bug#40733: 28.0.50; Emacs locks up on paste (yank) of unicode characters

[Robert Pluim]

>>>>> On Mon, 20 Apr 2020 06:05:58 -0500, Will Bush <will.g.bush@gmail.com> 
>>>>> said:

    Will> Emacs freezes using 100% CPU after pasting the following into a 
scratch
    Will> buffer:

    Will> (╯°□°)╯ ︵ ┻━┻

Does it require all of them, or is there a specific character in that
sequence that triggers it?

Any chance of running emacs using gdb so we can see where the CPU
usage is?

    Will> I verified using `emacs -Q` and pasting it `C-y`. I installed Emacs 
26,
    Will> tried the same thing, and didn't run into an issue.

    Will> Note I am assuming the above is unicode. I did not check.

Yes, it is.

    Will> In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 
3.24.14,
    Will> cairo version 1.16.0)

Iʼm confused, this is GNU/Linux, but:

    Will> Configured using:
    Will>  'configure
    Will>  
--prefix=/nix/store/2142cl219v49czkkrrddh3jy3415nax0-emacs-git-20200420.0
    Will>  --disable-build-details --with-modules --with-x-toolkit=gtk3 
--with-xft
    Will>  CFLAGS=-DMAC_OS_X_VERSION_MAX_ALLOWED=101200'

macOS defines?

If you could paste the characters one by one to see if itʼs a specific
one that causes this, and do 'C-u C-x =' on them so we know what font
is being used, that would help.

FWIW I donʼt see this on GNU/Linux. Itʼs possible itʼs font dependent.

Robert