Flatten tree

book/src/configuration/misc.md

@@ -186,6 +186,20 @@ The value should be a keysym name (see the
 [xkbcommon keysym list](https://github.com/xkbcommon/libxkbcommon/blob/master/include/xkbcommon/xkbcommon-keysyms.h)
 with the `XKB_KEY_` prefix removed).
 
+## Flatten Tree
+
+When a window is removed from a container (e.g. moved to another workspace or
+floated), the container may end up with only one child. By default the
+container is kept, resulting in redundant nesting.
+
+Setting `flatten-tree` to `true` automatically collapses
+such containers by replacing them with their only remaining child, keeping the
+window tree flat.
+
+```toml
+flatten-tree = true
+```
+
 ## Middle-Click Paste
 
 Controls whether middle-clicking pastes the primary selection. Changing this

jay-config/src/_private/client.rs

@@ -1101,6 +1101,10 @@ impl ConfigClient {
         self.send(&ClientMessage::SetMiddleClickPasteEnabled { enabled });
     }
 
+    pub fn set_flatten_tree(&self, enabled: bool) {
+        self.send(&ClientMessage::SetFlattenTree { enabled });
+    }
+
     pub fn open_control_center(&self) {
         self.send(&ClientMessage::OpenControlCenter);
     }

jay-config/src/_private/ipc.rs

@@ -756,6 +756,9 @@ pub enum ClientMessage<'a> {
     SetMiddleClickPasteEnabled {
         enabled: bool,
     },
+    SetFlattenTree {
+        enabled: bool,
+    },
     SeatCreateMark {
         seat: Seat,
         kc: Option<u32>,

jay-config/src/lib.rs

@@ -520,6 +520,16 @@ pub fn set_middle_click_paste_enabled(enabled: bool) {
     get!().set_middle_click_paste_enabled(enabled);
 }
 
+/// Enables or disables tree flattening.
+///
+/// When enabled, a container with only one child is automatically collapsed
+/// by replacing it with its child, keeping the tree tidy.
+///
+/// The default is `false`.
+pub fn set_flatten_tree(enabled: bool) {
+    get!().set_flatten_tree(enabled);
+}
+
 /// Opens the control center.
 pub fn open_control_center() {
     get!().open_control_center();

src/compositor.rs

@@ -375,6 +375,7 @@ fn start_compositor2(
         color_management_enabled: Cell::new(false),
         color_manager,
         float_above_fullscreen: Cell::new(false),
+        flatten_tree: Cell::new(false),
         icons: Default::default(),
         show_pin_icon: Cell::new(false),
         cl_matcher_manager: ClMatcherManager::new(&crit_ids),

src/config/handler.rs

@@ -2595,6 +2595,10 @@ impl ConfigProxyHandler {
         self.state.set_primary_selection_enabled(enabled);
     }
 
+    fn handle_set_flatten_tree(&self, enabled: bool) {
+        self.state.set_flatten_tree(enabled);
+    }
+
     fn handle_seat_create_mark(&self, seat: Seat, kc: Option<u32>) -> Result<(), CphError> {
         let seat = self.get_seat(seat)?;
         if let Some(kc) = kc {
@@ -3625,6 +3629,7 @@ impl ConfigProxyHandler {
             ClientMessage::SetMiddleClickPasteEnabled { enabled } => {
                 self.handle_set_middle_click_paste_enabled(enabled)
             }
+            ClientMessage::SetFlattenTree { enabled } => self.handle_set_flatten_tree(enabled),
             ClientMessage::SetWorkspaceDisplayOrder { order } => {
                 self.handle_set_workspace_display_order(order)
             }

src/state.rs

@@ -284,6 +284,7 @@ pub struct State {
     pub color_management_enabled: Cell<bool>,
     pub color_manager: Rc<ColorManager>,
     pub float_above_fullscreen: Cell<bool>,
+    pub flatten_tree: Cell<bool>,
     pub icons: Icons,
     pub show_pin_icon: Cell<bool>,
     pub cl_matcher_manager: ClMatcherManager,
@@ -2096,6 +2097,10 @@ impl State {
         self.root.update_visible(self);
     }
 
+    pub fn set_flatten_tree(&self, v: bool) {
+        self.flatten_tree.set(v);
+    }
+
     pub fn reset_sizes(&self) {
         self.theme.sizes.reset();
         self.spaces_changed();

src/tree/container.rs

@@ -300,6 +300,10 @@ impl ContainerNode {
         slf
     }
 
+    pub fn num_children(&self) -> usize {
+        self.num_children.get()
+    }
+
     pub fn prepend_child(self: &Rc<Self>, new: Rc<dyn ToplevelNode>) {
         if let Some(child) = self.children.first() {
             self.add_child_before_(&child, new);
@@ -2114,6 +2118,24 @@ impl ContainingNode for ContainerNode {
             self.tl_destroy();
             return;
         }
+        if num_children == 1 && self.state.flatten_tree.get() {
+            if let Some(parent) = self.toplevel_data.parent.get()
+                && !self.toplevel_data.is_fullscreen.get()
+            {
+                let remaining = {
+                    let cn = self.child_nodes.borrow();
+                    let (_, v) = cn.iter().next().unwrap();
+                    v.node.clone()
+                };
+                if parent.cnode_accepts_child(&*remaining) {
+                    parent.cnode_replace_child(self.deref(), remaining);
+                    self.toplevel_data.parent.take();
+                    self.child_nodes.borrow_mut().clear();
+                    self.tl_destroy();
+                    return;
+                }
+            }
+        }
         self.update_content_size();
         let rem = 1.0 - node.factor.get();
         let mut sum = 0.0;

src/tree/toplevel.rs

@@ -1067,6 +1067,13 @@ pub fn toplevel_create_split(state: &Rc<State>, tl: Rc<dyn ToplevelNode>, axis:
         Some(pn) => pn,
         _ => return,
     };
+    if let Some(container) = pn.clone().node_into_container()
+        && container.num_children() == 1
+        && state.flatten_tree.get()
+    {
+        container.set_split(axis);
+        return;
+    }
     if let Some(pn) = pn.node_into_containing_node() {
         let cn = ContainerNode::new(state, &ws, tl.clone(), axis);
         pn.cnode_replace_child(&*tl, cn);

toml-config/src/config.rs

@@ -573,6 +573,7 @@ pub struct Config {
     pub use_hardware_cursor: Option<bool>,
     pub show_bar: Option<bool>,
     pub show_titles: Option<bool>,
+    pub flatten_tree: Option<bool>,
     pub focus_history: Option<FocusHistory>,
     pub middle_click_paste: Option<bool>,
     pub input_modes: AHashMap<String, InputMode>,

toml-config/src/config/parsers/config.rs

@@ -158,7 +158,7 @@ impl Parser for ConfigParser<'_> {
                 clean_logs_older_than_val,
                 mouse_follows_focus,
             ),
-            (session_management_val, workspaces_val),
+            (session_management_val, workspaces_val, flatten_tree),
         ) = ext.extract((
             (
                 opt(val("keymap")),
@@ -220,7 +220,11 @@ impl Parser for ConfigParser<'_> {
                 opt(val("clean-logs-older-than")),
                 recover(opt(bol("unstable-mouse-follows-focus"))),
             ),
-            (opt(val("session-management")), opt(val("workspaces"))),
+            (
+                opt(val("session-management")),
+                opt(val("workspaces")),
+                recover(opt(bol("flatten-tree"))),
+            ),
         ))?;
         let mut keymap = None;
         if let Some(value) = keymap_val {
@@ -633,6 +637,7 @@ impl Parser for ConfigParser<'_> {
             use_hardware_cursor: use_hardware_cursor.despan(),
             show_bar: show_bar.despan(),
             show_titles: show_titles.despan(),
+            flatten_tree: flatten_tree.despan(),
             focus_history,
             middle_click_paste: middle_click_paste.despan(),
             input_modes,

toml-config/src/lib.rs

@@ -38,7 +38,7 @@ use {
         logging::{clean_logs_older_than, set_log_level},
         on_devices_enumerated, on_idle, on_unload, open_control_center, quit, reload,
         set_color_management_enabled, set_default_workspace_capture, set_explicit_sync_enabled,
-        set_float_above_fullscreen, set_idle, set_idle_grace_period,
+        set_flatten_tree, set_float_above_fullscreen, set_idle, set_idle_grace_period,
         set_middle_click_paste_enabled, set_session_management_enabled, set_show_bar,
         set_show_float_pin_icon, set_show_titles, set_ui_drag_enabled, set_ui_drag_threshold,
         status::{set_i3bar_separator, set_status, set_status_command, unset_status_command},
@@ -1677,6 +1677,9 @@ fn load_config(initial_load: bool, auto_reload: bool, persistent: &Rc<Persistent
     if let Some(v) = config.show_titles {
         set_show_titles(v);
     }
+    if let Some(v) = config.flatten_tree {
+        set_flatten_tree(v);
+    }
     if let Some(v) = config.theme.bar_position {
         set_bar_position(v);
     }

toml-spec/spec/spec.generated.json

@@ -1237,6 +1237,10 @@
           "type": "boolean",
           "description": "Configures whether title bars on windows are shown.\n\nThe default is `true`.\n"
         },
+        "flatten-tree": {
+          "type": "boolean",
+          "description": "Configures whether containers with only a single child are automatically\ncollapsed by replacing them with their child, keeping the window tree\nflat.\n\nWhen a window is moved away from a container and the container ends up\nwith a single remaining window, enabling this option removes the\ncontainer and places the remaining window directly in the parent\ncontainer.\n\nThe default is `false`.\n"
+        },
         "focus-history": {
           "description": "Configures the focus-history settings.\n\n- Example:\n\n  ```toml\n  [focus-history]\n  only-visible: true\n  same-workspace: true\n  ```\n",
           "$ref": "#/$defs/FocusHistory"

toml-spec/spec/spec.generated.md

@@ -2461,6 +2461,21 @@ The table has the following fields:
 
   The value of this field should be a boolean.
 
+- `flatten-tree` (optional):
+
+  Configures whether containers with only a single child are automatically
+  collapsed by replacing them with their child, keeping the window tree
+  flat.
+
+  When a window is moved away from a container and the container ends up
+  with a single remaining window, enabling this option removes the
+  container and places the remaining window directly in the parent
+  container.
+
+  The default is `false`.
+
+  The value of this field should be a boolean.
+
 - `focus-history` (optional):
 
   Configures the focus-history settings.

toml-spec/spec/spec.yaml

@@ -3249,6 +3249,20 @@ Config:
         Configures whether title bars on windows are shown.
 
         The default is `true`.
+    flatten-tree:
+      kind: boolean
+      required: false
+      description: |
+        Configures whether containers with only a single child are automatically
+        collapsed by replacing them with their child, keeping the window tree
+        flat.
+
+        When a window is moved away from a container and the container ends up
+        with a single remaining window, enabling this option removes the
+        container and places the remaining window directly in the parent
+        container.
+
+        The default is `false`.
     focus-history:
       ref: FocusHistory
       required: false