Noam Postavsky <npostavs@gmail.com> writes:

>>> This patch explicitly fails ./configure if `--with-json' is passed but
>>> cannot be fulfilled. Which means users without the Jansson headers
>>> won't be able to compile Emacs unless explicitly disabling it with
>>> `--without-json'; I don't know if that is too extreme,
>
> This seems a bit too extreme to me, but I think giving an error on
> missing Jansson headers only if --with-json is explicitly passed would
> be okay.

I was reminded about this from some reddit posts:

https://old.reddit.com/r/emacs/comments/fwgpkd/weekly_tipstricketc_thread/fmo9d5v/

Here's a proposed patch implementing my suggestion above.