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.

5 files changed, 98 insertions, 5 deletions

diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 744fe7f69ee..017e7f9fa55 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -584,6 +584,38 @@ since it could result in memory overflow and make Emacs crash."
                        (const :tag "Grow only" :value grow-only))
               "25.1")
              (display-raw-bytes-as-hex display boolean "26.1")
+             (display-line-numbers display
+                                   (choice
+                                    (const :tag "Off (nil)" :value nil)
+                                    (const :tag "Absolute line numbers"
+                                           :value t)
+                                    (const :tag "Relative line numbers"
+                                           :value relative)
+                                    (const :tag "Visually relative line numbers"
+                                           :value visual))
+                                   "26.1")
+             (display-line-number-width display
+                                 (choice
+                                  (const :tag "Dynamically computed"
+                                         :value nil)
+                                  (integer :menu-tag "Fixed number of columns"
+                                           :value 2
+                                           :format "%v"))
+                                 "26.1")
+             (display-line-numbers-current-absolute display
+                                 (choice
+                                  (const :tag "Display actual number of current line"
+                                         :value t)
+                                  (const :tag "Display zero as number of current line"
+                                         :value nil))
+                                 "26.1")
+             (display-line-numbers-widen display
+                                 (choice
+                                  (const :tag "Disregard narrowing when calculating line numbers"
+                                         :value t)
+                                  (const :tag "Count lines from beinning of narrowed region"
+                                         :value nil))
+                                 "26.1")
              ;; xfaces.c
              (scalable-fonts-allowed display boolean "22.1")
              ;; xfns.c
diff --git a/lisp/faces.el b/lisp/faces.el
index 9a8a1344caf..c3693d16631 100644
--- a/lisp/faces.el
+++ b/lisp/faces.el
@@ -2465,6 +2465,33 @@ If you set `term-file-prefix' to nil, this function does nothing."
   :version "21.1"
   :group 'basic-faces)
 
+;; Definition stolen from linum.el.
+(defface line-number
+  '((t :inherit (shadow default)))
+  "Face for displaying line numbers.
+This face is used when `display-line-numbers' is non-nil.
+
+If you customize the font of this face, make sure it is a
+monospaced font, otherwise line numbers will not line up,
+and text lines might move horizontally as you move through
+the buffer."
+  :version "26.1"
+  :group 'basic-faces)
+
+(defface line-number-current-line
+  '((t :inherit line-number))
+  "Face for displaying the current line number.
+This face is used when `display-line-numbers' is non-nil.
+
+If you customize the font of this face, make sure it is a
+monospaced font, otherwise line numbers will not line up,
+and text lines might move horizontally as you move through
+the buffer.  Similarly, making this face's font different
+from that of the `line-number' face could produce such
+unwanted effects."
+  :version "26.1"
+  :group 'basic-faces)
+
 (defface escape-glyph
   '((((background dark)) :foreground "cyan")
     ;; See the comment in minibuffer-prompt for
diff --git a/lisp/frame.el b/lisp/frame.el
index b54df6fa160..c629a9497c0 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -2466,6 +2466,10 @@ See also `toggle-frame-maximized'."
         line-prefix
         wrap-prefix
         truncate-lines
+        display-line-numbers
+        display-line-number-width
+        display-line-numbers-current-absolute
+        display-line-numbers-widen
         bidi-paragraph-direction
         bidi-display-reordering))
 
diff --git a/lisp/menu-bar.el b/lisp/menu-bar.el
index 9c7bcffbaab..06f8c7872b7 100644
--- a/lisp/menu-bar.el
+++ b/lisp/menu-bar.el
@@ -1101,17 +1101,32 @@ The selected font will be the default on both the existing and future frames."
                     :button (:radio . (eq tool-bar-mode nil))))
       menu)))
 
+(defun toggle-display-line-numbers ()
+  (interactive)
+  (if display-line-numbers
+      (setq display-line-numbers nil)
+    (setq display-line-numbers t))
+  (force-mode-line-update))
+
 (defvar menu-bar-showhide-menu
   (let ((menu (make-sparse-keymap "Show/Hide")))
 
+    (bindings--define-key menu [display-line-numbers]
+      `(menu-item "Line Numbers for all lines"
+                  ,(lambda ()
+                     (interactive)
+                     (toggle-display-line-numbers))
+                  :help "Show the line number alongside each line"
+                  :button (:toggle . display-line-numbers)))
+
     (bindings--define-key menu [column-number-mode]
       (menu-bar-make-mm-toggle column-number-mode
-                               "Column Numbers"
+                               "Column Numbers in Mode Line"
                                "Show the current column number in the mode line"))
 
     (bindings--define-key menu [line-number-mode]
       (menu-bar-make-mm-toggle line-number-mode
-                               "Line Numbers"
+                               "Line Numbers in Mode Line"
                                "Show the current line number in the mode line"))
 
     (bindings--define-key menu [size-indication-mode]
diff --git a/lisp/simple.el b/lisp/simple.el
index 1db14a859d6..3d23fc35596 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -5942,6 +5942,10 @@ columns by which window is scrolled from left margin.
 When the `track-eol' feature is doing its job, the value is
 `most-positive-fixnum'.")
 
+(defvar last--line-number-width 0
+  "Last value of width used for displaying line numbers.
+Used internally by `line-move-visual'.")
+
 (defcustom line-move-ignore-invisible t
   "Non-nil means commands that move by lines ignore invisible newlines.
 When this option is non-nil, \\[next-line], \\[previous-line], \\[move-end-of-line], and \\[move-beginning-of-line] behave
@@ -6212,6 +6216,7 @@ not vscroll."
 If NOERROR, don't signal an error if we can't move that many lines."
   (let ((opoint (point))
         (hscroll (window-hscroll))
+        (lnum-width (line-number-display-width t))
         target-hscroll)
     ;; Check if the previous command was a line-motion command, or if
     ;; we were called from some other command.
@@ -6219,9 +6224,19 @@ If NOERROR, don't signal an error if we can't move that many lines."
              (memq last-command `(next-line previous-line ,this-command)))
         ;; If so, there's no need to reset `temporary-goal-column',
         ;; but we may need to hscroll.
-        (if (or (/= (cdr temporary-goal-column) hscroll)
-                (>  (cdr temporary-goal-column) 0))
-            (setq target-hscroll (cdr temporary-goal-column)))
+        (progn
+          (if (or (/= (cdr temporary-goal-column) hscroll)
+                  (>  (cdr temporary-goal-column) 0))
+              (setq target-hscroll (cdr temporary-goal-column)))
+          ;; Update the COLUMN part of temporary-goal-column if the
+          ;; line-number display changed its width since the last
+          ;; time.
+          (setq temporary-goal-column
+                (cons (+ (car temporary-goal-column)
+                         (/ (float (- lnum-width last--line-number-width))
+                            (frame-char-width)))
+                      (cdr temporary-goal-column)))
+          (setq last--line-number-width lnum-width))
       ;; Otherwise, we should reset `temporary-goal-column'.
       (let ((posn (posn-at-point))
             x-pos)