Implement view transpose (#2461)

Change the layout of existing split view from horizontal to vertical and
vica-versa. It only effects the focused view and its siblings, i.e. not
recursive.

Command is mapped to 't' or 'C-t' under the Window menus.

helix-term/src/commands.rs

@@ -360,6 +360,7 @@ pub fn doc(&self) -> &str {
         jump_view_left, "Jump to the split to the left",
         jump_view_up, "Jump to the split above",
         jump_view_down, "Jump to the split below",
+        transpose_view, "Transpose splits",
         rotate_view, "Goto next window",
         hsplit, "Horizontal bottom split",
         hsplit_new, "Horizontal bottom split scratch buffer",
@@ -3863,6 +3864,10 @@ fn jump_view_down(cx: &mut Context) {
     cx.editor.focus_down()
 }
 
+fn transpose_view(cx: &mut Context) {
+    cx.editor.transpose_view()
+}
+
 // split helper, clear it later
 fn split(cx: &mut Context, action: Action) {
     let (view, doc) = current!(cx.editor);

helix-term/src/keymap/default.rs

@@ -171,6 +171,7 @@ pub fn default() -> HashMap<Mode, Keymap> {
             "C-w" | "w" => rotate_view,
             "C-s" | "s" => hsplit,
             "C-v" | "v" => vsplit,
+            "C-t" | "t" => transpose_view,
             "f" => goto_file_hsplit,
             "F" => goto_file_vsplit,
             "C-q" | "q" => wclose,
@@ -226,6 +227,7 @@ pub fn default() -> HashMap<Mode, Keymap> {
                 "C-w" | "w" => rotate_view,
                 "C-s" | "s" => hsplit,
                 "C-v" | "v" => vsplit,
+                "C-t" | "t" => transpose_view,
                 "f" => goto_file_hsplit,
                 "F" => goto_file_vsplit,
                 "C-q" | "q" => wclose,

helix-view/src/editor.rs

@@ -885,6 +885,10 @@ pub fn focus_down(&mut self) {
         self.tree.focus_direction(tree::Direction::Down);
     }
 
+    pub fn transpose_view(&mut self) {
+        self.tree.transpose();
+    }
+
     pub fn should_close(&self) -> bool {
         self.tree.is_empty()
     }

helix-view/src/tree.rs

@@ -526,6 +526,18 @@ pub fn focus_next(&mut self) {
         }
     }
 
+    pub fn transpose(&mut self) {
+        let focus = self.focus;
+        let parent = self.nodes[focus].parent;
+        if let Content::Container(container) = &mut self.nodes[parent].content {
+            container.layout = match container.layout {
+                Layout::Vertical => Layout::Horizontal,
+                Layout::Horizontal => Layout::Vertical,
+            };
+            self.recalculate();
+        }
+    }
+
     pub fn area(&self) -> Rect {
         self.area
     }