bug#57562: [PATCH] * lisp/emacs-lisp/comp.el (comp-run-async-workers): Fail more gracefully

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

>> From: Stefan Monnier <monnier@iro.umontreal.ca>
>> Cc: 57562@debbugs.gnu.org
>> Date: Sat, 03 Sep 2022 11:41:14 -0400
>> 
>> >> > I have trouble seeing the actual change amongst unrelated whitespace
>> >> > changes.  Please show a patch with the minimal necessary change,
>> >> > without all the reformatting.  Emacs 28.2 is so close to a release
>> >> > that playing whitespace and formatting games is not appropriate there.
>> >> Hmm... looks like I sent the patch I had on `master`, sorry.
>> >> Here is the cleaner `emacs-28` version.
>> > So this means we will silently skip native-compilation, leaving an
>> > obscure message in a buffer, is that right?
>> 
>> In *Messages*, I think, yes.
>
> I guess that's enough for Emacs 28.  (And I do wonder how come people
> come up with unwritable home directories.)

In the discussion of that Debian bug#1017739, Russ Allbery mentions
a(n unrelated) problem which can lead to this:

    % su
    # emacs

If the user hasn't yet used Emacs (and depending on the details of which
version of `su` you use) this can create
a /home/<user>/.emacs.d/eln-cache that's owned by root because we create
that dir according to `~$USER` rather than according to `$HOME`.

>> > Maybe this is the best we can do for emacs-28 so close to the release,
>> > but for master wouldn't it be better to use delayed-warning instead?
>> 
>> Sounds about right, tho I suspect we might need to do even a bit more on
>> `master`, like disabling lazy native compilation when we bump into this
>> problem, to avoid repeating that same error message, or trying harder to
>> find a writable directory.
>
> I'm more bothered about letting the user know than about working
> around the problem.

Good.


        Stefan