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.

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/emacs/display.texi b/doc/emacs/display.texi
index 61ca7e24f84..083fcdf97a6 100644
--- a/doc/emacs/display.texi
+++ b/doc/emacs/display.texi
@@ -1756,6 +1756,14 @@ zero.  This is handy if you don't care about the number of the current
 line, and want to leave more horizontal space for text in large
 buffers.
 
+@vindex display-line-numbers-widen
+In a narrowed buffer (@pxref{Narrowing}) lines are normally numbered
+starting at the beginning of the narrowing.  However, if you customize
+the variable @code{display-line-numbers-widen} to a non-@code{nil}
+value, line numbers will disregard any narrowing and will start at the
+first character of the buffer.
+
+@cindex line-number face
 The line numbers are displayed in a special face @code{line-number}.
 The current line number is displayed in a different face,
 @code{line-number-current-line}, so you can make the current line's