bug#62009: 29.0.60; Emacs crashes on setf symbol-name

[Gregory Heytings]

> diff --git a/src/lisp.h b/src/lisp.h
> index 1276285e2f2..80bbb047824 100644
> --- a/src/lisp.h
> +++ b/src/lisp.h
> @@ -1685,6 +1685,8 @@ SREF (Lisp_Object string, ptrdiff_t index)
> INLINE void
> SSET (Lisp_Object string, ptrdiff_t index, unsigned char new)
> {
> +  if (XSTRING (string)->u.s.size_byte == -2)
> +    Fsignal (Qsetting_constant, string);
>   SDATA (string)[index] = new;
> }
> INLINE ptrdiff_t

That flag is useful only for the first part of the bug: setting the symbol 
name of a function defined in C.  It does not prevent changing symbol 
names in general, e.g. (aset (symbol-name 'find-file) 1 ?o).