bug#39995: 28.0.50; Suboptimal error formatting for missing struct slot

[Philipp Stephani]

Am Mo., 9. März 2020 um 09:09 Uhr schrieb Philipp Stephani
<p.stephani2@gmail.com>:
>
>
> The following happens at least in Emacs 27, I haven't checked other
> versions.
>
> $ emacs -Q -batch -l backtrace -l cl-lib -l cl-macs -eval 
> '(cl-struct-slot-offset (quote backtrace-frame) (quote foobar))'
> struct %S has no slot %S: backtrace-frame, foobar
>
> This is because the error symbol `cl-struct-unknown-slot' has the
> message "struct %S has no slot %S", but the error system doesn't use the
> message as a format template.  Probably the error message should just be
> "struct has no slot" or so.

Fixed with commit 36873ef2b2.