Subject: bug#45054: 27.1; Can get point into the middle of a run of characters with a replacing display spec

From: Zack Weinberg <[email-masked]>
Date: Sat, 5 Dec 2020 17:12:35 -0500

On Sat, Dec 5, 2020 at 4:54 PM Zack Weinberg <[email-masked]> wrote:
> As a matter of fact, for the larger goal, I think I can just ... use
> prettify-symbols-mode. :)  Thanks for the pointer, I missed that that
> had been added.

prettify-symbols-mode exhibits the same bug!

Simpler reproduction recipe:

type "ambda" in a lisp-interaction-mode buffer
place point immediately before the first "a"
M-x prettify-symbols-mode
type "l"; the word "lambda" will vanish and a λ will appear in its
place; the visible cursor will be just after the λ
type "x"; the λ will disappear and "lxambda" will appear, the visible
cursor will be just after the "x".

This might mean that the bug also affects writing ordinary text in
scripts where composite.el is necessary for correct appearance; I'm
not familiar enough with any of those to say for sure.

zw