Infinite loop triggered by extglob +(!(x))y

[andrej]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -march=x86-64 -mtune=generic -O2 -pipe -fno-plt 
-DDEFAULT_PATH_VALUE='/usr/local/sbin:/usr/local/bin:/usr/bin' 
-DSTANDARD_UTILS_PATH='/usr/bin' -DSYS_BASHRC='/etc/bash.bashrc' 
-DSYS_BASH_LOGOUT='/etc/bash.bash_logout' -DNON_INTERACTIVE_LOGIN_SHELLS 
uname output: Linux charon.podzimek.org 5.12.15-arch1-1-zen2 #1 SMP PREEMPT 
Sun, 11 Jul 2021 10:50:03 +0000 x86_64 GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.1
Patch Level: 8
Release Status: release

Description:
        An extglob like +(!(x))y causes Bash to freeze with a 100% CPU 
utilization.
        At the first glance the freeze doesn't seem to depend on the 
(non-)existence of matching paths.

Repeat-By:
        echo +(!(x))y  # This freezes!
        echo y+(!(x))  # Yet this does *not* freeze.
        echo +(!(x))*  # And this does *not* freeze.
        echo *+(!(x))  # And this does *not* freeze.