GNU bug report logs - #39390
28.0.50; prettify-symbols-mode confuses display when start/end faces are different

Previous Next

Full log

Message #59 received at 39390 <at> debbugs.gnu.org (full text, mbox):

From: Tassilo Horn <tsdh <at> gnu.org>
To: Raphael 'kena' Poss <knz <at> thaumogen.net>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 39390 <at> debbugs.gnu.org
Subject: Re: bug#39390: 28.0.50; prettify-symbols-mode confuses display when
 start/end faces are different
Date: Mon, 17 Feb 2020 12:17:19 +0100

Raphael 'kena' Poss <knz <at> thaumogen.net> writes:

> https://asciinema.org/a/3nOh1zCJYHOeQ4uXk0rQ9akv8

No doubt you get strange display effects in your example, but I don't
know if that can be considered a bug given that your configuration is
illegal anyway.  See the docs of prettify-symbols-alist:

,----[ C-h v prettify-symbols-alist RET ]
| prettify-symbols-alist is a variable defined in ‘prog-mode.el’.
| Its value is nil
| 
|   Automatically becomes buffer-local when set.
| 
| Documentation:
| Alist of symbol prettifications.
| Each element looks like (SYMBOL . CHARACTER), where the symbol
| matching SYMBOL (a string, not a regexp) will be shown as
| CHARACTER instead.
| 
| CHARACTER can be a character, or it can be a list or vector, in
| which case it will be used to compose the new symbol as per the
| third argument of ‘compose-region’.
`----

I.e., the second element of each pair in `prettify-symbols-alist' is a
simple replacement glyph only in the case were it is a character.  You
provide strings instead, so the outcome can only be determined by
checking what `compose-region' does with that input.

AFAIK, `prettify-symbols-mode's intent is to replace programming
language symbols (like "lambda" in Lisp or >>= in Haskell) with a fancy
single Unicode character each, not to replace any text with any
arbitrary other text.  (Also, using multi-word matches like "setq abc"
or unbalanced expressions like "(push" is definitely asking for
trouble.)

Bye,
Tassilo

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.