fix(screen): restart win_update() if a decor provider changes signcols (#18768)

src/nvim/screen.c

@@ -326,10 +326,11 @@ int update_screen(int type)
       type = must_redraw;
     }
 
-    /* must_redraw is reset here, so that when we run into some weird
+    // must_redraw is reset here, so that when we run into some weird
-    * reason to redraw while busy redrawing (e.g., asynchronous
+    // reason to redraw while busy redrawing (e.g., asynchronous
-    * scrolling), or update_topline() in win_update() will cause a
+    // scrolling), or update_topline() in win_update() will cause a
-    * scroll, the screen will be redrawn later or in win_update(). */
+    // scroll, or a decoration provider requires a redraw, the screen
+    // will be redrawn later or in win_update().
     must_redraw = 0;
   }
 
@@ -689,6 +690,9 @@ bool win_cursorline_standout(const win_T *wp)
  */
 static void win_update(win_T *wp, DecorProviders *providers)
 {
+  bool called_decor_providers = false;
+win_update_start:
+  ;
   buf_T *buf = wp->w_buffer;
   int type;
   int top_end = 0;              /* Below last row of the top area that needs
@@ -1306,6 +1310,14 @@ static void win_update(win_T *wp, DecorProviders *providers)
 
   DecorProviders line_providers;
   decor_providers_invoke_win(wp, providers, &line_providers, &provider_err);
+  (void)win_signcol_count(wp);  // check if provider changed signcol width
+  if (must_redraw != 0) {
+    must_redraw = 0;
+    if (!called_decor_providers) {
+      called_decor_providers = true;
+      goto win_update_start;
+    }
+  }
 
   bool cursorline_standout = win_cursorline_standout(wp);
 

test/functional/ui/decorations_spec.lua

@@ -30,6 +30,7 @@ describe('decorations providers', function()
       [11] = {foreground = Screen.colors.Red, background = tonumber('0x005028')};
       [12] = {foreground = tonumber('0x990000')};
       [13] = {background = Screen.colors.LightBlue};
+      [14] = {background = Screen.colors.WebGray, foreground = Screen.colors.DarkBlue};
     }
   end)
 
@@ -404,6 +405,50 @@ describe('decorations providers', function()
                                               |
     ]]}
   end)
+
+  it('can create and remove signs when CursorMoved autocommand validates botline #18661', function()
+    exec_lua([[
+      local lines = {}
+      for i = 1, 200 do
+        lines[i] = 'hello' .. tostring(i)
+      end
+      vim.api.nvim_buf_set_lines(0, 0, -1, false, lines)
+    ]])
+    setup_provider([[
+      local function on_do(kind, winid, bufnr, topline, botline_guess)
+        if kind == 'win' then
+          if topline < 100 and botline_guess > 100 then
+            vim.api.nvim_buf_set_extmark(bufnr, ns1, 99, -1, { sign_text = 'X' })
+          else
+            vim.api.nvim_buf_clear_namespace(bufnr, ns1, 0, -1)
+          end
+        end
+      end
+    ]])
+    command([[autocmd CursorMoved * call line('w$')]])
+    meths.win_set_cursor(0, {100, 0})
+    screen:expect([[
+      {14:  }hello97                               |
+      {14:  }hello98                               |
+      {14:  }hello99                               |
+      X ^hello100                              |
+      {14:  }hello101                              |
+      {14:  }hello102                              |
+      {14:  }hello103                              |
+                                              |
+    ]])
+    meths.win_set_cursor(0, {1, 0})
+    screen:expect([[
+      ^hello1                                  |
+      hello2                                  |
+      hello3                                  |
+      hello4                                  |
+      hello5                                  |
+      hello6                                  |
+      hello7                                  |
+                                              |
+    ]])
+  end)
 end)
 
 describe('extmark decorations', function()