Kévin Le Gouguec <kevin.legouguec@gmail.com> writes:

> Hello,
>
> This is sort of a garbage-in, garbage-out situation, so I'll just let
> the reproducer speak for itself:
>
> $ emacs -Q
> M-! ./nosuchcommand C-b TAB
>
> - In Emacs 27.1, this simply says "[No match]".
> - In Emacs 28.0.60, this errors out:
>
>> completion--some: Args out of range: "./nosuchcomma", 0, 14
>
> I'm attaching the backtrace obtained with M-x toggle-debug-on-error.
>
> I'm not on the most ideal setup for compiling ATM, so I apologize for
> not bisecting this (and for not trying with 27.2; Debian stable only has
> 27.1); I'll get to it eventually if no-one beats me.

Alright, if I didn't botch the bisection, then we're looking at
2021-04-23 "Fix small bug in 'completion-table-subvert'." (3806d2168b).
Bisection session attached, FWIW.