bug#23203: 25.0.91; some loaddefs files have auto-save remnants after building (and install doesn't ignore them)

[Eli Zaretskii <eliz@gnu.org>]

> From: phillip.lord@russet.org.uk (Phillip Lord)
> Cc: 23203@debbugs.gnu.org,  stromeko@nexgo.de
> Date: Mon, 04 Apr 2016 23:12:57 +0100
> 
> > How about this alternative: only disable backing up the initial
> > (effectively empty) contents of the autoloads file?  AFAICT, the
> > backup files are created during a bootstrap only because we first
> > write the initial "rubric" into it, using write-region, and only after
> > that visit it.  This defeats the normal mechanism of backing up just
> > once per session, and leaves a backup file whose contents are not
> > interesting.
> 
> That sounds plausible.
> 
> >
> > So an alternative would be to modify autoload-ensure-default-file so
> > that it returns some indication about the fact it created the file,
> > and then change its caller to set buffer-backed-up after it visits the
> > file, thus preventing the backup _only_ when the file is first
> > created.
> >
> > This should at least solve Achim's problem, but without affecting
> > anything else.
> >
> > WDYT?
> 
> Also, it sounds reasonable -- I've attached a patch with a variation on
> this theme.

Thanks.  There seem to be spurious unrelated whitespace changes in the
patch.

Also, wouldn't it be more elegant to have autoload-ensure-default-file
return a cons cell reporting whether the file did exist before, so
that autoload-find-generated-file could act on that?  But if you
prefer your implementation, I won't argue.

> My concerns is that we will still produce backup files which may end up
> in a dist build. Consider these commands:
> 
> make (from bootstrap)
> rm lisp/loaddefs.el
> make
> 
> Removing loaddefs will result in generation of all the associated
> loaddef files, all of which will now be backups.
> 
> So, we need to make sure that the packaging system does not copy backup
> files.

"make install" already removes backup files from the target tree, so
is there any problem left?