Emacs < 28.0.50 hang/freeze: racket-xp-mode, ligatures

[greghendershott]

Prior to Emacs 28.0.50, things like auto-composition-mode or ligature-mode that use composition-function-table to display ligatures can cause Emacs to freeze. This can happen when an Emacs overlay displays a string containing such a ligature. Although the problem is not limited to Racket Mode, it affects the overlays created by racket-show-pseudo-tooltip, as used by racket-xp-mode. The only known work-around -- aside from using Emacs 28.0.50 or newer -- is to change the value of racket-show-functions to something “boring” such as '(racket-show-echo-area).

-- Ligatures.

This came to light in #523 but enough time elapsed that I forgot about it by the time of #609.

So I'm making this pinned issue as a reminder for myself. Also some folks might notice it when coming to report a problem with Emacs freezing.