bug#44341: 27.1; define-minor-mode generates inaccurate docstring

[Philipp Stephani]

Am So., 1. Nov. 2020 um 16:30 Uhr schrieb Stefan Monnier
<monnier@iro.umontreal.ca>:

> >     disable ; Should disable (as a random symbol)
> >     disable ; Again
> >     "What?" ; Same.
>
> These should be considered as errors.  Whether we catch them and signal
> an error or silently do something else is not particular important
> to me.

We should definitely signal an error here. A form such as (my-mode
'enable) actually disabling the mode is very confusing. The mode
function needs to check for the various cases anyway, it might as well
use `cond' and signal an error in the non-matching case.