LibGUI: Make TreeView use the view cursor properly

TreeView was still partly sticking to the pre-cursor way of using the
first index in the selection as the implied cursor. This patch fixes
all of the TreeView code to operate on the cursor instead.

This makes trees behave much more intuitively when alternating between
mouse and keyboard interaction.

Libraries/LibGUI/TreeView.cpp

@@ -434,17 +434,16 @@ void TreeView::keydown_event(KeyEvent& event)
 {
     if (!model())
         return;
-    auto cursor_index = selection().first();
 
     if (event.key() == KeyCode::Key_Space) {
-        if (model()->row_count(cursor_index))
-            toggle_index(cursor_index);
+        if (model()->row_count(cursor_index()))
+            toggle_index(cursor_index());
         return;
     }
 
     auto open_tree_node = [&](bool open, MetadataForIndex& metadata) {
         if (on_toggle)
-            on_toggle(cursor_index, open);
+            on_toggle(cursor_index(), open);
         metadata.open = open;
         update_column_sizes();
         update_content_size();
@@ -452,47 +451,46 @@ void TreeView::keydown_event(KeyEvent& event)
     };
 
     if (event.key() == KeyCode::Key_Left) {
-        if (cursor_index.is_valid() && model()->row_count(cursor_index)) {
+        if (cursor_index().is_valid() && model()->row_count(cursor_index())) {
             if (event.ctrl()) {
-                collapse_tree(cursor_index);
+                collapse_tree(cursor_index());
                 return;
             }
 
-            auto& metadata = ensure_metadata_for_index(cursor_index);
+            auto& metadata = ensure_metadata_for_index(cursor_index());
             if (metadata.open) {
                 open_tree_node(false, metadata);
                 return;
             }
         }
-        if (cursor_index.is_valid() && cursor_index.parent().is_valid()) {
-            selection().set(cursor_index.parent());
-            scroll_into_view(selection().first(), false, true);
+        if (cursor_index().is_valid() && cursor_index().parent().is_valid()) {
+            set_cursor(cursor_index().parent(), SelectionUpdate::Set);
             return;
         }
     }
 
     if (event.key() == KeyCode::Key_Right) {
-        if (cursor_index.is_valid() && model()->row_count(cursor_index)) {
+        if (cursor_index().is_valid() && model()->row_count(cursor_index())) {
             if (event.ctrl()) {
-                expand_tree(cursor_index);
+                expand_tree(cursor_index());
                 return;
             }
 
-            auto& metadata = ensure_metadata_for_index(cursor_index);
+            auto& metadata = ensure_metadata_for_index(cursor_index());
             if (!metadata.open) {
                 open_tree_node(true, metadata);
                 return;
             }
 
-            selection().set(model()->index(0, model()->tree_column(), cursor_index));
-            scroll_into_view(selection().first(), false, true);
+            auto new_cursor = model()->index(0, model()->tree_column(), cursor_index());
+            set_cursor(new_cursor, SelectionUpdate::Set);
             return;
         }
     }
 
     if (event.key() == KeyCode::Key_Return) {
-        if (cursor_index.is_valid() && model()->row_count(cursor_index)) {
-            toggle_index(cursor_index);
+        if (cursor_index().is_valid() && model()->row_count(cursor_index())) {
+            toggle_index(cursor_index());
             return;
         }
     }
@@ -500,45 +498,37 @@ void TreeView::keydown_event(KeyEvent& event)
     AbstractTableView::keydown_event(event);
 }
 
-void TreeView::move_cursor(CursorMovement movement, SelectionUpdate)
+void TreeView::move_cursor(CursorMovement movement, SelectionUpdate selection_update)
 {
-    auto cursor_index = selection().first();
-
     switch (movement) {
     case CursorMovement::Up: {
         ModelIndex previous_index;
         ModelIndex found_index;
         traverse_in_paint_order([&](const ModelIndex& index, const Gfx::IntRect&, const Gfx::IntRect&, int) {
-            if (index == cursor_index) {
+            if (index == cursor_index()) {
                 found_index = previous_index;
                 return IterationDecision::Break;
             }
             previous_index = index;
             return IterationDecision::Continue;
         });
-        if (found_index.is_valid()) {
-            selection().set(found_index);
-            scroll_into_view(selection().first(), false, true);
-            update();
-        }
+        if (found_index.is_valid())
+            set_cursor(found_index, selection_update);
         break;
     }
     case CursorMovement::Down: {
         ModelIndex previous_index;
         ModelIndex found_index;
         traverse_in_paint_order([&](const ModelIndex& index, const Gfx::IntRect&, const Gfx::IntRect&, int) {
-            if (previous_index == cursor_index) {
+            if (previous_index == cursor_index()) {
                 found_index = index;
                 return IterationDecision::Break;
             }
             previous_index = index;
             return IterationDecision::Continue;
         });
-        if (found_index.is_valid()) {
-            selection().set(found_index);
-            scroll_into_view(selection().first(), false, true);
-            update();
-        }
+        if (found_index.is_valid())
+            set_cursor(found_index, selection_update);
         return;
     }