bug#23407: .dir-local settings get obliterated on running a major mode function.

[Alan Mackenzie]

Hello, Stefan.

Thanks for looking at my patch.

On Mon, May 02, 2016 at 12:02:11AM -0400, Stefan Monnier wrote:
> > Anyhow, I've hacked a patch together.  The idea is to call
> > `hack-local-variables' from `run-mode-hooks' rather than from
> > `normal-mode'.

> Good idea.

> > +    ;; delay-mode-hooks is set when `byte-compile-file' is the caller.
> > +    ;; It is essential that we call `hack-local-variables' in order to
> > +    ;; set up `lexical-binding', since `run-mode-hooks' is prevented
> > +    ;; from doing its job.
> > +    (when delay-mode-hooks
> > +      (with-demoted-errors "File local-variables error: %s"
> > +        (hack-local-variables 'no-mode))))

> But this seems terribly brittle.  Do we care about delay-mode-hooks (as
> the code says) or about byte-compile-file (as the comment says)?

This bit of code was necessitated by:

#########################################################################
commit 3ba6b3a9c1e0565ee5f45f11a9c09702a24f8453
Author: Artur Malabarba <bruce.connor.am@gmail.com>
Date:   Sun Apr 12 03:23:35 2015 +0100

    Speed up byte-compilation and autoload generation by avoiding mode-hooks

    This prevents emacs-lisp-mode-hook from being run everytime an
    autoload file is generated, which can account for a fraction of
    package installation time depending on the hooks the user has
    configured.

    * lisp/emacs-lisp/bytecomp.el (byte-compile-file): Use
    * delay-mode-hooks.

    * lisp/emacs-lisp/autoload.el (autoload-find-file)
    (autoload-find-generated-file): Use delay-mode-hooks.
#########################################################################

if hack-local-variables isn't run, lexical-binding (for example) doesn't
get set up, and make bootstrap fails.

> If it's the former, then the comment needs to be fixed, if it's the
> latter, than we need to find some other way to tell this code what's
> going on.

I don't really understand the question.  Sure, that bit of code is ugly.
But the comment both motivates ("it's `byte-compile-file''s fault") and
explains the problem (which is that `delay-mode-hooks' being set would
prevent `run-mode-hook', and thus `hack-local-variable' from running).
It is possible that other stuff might call `normal-mode' like this.
What sort of changes do you advocate for the comment (or for the code)?

>         Stefan

-- 
Alan Mackenzie (Nuremberg, Germany).