Report lock update status back to frontend

This allows us to handle more comples scenarios.

Issue #983
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/static/loader-bootstrap.js

@@ -747,7 +747,19 @@ $(function () {
     /* Lock updates */
     if ($('#js-lock').length > 0) {
         var jsLockUpdate = window.setInterval(function () {
-            $.get($('#js-lock').attr('href'));
+            $.ajax({
+                url: $('#js-lock').attr('href'),
+                success: function(data) {
+                    console.log(data);
+                    if (! data.status) {
+                        $('.lock-error').remove();
+                        var message = $('<div class="alert lock-error alert-danger"></div>');
+                        message.text(data.message);
+                        $('.content').prepend(message);
+                    }
+                },
+                dataType: 'json'
+            });
         }, 19000);
         window.setInterval(function () {
             window.clearInterval(jsLockUpdate);

weblate/trans/models/translation.py

@@ -349,17 +349,19 @@ class Translation(models.Model, URLMixin, PercentMixin, LoggerMixin):
         '''
         # Check if we can lock
         if self.is_user_locked(user):
-            return
+            return False
 
         # Update timestamp
         if self.lock_user == user:
             self.update_lock_time()
-            return
+            return True
 
         # Auto lock if we should
         if appsettings.AUTO_LOCK and create:
             self.create_lock(user)
-            return
+            return True
+
+        return False
 
     def _reverse_url_name(self):
         '''

weblate/trans/views/lock.py

@@ -19,7 +19,7 @@
 #
 
 from django.utils.translation import ugettext as _
-from django.http import HttpResponse
+from django.http import HttpResponse, JsonResponse
 from django.shortcuts import redirect
 from django.contrib import messages
 from django.contrib.auth.decorators import login_required
@@ -37,9 +37,17 @@ from weblate.trans.permissions import (
 def update_lock(request, project, subproject, lang):
     obj = get_translation(request, project, subproject, lang)
 
-    obj.update_lock(request.user, False)
+    if obj.update_lock(request.user, False):
+        return JsonResponse(
+            data={'status': True}
+        )
 
-    return HttpResponse('ok')
+    return JsonResponse(
+        data={
+            'status': False,
+            'message': _('Failed to update lock, probably session has expired'),
+        },
+    )
 
 
 @login_required