fix: preserve context in for rejected promises (#428)

currently, context is lost in case of an unhandled promise rejection. This fix keeps track of the context by looking into the rejected promise domain. This fix has been tested in my production environment and seems to do the trick there.

lib/client.js

@@ -120,8 +120,9 @@ extend(Raven.prototype, {
 
     if (this.captureUnhandledRejections) {
       var self = this;
-      global.process.on('unhandledRejection', function(reason) {
-        self.captureException(reason, function(sendErr, eventId) {
+      global.process.on('unhandledRejection', function(reason, promise) {
+        var context = promise.domain && promise.domain.sentryContext;
+        self.captureException(reason, context || {}, function(sendErr, eventId) {
           if (!sendErr) utils.consoleAlert('unhandledRejection captured: ' + eventId);
         });
       });

test/raven.client.js

@@ -427,6 +427,59 @@ describe('raven.Client', function() {
       }
     });
 
+    it('should preserve context on unhandledRejection', function(done) {
+      var listeners = process.listeners('unhandledRejection');
+      listeners.length.should.equal(0);
+
+      var scope = nock('https://app.getsentry.com')
+        .filteringRequestBody(/.*/, '*')
+        .post('/api/269/store/', '*')
+        .reply(200, function(uri, body) {
+          zlib.inflate(new Buffer(body, 'base64'), function(err, dec) {
+            if (err) return done(err);
+            var msg = JSON.parse(dec.toString());
+
+            msg.user.should.eql({
+              id: '123'
+            });
+
+            scope.done();
+            done();
+          });
+          return 'OK';
+        });
+
+      client = new raven.Client(dsn, {captureUnhandledRejections: true});
+      client.install();
+
+      listeners = process.listeners('unhandledRejection');
+      listeners.length.should.equal(1);
+
+      client.context(function() {
+        client.setContext({
+          user: {
+            id: '123'
+          }
+        });
+
+        // promises didn't include domain property until 8.0.0
+        // see: https://nodejs.org/api/domain.html#domain_domains_and_promises
+        // also: https://github.com/nodejs/node/pull/12489
+        if (process.version >= 'v8.0.0') {
+          // eslint-disable-next-line no-new
+          new Promise(function(resolve, reject) {
+            reject(new Error('rejected!'));
+          });
+        } else {
+          setTimeout(function() {
+            var error = new Error('rejected!');
+            var promise = Promise.reject(error);
+            process.emit('unhandledRejection', error, promise);
+          });
+        }
+      });
+    });
+
     it('should add itself to the uncaughtException event list', function() {
       var listeners = process.listeners('uncaughtException');
       listeners.length.should.equal(0);