On Wed, Jul 28, 2021 at 11:26 AM Lars Ingebrigtsen <
larsi@gnus.org> wrote:
Pierre Rouleau <prouleau001@gmail.com> writes:
> (defun f-or ()
> "Use or."
> (when (or (null (boundp 'foo))
> (null foo)) ;=> ``Warning: reference to free variable ‘foo’``
> (message "foo is not set")))
The message about invalid stuff is only discarded if Emacs is trivially
able to deduce that it'll never be evaluated -- and as you've found out,
it's easy to make that heuristic not be heeded (see
`byte-compile-maybe-guarded' for details).
Thanks. I must admit I do not know the byte compiler code much at this point.
So I'm not sure this is a bug -- Emacs can't determine all cases where
we won't be executing the code in question at compile time.
Well, from the perspective of a user, that would look at the
very least as a technical limitation.
The byte compiler is able to report unused lexical variables.
It's able to report access to unbound symbols in a large
number of code patterns. That helps detect a lot of coding mistakes
and that's very valuable.
It may be difficult, or perhaps even not possible, to prevent the warning
in the situation I reported. If the byte compiler cannot be improve to handle
this situation, could this scenario be added to the list of know limitations
of the byte-compiler? Maybe someday it will become possible to handle it
and this scenario will help the process?