Start display-fill-column-indicator-mode.

1 files changed, 170 insertions, 9 deletions

diff --git a/src/xdisp.c b/src/xdisp.c
index 3bdb8ea1b0f..f1609664277 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -20152,15 +20152,49 @@ append_space_for_newline (struct it *it, bool default_face_p)
           it->what = IT_CHARACTER;
           memset (&it->position, 0, sizeof it->position);
           it->object = Qnil;
-          it->c = it->char_to_display = ' ';
           it->len = 1;
 
+          int local_default_face_id =
+            lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID);
+          struct face* default_face =
+            FACE_FROM_ID_OR_NULL (it->f, local_default_face_id);
+
+          /* Corner case for when display-fill-column-indicator-mode
+             is active and the extra character should be added in the
+             same place than the line */
+          if (!NILP (Vdisplay_fill_column_indicator)
+              && (it->w->pseudo_window_p == 0)
+              && FIXNATP (Vdisplay_fill_column_indicator_column)
+              && FIXNATP (Vdisplay_fill_column_indicator_character))
+            {
+               struct font *font =
+                 default_face->font ? default_face->font : FRAME_FONT (it->f);
+               const int char_width =
+                 font->average_width ? font->average_width : font->space_width;
+               const int fill_column =
+                 XFIXNAT (Vdisplay_fill_column_indicator_column);
+               const int column_x =
+                 char_width * fill_column + it->lnum_pixel_width;
+
+               if (it->current_x == column_x)
+                 {
+                   it->c = it->char_to_display =
+                     XFIXNAT (Vdisplay_fill_column_indicator_character);
+                   it->face_id =
+                     merge_faces (it->w, Qfill_column_face, 0, DEFAULT_FACE_ID);
+                   face = FACE_FROM_ID(it->f, it->face_id);
+                   goto produce_glyphs;
+                 }
+            }
+
+          it->c = it->char_to_display = ' ';
           /* If the default face was remapped, be sure to use the
              remapped face for the appended newline.  */
           if (default_face_p)
-            it->face_id = lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID);
+            it->face_id = local_default_face_id;
           else if (it->face_before_selective_p)
             it->face_id = it->saved_face_id;
+
           face = FACE_FROM_ID (it->f, it->face_id);
           it->face_id = FACE_FOR_CHAR (it->f, face, 0, -1, Qnil);
           /* In R2L rows, we will prepend a stretch glyph that will
@@ -20169,11 +20203,12 @@ append_space_for_newline (struct it *it, bool default_face_p)
              set.  */
           if (it->glyph_row->reversed_p
               /* But if the appended newline glyph goes all the way to
-                 the end of the row, there will be no stretch glyph,
-                 so leave the box flag set.  */
+              the end of the row, there will be no stretch glyph,
+              so leave the box flag set.  */
               && saved_x + FRAME_COLUMN_WIDTH (it->f) < it->last_visible_x)
             it->end_of_box_run_p = false;
 
+        produce_glyphs:
           PRODUCE_GLYPHS (it);
 
 #ifdef HAVE_WINDOW_SYSTEM
@@ -20322,7 +20357,8 @@ extend_face_to_end_of_line (struct it *it)
 #ifdef HAVE_WINDOW_SYSTEM
       && !face->stipple
 #endif
-      && !it->glyph_row->reversed_p)
+      && !it->glyph_row->reversed_p
+      && NILP (Vdisplay_fill_column_indicator))
     return;
 
   /* Set the glyph row flag indicating that the face of the last glyph
@@ -20374,8 +20410,81 @@ extend_face_to_end_of_line (struct it *it)
                 default_face->id;
               it->glyph_row->used[RIGHT_MARGIN_AREA] = 1;
             }
+
+          /* Display fill column indicator if not in modeline or
+             toolbar and display fill column indicator mode is
+             active */
+          if (!NILP (Vdisplay_fill_column_indicator)
+              && (it->w->pseudo_window_p == 0)
+              && FIXNATP (Vdisplay_fill_column_indicator_column)
+              && FIXNATP (Vdisplay_fill_column_indicator_character))
+            {
+              struct font *font =
+                default_face->font ? default_face->font : FRAME_FONT (f);
+              const int char_width =
+                font->average_width ? font->average_width : font->space_width;
+
+              const int fill_column =
+                XFIXNAT (Vdisplay_fill_column_indicator_column);
+
+              const int column_x = char_width * fill_column + it->lnum_pixel_width;
+
+              if ((it->current_x <= column_x)
+                  && (column_x <= it->last_visible_x))
+                {
+                  const char saved_char = it->char_to_display;
+                  const struct text_pos saved_pos = it->position;
+                  const bool saved_avoid_cursor = it->avoid_cursor_p;
+                  const int saved_face_id = it->face_id;
+                  const bool saved_box_start = it->start_of_box_run_p;
+                  Lisp_Object save_object = it->object;
+
+                  /* The stretch width needs to considet the latter added glyph */
+                  const int stretch_width = column_x - it->current_x - char_width;
+
+                  memset (&it->position, 0, sizeof it->position);
+                  it->avoid_cursor_p = true;
+                  it->object = Qnil;
+
+                  /* Only generate a stretch glysph if there is distance between
+                     current_x and and the indicator position */
+                  if (stretch_width > 0)
+                {
+                  int stretch_ascent = (((it->ascent + it->descent)
+                                     * FONT_BASE (font)) / FONT_HEIGHT (font));
+                      append_stretch_glyph (it, Qnil, stretch_width,
+                                         it->ascent + it->descent, stretch_ascent);
+                }
+
+                  /* Generate the glysph indicator only if append_space_for_newline
+                     didn't already. */
+                  if (it->current_x < column_x)
+                    {
+                  it->char_to_display =
+                        XFIXNAT (Vdisplay_fill_column_indicator_character);
+                      it->face_id =
+                        merge_faces (it->w, Qfill_column_face, 0, DEFAULT_FACE_ID);
+                      PRODUCE_GLYPHS (it);
+                    }
+
+                  /* Restore the face after the indicator was generated */
+                  it->face_id = saved_face_id;
+
+                  /* If there is space after the indicator generate an extra
+                     empty glysph to restore the face. */
+                  it->char_to_display = ' ';
+                  PRODUCE_GLYPHS (it);
+
+                  it->char_to_display = saved_char;
+                  it->position = saved_pos;
+                  it->avoid_cursor_p = saved_avoid_cursor;
+                  it->start_of_box_run_p = saved_box_start;
+                  it->object = save_object;
+                }
+            }
         }
 #ifdef HAVE_WINDOW_SYSTEM
+
       if (it->glyph_row->reversed_p)
         {
           /* Prepend a stretch glyph to the row, such that the
@@ -20495,10 +20604,37 @@ extend_face_to_end_of_line (struct it *it)
         it->face_id = default_face->id;
       else
         it->face_id = face->id;
-      PRODUCE_GLYPHS (it);
 
-      while (it->current_x <= it->last_visible_x)
-        PRODUCE_GLYPHS (it);
+      /* Display fill-column-line if mode is active */
+      if (!NILP (Vdisplay_fill_column_indicator))
+        {
+          const int fill_column_indicator_line =
+            XFIXNAT (Vdisplay_fill_column_indicator_column)
+              + it->lnum_pixel_width;
+          do
+            {
+              if (it->current_x == fill_column_indicator_line)
+                {
+                  const int saved_face = it->face_id;
+                  it->face_id =
+                    merge_faces (it->w, Qfill_column_face, 0, DEFAULT_FACE_ID);
+                  it->c = it->char_to_display =
+                    XFIXNAT (Vdisplay_fill_column_indicator_character);
+                  PRODUCE_GLYPHS (it);
+                  it->face_id = saved_face;
+                  it->c = it->char_to_display = ' ';
+                }
+              else
+                PRODUCE_GLYPHS (it);
+            } while (it->current_x <= it->last_visible_x);
+        }
+      else
+        {
+          do
+            {
+              PRODUCE_GLYPHS (it);
+            } while (it->current_x <= it->last_visible_x);
+        }
 
       if (WINDOW_RIGHT_MARGIN_WIDTH (it->w) > 0
           && (it->glyph_row->used[RIGHT_MARGIN_AREA]
@@ -20588,7 +20724,8 @@ highlight_trailing_whitespace (struct it *it)
       if (!row->reversed_p)
         {
           while (glyph >= start
-                 && glyph->type == CHAR_GLYPH
+                 && (glyph->type == CHAR_GLYPH
+                     || glyph->type == STRETCH_GLYPH)
                  && NILP (glyph->object))
             --glyph;
         }
@@ -32663,6 +32800,9 @@ be let-bound around code that needs to disable messages temporarily. */);
   /* Name of a text property which disables line-number display.  */
   DEFSYM (Qdisplay_line_numbers_disable, "display-line-numbers-disable");
 
+  /* Names of the face used to display fill column indicator character.  */
+  DEFSYM (Qfill_column_face, "fill-column-face");
+
   /* Name and number of the face used to highlight escape glyphs.  */
   DEFSYM (Qescape_glyph, "escape-glyph");
 
@@ -33235,6 +33375,27 @@ either `relative' or `visual'.  */);
   DEFSYM (Qdisplay_line_numbers_widen, "display-line-numbers-widen");
   Fmake_variable_buffer_local (Qdisplay_line_numbers_widen);
 
+  DEFVAR_LISP ("display-fill-column-indicator", Vdisplay_fill_column_indicator,
+    doc: /* Non-nil means display the fill column indicator.  */);
+  Vdisplay_fill_column_indicator = Qnil;
+  DEFSYM (Qdisplay_fill_column_indicator, "display-fill-column-indicator");
+  Fmake_variable_buffer_local (Qdisplay_fill_column_indicator);
+
+  DEFVAR_LISP ("display-fill-column-indicator-column", Vdisplay_fill_column_indicator_column,
+    doc: /* Column to draw the indicator when `display-fill-column-indicator' is non-nil.
+The default value is the variable `fill-column' if not other value is given. */);
+  Vdisplay_fill_column_indicator_column = Qnil;
+  DEFSYM (Qdisplay_fill_column_indicator_column, "display-fill-column-indicator-column");
+  Fmake_variable_buffer_local (Qdisplay_fill_column_indicator_column);
+
+  DEFVAR_LISP ("display-fill-column-indicator-character", Vdisplay_fill_column_indicator_character,
+    doc: /* Character to draw the indicator when `display-fill-column-indicator' is non-nil.
+The default is U+2502 but a good alternative is (ascii 124) if
+the font in fill-column-face does not support Unicode characters.  */);
+  Vdisplay_fill_column_indicator_character = Qnil;
+  DEFSYM (Qdisplay_fill_column_indicator_character, "display-fill-column-indicator-character");
+  Fmake_variable_buffer_local (Qdisplay_fill_column_indicator_character);
+
   DEFVAR_BOOL ("inhibit-eval-during-redisplay", inhibit_eval_during_redisplay,
     doc: /* Non-nil means don't eval Lisp during redisplay.  */);
   inhibit_eval_during_redisplay = false;