Don't use hook pre-redisplay-functions. Set buffer-local tab-line-format.

* lisp/tab-line.el (tab-line-format): Move to C.
(tab-line-update-window-parameter): Remove function.
(global-tab-line-mode): Set the default value of tab-line-format.

* src/buffer.c (syms_of_buffer): Define buffer-local variable
tab-line-format.

* src/buffer.h (struct buffer): Add tab_line_format_.

* src/window.c (window_wants_tab_line):
* src/xdisp.c (pos_visible_p, display_mode_lines):
Check for buffer-local tab_line_format.

4 files changed, 28 insertions, 3 deletions

diff --git a/src/buffer.c b/src/buffer.c
index ad9feee92a4..233a95c2597 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -249,6 +249,11 @@ bset_header_line_format (struct buffer *b, Lisp_Object val)
   b->header_line_format_ = val;
 }
 static void
+bset_tab_line_format (struct buffer *b, Lisp_Object val)
+{
+  b->tab_line_format_ = val;
+}
+static void
 bset_indicate_buffer_boundaries (struct buffer *b, Lisp_Object val)
 {
   b->indicate_buffer_boundaries_ = val;
@@ -5188,6 +5193,7 @@ init_buffer_once (void)
   XSETFASTINT (BVAR (&buffer_local_flags, scroll_up_aggressively), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, scroll_down_aggressively), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, header_line_format), idx); ++idx;
+  XSETFASTINT (BVAR (&buffer_local_flags, tab_line_format), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, cursor_type), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, extra_line_spacing), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, cursor_in_non_selected_windows), idx); ++idx;
@@ -5233,6 +5239,7 @@ init_buffer_once (void)
   /* real setup is done in bindings.el */
   bset_mode_line_format (&buffer_defaults, build_pure_c_string ("%-"));
   bset_header_line_format (&buffer_defaults, Qnil);
+  bset_tab_line_format (&buffer_defaults, Qnil);
   bset_abbrev_mode (&buffer_defaults, Qnil);
   bset_overwrite_mode (&buffer_defaults, Qnil);
   bset_case_fold_search (&buffer_defaults, Qt);
@@ -5504,6 +5511,13 @@ syms_of_buffer (void)
   Fput (Qprotected_field, Qerror_message,
         build_pure_c_string ("Attempt to modify a protected field"));
 
+  DEFVAR_PER_BUFFER ("tab-line-format",
+                     &BVAR (current_buffer, tab_line_format),
+                     Qnil,
+                     doc: /* Analogous to `mode-line-format', but controls the tab line.
+The tab line appears, optionally, at the top of a window;
+the mode line appears at the bottom.  */);
+
   DEFVAR_PER_BUFFER ("header-line-format",
                      &BVAR (current_buffer, header_line_format),
                      Qnil,
diff --git a/src/buffer.h b/src/buffer.h
index 2080a6f40b7..e411ab5461d 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -539,6 +539,10 @@ struct buffer
      of windows.  Nil means don't display that line.  */
   Lisp_Object header_line_format_;
 
+  /* Analogous to mode_line_format for the line displayed at the top
+     of windows.  Nil means don't display that line.  */
+  Lisp_Object tab_line_format_;
+
   /* Keys that are bound local to this buffer.  */
   Lisp_Object keymap_;
 
diff --git a/src/window.c b/src/window.c
index 30b53d1a06d..6749ffde4c1 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5419,7 +5419,8 @@ window_wants_tab_line (struct window *w)
            && !MINI_WINDOW_P (w)
            && !WINDOW_PSEUDO_P (w)
            && !EQ (window_tab_line_format, Qnone)
-           && !NILP (window_tab_line_format)
+           && (!NILP (window_tab_line_format)
+               || !NILP (BVAR (XBUFFER (WINDOW_BUFFER (w)), tab_line_format)))
            && (WINDOW_PIXEL_HEIGHT (w)
                > (((window_wants_mode_line (w) ? 1 : 0)
                    + (window_wants_header_line (w) ? 1 : 0)
diff --git a/src/xdisp.c b/src/xdisp.c
index eca47d26c38..9f999c79031 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -1478,7 +1478,10 @@ pos_visible_p (struct window *w, ptrdiff_t charpos, int *x, int *y,
         = window_parameter (w, Qtab_line_format);
 
       w->tab_line_height
-        = display_mode_line (w, TAB_LINE_FACE_ID, window_tab_line_format);
+        = display_mode_line (w, TAB_LINE_FACE_ID,
+                             NILP (window_tab_line_format)
+                             ? BVAR (current_buffer, tab_line_format)
+                             : window_tab_line_format);
     }
 
   if (window_wants_header_line (w))
@@ -24743,7 +24746,10 @@ display_mode_lines (struct window *w)
       Lisp_Object window_tab_line_format
         = window_parameter (w, Qtab_line_format);
 
-      display_mode_line (w, TAB_LINE_FACE_ID, window_tab_line_format);
+      display_mode_line (w, TAB_LINE_FACE_ID,
+                         NILP (window_tab_line_format)
+                         ? BVAR (current_buffer, tab_line_format)
+                         : window_tab_line_format);
       ++n;
     }