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

[Gregory Heytings]

> > > AFAICT, they _are_ frozen.  These names are in read-only memory, where 
> > > you cannot write.  That's why Emacs crashes, AFAIU: the code is trying 
> > > to write to protected memory.
> > >
> > > Just don't do that, cause it's gonna hurt...
> >
> > Is it not possible to detect this before the illegal memory access, and 
> > raise a signal in Emacs Lisp?
>
> It won't be easy, if at all possible.  And I'm not sure we even want to 
> do that.  What would be the purpose of supporting such a use of Emacs?

Instead of raising a signal, I suggest:

diff --git a/src/data.c b/src/data.c
index 0f1d881e00b..76867d6787e 100644
--- a/src/data.c
+++ b/src/data.c
@@ -780,7 +780,7 @@ DEFUN ("symbol-name", Fsymbol_name, Ssymbol_name, 1, 
1, 0,

   CHECK_SYMBOL (symbol);
   name = SYMBOL_NAME (symbol);
-  return name;
+  return build_string (SSDATA (name));
 }

 DEFUN ("bare-symbol", Fbare_symbol, Sbare_symbol, 1, 1, 0,