fix(menu): fix listing of submenus (#34315)

Problem:  Listing submenus with :menu doesn't work.
Solution: Don't go to the parent of the return value of find_menu(), and
          handle empty path at the caller.

Related #8194, which actually only fixed the problem for menu_get(), not
for :menu Ex command.

(cherry picked from commit 5e470c7af5)

src/nvim/menu.c

@@ -708,9 +708,12 @@ static dict_T *menu_get_recursive(const vimmenu_T *menu, int modes)
 /// @return false if could not find path_name
 bool menu_get(char *const path_name, int modes, list_T *list)
 {
-  vimmenu_T *menu = find_menu(*get_root_menu(path_name), path_name, modes);
-  if (!menu) {
-    return false;
+  vimmenu_T *menu = *get_root_menu(path_name);
+  if (*path_name != NUL) {
+    menu = find_menu(menu, path_name, modes);
+    if (!menu) {
+      return false;
+    }
   }
   for (; menu != NULL; menu = menu->next) {
     dict_T *d = menu_get_recursive(menu, modes);
@@ -726,13 +729,15 @@ bool menu_get(char *const path_name, int modes, list_T *list)
   return true;
 }
 
-/// Find menu matching `name` and `modes`.
+/// Find menu matching `name` and `modes`. Does not handle empty `name`.
 ///
 /// @param menu top menu to start looking from
 /// @param name path towards the menu
-/// @return menu if \p name is null, found menu or NULL
+/// @return found menu or NULL
 static vimmenu_T *find_menu(vimmenu_T *menu, char *name, int modes)
 {
+  assert(*name);
+
   while (*name) {
     // find the end of one dot-separated name and put a NUL at the dot
     char *p = menu_name_skip(name);
@@ -759,31 +764,29 @@ static vimmenu_T *find_menu(vimmenu_T *menu, char *name, int modes)
     }
     // Found a match, search the sub-menu.
     name = p;
+    assert(*name);
     menu = menu->children;
   }
-  return menu;
+
+  abort();
 }
 
 /// Show the mapping associated with a menu item or hierarchy in a sub-menu.
 static int show_menus(char *const path_name, int modes)
 {
-  vimmenu_T *menu = *get_root_menu(path_name);
-  if (menu != NULL) {
+  vimmenu_T *menu = NULL;
+  if (*path_name != NUL) {
     // First, find the (sub)menu with the given name
-    menu = find_menu(menu, path_name, modes);
+    menu = find_menu(*get_root_menu(path_name), path_name, modes);
     if (menu == NULL) {
       return FAIL;
     }
   }
-  // When there are no menus at all, the title still needs to be shown.
 
-  // Now we have found the matching menu, and we list the mappings
-  // Highlight title
+  // Now we have found the matching menu, and we list the mappings.
   msg_puts_title(_("\n--- Menus ---"));
+  show_menus_recursive(menu, modes, 0);
 
-  if (menu != NULL) {
-    show_menus_recursive(menu->parent, modes, 0);
-  }
   return OK;
 }
 

test/functional/ex_cmds/menu_spec.lua

@@ -59,26 +59,80 @@ describe(':emenu', function()
   end)
 end)
 
+local test_menus_cmd = [=[
+  aunmenu *
+
+  nnoremenu &Test.Test inormal<ESC>
+  inoremenu Test.Test insert
+  vnoremenu Test.Test x
+  cnoremenu Test.Test cmdmode
+  menu Test.Nested.test level1
+  menu Test.Nested.Nested2 level2
+
+  nnoremenu <script> Export.Script p
+  tmenu Export.Script This is the tooltip
+  menu ]Export.hidden thisoneshouldbehidden
+
+  nnoremenu Edit.Paste p
+  cnoremenu Edit.Paste <C-R>"
+]=]
+
+describe(':menu listing', function()
+  before_each(function()
+    clear()
+    command(test_menus_cmd)
+  end)
+
+  it('matches by path argument', function()
+    eq(
+      [[
+--- Menus ---
+500 Edit
+  500 Paste
+      c*   <C-R>"]],
+      n.exec_capture('cmenu Edit')
+    )
+    eq(
+      [[
+--- Menus ---
+500 &Test
+  500 Test
+      n*   inormal<Esc>
+  500 Nested
+    500 test
+        n    level1
+    500 Nested2
+        n    level2]],
+      n.exec_capture('nmenu Test')
+    )
+    eq(
+      [[
+--- Menus ---
+500 Nested
+  500 test
+      o    level1
+  500 Nested2
+      o    level2]],
+      n.exec_capture('omenu Test.Nested')
+    )
+    eq(
+      [[
+--- Menus ---
+500 Test
+    n*   inormal<Esc>
+    v*   x
+    s*   x
+    i*   insert
+    c*   cmdmode]],
+      n.exec_capture('amenu Test.Test')
+    )
+  end)
+end)
+
 describe('menu_get', function()
   before_each(function()
     clear()
-    command([=[
-      aunmenu *
-
-      nnoremenu &Test.Test inormal<ESC>
-      inoremenu Test.Test insert
-      vnoremenu Test.Test x
-      cnoremenu Test.Test cmdmode
-      menu Test.Nested.test level1
-      menu Test.Nested.Nested2 level2
-
-      nnoremenu <script> Export.Script p
-      tmenu Export.Script This is the tooltip
-      menu ]Export.hidden thisoneshouldbehidden
-
-      nnoremenu Edit.Paste p
-      cnoremenu Edit.Paste <C-R>"
-    ]=])
+    command(test_menus_cmd)
   end)
 
   it("path='', modes='a'", function()