feat(ui): add `'winbar'`

Adds support for a bar at the top of each window, enabled through the
`'winbar'` option.

Co-authored-by: Björn Linse <bjorn.linse@gmail.com>

18 files changed, 314 insertions, 161 deletions

diff --git a/src/nvim/api/keysets.lua b/src/nvim/api/keysets.lua
index 78f8ed3cca..27228204e0 100644
--- a/src/nvim/api/keysets.lua
+++ b/src/nvim/api/keysets.lua
@@ -80,6 +80,7 @@ return {
     "maxwidth";
     "fillchar";
     "highlights";
+    "use_winbar";
     "use_tabline";
   };
   option = {
diff --git a/src/nvim/api/private/helpers.c b/src/nvim/api/private/helpers.c
index dcede27bcb..7bd68f277b 100644
--- a/src/nvim/api/private/helpers.c
+++ b/src/nvim/api/private/helpers.c
@@ -1418,14 +1418,14 @@ bool set_mark(buf_T *buf, String name, Integer line, Integer col, Error *err)
 }
 
 /// Get default statusline highlight for window
-const char *get_default_stl_hl(win_T *wp)
+const char *get_default_stl_hl(win_T *wp, bool use_winbar)
 {
   if (wp == NULL) {
     return "TabLineFill";
-  } else if (wp == curwin) {
-    return "StatusLine";
+  } else if (use_winbar) {
+    return (wp == curwin) ? "WinBar" : "WinBarNC";
   } else {
-    return "StatusLineNC";
+    return (wp == curwin) ? "StatusLine" : "StatusLineNC";
   }
 }
 
diff --git a/src/nvim/api/vim.c b/src/nvim/api/vim.c
index a257dd6478..3c378e73e1 100644
--- a/src/nvim/api/vim.c
+++ b/src/nvim/api/vim.c
@@ -2274,8 +2274,9 @@ Array nvim_get_mark(String name, Dictionary opts, Error *err)
 ///           - fillchar: (string) Character to fill blank spaces in the statusline (see
 ///                                'fillchars'). Treated as single-width even if it isn't.
 ///           - highlights: (boolean) Return highlight information.
+///           - use_winbar: (boolean) Evaluate winbar instead of statusline.
 ///           - use_tabline: (boolean) Evaluate tabline instead of statusline. When |TRUE|, {winid}
-///                                    is ignored.
+///                                    is ignored. Mutually exclusive with {use_winbar}.
 ///
 /// @param[out] err Error details, if any.
 /// @return Dictionary containing statusline information, with these keys:
@@ -2294,6 +2295,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
   int maxwidth;
   int fillchar = 0;
   Window window = 0;
+  bool use_winbar = false;
   bool use_tabline = false;
   bool highlights = false;
 
@@ -2313,7 +2315,6 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
 
     window = (Window)opts->winid.data.integer;
   }
-
   if (HAS_KEY(opts->fillchar)) {
     if (opts->fillchar.type != kObjectTypeString || opts->fillchar.data.string.size == 0
         || ((size_t)utf_ptr2len(opts->fillchar.data.string.data)
@@ -2323,7 +2324,6 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
     }
     fillchar = utf_ptr2char(opts->fillchar.data.string.data);
   }
-
   if (HAS_KEY(opts->highlights)) {
     highlights = api_object_to_bool(opts->highlights, "highlights", false, err);
 
@@ -2331,7 +2331,13 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
       return result;
     }
   }
+  if (HAS_KEY(opts->use_winbar)) {
+    use_winbar = api_object_to_bool(opts->use_winbar, "use_winbar", false, err);
 
+    if (ERROR_SET(err)) {
+      return result;
+    }
+  }
   if (HAS_KEY(opts->use_tabline)) {
     use_tabline = api_object_to_bool(opts->use_tabline, "use_tabline", false, err);
 
@@ -2339,6 +2345,10 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
       return result;
     }
   }
+  if (use_winbar && use_tabline) {
+    api_set_error(err, kErrorTypeValidation, "use_winbar and use_tabline are mutually exclusive");
+    return result;
+  }
 
   win_T *wp, *ewp;
 
@@ -2348,7 +2358,6 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
     fillchar = ' ';
   } else {
     wp = find_window_by_handle(window, err);
-
     if (wp == NULL) {
       api_set_error(err, kErrorTypeException, "unknown winid %d", window);
       return result;
@@ -2356,8 +2365,12 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
     ewp = wp;
 
     if (fillchar == 0) {
-      int attr;
-      fillchar = fillchar_status(&attr, wp);
+      if (use_winbar) {
+        fillchar = wp->w_p_fcs_chars.wbr;
+      } else {
+        int attr;
+        fillchar = fillchar_status(&attr, wp);
+      }
     }
   }
 
@@ -2369,7 +2382,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
 
     maxwidth = (int)opts->maxwidth.data.integer;
   } else {
-    maxwidth = (use_tabline || global_stl_height() > 0) ? Columns : wp->w_width;
+    maxwidth = (use_tabline || (!use_winbar && global_stl_height() > 0)) ? Columns : wp->w_width;
   }
 
   char buf[MAXPATHL];
@@ -2404,7 +2417,7 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
     // add the default highlight at the beginning of the highlight list
     if (hltab->start == NULL || ((char *)hltab->start - buf) != 0) {
       Dictionary hl_info = ARRAY_DICT_INIT;
-      grpname = get_default_stl_hl(wp);
+      grpname = get_default_stl_hl(wp, use_winbar);
 
       PUT(hl_info, "start", INTEGER_OBJ(0));
       PUT(hl_info, "group", CSTR_TO_OBJ(grpname));
@@ -2418,22 +2431,18 @@ Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Error *
       PUT(hl_info, "start", INTEGER_OBJ((char *)sp->start - buf));
 
       if (sp->userhl == 0) {
-        grpname = get_default_stl_hl(wp);
+        grpname = get_default_stl_hl(wp, use_winbar);
       } else if (sp->userhl < 0) {
         grpname = (char *)syn_id2name(-sp->userhl);
       } else {
         snprintf(user_group, sizeof(user_group), "User%d", sp->userhl);
         grpname = user_group;
       }
-
       PUT(hl_info, "group", CSTR_TO_OBJ(grpname));
-
       ADD(hl_values, DICTIONARY_OBJ(hl_info));
     }
-
     PUT(result, "highlights", ARRAY_OBJ(hl_values));
   }
-
   PUT(result, "str", CSTR_TO_OBJ((char *)buf));
 
   return result;
diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index 2adeeadbca..9efa540210 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -233,6 +233,8 @@ typedef struct {
 #define w_p_sbr w_onebuf_opt.wo_sbr    // 'showbreak'
   char_u *wo_stl;
 #define w_p_stl w_onebuf_opt.wo_stl     // 'statusline'
+  char *wo_wbr;
+#define w_p_wbr w_onebuf_opt.wo_wbr   // 'winbar'
   int wo_scb;
 #define w_p_scb w_onebuf_opt.wo_scb    // 'scrollbind'
   int wo_diff_saved;           // options were saved for starting diff mode
@@ -1235,6 +1237,7 @@ struct window_S {
   struct {
     int stl;
     int stlnc;
+    int wbr;
     int horiz;
     int horizup;
     int horizdown;
@@ -1282,14 +1285,20 @@ struct window_S {
   //
   int w_winrow;                     // first row of window in screen
   int w_height;                     // number of rows in window, excluding
-                                    // status/command/winbar line(s)
+                                    // status/command line(s)
   int w_status_height;              // number of status lines (0 or 1)
+  int w_winbar_height;              // number of window bars (0 or 1)
   int w_wincol;                     // Leftmost column of window in screen.
   int w_width;                      // Width of window, excluding separation.
   int w_hsep_height;                // Number of horizontal separator rows (0 or 1)
   int w_vsep_width;                 // Number of vertical separator columns (0 or 1).
   pos_save_T w_save_cursor;         // backup of cursor pos and topline
 
+  int w_winrow_off;  ///< offset from winrow to the inner window area
+  int w_wincol_off;  ///< offset from wincol to the inner window area
+                     ///< this includes float border but excludes special columns
+                     ///< implemented in win_line() (i.e. signs, folds, numbers)
+
   // inner size of window, which can be overridden by external UI
   int w_height_inner;
   int w_width_inner;
@@ -1379,6 +1388,7 @@ struct window_S {
   linenr_T w_redraw_top;            // when != 0: first line needing redraw
   linenr_T w_redraw_bot;            // when != 0: last line needing redraw
   bool w_redr_status;               // if true status line must be redrawn
+  bool w_redr_winbar;               // if true window bar must be redrawn
   bool w_redr_border;               // if true border must be redrawn
 
   // remember what is shown in the ruler for this window (if 'ruler' set)
@@ -1408,6 +1418,7 @@ struct window_S {
 
   // A few options have local flags for P_INSECURE.
   uint32_t w_p_stl_flags;           // flags for 'statusline'
+  uint32_t w_p_wbr_flags;           // flags for 'winbar'
   uint32_t w_p_fde_flags;           // flags for 'foldexpr'
   uint32_t w_p_fdt_flags;           // flags for 'foldtext'
   int *w_p_cc_cols;         // array of columns to highlight or NULL
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 9c2069663d..f9c6b6fbb2 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -6405,7 +6405,7 @@ dict_T *get_win_info(win_T *wp, int16_t tpnr, int16_t winnr)
   tv_dict_add_nr(dict, S_LEN("winrow"), wp->w_winrow + 1);
   tv_dict_add_nr(dict, S_LEN("topline"), wp->w_topline);
   tv_dict_add_nr(dict, S_LEN("botline"), wp->w_botline - 1);
-  tv_dict_add_nr(dict, S_LEN("winbar"), 0);
+  tv_dict_add_nr(dict, S_LEN("winbar"), wp->w_winbar_height);
   tv_dict_add_nr(dict, S_LEN("width"), wp->w_width);
   tv_dict_add_nr(dict, S_LEN("bufnr"), wp->w_buffer->b_fnum);
   tv_dict_add_nr(dict, S_LEN("wincol"), wp->w_wincol + 1);
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 68c2e37f22..ad133b5b5f 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -3611,8 +3611,8 @@ static void f_getmousepos(typval_T *argvars, typval_T *rettv, FunPtr fptr)
     // necessary for a top border since `row` starts at -1 in that case.
     if (row < height + wp->w_border_adj[2]) {
       winid = wp->handle;
-      winrow = row + 1 + wp->w_border_adj[0];  // Adjust by 1 for top border
-      wincol = col + 1 + wp->w_border_adj[3];  // Adjust by 1 for left border
+      winrow = row + 1 + wp->w_winrow_off;  // Adjust by 1 for top border
+      wincol = col + 1 + wp->w_wincol_off;  // Adjust by 1 for left border
       if (row >= 0 && row < wp->w_height && col >= 0 && col < wp->w_width) {
         (void)mouse_comp_pos(wp, &row, &col, &lnum);
         col = vcol2col(wp, lnum, col);
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index e845073c12..0510faa57d 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -8831,7 +8831,7 @@ static void ex_redraw(exarg_T *eap)
   ui_flush();
 }
 
-/// ":redrawstatus": force redraw of status line(s)
+/// ":redrawstatus": force redraw of status line(s) and window bar(s)
 static void ex_redrawstatus(exarg_T *eap)
 {
   if (State & MODE_CMDPREVIEW) {
@@ -8847,8 +8847,7 @@ static void ex_redrawstatus(exarg_T *eap)
   } else {
     status_redraw_curbuf();
   }
-  update_screen(VIsual_active ? INVERTED :
-                0);
+  update_screen(VIsual_active ? INVERTED : 0);
   RedrawingDisabled = r;
   p_lz = p;
   ui_flush();
diff --git a/src/nvim/highlight_defs.h b/src/nvim/highlight_defs.h
index 0515842b61..d293865efd 100644
--- a/src/nvim/highlight_defs.h
+++ b/src/nvim/highlight_defs.h
@@ -111,7 +111,9 @@ typedef enum {
   HLF_NFLOAT,     // Floating window
   HLF_MSG,        // Message area
   HLF_BORDER,     // Floating window border
-  HLF_COUNT,  // MUST be the last one
+  HLF_WBR,        // Window bars
+  HLF_WBRNC,      // Window bars of not-current windows
+  HLF_COUNT,      // MUST be the last one
 } hlf_T;
 
 EXTERN const char *hlf_names[] INIT(= {
@@ -172,6 +174,8 @@ EXTERN const char *hlf_names[] INIT(= {
   [HLF_NFLOAT] = "NormalFloat",
   [HLF_MSG] = "MsgArea",
   [HLF_BORDER] = "FloatBorder",
+  [HLF_WBR] = "WinBar",
+  [HLF_WBRNC] = "WinBarNC",
 });
 
 
diff --git a/src/nvim/highlight_group.c b/src/nvim/highlight_group.c
index 240a96cb4b..0047cb02d6 100644
--- a/src/nvim/highlight_group.c
+++ b/src/nvim/highlight_group.c
@@ -103,9 +103,11 @@ static const char *highlight_init_both[] = {
   "TabLineFill  cterm=reverse gui=reverse",
   "TabLineSel   cterm=bold gui=bold",
   "TermCursor   cterm=reverse gui=reverse",
+  "WinBar       cterm=bold gui=bold",
   "WildMenu     ctermbg=Yellow ctermfg=Black guibg=Yellow guifg=Black",
   "default link VertSplit Normal",
   "default link WinSeparator VertSplit",
+  "default link WinBarNC WinBar",
   "default link EndOfBuffer NonText",
   "default link LineNrAbove LineNr",
   "default link LineNrBelow LineNr",
diff --git a/src/nvim/mouse.c b/src/nvim/mouse.c
index 8038ba2cad..3a1cc6b557 100644
--- a/src/nvim/mouse.c
+++ b/src/nvim/mouse.c
@@ -68,12 +68,12 @@ bool is_mouse_key(int c)
 /// mouse was previously on a status line, then the status line may be dragged.
 ///
 /// If flags has MOUSE_MAY_VIS, then VIsual mode will be started before the
-/// cursor is moved unless the cursor was on a status line.
+/// cursor is moved unless the cursor was on a status line or window bar.
 /// This function returns one of IN_UNKNOWN, IN_BUFFER, IN_STATUS_LINE or
 /// IN_SEP_LINE depending on where the cursor was clicked.
 ///
 /// If flags has MOUSE_MAY_STOP_VIS, then Visual mode will be stopped, unless
-/// the mouse is on the status line of the same window.
+/// the mouse is on the status line or window bar of the same window.
 ///
 /// If flags has MOUSE_DID_MOVE, nothing is done if the mouse didn't move since
 /// the last call.
@@ -87,6 +87,7 @@ int jump_to_mouse(int flags, bool *inclusive, int which_button)
 {
   static int on_status_line = 0;        // #lines below bottom of window
   static int on_sep_line = 0;           // on separator right of window
+  static bool on_winbar = false;
   static int prev_row = -1;
   static int prev_col = -1;
   static win_T *dragwin = NULL;         // window being dragged
@@ -126,6 +127,9 @@ retnomove:
     if (on_sep_line) {
       return IN_SEP_LINE;
     }
+    if (on_winbar) {
+      return IN_OTHER_WIN | MOUSE_WINBAR;
+    }
     if (flags & MOUSE_MAY_STOP_VIS) {
       end_visual_mode();
       redraw_curbuf_later(INVERTED);            // delete the inversion
@@ -155,9 +159,11 @@ retnomove:
     fdc = win_fdccol_count(wp);
     dragwin = NULL;
 
-    if (row == -1) {
-      return IN_OTHER_WIN;
+    if (row == -1 + wp->w_winbar_height) {
+      on_winbar = !!wp->w_winbar_height;
+      return IN_OTHER_WIN | (on_winbar ? MOUSE_WINBAR : 0);
     }
+    on_winbar = false;
 
     // winpos and height may change in win_enter()!
     if (grid == DEFAULT_GRID_HANDLE && row >= wp->w_height) {
@@ -253,6 +259,9 @@ retnomove:
       did_drag |= count;
     }
     return IN_SEP_LINE;                         // Cursor didn't move
+  } else if (on_winbar) {
+    // After a click on the window bar don't start Visual mode.
+    return IN_OTHER_WIN | MOUSE_WINBAR;
   } else {
     // keep_window_focus must be true
     // before moving the cursor for a left click, stop Visual mode
@@ -497,6 +506,7 @@ win_T *mouse_find_win(int *gridp, int *rowp, int *colp)
   // exist.
   FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
     if (wp == fp->fr_win) {
+      *rowp -= wp->w_winrow_off - wp->w_winbar_height;
       return wp;
     }
   }
diff --git a/src/nvim/move.c b/src/nvim/move.c
index 11feb497ea..97ce92f6a9 100644
--- a/src/nvim/move.c
+++ b/src/nvim/move.c
@@ -1016,7 +1016,7 @@ void textpos2screenpos(win_T *wp, pos_T *pos, int *rowp, int *scolp, int *ccolp,
     col -= wp->w_leftcol;
 
     if (col >= 0 && col < wp->w_width) {
-      coloff = col - scol + (local ? 0 : wp->w_wincol + wp->w_border_adj[3]) + 1;
+      coloff = col - scol + (local ? 0 : wp->w_wincol + wp->w_wincol_off) + 1;
     } else {
       scol = ccol = ecol = 0;
       // character is left or right of the window
@@ -1027,7 +1027,7 @@ void textpos2screenpos(win_T *wp, pos_T *pos, int *rowp, int *scolp, int *ccolp,
       }
     }
   }
-  *rowp = (local ? 0 : wp->w_winrow + wp->w_border_adj[0]) + row + rowoff;
+  *rowp = (local ? 0 : wp->w_winrow + wp->w_winrow_off) + row + rowoff;
   *scolp = scol + coloff;
   *ccolp = ccol + coloff;
   *ecolp = ecol + coloff;
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 2826b7dad1..1692970a97 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1280,7 +1280,8 @@ static void normal_redraw(NormalState *s)
   validate_cursor();
 
   if (VIsual_active) {
-    update_curbuf(INVERTED);  // update inverted part
+    redraw_curbuf_later(INVERTED);  // update inverted part
+    update_screen(INVERTED);
   } else if (must_redraw) {
     update_screen(0);
   } else if (redraw_cmdline || clear_cmdline) {
@@ -1850,6 +1851,11 @@ bool do_mouse(oparg_T *oap, int c, int dir, long count, bool fixindent)
                              oap == NULL ? NULL : &(oap->inclusive),
                              which_button);
 
+  // A click in the window bar has no side effects.
+  if (jump_flags & MOUSE_WINBAR) {
+    return false;
+  }
+
   moved = (jump_flags & CURSOR_MOVED);
   in_status_line = (jump_flags & IN_STATUS_LINE);
   in_sep_line = (jump_flags & IN_SEP_LINE);
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 8267bcf9da..2ee6c175bb 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -2149,6 +2149,8 @@ static uint32_t *insecure_flag(win_T *const wp, int opt_idx, int opt_flags)
     switch ((int)options[opt_idx].indir) {
     case PV_STL:
       return &wp->w_p_stl_flags;
+    case PV_WBR:
+      return &wp->w_p_wbr_flags;
     case PV_FDE:
       return &wp->w_p_fde_flags;
     case PV_FDT:
@@ -2930,8 +2932,8 @@ ambw_end:
       curbuf->b_help = (curbuf->b_p_bt[0] == 'h');
       redraw_titles();
     }
-  } else if (gvarp == &p_stl || varp == &p_tal || varp == &p_ruf) {
-    // 'statusline', 'tabline' or 'rulerformat'
+  } else if (gvarp == &p_stl || gvarp == (char_u **)&p_wbr || varp == &p_tal || varp == &p_ruf) {
+    // 'statusline', 'winbar', 'tabline' or 'rulerformat'
     int wid;
 
     if (varp == &p_ruf) {       // reset ru_wid first
@@ -2950,12 +2952,16 @@ ambw_end:
         errmsg = check_stl_option(p_ruf);
       }
     } else if (varp == &p_ruf || s[0] != '%' || s[1] != '!') {
-      // check 'statusline' or 'tabline' only if it doesn't start with "%!"
+      // check 'statusline', 'winbar' or 'tabline' only if it doesn't start with "%!"
       errmsg = check_stl_option(s);
     }
     if (varp == &p_ruf && errmsg == NULL) {
       comp_col();
     }
+    // add / remove window bars for 'winbar'
+    if (gvarp == (char_u **)&p_wbr) {
+      set_winbar();
+    }
   } else if (gvarp == &p_cpt) {
     // check if it is a valid value for 'complete' -- Acevedo
     for (s = *varp; *s;) {
@@ -3570,6 +3576,7 @@ static char *set_chars_option(win_T *wp, char_u **varp, bool set)
   struct chars_tab fcs_tab[] = {
     { &wp->w_p_fcs_chars.stl,        "stl",        ' '  },
     { &wp->w_p_fcs_chars.stlnc,      "stlnc",      ' '  },
+    { &wp->w_p_fcs_chars.wbr,        "wbr",        ' '  },
     { &wp->w_p_fcs_chars.horiz,      "horiz",      9472 },  // ─
     { &wp->w_p_fcs_chars.horizup,    "horizup",    9524 },  // ┴
     { &wp->w_p_fcs_chars.horizdown,  "horizdown",  9516 },  // ┬
@@ -3612,15 +3619,15 @@ static char *set_chars_option(win_T *wp, char_u **varp, bool set)
     if (*p_ambw == 'd') {
       // XXX: If ambiwidth=double then some characters take 2 columns,
       // which is forbidden (TUI limitation?). Set old defaults.
-      fcs_tab[2].def  = '-';
       fcs_tab[3].def  = '-';
       fcs_tab[4].def  = '-';
-      fcs_tab[5].def  = '|';
+      fcs_tab[5].def  = '-';
       fcs_tab[6].def  = '|';
       fcs_tab[7].def  = '|';
-      fcs_tab[8].def  = '+';
-      fcs_tab[9].def  = '-';
-      fcs_tab[12].def = '|';
+      fcs_tab[8].def  = '|';
+      fcs_tab[9].def  = '+';
+      fcs_tab[10].def  = '-';
+      fcs_tab[13].def = '|';
     }
   }
 
@@ -4766,7 +4773,7 @@ static void check_redraw(uint32_t flags)
   bool doclear = (flags & P_RCLR) == P_RCLR;
   bool all = ((flags & P_RALL) == P_RALL || doclear);
 
-  if ((flags & P_RSTAT) || all) {  // mark all status lines dirty
+  if ((flags & P_RSTAT) || all) {  // mark all status lines and window bars dirty
     status_redraw_all();
   }
 
@@ -5814,6 +5821,9 @@ void unset_global_local_option(char *name, void *from)
   case PV_STL:
     clear_string_option(&((win_T *)from)->w_p_stl);
     break;
+  case PV_WBR:
+    clear_string_option((char_u **)&((win_T *)from)->w_p_wbr);
+    break;
   case PV_UL:
     buf->b_p_ul = NO_LOCAL_UNDOLEVEL;
     break;
@@ -5891,6 +5901,8 @@ static char_u *get_varp_scope(vimoption_T *p, int opt_flags)
       return (char_u *)&(curwin->w_p_sbr);
     case PV_STL:
       return (char_u *)&(curwin->w_p_stl);
+    case PV_WBR:
+      return (char_u *)&(curwin->w_p_wbr);
     case PV_UL:
       return (char_u *)&(curbuf->b_p_ul);
     case PV_LW:
@@ -5984,6 +5996,9 @@ static char_u *get_varp(vimoption_T *p)
   case PV_STL:
     return *curwin->w_p_stl != NUL
            ? (char_u *)&(curwin->w_p_stl) : p->var;
+  case PV_WBR:
+    return *curwin->w_p_wbr != NUL
+           ? (char_u *)&(curwin->w_p_wbr) : p->var;
   case PV_UL:
     return curbuf->b_p_ul != NO_LOCAL_UNDOLEVEL
            ? (char_u *)&(curbuf->b_p_ul) : p->var;
@@ -6252,6 +6267,7 @@ void copy_winopt(winopt_T *from, winopt_T *to)
   to->wo_rlc = vim_strsave(from->wo_rlc);
   to->wo_sbr = vim_strsave(from->wo_sbr);
   to->wo_stl = vim_strsave(from->wo_stl);
+  to->wo_wbr = xstrdup(from->wo_wbr);
   to->wo_wrap = from->wo_wrap;
   to->wo_wrap_save = from->wo_wrap_save;
   to->wo_lbr = from->wo_lbr;
@@ -6327,6 +6343,7 @@ static void check_winopt(winopt_T *wop)
   check_string_option(&wop->wo_fcs);
   check_string_option(&wop->wo_lcs);
   check_string_option(&wop->wo_ve);
+  check_string_option((char_u **)&wop->wo_wbr);
 }
 
 /// Free the allocated memory inside a winopt_T.
@@ -6352,6 +6369,7 @@ void clear_winopt(winopt_T *wop)
   clear_string_option(&wop->wo_fcs);
   clear_string_option(&wop->wo_lcs);
   clear_string_option(&wop->wo_ve);
+  clear_string_option((char_u **)&wop->wo_wbr);
 }
 
 void didset_window_options(win_T *wp)
diff --git a/src/nvim/option_defs.h b/src/nvim/option_defs.h
index e358a29622..f5c7ae07bb 100644
--- a/src/nvim/option_defs.h
+++ b/src/nvim/option_defs.h
@@ -618,6 +618,7 @@ EXTERN int p_stmp;              // 'shelltemp'
 EXTERN int p_ssl;               // 'shellslash'
 #endif
 EXTERN char_u *p_stl;         // 'statusline'
+EXTERN char *p_wbr;         // 'winbar'
 EXTERN int p_sr;                // 'shiftround'
 EXTERN char_u *p_shm;         // 'shortmess'
 EXTERN char_u *p_sbr;         // 'showbreak'
@@ -897,6 +898,7 @@ enum {
   WV_FCS,
   WV_LCS,
   WV_WINBL,
+  WV_WBR,
   WV_COUNT,  // must be the last one
 };
 
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 313cace4b2..eb92d47fc8 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -2832,6 +2832,16 @@ return {
       defaults={if_true="menu"}
     },
     {
+      full_name='winbar', abbreviation='wbr',
+      short_desc=N_("custom format for the window bar"),
+      type='string', scope={'global', 'window'},
+      alloced=true,
+      modelineexpr=true,
+      redraw={'statuslines'},
+      varname='p_wbr',
+      defaults={if_true=""}
+    },
+    {
       full_name='winblend', abbreviation='winbl',
       short_desc=N_("Controls transparency level for floating windows"),
       type='number', scope={'window'},
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 686516f17b..b2490fb9c5 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -276,25 +276,25 @@ void redrawWinline(win_T *wp, linenr_T lnum)
   }
 }
 
-/*
- * update all windows that are editing the current buffer
- */
-void update_curbuf(int type)
-{
-  redraw_curbuf_later(type);
-  update_screen(type);
-}
-
 /// called when the status bars for the buffer 'buf' need to be updated
 void redraw_buf_status_later(buf_T *buf)
 {
   FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-    if (wp->w_buffer == buf
-        && (wp->w_status_height || (wp == curwin && global_stl_height()))) {
+    if (wp->w_buffer != buf) {
+      continue;
+    }
+    bool redraw = false;
+
+    if (wp->w_status_height || (wp == curwin && global_stl_height())) {
       wp->w_redr_status = true;
-      if (must_redraw < VALID) {
-        must_redraw = VALID;
-      }
+      redraw = true;
+    }
+    if (wp->w_winbar_height) {
+      wp->w_redr_winbar = true;
+      redraw = true;
+    }
+    if (redraw && must_redraw < VALID) {
+      must_redraw = VALID;
     }
   }
 }
@@ -400,6 +400,9 @@ int update_screen(int type)
           if (wp->w_floating) {
             continue;
           }
+          if (wp->w_winrow + wp->w_winbar_height > valid) {
+            wp->w_redr_winbar = true;
+          }
           if (W_ENDROW(wp) > valid) {
             wp->w_redr_type = MAX(wp->w_redr_type, NOT_VALID);
           }
@@ -431,6 +434,9 @@ int update_screen(int type)
             wp->w_redr_type = REDRAW_TOP;
           } else {
             wp->w_redr_type = NOT_VALID;
+            if (wp->w_winrow + wp->w_winbar_height <= msg_scrolled) {
+              wp->w_redr_winbar = true;
+            }
             if (!is_stl_global && W_ENDROW(wp) + wp->w_status_height <= msg_scrolled) {
               wp->w_redr_status = true;
             }
@@ -585,10 +591,13 @@ int update_screen(int type)
       win_update(wp, &providers);
     }
 
-    // redraw status line after the window to minimize cursor movement
+    // redraw status line and window bar after the window to minimize cursor movement
     if (wp->w_redr_status) {
       win_redr_status(wp);
     }
+    if (wp->w_redr_winbar) {
+      win_redr_winbar(wp);
+    }
   }
 
   end_search_hl();
@@ -743,6 +752,7 @@ static void win_update(win_T *wp, DecorProviders *providers)
 
   if (type >= NOT_VALID) {
     wp->w_redr_status = true;
+    wp->w_redr_winbar = true;
     wp->w_lines_valid = 0;
   }
 
@@ -4528,42 +4538,55 @@ void rl_mirror(char_u *str)
   }
 }
 
-/*
- * mark all status lines for redraw; used after first :cd
- */
+/// Mark all status lines and window bars for redraw; used after first :cd
 void status_redraw_all(void)
 {
-  if (global_stl_height()) {
-    curwin->w_redr_status = true;
-    redraw_later(curwin, VALID);
-  } else {
-    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-      if (wp->w_status_height) {
-        wp->w_redr_status = true;
-        redraw_later(wp, VALID);
-      }
+  bool is_stl_global = global_stl_height() != 0;
+
+  FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
+    bool redraw = false;
+
+    if ((!is_stl_global && wp->w_status_height) || (is_stl_global && wp == curwin)) {
+      wp->w_redr_status = true;
+      redraw = true;
+    }
+    if (wp->w_winbar_height) {
+      wp->w_redr_winbar = true;
+      redraw = true;
+    }
+    if (redraw) {
+      redraw_later(wp, VALID);
     }
   }
 }
 
-/// Marks all status lines of the current buffer for redraw.
+/// Marks all status lines and window bars of the current buffer for redraw.
 void status_redraw_curbuf(void)
 {
   status_redraw_buf(curbuf);
 }
 
-/// Marks all status lines of the specified buffer for redraw.
+/// Marks all status lines and window bars of the given buffer for redraw.
 void status_redraw_buf(buf_T *buf)
 {
-  if (global_stl_height() != 0 && curwin->w_buffer == buf) {
-    curwin->w_redr_status = true;
-    redraw_later(curwin, VALID);
-  } else {
-    FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
-      if (wp->w_status_height != 0 && wp->w_buffer == buf) {
-        wp->w_redr_status = true;
-        redraw_later(wp, VALID);
-      }
+  bool is_stl_global = global_stl_height() != 0;
+
+  FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
+    if (wp->w_buffer != buf) {
+      continue;
+    }
+    bool redraw = false;
+
+    if ((!is_stl_global && wp->w_status_height) || (is_stl_global && wp == curwin)) {
+      wp->w_redr_status = true;
+      redraw = true;
+    }
+    if (wp->w_winbar_height) {
+      wp->w_redr_winbar = true;
+      redraw = true;
+    }
+    if (redraw) {
+      redraw_later(wp, VALID);
     }
   }
 }
@@ -4577,6 +4600,9 @@ void redraw_statuslines(void)
     if (wp->w_redr_status) {
       win_redr_status(wp);
     }
+    if (wp->w_redr_winbar) {
+      win_redr_winbar(wp);
+    }
   }
   if (redraw_tabline) {
     draw_tabline();
@@ -5075,7 +5101,7 @@ static void redraw_custom_statusline(win_T *wp)
   entered = true;
 
   did_emsg = false;
-  win_redr_custom(wp, false);
+  win_redr_custom(wp, false, false);
   if (did_emsg) {
     // When there is an error disable the statusline, otherwise the
     // display is messed up with errors and a redraw triggers the problem
@@ -5088,6 +5114,41 @@ static void redraw_custom_statusline(win_T *wp)
   entered = false;
 }
 
+static void win_redr_winbar(win_T *wp)
+{
+  static bool entered = false;
+
+  // Return when called recursively. This can happen when the winbar contains an expression
+  // that triggers a redraw.
+  if (entered) {
+    return;
+  }
+  entered = true;
+
+  wp->w_redr_winbar = false;
+  if (wp->w_winbar_height == 0) {
+    // No window bar, do nothing.
+  } else if (!redrawing()) {
+    // Don't redraw right now, do it later.
+    wp->w_redr_winbar = true;
+  } else if (*p_wbr != NUL || *wp->w_p_wbr != NUL) {
+    int saved_did_emsg = did_emsg;
+
+    did_emsg = false;
+    win_redr_custom(wp, true, false);
+    if (did_emsg) {
+      // When there is an error disable the winbar, otherwise the
+      // display is messed up with errors and a redraw triggers the problem
+      // again and again.
+      set_string_option_direct("winbar", -1, (char_u *)"",
+                               OPT_FREE | (*wp->w_p_stl != NUL
+