fix(ui): always use stl/stlnc fillchars when drawing statusline (#25267)

7 files changed, 32 insertions, 29 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 9b4f36cbce..b26c181f28 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -2465,8 +2465,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	and the value of that item:
 
 	  item		default		Used for ~
-	  stl		' ' or '^'	statusline of the current window
-	  stlnc		' ' or '='	statusline of the non-current windows
+	  stl		' '		statusline of the current window
+	  stlnc		' '		statusline of the non-current windows
 	  wbr		' '		window bar
 	  horiz		'─' or '-'	horizontal separators |:split|
 	  horizup	'┴' or '-'	upwards facing horizontal separator
@@ -2485,9 +2485,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 	  eob		'~'		empty lines at the end of a buffer
 	  lastline	'@'		'display' contains lastline/truncate
 
-	Any one that is omitted will fall back to the default.  For "stl" and
-	"stlnc" the space will be used when there is highlighting, '^' or '='
-	otherwise.
+	Any one that is omitted will fall back to the default.
 
 	Note that "horiz", "horizup", "horizdown", "vertleft", "vertright" and
 	"verthoriz" are only used when 'laststatus' is 3, since only vertical
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index c15b41f9aa..e1053b54f1 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -5322,8 +5322,6 @@ SpellRare	Word that is recognized by the spellchecker as one that is
 StatusLine	Status line of current window.
 							*hl-StatusLineNC*
 StatusLineNC	Status lines of not-current windows.
-		Note: If this is equal to "StatusLine", Vim will use "^^^" in
-		the status line of the current window.
 							*hl-TabLine*
 TabLine		Tab pages line, not active tab page label.
 							*hl-TabLineFill*
diff --git a/runtime/doc/vim_diff.txt b/runtime/doc/vim_diff.txt
index 8a6e5461c3..d65e470dcf 100644
--- a/runtime/doc/vim_diff.txt
+++ b/runtime/doc/vim_diff.txt
@@ -534,6 +534,10 @@ Vimscript compatibility:
   `shell_error` does not alias to |v:shell_error|
   `this_session` does not alias to |v:this_session|
 
+UI/Display:
+  'statusline' always uses the "stl" and "stlnc" fields of 'fillchars', even
+  if they are the same and |hl-StatusLine| and |hl-StatusLineNC| are equal.
+
 Working directory (Vim implemented some of these after Nvim):
 - |DirChanged| and |DirChangedPre| can be triggered when switching to another
   window or tab.
diff --git a/runtime/lua/vim/_meta/options.lua b/runtime/lua/vim/_meta/options.lua
index baf53c5ccc..f8a51da9b5 100644
--- a/runtime/lua/vim/_meta/options.lua
+++ b/runtime/lua/vim/_meta/options.lua
@@ -2181,8 +2181,8 @@ vim.bo.ft = vim.bo.filetype
 --- and the value of that item:
 ---
 ---   item		default		Used for ~
----   stl		' ' or '^'	statusline of the current window
----   stlnc		' ' or '='	statusline of the non-current windows
+---   stl		' '		statusline of the current window
+---   stlnc		' '		statusline of the non-current windows
 ---   wbr		' '		window bar
 ---   horiz		'─' or '-'	horizontal separators `:split`
 ---   horizup	'┴' or '-'	upwards facing horizontal separator
@@ -2201,9 +2201,7 @@ vim.bo.ft = vim.bo.filetype
 ---   eob		'~'		empty lines at the end of a buffer
 ---   lastline	'@'		'display' contains lastline/truncate
 ---
---- Any one that is omitted will fall back to the default.  For "stl" and
---- "stlnc" the space will be used when there is highlighting, '^' or '='
---- otherwise.
+--- Any one that is omitted will fall back to the default.
 ---
 --- Note that "horiz", "horizup", "horizdown", "vertleft", "vertright" and
 --- "verthoriz" are only used when 'laststatus' is 3, since only vertical
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 5fd7e86993..258145e85e 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -2790,8 +2790,8 @@ return {
         and the value of that item:
 
           item		default		Used for ~
-          stl		' ' or '^'	statusline of the current window
-          stlnc		' ' or '='	statusline of the non-current windows
+          stl		' '		statusline of the current window
+          stlnc		' '		statusline of the non-current windows
           wbr		' '		window bar
           horiz		'─' or '-'	horizontal separators |:split|
           horizup	'┴' or '-'	upwards facing horizontal separator
@@ -2810,9 +2810,7 @@ return {
           eob		'~'		empty lines at the end of a buffer
           lastline	'@'		'display' contains lastline/truncate
 
-        Any one that is omitted will fall back to the default.  For "stl" and
-        "stlnc" the space will be used when there is highlighting, '^' or '='
-        otherwise.
+        Any one that is omitted will fall back to the default.
 
         Note that "horiz", "horizup", "horizdown", "vertleft", "vertright" and
         "verthoriz" are only used when 'laststatus' is 3, since only vertical
diff --git a/src/nvim/statusline.c b/src/nvim/statusline.c
index a6f1da8761..4d318f8c59 100644
--- a/src/nvim/statusline.c
+++ b/src/nvim/statusline.c
@@ -637,18 +637,7 @@ int fillchar_status(int *attr, win_T *wp)
     *attr = win_hl_attr(wp, HLF_SNC);
     fill = wp->w_p_fcs_chars.stlnc;
   }
-  // Use fill when there is highlighting, and highlighting of current
-  // window differs, or the fillchars differ, or this is not the
-  // current window
-  if (*attr != 0 && ((win_hl_attr(wp, HLF_S) != win_hl_attr(wp, HLF_SNC)
-                      || !is_curwin || ONE_WINDOW)
-                     || (wp->w_p_fcs_chars.stl != wp->w_p_fcs_chars.stlnc))) {
-    return fill;
-  }
-  if (is_curwin) {
-    return '^';
-  }
-  return '=';
+  return fill;
 }
 
 /// Redraw the status line according to 'statusline' and take care of any
diff --git a/test/functional/ui/statusline_spec.lua b/test/functional/ui/statusline_spec.lua
index 7967fb6865..182e0cdadf 100644
--- a/test/functional/ui/statusline_spec.lua
+++ b/test/functional/ui/statusline_spec.lua
@@ -799,3 +799,21 @@ it("shows correct ruler in cmdline with no statusline", function()
                    3longlonglong  |
   ]]
 end)
+
+it('uses "stl" and "stlnc" fillchars even if they are the same #19803', function()
+  clear()
+  local screen = Screen.new(53, 4)
+  screen:attach()
+  screen:set_default_attr_ids({
+    [1] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
+  })
+  command('hi clear StatusLine')
+  command('hi clear StatusLineNC')
+  command('vsplit')
+  screen:expect{grid=[[
+    ^                          │                          |
+    {1:~                         }│{1:~                         }|
+    [No Name]                  [No Name]                 |
+                                                         |
+  ]]}
+end)