notmuch-emacs: avoiding deprecated message-default-charset

[David Bremner]

Daniel Kahn Gillmor <dkg at fifthhorseman.net> writes:

> When i'm building notmuch in a debian environment with emacs
> 1:26.1+1-3.2, i notice the following deprecation warnings:
>
> In notmuch-maildir-setup-message-for-saving:
> emacs/notmuch-maildir-fcc.el:172:31:Warning: ‘message-default-charset’ is an
>     obsolete variable (as of 26.1); The default charset comes from the
>     language environment
>
> I'm not enough of an emacs guru to know the right way to avoid this
> warning, but i'm hoping that someonen else can take a stab at it, since
> extraneous warnings make it easier to ignore real problems.

Good question. I looked at message.el in emacs master and it

     1) Obsoletes message-default-charset as in 26.1
     2) Still uses it in exactly the construction we do.

I'm not sure if it's exactly a reportable bug in emacs, but it is a bit
annoying.

There is a variable byte-compile-not-obsolete-vars that (probably) can
be used to suppress that warning, but it's not clear that's a good
idea (we currently do something similar for Xapian obsolescence warnings
that we can't fix).

d