> > User customization could be accommodated by something like the below (naive) patch. We define
> > fill-column-indicator face to have unspecified background; when displaying the indicator we merge the
> > indicator face into the current it->face_id (the same face used for the stretch glyph preceding the indicator).
>
> What about the case there's no stretch, i.e. the indicator directly
> follows the last character of the line?

Apologies for my poor phrasing, but I think you might misunderstand the intent. I meant that we use the background that is in effect before we draw anything related to the indicator, not that we take the face *from* the stretch glyph.

I did miss that the indicator is also drawn in append_space_for_newline. Revised patch below.

diff --git a/lisp/faces.el b/lisp/faces.el

index b933279064..207b627f25 100644

--- a/lisp/faces.el

+++ b/lisp/faces.el

@@ -2502,7 +2502,9 @@ line-number-current-line

;; Definition stolen from display-line-numbers.

(defface fill-column-indicator

- '((t :inherit (shadow default)))

+ '((t :inherit shadow :weight normal :slant normal

+ :underline nil :overline nil :strike-through nil

+ :box nil :invert-video nil :stipple nil))

"Face for displaying fill column indicator.

This face is used when `display-fill-column-indicator-mode' is

non-nil."

diff --git a/src/xdisp.c b/src/xdisp.c

index 1782748144..61ea050b4a 100644

--- a/src/xdisp.c

+++ b/src/xdisp.c

@@ -20201,7 +20201,7 @@ append_space_for_newline (struct it *it, bool default_face_p)

XFIXNAT (Vdisplay_fill_column_indicator_character);

it->face_id =

merge_faces (it->w, Qfill_column_indicator,

- 0, DEFAULT_FACE_ID);

+ 0, saved_face_id);

face = FACE_FROM_ID(it->f, it->face_id);

goto produce_glyphs;

}

@@ -20494,7 +20494,7 @@ extend_face_to_end_of_line (struct it *it)

XFIXNAT (Vdisplay_fill_column_indicator_character);

it->face_id =

merge_faces (it->w, Qfill_column_indicator,

- 0, DEFAULT_FACE_ID);

+ 0, saved_face_id);

PRODUCE_GLYPHS (it);

}

@@ -20658,7 +20658,7 @@ extend_face_to_end_of_line (struct it *it)

{

const int saved_face = it->face_id;

it->face_id =

- merge_faces (it->w, Qfill_column_indicator, 0, DEFAULT_FACE_ID);

+ merge_faces (it->w, Qfill_column_indicator, 0, saved_face);

it->c = it->char_to_display =

XFIXNAT (Vdisplay_fill_column_indicator_character);

PRODUCE_GLYPHS (it);