then(() => {
+      const collection = client.db(this.configuration.db).collection('doesnt_matter');
+
+      return testPropagationOfBulkWriteError(collection.initializeUnorderedBulkOp());
+    });
+  });
 });