Re: buffer.c/buffer.h: How to add new buffer-local variables?

[Michael Welsh Duggan <mwd@md5i.com>]

I would suggest that there be a 

#define BUFFER_STRUCT_LAST_LISP_OBJECT cursor_in_non_selected_windows_

which would be properly commented and used in BUFFER_LISP_SIZE.  This
would, I think, make it easier to notice that this needs to change when
more items get added to the list.  I would also add a comment after the
cursor_in_non_selected_windows_ entry to the effect that the define
needs to be updated if more are added afterward.

Paul Eggert <eggert@cs.ucla.edu> writes:

> diff --git a/src/buffer.h b/src/buffer.h
> index 63b162161c..f42c3e97b9 100644
> --- a/src/buffer.h
> +++ b/src/buffer.h
> @@ -741,8 +741,8 @@ struct buffer
>       See `cursor-type' for other values.  */
>    Lisp_Object cursor_in_non_selected_windows_;
>  
> -  /* No more Lisp_Object beyond this point.  Except undo_list,
> -     which is handled specially in Fgarbage_collect.  */
> +  /* No more Lisp_Object beyond cursor_in_non_selected_windows_.
> +     Except undo_list, which is handled specially in Fgarbage_collect.  */
>  
>    /* This structure holds the coordinates of the buffer contents
>       in ordinary buffers.  In indirect buffers, this is not used.  */
> @@ -1019,14 +1019,12 @@ bset_width_table (struct buffer *b, Lisp_Object val)
>     structure, make sure that this is still correct.  */
>  
>  #define BUFFER_LISP_SIZE						\
> -  ((offsetof (struct buffer, own_text) - header_size) / word_size)
> +  PSEUDOVECSIZE (struct buffer, cursor_in_non_selected_windows_)
>  
> -/* Size of the struct buffer part beyond leading Lisp_Objects, in word_size
> -   units.  Rounding is needed for --with-wide-int configuration.  */
> +/* Allocated size of the struct buffer part beyond leading
> +   Lisp_Objects, in word_size units.  */
>  
> -#define BUFFER_REST_SIZE						\
> -  ((((sizeof (struct buffer) - offsetof (struct buffer, own_text))	\
> -     + (word_size - 1)) & ~(word_size - 1)) / word_size)
> +#define BUFFER_REST_SIZE (VECSIZE (struct buffer) - BUFFER_LISP_SIZE)
>  
>  /* Initialize the pseudovector header of buffer object.  BUFFER_LISP_SIZE
>     is required for GC, but BUFFER_REST_SIZE is set up just to be consistent

-- 
Michael Welsh Duggan
(md5i@md5i.com)