fix(ui): command line issues with external messages (#21709)

* fix: don't truncate external messages
* fix: avoid resizing command line with external messages

src/nvim/message.c

@@ -919,9 +919,11 @@ char *msg_trunc_attr(char *s, bool force, int attr)
 /// @note: May change the message by replacing a character with '<'.
 char *msg_may_trunc(bool force, char *s)
 {
-  int room;
+  if (ui_has(kUIMessages)) {
+    return s;
+  }
 
-  room = (Rows - cmdline_row - 1) * Columns + sc_col - 1;
+  int room = (Rows - cmdline_row - 1) * Columns + sc_col - 1;
   if ((force || (shortmess(SHM_TRUNC) && !exmode_active))
       && (int)strlen(s) - room > 0) {
     int size = vim_strsize(s);

src/nvim/window.c

@@ -5780,6 +5780,10 @@ static void frame_setheight(frame_T *curfrp, int height)
 
   if (curfrp->fr_parent == NULL) {
     // topframe: can only change the command line height
+    // Avoid doing so with external messages.
+    if (ui_has(kUIMessages)) {
+      return;
+    }
     if (height > ROWS_AVAIL) {
       // If height is greater than the available space, try to create space for
       // the frame by reducing 'cmdheight' if possible, while making sure
@@ -6115,13 +6119,13 @@ void win_setminwidth(void)
 /// Status line of dragwin is dragged "offset" lines down (negative is up).
 void win_drag_status_line(win_T *dragwin, int offset)
 {
-  // If the user explicitly set 'cmdheight' to zero, then allow for dragging
-  // the status line making it zero again.
-  if (p_ch == 0) {
-    p_ch_was_zero = true;
+  frame_T *fr = dragwin->w_frame;
+
+  // Avoid changing command line height with external messages.
+  if (fr->fr_next == NULL && ui_has(kUIMessages)) {
+    return;
   }
 
-  frame_T *fr = dragwin->w_frame;
   frame_T *curfr = fr;
   if (fr != topframe) {         // more than one window
     fr = fr->fr_parent;

test/functional/ui/cmdline_spec.lua

@@ -8,6 +8,7 @@ local exec = helpers.exec
 local eval = helpers.eval
 local eq = helpers.eq
 local is_os = helpers.is_os
+local meths = helpers.meths
 
 local function new_screen(opt)
   local screen = Screen.new(25, 5)
@@ -1387,17 +1388,20 @@ describe('cmdheight=0', function()
     ]])
   end)
 
-  it("clears cmdline area when resized with external messages", function()
+  it("cannot be resized at all with external messages", function()
     clear()
     screen = new_screen({rgb=true, ext_messages=true})
-    command('set laststatus=2 cmdheight=0')
+    command('set laststatus=2 mouse=a')
     command('resize -1')
     screen:expect([[
       ^                         |
       {1:~                        }|
       {1:~                        }|
+      {1:~                        }|
       {3:[No Name]                }|
-                               |
     ]])
+    meths.input_mouse('left', 'press', '', 0, 6, 10)
+    meths.input_mouse('left', 'drag', '', 0, 5, 10)
+    screen:expect_unchanged()
   end)
 end)

test/functional/ui/messages_spec.lua

@@ -908,6 +908,13 @@ stack traceback:
       {1:~                        }|
     ]]}
   end)
+
+  it('does not truncate messages', function()
+    command('write Xtest')
+    screen:expect({messages={
+      {content = { { '"Xtest" [New] 0L, 0B written' } }, kind = "" }
+    }})
+  end)
 end)
 
 describe('ui/builtin messages', function()