feat(api): allow win_hide to close cmdwin or non-previous windows

This aligns its behaviour better with `nvim_win_close`.

Note that `:hide` is actually incapable of closing the cmdwin, unlike `:close`
and `:quit`, so this is a bit of a difference in behaviour.

runtime/doc/api.txt

@@ -2897,7 +2897,7 @@ nvim_win_hide({window})                                      *nvim_win_hide()*
     or |nvim_win_close()|, which will close the buffer.
 
     Attributes: ~
-        not allowed when |textlock| is active or in the |cmdwin|
+        not allowed when |textlock| is active
 
     Parameters: ~
       • {window}  Window handle, or 0 for current window

src/nvim/api/window.c

@@ -362,10 +362,10 @@ Boolean nvim_win_is_valid(Window window)
 /// @param[out] err Error details, if any
 void nvim_win_hide(Window window, Error *err)
   FUNC_API_SINCE(7)
-  FUNC_API_TEXTLOCK
+  FUNC_API_TEXTLOCK_ALLOW_CMDWIN
 {
   win_T *win = find_window_by_handle(window, err);
-  if (!win) {
+  if (!win || !can_close_in_cmdwin(win, err)) {
     return;
   }
 
@@ -397,20 +397,10 @@ void nvim_win_close(Window window, Boolean force, Error *err)
   FUNC_API_TEXTLOCK_ALLOW_CMDWIN
 {
   win_T *win = find_window_by_handle(window, err);
-  if (!win) {
+  if (!win || !can_close_in_cmdwin(win, err)) {
     return;
   }
 
-  if (cmdwin_type != 0) {
-    if (win == curwin) {
-      cmdwin_result = Ctrl_C;
-      return;
-    } else if (win == cmdwin_old_curwin) {
-      api_set_error(err, kErrorTypeException, "%s", e_cmdwin);
-      return;
-    }
-  }
-
   tabpage_T *tabpage = win_find_tabpage(win);
   TryState tstate;
   try_enter(&tstate);

src/nvim/window.c

@@ -2670,6 +2670,23 @@ static bool can_close_floating_windows(void)
   return true;
 }
 
+/// @return true if, considering the cmdwin, `win` is safe to close.
+/// If false and `win` is the cmdwin, it is closed; otherwise, `err` is set.
+bool can_close_in_cmdwin(win_T *win, Error *err)
+  FUNC_ATTR_NONNULL_ALL
+{
+  if (cmdwin_type != 0) {
+    if (win == curwin) {
+      cmdwin_result = Ctrl_C;
+      return false;
+    } else if (win == cmdwin_old_curwin) {
+      api_set_error(err, kErrorTypeException, "%s", e_cmdwin);
+      return false;
+    }
+  }
+  return true;
+}
+
 /// Close the possibly last window in a tab page.
 ///
 /// @param  win          window to close

test/functional/api/window_spec.lua

@@ -615,6 +615,24 @@ describe('API/win', function()
       eq({oldwin}, meths.list_wins())
       eq({oldbuf}, meths.list_bufs())
     end)
+    it('in the cmdwin', function()
+      feed('q:')
+      -- Can close the cmdwin.
+      meths.win_hide(0)
+      eq('', funcs.getcmdwintype())
+
+      local old_win = meths.get_current_win()
+      local other_win = meths.open_win(0, false, {
+        relative='win', row=3, col=3, width=12, height=3
+      })
+      feed('q:')
+      -- Cannot close the previous window.
+      eq('E11: Invalid in command-line window; <CR> executes, CTRL-C quits',
+         pcall_err(meths.win_hide, old_win))
+      -- Can close other windows.
+      meths.win_hide(other_win)
+      eq(false, meths.win_is_valid(other_win))
+    end)
   end)
 
   describe('text_height', function()

test/functional/vimscript/api_functions_spec.lua

@@ -73,9 +73,10 @@ describe('eval-API', function()
 
     -- Some functions checking textlock (usually those that may change the current window or buffer)
     -- also ought to not be usable in the cmdwin.
+    local old_win = meths.get_current_win()
     feed("q:")
     eq('E11: Invalid in command-line window; <CR> executes, CTRL-C quits',
-       pcall_err(meths.win_hide, 0))
+       pcall_err(meths.set_current_win, old_win))
 
     -- But others, like nvim_buf_set_lines(), which just changes text, is OK.
     curbufmeths.set_lines(0, -1, 1, {"wow!"})