On Thu, 04 Mar 2021 19:16:29 +0100 Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Mattias Engdegård <mattiase@acm.org> writes:
>
>> `rx-define` is new in Emacs 27, and the patch was apparently intended
>> to work with 26.1.
>
> I was fooled by the version guesser:
>
> ---
> rx-define is an autoloaded Lisp macro in ‘rx.el’.
>
> (rx-define NAME [(ARGS...)] RX)
>
>   Probably introduced at or before Emacs version 24.
> ---
>
> I wonder where that is coming from...  rx-define isn't mentioned in
> NEWS.24?

It's because help-fns--first-release finds this line in NEWS.27:

** Further functions and variables obsolete since Emacs 24 have been removed:

On the assumption that in the NEWS files a first-level outline header
contains the relevant reference to the first release and doesn't contain
a reference to an earlier release, the following patch fixes the bug: