tree: don't nest redundant containers on repeated split

Splitting a toplevel that is the only child of its parent container
wrapped it in yet another single-child container. Repeating the action
produced a chain of redundant nesting levels. Change the split direction
of the existing container instead.

Author: michaeladler

book/src/configuration/misc.md

@@ -214,6 +214,19 @@ window-management-key = "Alt_L"
 The value should be a keysym name from
 [KBVM](https://docs.rs/kbvm/latest/kbvm/syms/index.html).
 
+## Split Reuses Container
+
+Controls whether splitting a window that is the only window in its container
+reuses that container.
+
+If this is disabled, splitting such a window wraps it in another container,
+creating a redundant nesting level. If this is enabled, the split direction of
+the existing container is changed instead.
+
+```toml
+split-reuses-container = false  # default
+```
+
 ## Middle-Click Paste
 
 Controls whether middle-clicking pastes the primary selection. Changing this

jay-config/src/_private/client.rs

@@ -1125,6 +1125,16 @@ impl ConfigClient {
         above
     }
 
+    pub fn set_split_reuses_container(&self, reuse: bool) {
+        self.send(&ClientMessage::SetSplitReusesContainer { reuse });
+    }
+
+    pub fn get_split_reuses_container(&self) -> bool {
+        let res = self.send_with_response(&ClientMessage::GetSplitReusesContainer);
+        get_response!(res, false, GetSplitReusesContainer { reuse });
+        reuse
+    }
+
     pub fn set_show_bar(&self, show: bool) {
         self.send(&ClientMessage::SetShowBar { show });
     }

jay-config/src/_private/ipc.rs

@@ -1008,6 +1008,10 @@ pub enum ClientMessage<'a> {
     GetPlaneColorPipelinesEnabled {
         device: DrmDevice,
     },
+    SetSplitReusesContainer {
+        reuse: bool,
+    },
+    GetSplitReusesContainer,
 }
 
 #[derive(Serialize, Deserialize, Debug)]
@@ -1282,6 +1286,9 @@ pub enum Response {
     GetPlaneColorPipelinesEnabled {
         enabled: bool,
     },
+    GetSplitReusesContainer {
+        reuse: bool,
+    },
 }
 
 #[derive(Serialize, Deserialize, Debug)]

jay-config/src/lib.rs

@@ -473,6 +473,31 @@ pub fn set_show_float_pin_icon(show: bool) {
     get!().set_show_float_pin_icon(show);
 }
 
+/// Sets whether splitting a window that is the only child of its container reuses
+/// that container.
+///
+/// If disabled, splitting such a window wraps it in another container, creating a
+/// redundant nesting level. If enabled, the split direction of the existing container
+/// is changed instead.
+///
+/// The default is `false`.
+pub fn set_split_reuses_container(reuse: bool) {
+    get!().set_split_reuses_container(reuse)
+}
+
+/// Returns whether splitting a window that is the only child of its container reuses
+/// that container.
+pub fn get_split_reuses_container() -> bool {
+    get!(false).get_split_reuses_container()
+}
+
+/// Toggles whether splitting a window that is the only child of its container reuses
+/// that container.
+pub fn toggle_split_reuses_container() {
+    let get = get!();
+    get.set_split_reuses_container(!get.get_split_reuses_container());
+}
+
 /// Sets whether the built-in bar is shown.
 ///
 /// The default is `true`.

src/compositor.rs

@@ -449,6 +449,7 @@ fn start_compositor2(
         backend_connector_state_serials: Default::default(),
         head_names: Default::default(),
         show_bar: Cell::new(true),
+        split_reuses_container: Cell::new(false),
         enable_primary_selection: Cell::new(true),
         workspace_display_order: Cell::new(WorkspaceDisplayOrder::Manual),
         outputs_without_hc: Default::default(),

src/config/handler.rs

@@ -1816,6 +1816,16 @@ impl ConfigProxyHandler {
         });
     }
 
+    fn handle_set_split_reuses_container(&self, reuse: bool) {
+        self.state.split_reuses_container.set(reuse);
+    }
+
+    fn handle_get_split_reuses_container(&self) {
+        self.respond(Response::GetSplitReusesContainer {
+            reuse: self.state.split_reuses_container.get(),
+        });
+    }
+
     fn handle_set_show_bar(&self, show: bool) {
         self.state.set_show_bar(show);
     }
@@ -3832,6 +3842,10 @@ impl ConfigProxyHandler {
             ClientMessage::GetContentType { window } => self
                 .handle_get_content_type(window)
                 .wrn("get_content_type")?,
+            ClientMessage::SetSplitReusesContainer { reuse } => {
+                self.handle_set_split_reuses_container(reuse)
+            }
+            ClientMessage::GetSplitReusesContainer => self.handle_get_split_reuses_container(),
             ClientMessage::SetShowBar { show } => self.handle_set_show_bar(show),
             ClientMessage::GetShowBar => self.handle_get_show_bar(),
             ClientMessage::SetShowTitles { show } => self.handle_set_show_titles(show),

src/control_center/cc_look_and_feel.rs

@@ -119,6 +119,21 @@ impl LookAndFeelPane {
                 self.state.float_above_fullscreen.get(),
                 |v| self.state.set_float_above_fullscreen(v),
             );
+            bool_ui(
+                ui,
+                "Split Reuses Container",
+                |ui| {
+                    tip(ui, |ui| {
+                        ui.label(
+                            "Splitting the only window in a container changes the split \
+                             direction of that container.",
+                        );
+                        ui.label("Otherwise the window is wrapped in a new container.");
+                    });
+                },
+                self.state.split_reuses_container.get(),
+                |v| self.state.split_reuses_container.set(v),
+            );
             row(ui, "Font", |ui| {
                 let mut v = self.state.theme.font.get().to_string();
                 if text_edit(ui, &mut v).changed() {

src/it/test_config.rs

@@ -324,6 +324,16 @@ impl TestConfig {
         self.send(ClientMessage::SetBarPosition { position })
     }
 
+    pub fn set_split_reuses_container(&self, reuse: bool) -> TestResult {
+        self.send(ClientMessage::SetSplitReusesContainer { reuse })
+    }
+
+    pub fn get_split_reuses_container(&self) -> Result<bool, TestError> {
+        let reply = self.send_with_reply(ClientMessage::GetSplitReusesContainer)?;
+        get_response!(reply, GetSplitReusesContainer { reuse });
+        Ok(reuse)
+    }
+
     pub fn set_show_bar(&self, show: bool) -> TestResult {
         self.send(ClientMessage::SetShowBar { show })
     }

src/state.rs

@@ -402,6 +402,7 @@ pub struct State {
     pub backend_connector_state_serials: BackendConnectorStateSerials,
     pub head_names: HeadNames,
     pub show_bar: Cell<bool>,
+    pub split_reuses_container: Cell<bool>,
     pub enable_primary_selection: Cell<bool>,
     pub workspace_display_order: Cell<WorkspaceDisplayOrder>,
     pub outputs_without_hc: NumCell<usize>,

src/tree/container.rs

@@ -1231,6 +1231,10 @@ impl ContainerNode {
         self.update_title();
     }
 
+    pub fn num_children(&self) -> usize {
+        self.num_children.get()
+    }
+
     pub fn set_split(self: &Rc<Self>, split: ContainerSplit) {
         if self.set_ns_split(split) != split {
             self.update_content_size();