* etc/NEWS: Add 'tab-bar-mode' and 'global-tab-line-mode'.
* etc/TODO: Remove tab-related items.
* lisp/cus-start.el: Add tab-bar-mode, tab-bar-max-label-size.
* lisp/frame.el (frame-notice-user-settings): handle tab-bar-lines.
* lisp/loadup.el: Load "tab-bar".
* lisp/menu-bar.el (menu-bar-options-save): Add tab-bar-mode.
(menu-bar-showhide-menu): Define showhide-tab-bar.
* lisp/startup.el (tab-bar-images-pixel-height): New defconst.
(command-line): Reset tab-bar-mode.
(x-apply-session-resources): Add "tabBar", "TabBar".
* lisp/subr.el (read-key): Add tab-bar.
* lisp/tab-bar.el: New file.
* lisp/tab-line.el: New file.
* lisp/window.el (window--dump-frame): Add tab-bar-height.
* src/dispextern.h (enum window_part): Add ON_TAB_LINE.
(struct glyph_matrix): Add tab_line_p.
(struct glyph_row): Add tab_line_p.
(MATRIX_TAB_LINE_ROW): New macro.
(MATRIX_FIRST_TEXT_ROW): Handle more mode lines.
(MR_PARTIALLY_VISIBLE_AT_TOP): Add WINDOW_TAB_LINE_HEIGHT.
(MATRIX_TAB_LINE_HEIGHT, CURRENT_TAB_LINE_HEIGHT)
(DESIRED_TAB_LINE_HEIGHT): New macros.
(enum face_id): Add TAB_BAR_FACE_ID and TAB_LINE_FACE_ID.
(struct it): Add tab_line_p.
(tab_bar_item_idx, tab_bar_item_image): New enums.
(DEFAULT_TAB_BAR_LABEL_SIZE, DEFAULT_TAB_BAR_BUTTON_MARGIN)
(DEFAULT_TAB_BAR_BUTTON_RELIEF, DEFAULT_TAB_BAR_IMAGE_HEIGHT):
New constants.
* src/dispnew.c (adjust_glyph_matrix): Use window_wants_tab_line.
(shift_glyph_matrix): Add WINDOW_TAB_LINE_HEIGHT.
(clear_current_matrices, clear_desired_matrices):
Call clear_glyph_matrix on tab_bar_window.
(blank_row): Add WINDOW_TAB_LINE_HEIGHT.
(required_matrix_height): Change 2 to 3.
(fake_current_matrices): Reset tab_line_p.
(adjust_frame_glyphs_for_window_redisplay): Handle tab_bar_window.
Add FRAME_TAB_BAR_HEIGHT and FRAME_TAB_BAR_LINES.
(free_glyphs): Handle tab_bar_window.
(update_frame): Handle tab_bar_window.
(update_window): Handle row->tab_line_p.
(scrolling_window): Change arg type from bool to int.
Change header_line_p to tab_line_p.
(buffer_posn_from_coords): Add window_wants_tab_line.
(mode_line_string): Use MATRIX_TAB_LINE_ROW for part ON_TAB_LINE.
* src/frame.c (frame_default_tab_bar_height): New internal variable.
(adjust_frame_size): Handle tab_bar_window.
(make_frame): Reset tab_bar_redisplayed, tab_bar_resized and
last_tab_bar_item.
(Ftab_bar_pixel_width): New function.
(frame_parms): Add tab-bar-lines.
(gui_figure_window_size): Add new arg tabbar_p.
(syms_of_frame): Add Qtab_bar_size, Qupdate_frame_tab_bar,
Qfree_frame_tab_bar, Qtab_bar_lines, Stab_bar_pixel_width.
Add Qtab_bar_lines to frame_inhibit_implied_resize.
(tab-bar-mode): New variable.
* src/frame.h (GCALIGNED_STRUCT): Add tab_bar_window,
desired_tab_bar_string, current_tab_bar_string.
(GCALIGNED_STRUCT): Add tab_bar_items, last_tab_bar_item,
minimize_tab_bar_window_p, tab_bar_redisplayed, tab_bar_resized,
tab_bar_lines, tab_bar_height, n_tab_bar_rows, n_tab_bar_items.
(fset_tab_bar_items, fset_tab_bar_window)
(fset_current_tab_bar_string, fset_desired_tab_bar_string):
New inlines.
(FRAME_TAB_BAR_LINES, FRAME_TAB_BAR_HEIGHT): New macros.
(FRAME_TOP_MARGIN, FRAME_TOP_MARGIN_HEIGHT):
Use FRAME_TAB_BAR_LINES.
* src/fringe.c (draw_fringe_bitmap_1, update_window_fringes):
Add WINDOW_TAB_LINE_HEIGHT.
* src/gtkutil.c (xg_frame_set_char_size): Add FRAME_TABBAR_WIDTH.
(x_wm_set_size_hint): Add FRAME_TABBAR_WIDTH.
* src/keyboard.c (read_char): Handle Qtab_bar.
(kbd_buffer_get_event): Handle TAB_BAR_EVENT.
(make_lispy_position): Add WINDOW_TAB_LINE_HEIGHT.
Handle TAB_BAR_EVENT.
(tab_bar_items_vector, tab_bar_item_properties, ntab_bar_items):
New internal variables.
(tab_bar_items, process_tab_bar_item, set_prop_tab_bar)
(parse_tab_bar_item, init_tab_bar_items, append_tab_bar_item):
New functions.
(read_char_x_menu_prompt, read_key_sequence): Handle Qtab_bar.
(tab-bar-separator-image-expression): New variable.
* src/keymap.c (syms_of_keymap): Add Qtab_bar and Qtab_line.
* src/menu.c (x_popup_menu_1, Fx_popup_dialog): Handle Qtab_bar.
* src/termhooks.h (enum event_kind): Add TAB_BAR_EVENT.
(GCALIGNED_STRUCT): Add change_tab_bar_height_hook.
* src/w32fns.c (w32_frame_parm_handlers): Add w32_set_tab_bar_lines.
* src/w32term.c (w32_draw_window_cursor): Add WINDOW_TAB_LINE_HEIGHT.
* src/window.c (window_body_height): Add WINDOW_TAB_LINE_HEIGHT.
(Fwindow_tab_line_height): New function.
(coordinates_in_window): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(window_relative_x_coord): Add ON_TAB_LINE.
(Fcoordinates_in_window_p): Add ON_TAB_LINE.
(window_from_coordinates): Add new arg tab_bar_p.
(Fwindow_line_height): Use window_wants_tab_line with
WINDOW_TAB_LINE_HEIGHT.
(Fwindow_lines_pixel_dimensions): Add WINDOW_TAB_LINE_HEIGHT.
(make_window): Set tab_line_height to -1.
(window_wants_tab_line): New function.
(window_internal_height): Use window_wants_tab_line.
(window_scroll_pixel_based): Add WINDOW_TAB_LINE_HEIGHT.
(Frecenter): Set minimize_tab_bar_window_p to 1.
(GCALIGNED_STRUCT): Add frame_tab_bar_lines and frame_tab_bar_height.
(Fcurrent_window_configuration): Set frame_tab_bar_lines and
frame_tab_bar_height.
(set_window_scroll_bars): Add WINDOW_TAB_LINE_HEIGHT.
(syms_of_window): Add Qtab_line_format and Swindow_tab_line_height.
* src/window.h (GCALIGNED_STRUCT): Add tab_line_height.
(WINDOW_TAB_BAR_P, WINDOW_TAB_LINE_HEIGHT, WINDOW_TAB_LINE_LINES):
New macros.
(WINDOW_TOP_EDGE_Y, WINDOW_BOTTOM_EDGE_Y, WINDOW_TAB_LINE_HEIGHT):
Add WINDOW_TAB_BAR_P.
* src/xdisp.c (window_box_height): Add window_wants_tab_line with
MATRIX_TAB_LINE_ROW and CURRENT_TAB_LINE_HEIGHT.
(pos_visible_p): Use window_wants_tab_line.
Add WINDOW_TAB_LINE_HEIGHT.
(get_glyph_string_clip_rects): Add WINDOW_TAB_LINE_HEIGHT.
(get_phys_cursor_geometry): Add WINDOW_TAB_LINE_HEIGHT.
(remember_mouse_glyph): Use MATRIX_TAB_LINE_ROW for part
ON_TAB_LINE.
(init_iterator): Use MATRIX_TAB_LINE_ROW for TAB_LINE_FACE_ID.
Add WINDOW_TAB_LINE_HEIGHT. Add window_wants_tab_line.
(Fwindow_text_pixel_size): Add WINDOW_TAB_LINE_HEIGHT.
(prepare_menu_bars): Call update_tab_bar.
(update_tab_bar, build_desired_tab_bar_string)
(display_tab_bar_line, tab_bar_height, Ftab_bar_height)
(redisplay_tab_bar, tab_bar_item_info, get_tab_bar_item)
(handle_tab_bar_click, note_tab_bar_highlight): New functions.
(compute_window_start_on_continuation_line): Use window_wants_tab_line.
(try_cursor_movement): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(redisplay_window): Use window_wants_tab_line with
CURRENT_TAB_LINE_HEIGHT.
(try_window_reusing_current_matrix): Use window_wants_tab_line
with WINDOW_TAB_LINE_HEIGHT.
(Fdump_tab_bar_row): New function.
(compute_line_metrics): Add WINDOW_TAB_LINE_HEIGHT.
(display_line): Use window_wants_tab_line.
(display_mode_line): Set tab_line_p to true if face_id is
TAB_LINE_FACE_ID.
(Fformat_mode_line): Handle Qtab_line and Qtab_bar.
(gui_clear_end_of_line): Add WINDOW_TAB_LINE_HEIGHT.
(erase_phys_cursor): Use WINDOW_TAB_LINE_HEIGHT.
(show_mouse_face): Use tab_bar_window.
(note_mode_line_or_margin_highlight): Use MATRIX_TAB_LINE_ROW for
area ON_TAB_LINE.
(note_mouse_highlight): Call note_tab_bar_highlight,
(expose_frame): Handle tab_bar_window.
(syms_of_xdisp): Add Sdump_tab_bar_row and Stab_bar_height.
(auto-resize-tab-bars, auto-raise-tab-bar-buttons)
(tab-bar-border, tab-bar-button-margin, tab-bar-button-relief)
(tab-bar-max-label-size): New variables.
* src/xfaces.c (lookup_basic_face): Add TAB_LINE_FACE_ID and
TAB_BAR_FACE_ID.
(syms_of_xfaces): Define Qtab_bar and Qtab_line.
* src/xfns.c (x_set_tab_bar_lines, x_change_tab_bar_height):
New functions.
(xic_set_statusarea): Add FRAME_TABBAR_TOP_HEIGHT.
(frame_geometry): Add FRAME_TAB_BAR_HEIGHT and Qtab_bar_size.
* src/xterm.c (x_draw_image_relief): Use tab_bar_button_relief.
(x_draw_image_relief): Use TAB_BAR_FACE_ID.
(handle_one_xevent): Handle tab_bar_window.
(x_set_window_size_1): Add FRAME_TABBAR_WIDTH.
(x_create_terminal): Set change_tab_bar_height_hook.
* src/xterm.h (struct x_output): Add tabbar_top_height,
tabbar_bottom_height, tabbar_left_width, tabbar_right_width
tabbar_widget, tabbar_in_hbox, tabbar_is_packed.
(FRAME_TABBAR_TOP_HEIGHT): Add FRAME_TABBAR_TOP_HEIGHT,
FRAME_TABBAR_BOTTOM_HEIGHT, FRAME_TABBAR_HEIGHT,
FRAME_TABBAR_LEFT_WIDTH, FRAME_TABBAR_RIGHT_WIDTH,
FRAME_TABBAR_WIDTH.