Fix display of indicate-empty-lines when line numbers are displayed

* src/xdisp.c (row_text_area_empty): New function.
(display_line): 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.
(display_line): Delete the argument FORCE; all callers changed.
Remove the condition for actually producing the glyphs for the
line number, as even if the number didn't change we need to
produce empty space.

1 files changed, 158 insertions, 140 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index ebf5edc4d05..136e8391d46 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -833,7 +833,7 @@ static bool cursor_row_fully_visible_p (struct window *, bool, bool);
 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 *, bool);
+static void maybe_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);
@@ -8658,7 +8658,7 @@ move_it_in_display_line_to (struct it *it,
       /* If line numbers are being displayed, produce a line number.  */
       if (!NILP (Vdisplay_line_numbers)
           && it->current_x == it->first_visible_x)
-        maybe_produce_line_number (it, true);
+        maybe_produce_line_number (it);
       /* If there's a line-/wrap-prefix, handle it.  */
       if (it->method == GET_FROM_BUFFER)
         handle_line_prefix (it);
@@ -20693,14 +20693,13 @@ find_row_edges (struct it *it, struct glyph_row *row,
 
 /* Produce the line-number glyphs for the current glyph_row.  If
    IT->glyph_row is non-NULL, populate the row with the produced
-   glyphs.  FORCE non-zero means produce the glyphs even if the line
-   number didn't change since the last time this function was called;
-   this is used by move_it_in_display_line_to.  */
+   glyphs.  */
 static void
-maybe_produce_line_number (struct it *it, bool force)
+maybe_produce_line_number (struct it *it)
 {
   ptrdiff_t last_line = it->lnum;
   ptrdiff_t start_from, bytepos;
+  ptrdiff_t this_line;
 
   /* FIXME: Maybe reuse the data in it->w->base_line_number.  */
   if (!last_line)
@@ -20717,8 +20716,6 @@ maybe_produce_line_number (struct it *it, bool force)
       start_from = BEGV_BYTE;
     }
 
-  ptrdiff_t this_line;
-
   this_line =
     last_line + display_count_lines (start_from,
                                      IT_BYTEPOS (*it), IT_CHARPOS (*it),
@@ -20726,148 +20723,168 @@ maybe_produce_line_number (struct it *it, bool force)
   eassert (this_line > 0 || (this_line == 0 && start_from == BEGV_BYTE));
   eassert (bytepos == IT_BYTEPOS (*it));
 
-  /* Produce the glyphs for the line number if needed.  */
-  if (force
-      || !last_line
-      || this_line != last_line
-      || it->continuation_lines_width > 0
-      || (EQ (Vdisplay_line_numbers, Qrelative) && PT != it->w->last_point))
+  /* Produce the glyphs for the line number.  */
+  if (this_line != last_line || !last_line)
     {
-      if (this_line != last_line || !last_line)
-        {
-          it->lnum = this_line;
-          it->lnum_bytepos = IT_BYTEPOS (*it);
-        }
+      it->lnum = this_line;
+      it->lnum_bytepos = IT_BYTEPOS (*it);
+    }
 
-      void *itdata = bidi_shelve_cache ();
-      struct it tem_it;
-      char lnum_buf[INT_STRLEN_BOUND (ptrdiff_t) + 1];
-      bool beyond_zv = IT_BYTEPOS (*it) >= ZV_BYTE ? true : false;
-      ptrdiff_t lnum_offset = -1; /* to produce 1-based line numbers */
-      /* Compute point's line number if needed.  */
-      if (EQ (Vdisplay_line_numbers, Qrelative) && !it->pt_lnum)
-        {
-          ptrdiff_t ignored;
-          if (PT_BYTE > it->lnum_bytepos)
-            it->pt_lnum =
-              this_line + display_count_lines (it->lnum_bytepos, PT_BYTE, PT,
-                                               &ignored);
-          else
-            it->pt_lnum = display_count_lines (BEGV_BYTE, PT_BYTE, PT,
-                                               &ignored);
-        }
-      /* Compute the required width if needed.  */
-      if (!it->lnum_width)
+  void *itdata = bidi_shelve_cache ();
+  struct it tem_it;
+  char lnum_buf[INT_STRLEN_BOUND (ptrdiff_t) + 1];
+  bool beyond_zv = IT_BYTEPOS (*it) >= ZV_BYTE ? true : false;
+  ptrdiff_t lnum_offset = -1; /* to produce 1-based line numbers */
+  /* Compute point's line number if needed.  */
+  if (EQ (Vdisplay_line_numbers, Qrelative) && !it->pt_lnum)
+    {
+      ptrdiff_t ignored;
+      if (PT_BYTE > it->lnum_bytepos)
+        it->pt_lnum =
+          this_line + display_count_lines (it->lnum_bytepos, PT_BYTE, PT,
+                                           &ignored);
+      else
+        it->pt_lnum = display_count_lines (BEGV_BYTE, PT_BYTE, PT,
+                                           &ignored);
+    }
+  /* Compute the required width if needed.  */
+  if (!it->lnum_width)
+    {
+      if (NATNUMP (Vdisplay_line_width))
+        it->lnum_width = XFASTINT (Vdisplay_line_width);
+      else
         {
-          if (NATNUMP (Vdisplay_line_width))
-            it->lnum_width = XFASTINT (Vdisplay_line_width);
-          else
-            {
-              /* Max line number to be displayed cannot be more than
-                 the one corresponding to the last row of the desired
-                 matrix.  */
-              ptrdiff_t max_lnum;
+          /* Max line number to be displayed cannot be more than
+             the one corresponding to the last row of the desired
+             matrix.  */
+          ptrdiff_t max_lnum;
 
-              if (EQ (Vdisplay_line_numbers, Qrelative))
-                /* We subtract one more because the current line is
-                   always zero under relative line-number display.  */
-                max_lnum = it->w->desired_matrix->nrows - 2;
-              else
-                max_lnum =
-                  this_line + it->w->desired_matrix->nrows - 1 - it->vpos;
-              it->lnum_width = log10 (max_lnum) + 1;
-            }
-          eassert (it->lnum_width > 0);
-        }
-      if (EQ (Vdisplay_line_numbers, Qrelative))
-        lnum_offset = it->pt_lnum;
-
-      /* In L2R rows we need to append the blank separator, in R2L
-         rows we need to prepend it.  But this function is usually
-         called when no display elements were produced from the
-         following line, so the paragraph direction might be unknown.
-         Therefore we cheat and add 2 blanks, one on either side.  */
-      pint2str (lnum_buf, it->lnum_width + 1, eabs (this_line - lnum_offset));
-      strcat (lnum_buf, " ");
-
-      /* Setup for producing the glyphs.  */
-      init_iterator (&tem_it, it->w, -1, -1, &scratch_glyph_row,
-                     /* FIXME: Use specialized face.  */
-                     DEFAULT_FACE_ID);
-      scratch_glyph_row.reversed_p = false;
-      scratch_glyph_row.used[TEXT_AREA] = 0;
-      SET_TEXT_POS (tem_it.position, 0, 0);
-      tem_it.face_id = merge_faces (it->f, Qline_number, 0, DEFAULT_FACE_ID);
-      tem_it.bidi_it.type = WEAK_EN;
-      /* According to UAX#9, EN goes up 2 levels in L2R paragraph and
-         1 level in R2L paragraphs.  Emulate that, assuming we are in
-         an L2R paragraph.  */
-      tem_it.bidi_it.resolved_level = 2;
-
-      /* Produce glyphs for the line number in a scratch glyph_row.  */
-      int n_glyphs_before;
-      for (const char *p = lnum_buf; *p; p++)
-        {
-          /* For continuation lines and lines after ZV, instead of a
-             line number, produce a blank prefix of the same width.  */
-          if (beyond_zv || it->continuation_lines_width > 0)
-            tem_it.c = tem_it.char_to_display = ' ';
+          if (EQ (Vdisplay_line_numbers, Qrelative))
+            /* We subtract one more because the current line is
+               always zero under relative line-number display.  */
+            max_lnum = it->w->desired_matrix->nrows - 2;
           else
-            tem_it.c = tem_it.char_to_display = *p;
-          tem_it.len = 1;
-          n_glyphs_before = scratch_glyph_row.used[TEXT_AREA];
-          /* Make sure these glyphs will have a "position" of -1.  */
-          SET_TEXT_POS (tem_it.position, -1, -1);
-          PRODUCE_GLYPHS (&tem_it);
-
-          /* Stop producing glyphs if we don't have enough space on
-             this line.  FIXME: should we refrain from producing the
-             line number at all in that case?  */
-          if (tem_it.current_x > tem_it.last_visible_x)
-            {
-              scratch_glyph_row.used[TEXT_AREA] = n_glyphs_before;
-              break;
-            }
+            max_lnum =
+              this_line + it->w->desired_matrix->nrows - 1 - it->vpos;
+          it->lnum_width = log10 (max_lnum) + 1;
+        }
+      eassert (it->lnum_width > 0);
+    }
+  if (EQ (Vdisplay_line_numbers, Qrelative))
+    lnum_offset = it->pt_lnum;
+
+  /* In L2R rows we need to append the blank separator, in R2L
+     rows we need to prepend it.  But this function is usually
+     called when no display elements were produced from the
+     following line, so the paragraph direction might be unknown.
+     Therefore we cheat and add 2 blanks, one on either side.  */
+  pint2str (lnum_buf, it->lnum_width + 1, eabs (this_line - lnum_offset));
+  strcat (lnum_buf, " ");
+
+  /* Setup for producing the glyphs.  */
+  init_iterator (&tem_it, it->w, -1, -1, &scratch_glyph_row,
+                 /* FIXME: Use specialized face.  */
+                 DEFAULT_FACE_ID);
+  scratch_glyph_row.reversed_p = false;
+  scratch_glyph_row.used[TEXT_AREA] = 0;
+  SET_TEXT_POS (tem_it.position, 0, 0);
+  tem_it.face_id = merge_faces (it->f, Qline_number, 0, DEFAULT_FACE_ID);
+  tem_it.bidi_it.type = WEAK_EN;
+  /* According to UAX#9, EN goes up 2 levels in L2R paragraph and
+     1 level in R2L paragraphs.  Emulate that, assuming we are in
+     an L2R paragraph.  */
+  tem_it.bidi_it.resolved_level = 2;
+
+  /* Produce glyphs for the line number in a scratch glyph_row.  */
+  int n_glyphs_before;
+  for (const char *p = lnum_buf; *p; p++)
+    {
+      /* For continuation lines and lines after ZV, instead of a
+         line number, produce a blank prefix of the same width.  */
+      if (beyond_zv || it->continuation_lines_width > 0)
+        tem_it.c = tem_it.char_to_display = ' ';
+      else
+        tem_it.c = tem_it.char_to_display = *p;
+      tem_it.len = 1;
+      n_glyphs_before = scratch_glyph_row.used[TEXT_AREA];
+      /* Make sure these glyphs will have a "position" of -1.  */
+      SET_TEXT_POS (tem_it.position, -1, -1);
+      PRODUCE_GLYPHS (&tem_it);
+
+      /* Stop producing glyphs if we don't have enough space on
+         this line.  FIXME: should we refrain from producing the
+         line number at all in that case?  */
+      if (tem_it.current_x > tem_it.last_visible_x)
+        {
+          scratch_glyph_row.used[TEXT_AREA] = n_glyphs_before;
+          break;
         }
+    }
 
-      /* Copy the produced glyphs into IT's glyph_row.  */
-      struct glyph *g = scratch_glyph_row.glyphs[TEXT_AREA];
-      struct glyph *e = g + scratch_glyph_row.used[TEXT_AREA];
-      struct glyph *p = it->glyph_row ? it->glyph_row->glyphs[TEXT_AREA] : NULL;
-      short *u = it->glyph_row ? &it->glyph_row->used[TEXT_AREA] : NULL;
+  /* Copy the produced glyphs into IT's glyph_row.  */
+  struct glyph *g = scratch_glyph_row.glyphs[TEXT_AREA];
+  struct glyph *e = g + scratch_glyph_row.used[TEXT_AREA];
+  struct glyph *p = it->glyph_row ? it->glyph_row->glyphs[TEXT_AREA] : NULL;
+  short *u = it->glyph_row ? &it->glyph_row->used[TEXT_AREA] : NULL;
 
-      for ( ; g < e; g++)
+  for ( ; g < e; g++)
+    {
+      it->current_x += g->pixel_width;
+      /* The following is important when this function is called
+         from move_it_in_display_line_to: HPOS is incremented only
+         when we are in the visible portion of the glyph row.  */
+      if (it->current_x > it->first_visible_x)
+        it->hpos++;
+      if (p)
         {
-          it->current_x += g->pixel_width;
-          /* The following is important when this function is called
-             from move_it_in_display_line_to: HPOS is incremented only
-             when we are in the visible portion of the glyph row.  */
-          if (it->current_x > it->first_visible_x)
-            it->hpos++;
-          if (p)
-            {
-              *p++ = *g;
-              (*u)++;
-            }
+          *p++ = *g;
+          (*u)++;
         }
+    }
 
-      /* Update IT->glyph_row's metrics.  */
-      if (it->glyph_row)
-        {
-          struct glyph_row *row = it->glyph_row;
+  /* Update IT->glyph_row's metrics.  */
+  if (it->glyph_row)
+    {
+      struct glyph_row *row = it->glyph_row;
 
-          row->ascent = max (row->ascent, tem_it.max_ascent);
-          row->height = max (row->height,
-                             tem_it.max_ascent + tem_it.max_descent);
-          row->phys_ascent = max (row->phys_ascent, tem_it.max_phys_ascent);
-          row->phys_height = max (row->phys_height,
-                                  tem_it.max_phys_ascent + tem_it.max_phys_descent);
-          row->extra_line_spacing = max (row->extra_line_spacing,
-                                         tem_it.max_extra_line_spacing);
-        }
+      row->ascent = max (row->ascent, tem_it.max_ascent);
+      row->height = max (row->height,
+                         tem_it.max_ascent + tem_it.max_descent);
+      row->phys_ascent = max (row->phys_ascent, tem_it.max_phys_ascent);
+      row->phys_height = max (row->phys_height,
+                              tem_it.max_phys_ascent + tem_it.max_phys_descent);
+      row->extra_line_spacing = max (row->extra_line_spacing,
+                                     tem_it.max_extra_line_spacing);
+    }
 
-      bidi_unshelve_cache (itdata, false);
+  bidi_unshelve_cache (itdata, false);
+}
+
+/* Return true if ROW has no glyphs except those inserted by the
+   display engine.  This is needed for indicate-empty-lines and
+   similar features when the glyph row starts with glyphs which didn't
+   come from buffer or string.  */
+static bool
+row_text_area_empty (struct glyph_row *row)
+{
+  if (!row->reversed_p)
+    {
+      for (struct glyph *g = row->glyphs[TEXT_AREA];
+           g < row->glyphs[TEXT_AREA] + row->used[TEXT_AREA];
+           g++)
+        if (!NILP (g->object) || g->charpos > 0)
+          return false;
     }
+  else
+    {
+      for (struct glyph *g = row->glyphs[TEXT_AREA] + row->used[TEXT_AREA] - 1;
+           g > row->glyphs[TEXT_AREA];
+           g--)
+        if (!NILP ((g - 1)->object) || (g - 1)->charpos > 0)
+          return false;
+    }
+
+  return true;
 }
 
 /* Construct the glyph row IT->glyph_row in the desired matrix of
@@ -20978,13 +20995,13 @@ display_line (struct it *it, int cursor_vpos)
 
       /* Produce line number, if needed.  */
       if (!NILP (Vdisplay_line_numbers))
-        maybe_produce_line_number (it, false);
+        maybe_produce_line_number (it);
     }
   else if (it->area == TEXT_AREA)
     {
       /* Line numbers should precede the line-prefix or wrap-prefix.  */
       if (!NILP (Vdisplay_line_numbers))
-        maybe_produce_line_number (it, false);
+        maybe_produce_line_number (it);
 
       /* We only do this when not calling move_it_in_display_line_to
          above, because that function calls itself handle_line_prefix.  */
@@ -21055,7 +21072,8 @@ display_line (struct it *it, int cursor_vpos)
             row->exact_window_width_line_p = true;
           else if ((append_space_for_newline (it, true)
                     && row->used[TEXT_AREA] == 1)
-                   || row->used[TEXT_AREA] == 0)
+                   || row->used[TEXT_AREA] == 0
+                   || row_text_area_empty (row))
             {
               row->glyphs[TEXT_AREA]->charpos = -1;
               row->displays_text_p = false;
@@ -21146,7 +21164,7 @@ display_line (struct it *it, int cursor_vpos)
             {
               /* Line numbers should precede the line-prefix or wrap-prefix.  */
               if (!NILP (Vdisplay_line_numbers))
-                maybe_produce_line_number (it, false);
+                maybe_produce_line_number (it);
 
               pending_handle_line_prefix = false;
               handle_line_prefix (it);