Source file '.../killer-source.el' newer than byte-compiled file

[Emanuel Berg <moasenwood@zoho.eu>]

Often when I do some changes to Elisp files and
then run the byte-compiler with the following
Makefile [1] I get this message for several
files, but not all of them, and not always:

    Source file '~/path/to/killer-source.el' newer
    than byte-compiled file

But what is the purpose of this message and why
is it so capricious in terms of when
it appears?

What it says isn't radical, because isn't that
the way make(1) works, you have a target, and
a source, and if the source is newer
(i.e. more recently modified) than the target,
that means it has been edited since last
compilation, i.e., (re)compilation
should happen?

Why am I told this specifically, and why for
just certain files, not every one I edit?

Has it to do with files being `require'd before
compilation has gotten that far? So if a.el is
compiled into a.elc, but a requires b, only at
that time b.elc hasn't been compiled *but* b.el
has been edited?

If this theory is correct (?), do you even need
to compile one more time to get rid of the
message? Because at that time a.el hasn't been
changed, so it won't be recompiled, and thus
won't get access to the new b.elc anyway?

Only this in turn doesn't matter either in
practise as long as there is no change to the
interface of b, because when the user uses
b thru a, it'll still get the latest b.elc?


[1] http://user.it.uu.se/~embe8573/emacs-init/Makefile

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