Implement line numbers that disregard narrowing

* src/xdisp.c (display_count_lines_logically): New function,
counts line numbers disregarding narrowing.  Suggested by Andy
Moreton <andrewjmoreton@gmail.com>.
(maybe_produce_line_number): Call display_count_lines_logically
instead of display_count_lines.  Adapt BEGV, ZV, etc. to
display-line-numbers-widen.
(syms_of_xdisp) <display-line-numbers-widen>: New buffer-local
variable.

* lisp/cus-start.el (standard): Provide a customization form for
display-line-numbers-widen.
* lisp/frame.el: Add 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.

* doc/emacs/display.texi (Display Custom): Document
display-line-numbers-widen.

2 files changed, 11 insertions, 1 deletions

diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index a89d5dff0cd..017e7f9fa55 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -608,7 +608,14 @@ since it could result in memory overflow and make Emacs crash."
                                          :value t)
                                   (const :tag "Display zero as number of current line"
                                          :value nil))
-                                  "26.1")
+                                 "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/frame.el b/lisp/frame.el
index 8f51afa2a9a..f3e59edb2f5 100644
--- a/lisp/frame.el
+++ b/lisp/frame.el
@@ -2435,6 +2435,9 @@ See also `toggle-frame-maximized'."
         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))