[gnome-shell] appDisplay: Special-case dropping over page indicators

[Robert Mader <rmader src gnome org>]

commit 8f247971eb47e153df896ee173fa148c8b48d411
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed Jun 29 14:25:47 2022 -0300

    appDisplay: Special-case dropping over page indicators
    
    This brings back the ability to drop an icon beyong the last page.
    Because the acceptDrop() method does not have access to the target
    drop actor, to avoid an extra pick or manually calculating it from
    allocations, simply store it during DragMonitor.dragDrop(), and
    use the target actor in acceptDrop().
    
    This commit also removes the last usage of SidePages, so drop the
    enum too.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2335>

 js/ui/appDisplay.js | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)
---
diff --git a/js/ui/appDisplay.js b/js/ui/appDisplay.js
index cc7881c6e1..1b21f14dc8 100644
--- a/js/ui/appDisplay.js
+++ b/js/ui/appDisplay.js
@@ -79,13 +79,6 @@ const DEFAULT_FOLDERS = {
     },
 };
 
-var SidePages = {
-    NONE: 0,
-    PREVIOUS: 1 << 0,
-    NEXT: 1 << 1,
-    DND: 1 << 2,
-};
-
 function _getCategories(info) {
     let categoriesStr = info.get_categories();
     if (!categoriesStr)
@@ -884,6 +877,7 @@ var BaseAppView = GObject.registerClass({
     _onDragBegin() {
         this._dragMonitor = {
             dragMotion: this._onDragMotion.bind(this),
+            dragDrop: this._onDragDrop.bind(this),
         };
         DND.addDragMonitor(this._dragMonitor);
         this._appGridLayout.showPageIndicators();
@@ -908,6 +902,13 @@ var BaseAppView = GObject.registerClass({
         return DND.DragMotionResult.CONTINUE;
     }
 
+    _onDragDrop(dropEvent) {
+        // Because acceptDrop() does not receive the target actor, store it
+        // here and use this value in the acceptDrop() implementation below.
+        this._dropTarget = dropEvent.targetActor;
+        return DND.DragMotionResult.CONTINUE;
+    }
+
     _onDragEnd() {
         if (this._dragMonitor) {
             DND.removeDragMonitor(this._dragMonitor);
@@ -939,11 +940,15 @@ var BaseAppView = GObject.registerClass({
     }
 
     acceptDrop(source) {
+        const dropTarget = this._dropTarget;
+        delete this._dropTarget;
+
         if (!this._canAccept(source))
             return false;
 
-        if (this._dropPage) {
-            const increment = this._dropPage === SidePages.NEXT ? 1 : -1;
+        if (dropTarget === this._prevPageIndicator ||
+            dropTarget === this._nextPageIndicator) {
+            const increment = dropTarget === this._prevPageIndicator ? -1 : 1;
             const { currentPage, nPages } = this._grid;
             const page = Math.min(currentPage + increment, nPages);
             const position = page < nPages ? -1 : 0;