Re: Documentation not clear for the Lisp function set-variable

[Juanma Barranquero <lekktu@gmail.com>]

On 6/27/05, Juanma Barranquero <lekktu@gmail.com> wrote:
> Try this patch, please. It doesn't modify `set-variable' but
> `user-variable-p', so it returns t for non-obsolete aliases of user
> variables.

Well, it is also necessary to detect alias loops.  The problem is:
what should `user-variable-p' do when passed a variable which is in an
alias loop?  Throw an error or return nil?  I prefer the latter, as
`user-variable-p' is almost always used as predicate to completion
functions, apropos* or `mapatoms', where throwing an error would be
inappropriate.

-- 
                    /L/e/k/t/u


Index: src/eval.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/eval.c,v
retrieving revision 1.245
diff -u -2 -r1.245 eval.c
--- src/eval.c	27 Jun 2005 05:59:23 -0000	1.245
+++ src/eval.c	27 Jun 2005 15:37:53 -0000
@@ -94,4 +94,5 @@
 Lisp_Object Qdebug_on_error;
  Lisp_Object Qdeclare;
+Lisp_Object Qbyte_obsolete_variable;
 
 /* This holds either the symbol `run-hooks' or nil.
@@ -890,18 +891,35 @@
 }
 
+/* Error handler used in Fuser_variable_p.  */
+static Lisp_Object
+user_variable_p_eh (ignore)
+     Lisp_Object ignore;
+{
+  return Qnil;
+}
+
  DEFUN ("user-variable-p", Fuser_variable_p, Suser_variable_p, 1, 1, 0,
        doc: /* Returns t if VARIABLE is intended to be set and
modified by users.
 \(The alternative is a variable used internally in a Lisp program.)
 Determined by whether the first character of the documentation
-for the variable is `*' or if the variable is customizable (has a non-nil
-value of `standard-value' or of `custom-autoload' on its property list).  */)
+for the variable is `*', the variable is customizable (has a non-nil
+value of `standard-value' or of `custom-autoload' on its property list),
+or it is a non-obsolete alias for another user variable.  */)
      (variable)
      Lisp_Object variable;
 {
   Lisp_Object documentation;
+  struct Lisp_Symbol *sym;
 
   if (!SYMBOLP (variable))
       return Qnil;
 
+  sym = XSYMBOL (variable);
+  /* If indirect and there's an alias loop, don't check anything else.  */
+  if (sym->indirect_variable
+      && NILP (internal_condition_case_1 (indirect_variable, variable,
+                                          Qt, user_variable_p_eh)))
+    return Qnil;
+
   documentation = Fget (variable, Qvariable_documentation);
   if (INTEGERP (documentation) && XINT (documentation) < 0)
@@ -916,8 +934,15 @@
       && XINT (XCDR (documentation)) < 0)
     return Qt;
-  /* Customizable?  See `custom-variable-p'. */
+  /* Customizable?  See `custom-variable-p'.  */
   if ((!NILP (Fget (variable, intern ("standard-value"))))
       || (!NILP (Fget (variable, intern ("custom-autoload")))))
     return Qt;
+
+  /* An indirect variable?  Let's follow the chain.  */
+  sym = XSYMBOL (variable);
+  if (sym->indirect_variable
+      && NILP (Fget (variable, Qbyte_obsolete_variable)))
+    return Fuser_variable_p (sym->value);
+
   return Qnil;
 }
@@ -3410,4 +3435,7 @@
   staticpro (&Qdeclare);
 
+  Qbyte_obsolete_variable = intern ("byte-obsolete-variable");
+  staticpro (&Qbyte_obsolete_variable);
+
   /* Note that the process handling also uses Qexit, but we don't want
      to staticpro it twice, so we just do it here.  */