bug#25552: 26.0.50; load cl unintendedly

[npostavs]

Katsumi Yamaoka <yamaoka@jpl.org> writes:

> Recipe:
>
> emacs -Q
> M-x load-library RET gnus RET

Actually this step isn't needed.

> C-h v gnus-summ SPC
> C-g
>
> Then (featurep 'cl) gets to return t.  It is because:
> ûgnus.el has autoload settings that load gnus-mh for gnus-summ*.
> ûgnus-mh.el requires mh-e.
> ûmh-e.el requires mh-compat.
> ûmh-compat.el requires mh-acros.
> ûmh-acros.el requires cl unconditionally.
> û`C-h v' seems to load things related to "gnus-summ".

It's a new feature in master:

    ** New var 'definition-prefixes' is a hash table mapping prefixes to
    the files where corresponding definitions can be found.  This can be
    used to fetch definitions that are not yet loaded, for example for
    'C-h f'.

gnus-mh.el defines some things with prefix "gnus-", so completing a
string with such a prefix loads that file.