fix(layouts): nested attribute truncating (#2337)

zellij-server/src/tab/unit/snapshots/zellij_server__tab__tab_integration_tests__when_applying_a_truncated_swap_layout_child_attributes_are_not_ignored.snap

@@ -0,0 +1,26 @@
+---
+source: zellij-server/src/tab/./unit/tab_integration_tests.rs
+assertion_line: 6791
+expression: snapshot
+---
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+

zellij-server/src/tab/unit/tab_integration_tests.rs

@@ -6759,3 +6759,37 @@ fn when_resizing_whole_tab_with_auto_layout_and_floating_panes_the_layout_is_mai
     );
     assert_snapshot!(snapshot);
 }
+
+#[test]
+fn when_applying_a_truncated_swap_layout_child_attributes_are_not_ignored() {
+    // here we want to make sure that the nested borderless is preserved on resize (when the layout
+    // is reapplied, and thus is truncated to just one pane rather than a logical container pane
+    // and an actual pane as it is described here)
+    let layout = r#"
+        layout {
+            pane {
+                pane borderless=true
+            }
+        }
+    "#;
+    let size = Size {
+        cols: 121,
+        rows: 20,
+    };
+    let client_id = 1;
+    let mut tab = create_new_tab_with_layout(size, ModeInfo::default(), layout);
+    let mut output = Output::default();
+    let new_size = Size {
+        cols: 122,
+        rows: 20,
+    };
+    let _ = tab.resize_whole_tab(new_size);
+    tab.render(&mut output, None).unwrap();
+    let snapshot = take_snapshot(
+        output.serialize().unwrap().get(&client_id).unwrap(),
+        new_size.rows,
+        new_size.cols,
+        Palette::default(),
+    );
+    assert_snapshot!(snapshot);
+}

zellij-utils/src/input/layout.rs

@@ -569,6 +569,13 @@ impl TiledPaneLayout {
         // if max_panes is 1, it means there's only enough panes for this node,
         // if max_panes is 0, this is probably the root layout being called with 0 max panes
         if max_panes <= 1 {
+            while !self.children.is_empty() {
+                // this is a special case: we're truncating a pane that was previously a logical
+                // container but now should be an actual pane - so here we'd like to use its
+                // deepest "non-logical" child in order to get all its attributes (eg. borderless)
+                let first_child = self.children.remove(0);
+                drop(std::mem::replace(self, first_child));
+            }
             self.children.clear();
         } else if max_panes <= self.children.len() {
             self.children.truncate(max_panes);