Subject: bug#2061: 23.0.60; Add preference to force load of Elisp files when they are newer than corresponding byte-compiled file

From: Juanma Barranquero <[email-masked]>
Date: Wed, 28 Jan 2009 03:06:13 +0100

On Tue, Jan 27, 2009 at 16:54, Brent Goodrick <[email-masked]> wrote:

> The problem relates to when and how to notify the user that the stale
> .elc file is the one being loaded.  During development, I just
> `eval-buffer' repeatedly on a .el file, always unaware that there is a
> stale .elc file lying in wait to confuse me the next time I reload the
> entire Emacs process/session.

If you're going to modify/test the package with eval-buffer, you
should make sure there's no .elc sitting around.

> At init time, I only get a warning,
> among a ton of other benign warnings and messages, and that one
> critical warning is therefore not seen (of course, it is impractical
> to ask the user to read all of those messages).

As you know, that's trivially fixed:

(add-hook 'emacs-startup-hook
          (lambda ()
            (with-current-buffer (get-buffer "*Messages*")
              (goto-char (point-min))
              (while (re-search-forward "[Ss]ource file .*? newer" nil t)
                (warn "%s" (buffer-substring (line-beginning-position)
                                             (line-end-position)))))))

> Add the following logic to the C `load' function:
>
>  Before loading either the .el or .elc file, test for the condition
>  where the .el file is newer than the .elc file. If it is, then do
>  the following:
>
>    See if the `load-hook-stale-byte-compile-handlers' hook variable
>    is set to non-nil. When it is non-nil, run the hook variable with
>    `run-hook-with-args-until-success'. Each function the user has
>    added to that hook variable would do any logic s/he wishes,
>    including in my case to popup a minibuffer prompt asking what to
>    do. When the hook function thus called returns a 'prefer-el-file
>    symbol, `load' then loads the .el file and ignores the .elc
>    file. Likewise, when the hook function returns the
>    'prefer-elc-file symbol, then load the .elc file but give no
>    warning message and ignore the .el file. When nil is returned from
>    the `run-hook-with-args-until-success' function, just load the
>    .elc file and produce the stale file warning message as is done
>    today (i.e., preserve existing behavior).

That would work, but it is IMHO too much (interface, not code)
complexity for little gain. In most cases, having a .elc older than
its corresponding .el is a bug (or, let's call it, a temporary
situation), so getting a warning to remind the user about fixing it
seems much more economical.

That said, sometimes I would've liked to have a hook that runs when a
file is loaded; or the ability to defadvice Fload (you can, except
that Fload is also called from C code, for example for autoloads).

> I have tried doing that, but found it unworkable in practice, as
> byte-compiling upon each save ended up chewing up too much time during
> development (the byte-compile-upon-every-save penalty). Consider that
> I save frequently. :)

I didn't mean to byte-compile on saving, I meant to byte-compile on
eval-buffer (or whatever method you use to test your code).

> But that is a hack, so I am now trying to get the root problem
> addressed in the C code where it exists.

I agree that greater control over the loading process could sometimes
be useful; but I don't think this is a compelling use case.

    Juanma