Re: frame-local variables weirdness

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Another bug report from the pre-22.1 past.
> This one is an interaction between frame-local and buffer-local variables.

>  (defun test (sym bug)
>    ;; Default (global) value for the symbol
>    (set sym 'default)
>    (make-variable-frame-local sym)
>    ;; Frame-local value
>    (modify-frame-parameters nil (list (cons sym 'frame)))
>    (when bug
>      ;; Getting the value of sym changes the result
>      (symbol-value sym))
>    ;; Buffer-local value
>    (make-variable-buffer-local sym)
>    (set sym 'local)
>    ;; Now let's get back the local values
>    (list (local-variable-p sym)       ;; should be t
>          (symbol-value sym)           ;; should be 'local
>          (frame-parameter nil sym)))  ;; should be 'frame

> Note that passing t to the BUG argument only changes one thing: that
> (symbol-value sym) is run.

>   (test 'foo nil) => (t local frame)     ;; correct
>   (test 'bar t)   => (nil local local)   ;; incorrect

> Richard proposed the attached patch, with fixes the test case but
> causes other problems.

I'd much rather disallow variables that are both buffer-local and frame-local.
What is the use-case?


        Stefan


> Index: src/data.c
> ===================================================================
> RCS file: /sources/emacs/emacs/src/data.c,v
> retrieving revision 1.278
> diff -u -2 -r1.278 data.c
> --- src/data.c	10 Sep 2007 09:41:44 -0000	1.278
> +++ src/data.c	11 Oct 2007 09:30:16 -0000
> @@ -1238,7 +1238,8 @@
>  	  || (XBUFFER_LOCAL_VALUE (valcontents)->check_frame
>  	      && !EQ (selected_frame, XBUFFER_LOCAL_VALUE (valcontents)->frame))
> +	  /* After make-variable-buffer-local, if we haven't got a
> +	     buffer-local binding in place, we need to make one.  */
>  	  || (BUFFER_LOCAL_VALUEP (valcontents)
> -	      && EQ (XCAR (current_alist_element),
> -		     current_alist_element)))
> +	      && ! XBUFFER_LOCAL_VALUE (valcontents)->found_for_buffer))
>  	{
>  	  /* The currently loaded binding is not necessarily valid.


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