Special case broken in vc-backend-dispatch macro in vc.el

[era eriksson]

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In GNU Emacs 20.3.2 (i386-debian-linux-gnu, X toolkit)
 of Thu Jan 28 1999 on raven
configured using `configure  i386-debian-linux-gnu --prefix=/usr 
--sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib 
--infodir=/usr/info --with-pop=yes --with-x=yes --with-x-toolkit=yes'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

The function `vc-insert-headers' when invoked on a CVS-controlled file
prompts for confirmation when attempting to insert headers into a
file, stating that headers are already present even when this is
clearly not the case, such as in a completely empty file.

This seems to trace back to the macro `vc-backend-dispatch', which is
supposed to have a special case for the final argument; if the fourth
argument to the macro is 'RCS then the action for CVS should be the
action specified for RCS. However, I cannot get this to work as
specified; indeed, you can verify this yourself by evaluating the
following form in a CVS-controlled file:

    (vc-backend-dispatch buffer-file-name "one" "two" 'RCS)

This ought to return "two" but when I try it, I get 'RCS instead.
(In this *mail* buffer, of course, I get nil, because it's not under
version contol at all.)

As far as I can tell, this happens because the definition of the macro
`vc-backend-dispatch' is not adequately quoted. By using the the
following macro definition instead, I get the documented behavior:

(defmacro vc-backend-dispatch (f s r c)
  "Execute FORM1, FORM2 or FORM3 for SCCS, RCS or CVS respectively.
If FORM3 is `RCS', use FORM2 for CVS as well as RCS.
\(CVS shares some code with RCS)."
  (list 'let (list (list 'type (list 'vc-backend f)))
        (list 'cond
              (list (list 'eq 'type (quote 'SCCS)) s)   ;; SCCS
              (list (list 'eq 'type (quote 'RCS)) r)    ;; RCS
              (list (list 'eq 'type (quote 'CVS))       ;; CVS
                    ;; (if (eq c 'RCS) r c)) ;; Quoting bug! Replacement here:
                    (list 'if (list 'eq c (quote 'RCS)) r c))
              )))

Of course, some heretic might have the nerve to suggest using the
backquote facility, and/or documenting all the arguments consistently
(the f argument is the name of the file we are going to operate on).

For what it's worth, I found this special case of the macro used
exactly once in vc.el and not at all in vc-hook.el. (This is in the
function `vc-check-headers', which in turn appears to be used only by
the function `vc-insert-headers'.)

Sorry if this has been reported by someone else already -- I'm afraid
I don't have the resources to monitor the bleeding edge of Emacs
development.

/* era */


Recent input:
return escape : ( v c - b a c k e n d - d i s p a t 
c h SPC b u f f e r - f i l e - n a m e SPC \304 backspace 
' " backspace backspace " o n e " SPC " t o e backspace 
backspace w o " SPC \344 backspace ' R C S ) return 
escape : escape p return C-x v h n escape : escape 
p return C-x 1 escape x r e p o r t - e m tab return

Recent messages:
Please type y, n or r; or ? for help
Quit
Symbol's function definition is void: vc-backend-dispatch [2 times]
Loading vc...
Loading derived...
Loading derived...done
Loading vc...done
RCS
Loading emacsbug...
Loading emacsbug...done

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