bug#43725: 28.0.50; Include feature/native-comp into master

[Eli Zaretskii]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: larsi@gnus.org, monnier@iro.umontreal.ca, 43725@debbugs.gnu.org
> Date: Wed, 10 Mar 2021 15:45:49 +0000
> 
> this is not expected and I cannot reproduce it here.

OK, so just to be sure we are taking about the same scenario:

  . I touch comp.el while a comp-NNNNN.eln already exists in
    ~/.emacs.d/eln-cache.
  . I then start "emacs -Q" and invoke "C-h f" for some function whose
    .el file doesn't yet have a .eln file.  For example,

        C-h f ruler-mode RET

  . What I see next is that Emacs starts compiling in the background,
    and I later find that both ruler-mode.el and comp.el have been
    natively-compiled.

Hmmm... now I see that it doesn't happen every time.  So I guess some
additional factor is at work here, indeed.

> The file is hashed using the content + its filename so access and
> modification times should not come into play.  Are we sure the file
> content wasn't modified?

The file wasn't modified, that's for sure.

> Or we might be possibly looking at different issue here.

Probably.  I'll try to step through the code, but could you give me
some pointers: where do we decide whether to native-compile a file
that we load?

Thanks.