bug#5026: 23.1; add-hook buffer local vs single func

[Kevin Ryde <user42@zip.com.au>]

Evaluating

    (progn
      (defvar foo nil)

      (defun func1 ()
        (error "this is func 1"))
      (defun func2 ()
        (message "this if func 2"))


      (setq foo 'func1)
      (add-hook 'foo 'func2
                nil ;; prepend
                t)  ;; buffer-local

      (run-hooks 'foo))

returns nil, where I expected the run-hooks to run both func2 and func1,
raising the error in func1.

The elisp manual under "Setting Hooks" says

    `add-hook' can handle the cases where ... its value is
    a single function;

but that doesn't seem to be so when extending a single function to a
buffer-local value.

I suspect it's run-hooks which should be blamed rather than add-hook.
Should run-hooks allow a single-function global value when it follows a
`t' from a local value?

I expect this arises only rarely.  But if it does then it's a pretty
subtle way to miss out on a function you thought you had in a hook.




In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.16.5)
 of 2009-09-14 on raven, modified by Debian
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' '--localstatedir=/var/lib' '--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes' '--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim' '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g -O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t