Partial fix of hscroll of truncated lines with line numbers

* src/xdisp.c (x_produce_glyphs, hscroll_window_tree): Adjust
hscroll calculations to line-number display.
* src/term.c (produce_glyphs): Adjust tab stop to window's
hscroll.  These two changes fix horizontal scrolling when line
numbers are displayed.  But there's still a bug: the horizontal
shift of lines that begin with a TAB is different from the rest.
* src/xdisp.c (move_it_in_display_line_to): Call
should_produce_line_number to determine whether a line number
should be produced for this screen line.

2 files changed, 31 insertions, 5 deletions

diff --git a/src/term.c b/src/term.c
index b0e7e052e51..46d8bff73cc 100644
--- a/src/term.c
+++ b/src/term.c
@@ -1587,7 +1587,7 @@ produce_glyphs (struct it *it)
       /* Adjust for line numbers.  Kludge alert: the "2" below is
          because we add 2 blanks to the actual line number.  */
       if (!NILP (Vdisplay_line_numbers))
-        absolute_x -= it->lnum_width + 2;
+        absolute_x -= it->lnum_width + 2 - it->w->hscroll;
       int next_tab_x
         = (((1 + absolute_x + it->tab_width - 1)
             / it->tab_width)
diff --git a/src/xdisp.c b/src/xdisp.c
index d35170ed43e..d0673595390 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -834,6 +834,7 @@ static bool update_menu_bar (struct frame *, bool, bool);
 static bool try_window_reusing_current_matrix (struct window *);
 static int try_window_id (struct window *);
 static void maybe_produce_line_number (struct it *);
+static bool should_produce_line_number (struct it *);
 static bool display_line (struct it *, int);
 static int display_mode_lines (struct window *);
 static int display_mode_line (struct window *, enum face_id, Lisp_Object);
@@ -8656,7 +8657,7 @@ move_it_in_display_line_to (struct it *it,
   if (it->hpos == 0)
     {
       /* If line numbers are being displayed, produce a line number.  */
-      if (!NILP (Vdisplay_line_numbers)
+      if (should_produce_line_number (it)
           && it->current_x == it->first_visible_x)
         maybe_produce_line_number (it);
       /* If there's a line-/wrap-prefix, handle it.  */
@@ -13068,6 +13069,30 @@ hscroll_window_tree (Lisp_Object window)
             }
           bool row_r2l_p = cursor_row->reversed_p;
           bool hscl = hscrolling_current_line_p (w);
+          int x_offset = 0;
+          struct glyph *g;
+          if (!row_r2l_p)
+            {
+              for (g = cursor_row->glyphs[TEXT_AREA];
+                   g < cursor_row->glyphs[TEXT_AREA] + cursor_row->used[TEXT_AREA];
+                   g++)
+                {
+                  if (!(NILP (g->object) && g->charpos < 0))
+                    break;
+                  x_offset += g->pixel_width;
+                }
+            }
+          else
+            {
+              for (g = cursor_row->glyphs[TEXT_AREA] + cursor_row->used[TEXT_AREA];
+                   g > cursor_row->glyphs[TEXT_AREA];
+                   g--)
+                {
+                  if (!(NILP ((g - 1)->object) && (g - 1)->charpos < 0))
+                    break;
+                  x_offset += (g - 1)->pixel_width;
+                }
+            }
 
           text_area_width = window_box_width (w, TEXT_AREA);
 
@@ -13100,7 +13125,7 @@ hscroll_window_tree (Lisp_Object window)
                  inside the left margin and the window is already
                  hscrolled.  */
               && ((!row_r2l_p
-                   && ((w->hscroll && w->cursor.x <= h_margin)
+                   && ((w->hscroll && w->cursor.x <= h_margin + x_offset)
                        || (cursor_row->enabled_p
                            && cursor_row->truncated_on_right_p
                            && (w->cursor.x >= text_area_width - h_margin))))
@@ -13118,7 +13143,8 @@ hscroll_window_tree (Lisp_Object window)
                            && cursor_row->truncated_on_right_p
                            && w->cursor.x <= h_margin)
                           || (w->hscroll
-                              && (w->cursor.x >= text_area_width - h_margin))))
+                              && (w->cursor.x >= (text_area_width - h_margin
+                                                  - x_offset)))))
                   /* This last condition is needed when moving
                      vertically from an hscrolled line to a short line
                      that doesn't need to be hscrolled.  If we omit
@@ -27898,7 +27924,7 @@ x_produce_glyphs (struct it *it)
               /* Adjust for line numbers.  Kludge alert: the "2" below
                  is because we add 2 blanks to the actual line number.  */
               if (!NILP (Vdisplay_line_numbers))
-                x -= (it->lnum_width + 2) * font->space_width;
+                x -= (it->lnum_width + 2 - it->w->hscroll) * font->space_width;
               int next_tab_x = ((1 + x + tab_width - 1) / tab_width) * tab_width;
 
               /* If the distance from the current position to the next tab