bug#46256: [feature/native-comp] AOT eln files ignored if run from build tree

[Alan Mackenzie]

Hello, Eli.

On Tue, Mar 09, 2021 at 18:30:57 +0200, Eli Zaretskii wrote:
> > Date: Tue, 09 Mar 2021 14:55:57 +0200
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 46256@debbugs.gnu.org, andrewjmoreton@gmail.com, pipcet@gmail.com

> > > From: Andrea Corallo <akrl@sdf.org>
> > > Cc: pipcet@gmail.com, 46256@debbugs.gnu.org, andrewjmoreton@gmail.com
> > > Date: Tue, 09 Mar 2021 07:03:01 +0000

> > > > Can you tell why are we loading the same .eln files more than once?

> > > I guess `load' was called two times on the same filename.

> > Is this likely to happen?  Our code generally uses 'require', which
> > should avoid that.

> Answering my own question here: it can easily happen due to use of
> cc-require in cc-*.el files.  Alan, why does CC mode use this
> technique? what is the purpose of always loading a Lisp file even if
> it was already loaded?

Are you sure?  cc-require is intended just to compile a `require' form
(OK, it compiles (progn nil (require 'cc-vars)), but the byte compiler
will optimise the progn away).

When loading uncompiled cc-*.el, cc-require does fancy things to make
sure the cc-*.el is in the "correct" directory, but it shouldn't compile
any of this into the *.elc.  Maybe there's a bug, somewhere.

The code in this area was written by Martin Stjernholm (my predecessor),
who was evidently having trouble with "wrong" versions of the *.el files
getting loaded.

I've had a bit of a look at the thread for bug #46256, but I can't really
follow it, at least not without a lot of effort.  Might it be that the
..eln compiler is doing things on the .el file?  I'm not at all familiar
with how the native compilation works, I'm afraid.

-- 
Alan Mackenzie (Nuremberg, Germany).