Loading a large number of user emoji can break emoji rendering Emacs wide

[matthew-piziak]

I use the emacs-slack package with a Slack team that uses a large number of emoji. I've actually managed to throw a low-level REG_ESIZE error from regex-emacs.c because the compiled regular expression is too big for emacs.

For example, here's the backtrace for (emojify-string "❄"):

Debugger entered--Lisp error: (invalid-regexp "Regular expression too big")
  search-forward-regexp("\\(?::\\(?:\\(?:\\+11\\|0\\(?:2_\\(?:b\\(?:\\(?:lin\\|ore\\)d..." 3 t)
  #f(compiled-function (regexp) #<bytecode 0xe297d60576a0c31>)("\\(?::\\(?:\\(?:\\+11\\|0\\(?:2_\\(?:b\\(?:\\(?:lin\\|ore\\)d...")
  mapc(#f(compiled-function (regexp) #<bytecode 0xe297d60576a0c31>) ("\\(?::\\(?:\\(?:\\+11\\|0\\(?:2_\\(?:b\\(?:\\(?:lin\\|ore\\)d..." ":[[:alnum:]+_-]+:" "\\(?:#⃣\\|\\*⃣\\|0⃣\\|1⃣\\|2⃣\\|3⃣\\|4⃣\\|5⃣\\|6⃣\\|7⃣\\|8⃣\\|9..." "\\(?:#\\(?:-?)\\)\\|%\\(?:-?)\\)\\|'\\(?::\\(?:-[()D]\\|[()D..."))
  seq-do(#f(compiled-function (regexp) #<bytecode 0xe297d60576a0c31>) ("\\(?::\\(?:\\(?:\\+11\\|0\\(?:2_\\(?:b\\(?:\\(?:lin\\|ore\\)d..." ":[[:alnum:]+_-]+:" "\\(?:#⃣\\|\\*⃣\\|0⃣\\|1⃣\\|2⃣\\|3⃣\\|4⃣\\|5⃣\\|6⃣\\|7⃣\\|8⃣\\|9..." "\\(?:#\\(?:-?)\\)\\|%\\(?:-?)\\)\\|'\\(?::\\(?:-[()D]\\|[()D..."))
  emojify-display-emojis-in-region(1 3 nil)
  emojify-string(" ❄")
  eval-expression((emojify-string " ❄") nil nil 127)
  funcall-interactively(eval-expression (emojify-string " ❄") nil nil 127)
  command-execute(eval-expression)

Is there any way I can limit the number of emoji, compile down the regex, or increase the allocated regex space?

[matthew-piziak]

I see that this package already uses regexp-opt, that's good. I've created a kludge where I take only the first 2000 user emoji in emojify-set-emoji-data.