Order of fonts returned by list-fonts

Order of fonts returned by list-fonts

[Kévin Le Gouguec]

Hello Emacs,

My distro ships with Noto Color Emoji 13.1.  I have installed version 14
under ~/.local/share/fonts.  fc-match seems to prioritize the latter:

$ fc-match -f '%{fullname} %{file}\n' "Noto Color Emoji"
> Noto Color Emoji /home/peniblec/.local/share/fonts/NotoColorEmoji.ttf

Emacs, however, seems to favour the former:

(find-font (font-spec :family "Noto Color Emoji"))
> #<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
> normal normal 0 nil 100 0 ((:font-entity
> "/usr/share/fonts/truetype/NotoColorEmoji.ttf" . 0))>

(list-fonts (font-spec :family "Noto Color Emoji"))
> (#<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
>  normal normal 0 nil 100 0 ((:font-entity
>  "/usr/share/fonts/truetype/NotoColorEmoji.ttf" . 0))> 
>  #<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
>  normal normal 0 nil 100 0 ((:font-entity
>  "/home/peniblec/.local/share/fonts/NotoColorEmoji.ttf" . 0))>)

Could this be considered a bug?  I didn't dig into the code yet, beside
looking at font_list_entities (which led me to restart with
EMACS_FONT_LOG set; unfortunately font-show-log doesn't have much to say
about how font files are searched).

I don't know if my expectation (that Emacs and fc-match should agree on
how files are prioritized) is warranted; I know that Emacs relies on
Fontconfig APIs to some degree, but I'm sure there is more complexity
lurking under the hood.

I figured I'd ask around if the above makes sense to someone before
putting my spelunking hat on :)


FWIW: I originally "solved" the problem by uninstalling the version
shipped by my distro; unfortunately, today's upgrade seems to have
brought it back, presumably because another package has started
depending on it.

FWIW²: the bigger-picture fix would probably be to send a patch to the
distro to migrate to Noto Color Emoji 14; I might get to that at some
point, but I still would like to understand what's going on with Emacs.


In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.31, cairo version 1.16.0)
 of 2022-01-01 built on amdahl30
Repository revision: 1d3020908b4e4ff398c3faed9321aa4932fbaad1
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: openSUSE Tumbleweed

Configured using:
 'configure --with-cairo --with-gconf --with-xinput2'

Configured features:
ACL CAIRO DBUS FREETYPE GCONF GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ
JPEG JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
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TOOLKIT_SCROLL_BARS WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix

Re: Order of fonts returned by list-fonts

[Eli Zaretskii]

> From: Kévin Le Gouguec <kevin.legouguec@gmail.com>
> Date: Sat, 08 Jan 2022 23:59:28 +0100

This list is not the right place for discussions where you question
the correctness of low-level font-handling code in Emacs.  Please
consider moving this to emacs-devel.

> My distro ships with Noto Color Emoji 13.1.  I have installed version 14
> under ~/.local/share/fonts.  fc-match seems to prioritize the latter:
> 
> $ fc-match -f '%{fullname} %{file}\n' "Noto Color Emoji"
> > Noto Color Emoji /home/peniblec/.local/share/fonts/NotoColorEmoji.ttf
> 
> Emacs, however, seems to favour the former:
> 
> (find-font (font-spec :family "Noto Color Emoji"))
> > #<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
> > normal normal 0 nil 100 0 ((:font-entity
> > "/usr/share/fonts/truetype/NotoColorEmoji.ttf" . 0))>
> 
> (list-fonts (font-spec :family "Noto Color Emoji"))
> > (#<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
> >  normal normal 0 nil 100 0 ((:font-entity
> >  "/usr/share/fonts/truetype/NotoColorEmoji.ttf" . 0))> 
> >  #<font-entity ftcrhb GOOG Noto\ Color\ Emoji nil iso10646-1 regular
> >  normal normal 0 nil 100 0 ((:font-entity
> >  "/home/peniblec/.local/share/fonts/NotoColorEmoji.ttf" . 0))>)
> 
> Could this be considered a bug?  I didn't dig into the code yet, beside
> looking at font_list_entities (which led me to restart with
> EMACS_FONT_LOG set; unfortunately font-show-log doesn't have much to say
> about how font files are searched).

As you've probably seen, font_list_entities calls the font driver's
'list' method, and then reverses the resulting list.  That is supposed
to produce the list of fonts in the same order in which the font
driver lists the fonts.  Does that mean that Fontconfig produces
matching fonts with the best/newest/user-local one the last?

> I don't know if my expectation (that Emacs and fc-match should agree on
> how files are prioritized) is warranted; I know that Emacs relies on
> Fontconfig APIs to some degree, but I'm sure there is more complexity
> lurking under the hood.

Emacs doesn't assign any priorities to the fonts returned by the font
driver due to the order in which they are returned; it sorts the list
of fonts by other criteria.  However, after sorting (if there's more
than one candidate), Emacs will use the first matching font.  What
happens in your case can only be established by stepping through the
code with a debugger.