fix(statusline): clear ruler when it is no longer drawn #33765

Problem:  Ruler is not cleared from the screen/ext_messages state when
          it is no longer drawn after e.g. `set noruler` or when moving
          from a floating to a regular window.
Solution: Remember if ruler was drawn and clear it.

src/nvim/drawscreen.c

@@ -1118,20 +1118,7 @@ int showmode(void)
     clear_showcmd();
   }
 
-  // If the current or last window has no status line and global statusline is disabled,
-  // the ruler is after the mode message and must be redrawn
-  win_T *ruler_win = curwin->w_status_height == 0 ? curwin : lastwin_nofloating();
-  if (redrawing() && ruler_win->w_status_height == 0 && global_stl_height() == 0
-      && !(p_ch == 0 && !ui_has(kUIMessages))) {
-    if (!ui_has(kUIMessages)) {
-      grid_line_start(&msg_grid_adj, Rows - 1);
-    }
-    win_redr_ruler(ruler_win);
-    if (!ui_has(kUIMessages)) {
-      grid_line_flush();
-    }
-  }
-
+  redraw_ruler();      // check if ruler should be redrawn
   redraw_cmdline = false;
   redraw_mode = false;
   clear_cmdline = false;

src/nvim/statusline.c

@@ -333,9 +333,7 @@ static void win_redr_custom(win_T *wp, bool draw_winbar, bool draw_ruler)
   int start_col = col;
 
   // Draw each snippet with the specified highlighting.
-  if (!draw_ruler) {
-    screengrid_line_start(grid, row, 0);
-  }
+  screengrid_line_start(grid, row, 0);
 
   int curattr = attr;
   char *p = buf;
@@ -363,10 +361,7 @@ static void win_redr_custom(win_T *wp, bool draw_winbar, bool draw_ruler)
 
   // fill up with "fillchar"
   grid_line_fill(col, maxcol, fillchar, curattr);
-
-  if (!draw_ruler) {
-    grid_line_flush();
-  }
+  grid_line_flush();
 
   // Fill the tab_page_click_defs, w_status_click_defs or w_winbar_click_defs array for clicking
   // in the tab page line, status line or window bar
@@ -399,14 +394,24 @@ void win_redr_winbar(win_T *wp)
   entered = false;
 }
 
-/// must be called after a grid_line_start() at the intended row
-void win_redr_ruler(win_T *wp)
+void redraw_ruler(void)
 {
-  bool is_stl_global = global_stl_height() > 0;
+  static int did_ruler_col = -1;
   static bool did_show_ext_ruler = false;
+  win_T *wp = curwin->w_status_height == 0 ? curwin : lastwin_nofloating();
+  bool is_stl_global = global_stl_height() > 0;
 
-  // If 'ruler' off, don't do anything
-  if (!p_ru) {
+  // Check if ruler should be drawn, clear if it was drawn before.
+  if (!p_ru || wp->w_status_height > 0 || is_stl_global || (p_ch == 0 && !ui_has(kUIMessages))) {
+    if (did_ruler_col > 0 && ui_has(kUIMessages)) {
+      ui_call_msg_ruler((Array)ARRAY_DICT_INIT);
+      did_show_ext_ruler = false;
+    } else if (did_ruler_col > 0) {
+      msg_col = did_ruler_col;
+      msg_row = Rows - 1;
+      msg_clr_eos();
+    }
+    did_ruler_col = -1;
     return;
   }
 
@@ -418,8 +423,7 @@ void win_redr_ruler(win_T *wp)
 
   // Don't draw the ruler while doing insert-completion, it might overwrite
   // the (long) mode message.
-  win_T *ruler_win = curwin->w_status_height == 0 ? curwin : lastwin_nofloating();
-  if (wp == ruler_win && ruler_win->w_status_height == 0 && !is_stl_global) {
+  if (wp->w_status_height == 0 && !is_stl_global) {
     if (edit_submode != NULL) {
       return;
     }
@@ -513,6 +517,7 @@ void win_redr_ruler(win_T *wp)
     ADD_C(content, ARRAY_OBJ(chunk));
     ui_call_msg_ruler(content);
     did_show_ext_ruler = true;
+    did_ruler_col = 1;
   } else {
     if (did_show_ext_ruler) {
       ui_call_msg_ruler((Array)ARRAY_DICT_INIT);
@@ -528,8 +533,11 @@ void win_redr_ruler(win_T *wp)
       }
     }
 
-    int w = grid_line_puts(off + this_ru_col, buffer, -1, attr);
-    grid_line_fill(off + this_ru_col + w, off + width, fillchar, attr);
+    grid_line_start(&msg_grid_adj, Rows - 1);
+    did_ruler_col = off + this_ru_col;
+    int w = grid_line_puts(did_ruler_col, buffer, -1, attr);
+    grid_line_fill(did_ruler_col + w, off + width, fillchar, attr);
+    grid_line_flush();
   }
 }
 

test/functional/ui/messages_spec.lua

@@ -1834,31 +1834,33 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
 
   it('supports ruler with laststatus=0', function()
     command('set ruler laststatus=0')
-    screen:expect {
-      grid = [[
+    screen:expect([[
       ^                                                            |
       {1:~                                                           }|*5
                                                 0,0-1         All |
-    ]],
-    }
+    ]])
 
     command('hi MsgArea guibg=#333333')
-    screen:expect {
-      grid = [[
+    screen:expect([[
       ^                                                            |
       {1:~                                                           }|*5
       {101:                                          0,0-1         All }|
-    ]],
-    }
+    ]])
 
     command('set rulerformat=%15(%c%V\\ %p%%%)')
-    screen:expect {
-      grid = [[
+    screen:expect([[
       ^                                                            |
       {1:~                                                           }|*5
       {101:                                          0,0-1 100%        }|
-    ]],
-    }
+    ]])
+
+    -- Ruler is cleared when it is no longer drawn.
+    command('set noruler')
+    screen:expect([[
+      ^                                                            |
+      {1:~                                                           }|*5
+      {101:                                                            }|
+    ]])
   end)
 
   it('supports echo with CRLF line separators', function()