Merge branch '17932-move-to-project-dropdown' into 'master'

Move to project dropdown with infinite scroll for better performance

## What does this MR do?

On the Move dropdown on the edit issue page we introduced infinite scrolling to just return a limited number of projects, 50 items. So if the user can move the issue to 50 or more items when scroll down on the list a new set of projects will be requested to the server.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

See #17932

## What are the relevant issue numbers?

Closes #17932

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5686

2 files changed, 21 insertions, 6 deletions

diff --git a/app/assets/javascripts/issuable_form.js b/app/assets/javascripts/issuable_form.js
index 297d4f029f0..b7f92ae9883 100644
--- a/app/assets/javascripts/issuable_form.js
+++ b/app/assets/javascripts/issuable_form.js
@@ -102,20 +102,34 @@
     };
 
     IssuableForm.prototype.initMoveDropdown = function() {
-      var $moveDropdown;
+      var $moveDropdown, pageSize;
       $moveDropdown = $('.js-move-dropdown');
       if ($moveDropdown.length) {
+        pageSize = $moveDropdown.data('page-size');
         return $('.js-move-dropdown').select2({
           ajax: {
             url: $moveDropdown.data('projects-url'),
-            results: function(data) {
+            quietMillis: 125,
+            data: function(term, page, context) {
               return {
-                results: data
+                search: term,
+                offset_id: context
               };
             },
-            data: function(query) {
+            results: function(data) {
+              var context,
+                more;
+
+              if (data.length >= pageSize)
+                more = true;
+
+              if (data[data.length - 1])
+                context = data[data.length - 1].id;
+
               return {
-                search: query
+                results: data,
+                more: more,
+                context: context
               };
             }
           },
diff --git a/app/assets/stylesheets/framework/selects.scss b/app/assets/stylesheets/framework/selects.scss
index 21d87cc9d34..b2e22b60440 100644
--- a/app/assets/stylesheets/framework/selects.scss
+++ b/app/assets/stylesheets/framework/selects.scss
@@ -45,7 +45,8 @@
   min-width: 175px;
 }
 
-.select2-results .select2-result-label {
+.select2-results .select2-result-label,
+.select2-more-results {
   padding: 10px 15px;
 }