bug#27170: 26.0.50; Suggestion: Optionally send package build output to log file not *Messages*

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Sat, 29 Jan 2022 17:24:25 +0100
> Cc: nljlistbox2@gmail.com, 27170@debbugs.gnu.org, stefankangas@gmail.com
> 
> Richard Stallman <rms@gnu.org> writes:
> 
> >   > Sure, writing the output to a file would be fine, but I don't think
> >   > Emacs needs a logging framework for that.  If we can redirect messages
> >   > to a buffer, then package.el can do whatever it wants with the messages,
> >   > including writing them to a file if so desired.
> >
> > I agree.  Let's not make this more complex than the minimum.
> 
> This has now been added to Emacs 29 -- packages can bind
> `messages-buffer-name' to a different buffer name to redirect the
> output.

The "bind" part (also in the doc string of the variable) might mislead
someone into thinking that just binding this variable around some form
is enough to have all the relevant messages to go to that buffer.  But
that is not necessarily true, because some messages are produced after
the command exits; a prominent example is messages produced by the
display engine.

So basically, binding this variable will actually _split_ the messages
between *Messages* and some other buffer.