[PATCH] extensions: formalize concept of experimental extensions

[Jun Wu]

Excerpts from Gregory Szorc's message of 2017-03-12 19:48:35 -0700:
> 
> > On Mar 12, 2017, at 19:28, Jun Wu <quark at fb.com> wrote:
> > 
> > If I read it correctly, this means an "experimental" extension will end up
> > with:
> > 
> >             | ext=        | ext=!beta
> >  ----------------------------------------
> >  old client | load        | do not load
> >  new client | do not load | load
> > 
> > I think that's confusing.
> > 
> > I think we can have an "[extensions:experimental]" section instead, which
> > will only be processed by new mercurial.
> 
> For extensions distributed with Mercurial, old clients won't have the
> extension. So the old client plus ext= scenario results in no load.

I think it's better to make the "experimental" thing usable for 3rd party
extensions too.

Another concern is for hg developers / testers running different versions of
hg - they may share hgrc.

> Of course, you probably didn't have ext= in the first place because it
> would emit an annoying warning on every command. So I doubt ext= for
> experimental extensions will occur much in the wild.