bug#23692: 25.1.50; Package.el gets confused if file has no autoloads (could be a bug in update-directory-autoloads)

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> i) I guess now autoload will sometimes not create any output file.

I think this shouldn't happen.  Both in the sense that it would be
a bug, and that my understanding of the code makes me think it
won't happen.  We create the file before we even try to update it.

> ii) I wonder what this means for reproducibility of the loaddefs file.

Good question.

> iii) Would applying a move-if-change style logic be better?

Could be, indeed.  My only motivation for the original patch was to
avoid repeatedly re-dumping Emacs even when no significant change had
happened.  I wrote the patch years ago, and at that point the
time-stamps were always different, so the buffer's content was
definitely changed, tho in ways which had no impact on the dump, so
"move-if-changed" was not an option.
Now that we avoid time-stamps maybe we can actually compare the buffer's
content with the file and skip saving if it's identical.


        Stefan