Re: Native line numbers landed on master

[Juanma Barranquero <lekktu@gmail.com>]

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Incomplete patch (no docs other than the variable's docstring, etc.)

AFAICS, it implements the suggested behavior with respect to
relative/visual and narrowing.

Please check that it does what you (y'all ;-) expected.

TIA

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From 6f56e329cdf26cd5d0dab9fc9f8fa8835851275d Mon Sep 17 00:00:00 2001
From: Juanma Barranquero <lekktu@gmail.com>
Date: Sat, 5 Oct 2019 08:20:23 +0200
Subject: [PATCH] First shot at `display-line-numbers-offset'

---
 src/xdisp.c | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index 9d1fdecaff..334313bd45 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -22409,10 +22409,22 @@ maybe_produce_line_number (struct it *it)
   ptrdiff_t start_from, bytepos;
   ptrdiff_t this_line;
   bool first_time = false;
-  ptrdiff_t beg_byte = display_line_numbers_widen ? BEG_BYTE : BEGV_BYTE;
-  ptrdiff_t z_byte = display_line_numbers_widen ? Z_BYTE : ZV_BYTE;
+  ptrdiff_t beg_byte;
+  ptrdiff_t z_byte;
+  bool line_numbers_wide;
   void *itdata = bidi_shelve_cache ();
 
+  if (display_line_numbers_offset
+      && !display_line_numbers_widen
+      && !EQ (Vdisplay_line_numbers, Qvisual)
+      && !EQ (Vdisplay_line_numbers, Qrelative))
+    line_numbers_wide = true;
+  else
+    line_numbers_wide = display_line_numbers_widen;
+
+  beg_byte = line_numbers_wide ? BEG_BYTE : BEGV_BYTE;
+  z_byte = line_numbers_wide ? Z_BYTE : ZV_BYTE;
+
   if (EQ (Vdisplay_line_numbers, Qvisual))
     this_line = display_count_lines_visually (it);
   else
@@ -22427,7 +22439,7 @@ maybe_produce_line_number (struct it *it)
 		 numbers, so we cannot use its data if the user wants
 		 line numbers that disregard narrowing, or if the
 		 buffer's narrowing has just changed.  */
-	      && !(display_line_numbers_widen
+	      && !(line_numbers_wide
 		   && (BEG_BYTE != BEGV_BYTE || Z_BYTE != ZV_BYTE))
 	      && !current_buffer->clip_changed)
 	    {
@@ -22517,6 +22529,8 @@ maybe_produce_line_number (struct it *it)
     lnum_offset = it->pt_lnum;
   else if (EQ (Vdisplay_line_numbers, Qvisual))
     lnum_offset = 0;
+  else if (display_line_numbers_offset)
+    lnum_offset -= display_line_numbers_offset;
 
   /* Under 'relative', display the absolute line number for the
      current line, unless the user requests otherwise.  */
@@ -34619,6 +34633,15 @@ syms_of_xdisp (void)
   DEFSYM (Qdisplay_line_numbers_widen, "display-line-numbers-widen");
   Fmake_variable_buffer_local (Qdisplay_line_numbers_widen);
 
+  DEFVAR_INT ("display-line-numbers-offset", display_line_numbers_offset,
+    doc: /* A signed integer added to the current line number.
+This only has effect with absolute line numbers. Also, note that
+when this variable is non-zero, narrowing is disregarded as if
+`display-line-number-widen' were non-nil.  */);
+  display_line_numbers_offset = 0;
+  DEFSYM (Qdisplay_line_numbers_offset, "display-line-numbers-offset");
+  Fmake_variable_buffer_local (Qdisplay_line_numbers_offset);
+
   DEFVAR_BOOL ("display-fill-column-indicator", Vdisplay_fill_column_indicator,
     doc: /* Non-nil means display the fill column indicator.  */);
   Vdisplay_fill_column_indicator = false;
-- 
2.23.0.windows.1