Support display of line numbers natively

This merges branch 'line-numbers'.
* src/buffer.c (disable_line_numbers_overlay_at_eob): New
function.
* src/lisp.h (disable_line_numbers_overlay_at_eob): Add prototype.
* src/dispextern.h (struct it): New members pt_lnum, lnum,
lnum_bytepos, lnum_width, and lnum_pixel_width.
* src/indent.c (line_number_display_width): New function,
refactored from line-number width calculations in vertical-motion.
(Fvertical_motion): Call line_number_display_width when the width
of line-number display is needed.
(Fline_number_display_width): New defun.
(syms_of_indent): Defsubr it.
* src/indent.c (Fvertical_motion): Help C-n/C-p estimate correctly
the width used up by line numbers by looking near the window-start
point.  If window-start is outside of the accessible portion,
temporarily widen the buffer.
* src/term.c (produce_glyphs): Adjust tab stops for the horizontal
space taken by the line-number display.
* src/xdisp.c (display_count_lines_logically)
(display_count_lines_visually, maybe_produce_line_number)
(should_produce_line_number, row_text_area_empty): New functions.
(try_window_reusing_current_matrix): Don't use this method when
display-line-numbers is in effect.
(try_window_id, try_cursor_movement): Disable these optimizations
when the line-number-current-line face is different from
line-number face and for relative line numbers.
(try_window_id, redisplay_window, try_cursor_movement): For
visual line-number display, disable the same redisplay
optimizations as for relative.
(x_produce_glyphs): Adjust tab stops for the horizontal
space taken by the line-number display.
(hscroll_window_tree): Adjust hscroll calculations to line-number
display.
(DISP_INFINITY): Renamed from INFINITY to avoid clashes with
math.h; all users changed.
(set_cursor_from_row): Fix calculation of cursor X coordinate in
R2L rows with display-produced glyphs at the beginning.
(display_line): Use should_produce_line_number to determine
whether a line number should be produced for each glyph row, and
maybe_produce_line_number to produce line numbers.
Don't display line numbers in the minibuffer and in tooltip
frames.
Call row_text_area_empty to verify that a glyph
row's text area is devoid of any glyphs that came from a buffer or
a string.  This fixes a bug with empty-lines indication
disappearing when line numbers or line-prefix are displayed.
(syms_of_xdisp) <display-line-numbers, display-line-numbers-widen>
<display-line-number-width>: New buffer-local variables.
<display-line-numbers-current-absolute>: New variable.

* lisp/cus-start.el (standard): Provide customization forms for
display-line-numbers and its sub-features.
* lisp/faces.el (line-number, line-number-current-line): New faces.
* lisp/frame.el: Add display-line-numbers, display-line-numbers-widen,
display-line-numbers-current-absolute, and
display-line-number-width to the list of variables that should
trigger redisplay of the current buffer.
* lisp/menu-bar.el (menu-bar-showhide-menu): Add menu-bar item to
turn display-line-numbers on and off.
(toggle-display-line-numbers): New function.
* lisp/simple.el (last--line-number-width): New internal variable.
(line-move-visual): Use it to adjust temporary-goal-column when
line-number display changes its width.

* doc/emacs/basic.texi (Position Info): Add cross-reference to
"Display Custom", for line-number display.
* doc/emacs/custom.texi (Init Rebinding):
* doc/emacs/modes.texi (Minor Modes): Remove references to
linum-mode.
* doc/emacs/display.texi (Display Custom): Describe the
line-number display.
* doc/lispref/display.texi (Size of Displayed Text): Document
line-number-display-width.

* etc/NEWS: Document display-line-numbers and its customizations.

1 files changed, 51 insertions, 1 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 13805ce0da7..15c3009ae10 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -405,10 +405,60 @@ display of raw bytes from octal to hex.
 ** You can now provide explicit field numbers in format specifiers.
 For example, '(format "%2$s %1$s" "X" "Y")' produces "Y X".
 
-+++
 ** 'comment-indent-function' values may now return a cons to specify a
 range of indentation.
 
++++
+** Emacs now supports optional display of line numbers in the buffer.
+This is similar to what linum-mode provides, but much faster and
+doesn't usurp the display margin for the line numbers.  Customize the
+buffer-local variable 'display-line-numbers' to activate this optional
+display.  If set to t, Emacs will display the number of each line
+before the line.  If set to 'relative', Emacs will display the line
+number relative to the line showing point, with that line's number
+displayed as absolute.  If set to 'visual', Emacs will display a
+relative number for every screen line, i.e. it will count screen lines
+rather than buffer lines.  The default is nil, which doesn't display
+the line numbers.
+
+In 'relative' and 'visual' modes, the variable
+'display-line-numbers-current-absolute' controls what number is
+displayed for the line showing point.  By default, this variable's
+value is t, which means display the absolute line number for the line
+showing point.  Customizing this variable to a nil value will cause
+Emacs to show zero instead, which preserves horizontal space of the
+window in large buffers.
+
+Line numbers are not displayed at all in minibuffer windows and in
+tooltips, as they are not useful there.
+
+The new face 'line-number' is used to display the line numbers.  The
+new face 'line-number-current-line' can be customized to display the
+current line's number differently from all the other line numbers; by
+default these two faces are identical.
+
+You can also customize the new variable 'display-line-number-width' to
+specify a fixed minimal with of the area allocated to line-number
+display.  The default is nil, meaning that Emacs will dynamically
+calculate the area width, enlarging or shrinking it as needed.
+Setting it to a non-negative integer specifies that as the minimal
+width; selecting a value  that is large enough to display all line
+numbers in a buffer will then keep the line-number display area of
+constant width at all times, if that is desired.
+
+Lisp programs can disable line-number display for a particular screen
+line by putting the 'display-line-numbers-disable' text property or
+overlay property on the first character of that screen line.  This is
+intended for add-on packages that need a finer control of the display.
+
+Lisp programs that need to know how much screen estate is used up for
+line-number display in a window can use the new function
+'line-number-display-width'.
+
+Linum mode and all similar packages are henceforth becoming obsolete.
+Users and developers are encouraged to switch to this new feature
+instead.
+
 
 * Editing Changes in Emacs 26.1