folderIcon: Allow dropping application icons

Connect to the overview signals related to Drag n' Drop, and
allow dropping application icons in it. Dropping an icon
appends the application id to the folder's GSettings key.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/664

js/ui/appDisplay.js

@@ -81,6 +81,13 @@ function clamp(value, min, max) {
     return Math.max(min, Math.min(max, value));
 }
 
+function _getViewFromIcon(icon) {
+    let parent = icon.actor.get_parent();
+    if (!parent._delegate || !(parent._delegate instanceof BaseAppView))
+        return null;
+    return parent._delegate;
+}
+
 class BaseAppView {
     constructor(params, gridParams) {
         if (this.constructor === BaseAppView)
@@ -240,6 +247,7 @@ var AllView = class AllView extends BaseAppView {
         this.actor = new St.Widget({ layout_manager: new Clutter.BinLayout(),
                                      x_expand: true, y_expand: true });
         this.actor.add_actor(this._scrollView);
+        this._grid._delegate = this;
 
         this._scrollView.set_policy(St.PolicyType.NEVER,
                                     St.PolicyType.EXTERNAL);
@@ -1048,6 +1056,7 @@ var FolderView = class FolderView extends BaseAppView {
         this._grid.x_expand = true;
         this._folder = folder;
         this._parentView = parentView;
+        this._grid._delegate = this;
 
         this.actor = new St.ScrollView({ overlay_scrollbars: true });
         this.actor.set_policy(St.PolicyType.NEVER, St.PolicyType.AUTOMATIC);
@@ -1220,6 +1229,11 @@ var FolderIcon = class FolderIcon {
 
         this.view = new FolderView(this._folder, parentView);
 
+        Main.overview.connect('item-drag-begin',
+                              this._onDragBegin.bind(this));
+        Main.overview.connect('item-drag-end',
+                              this._onDragEnd.bind(this));
+
         this.actor.connect('clicked', this.open.bind(this));
         this.actor.connect('destroy', this.onDestroy.bind(this));
         this.actor.connect('notify::mapped', () => {
@@ -1253,6 +1267,57 @@ var FolderIcon = class FolderIcon {
         return this.view.getAllItems().map(item => item.id);
     }
 
+    _onDragBegin() {
+        this._parentView.inhibitEventBlocker();
+    }
+
+    _onDragEnd() {
+        this._parentView.uninhibitEventBlocker();
+    }
+
+    _canAccept(source) {
+        if (!(source instanceof AppIcon))
+            return false;
+
+        let view = _getViewFromIcon(source);
+        if (!view || !(view instanceof AllView))
+            return false;
+
+        if (this._folder.get_strv('apps').includes(source.id))
+            return false;
+
+        return true;
+    }
+
+    handleDragOver(source) {
+        if (!this._canAccept(source))
+            return DND.DragMotionResult.NO_DROP;
+
+        return DND.DragMotionResult.MOVE_DROP;
+    }
+
+    acceptDrop(source) {
+        if (!this._canAccept(source))
+            return true;
+
+        let app = source.app;
+        let folderApps = this._folder.get_strv('apps');
+        folderApps.push(app.id);
+
+        this._folder.set_strv('apps', folderApps);
+
+        // Also remove from 'excluded-apps' if the app id is listed
+        // there. This is only possible on categories-based folders.
+        let excludedApps = this._folder.get_strv('excluded-apps');
+        let index = excludedApps.indexOf(app.id);
+        if (index >= 0) {
+            excludedApps.splice(index, 1);
+            this._folder.set_strv('excluded-apps', excludedApps);
+        }
+
+        return true;
+    }
+
     _updateName() {
         let name = _getFolderName(this._folder);
         if (this.name == name)