Subject: bug#19363: Acknowledgement (24.4.1; Notifications can make ERC unusable)

From: Stefan Monnier <[email-masked]>
Date: Sun, 04 Jan 2015 14:52:07 -0500

> If we have some (eval-after-load 'erc ...) stuff then by the time this
> (defvar) is evaluated, the list may already have a value, so the defvar
> then does NOT add its value to the list. The patch explicitly changes
> the (defvar list default) idiom to
> (defvar list nil) (add-to-list 'list default) and thus the default value
> always appears in the list.

Thanks.  That's a good change.

The general rule is that a hook's initial/default value should be nil
(that's fairly strong "should", with relatively few exceptions.
This bug-report is a good example of why it should be that way).
It's also generally better if the hook's "normal" value is nil, tho
I think in this case it'd be probably inconvenient.

But I do wonder: if the function *has* to be on that hook for ERC to
work correctly, then maybe that function's place is not in the hook but
right at those places where the hook is run (i.e. hard-coded).
Could you (or someone who understands the code better than I do) take
a look to see if such a change would be even better?

        Stefan

>> From 28bc9430ce6342d210e986586af7b6f12e103043 Mon Sep 17 00:00:00 2001
> From: Dima Kogan <[email-masked]>
> Date: Wed, 31 Dec 2014 08:13:57 -0800
> Subject: [PATCH] ERC no longer gets confused by (eval-after-load 'erc ...)

> ERC was initializing one of its lists with (defvar list default).  If
> the list already had a value due to (eval-after-load 'erc ...) for
> instance, then (defvar) would see an initialized variable, and would NOT
> add the default value to the list.  This was breaking things.  This
> patch changes the above defvar idiom to

>  (defvar list nil)
>  (add-to-list 'list default)

> This way the default value is added to the list unconditionally

> Closes: #19363
> ---
>  lisp/erc/erc-backend.el | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)

> diff --git a/lisp/erc/erc-backend.el b/lisp/erc/erc-backend.el
> index fa95d7e..43e56c0 100644
> --- a/lisp/erc/erc-backend.el
> +++ b/lisp/erc/erc-backend.el
> @@ -1179,8 +1179,11 @@ add things to `%s' instead."
>            (cl-loop for alias in aliases
>                     collect (intern (format "erc-server-%s-functions" alias)))))
>      `(prog2
> -         ;; Normal hook variable.
> -         (defvar ,hook-name ',fn-name ,(format hook-doc name))
> +         ;; Normal hook variable.  The variable may already have a
> +         ;; value at this point, so I default to nil, and (add-hook)
> +         ;; unconditionally
> +         (defvar ,hook-name nil ,(format hook-doc name))
> +         (add-to-list ',hook-name ',fn-name)
>           ;; Handler function
>           (defun ,fn-name (proc parsed)
>             ,fn-doc
> -- 
> 2.1.3