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

[Juanma Barranquero]

> This patch produces the following text:
> 
>    Determined by whether the first character of the documentation
>   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.
> 
> Does anyone else think that this sentence is so confusing in its
> structure as to be almost unparsable?  (The old sentence was even less
> clear.)

Unparsable I wouldn't say, but certainly not very good. But anyway,
Richard just said that obsolete aliases should be set-variable too.

> I think this sentence sorely needs rephrasing.  For starters, it
> should not use passive tense.

What about this patch? Do you like it a bit more?

-- 
                    /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 21:32:36 -0000
@@ -890,10 +890,22 @@
 }
 
+/* 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.
+       doc: /* Return 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).  */)
+VARIABLE is considered to be a `user variable' if
+\(1) the first character of its documentation is `*', or
+\(2) it is customizable (its property list contains a non-nil value
+    of `standard-value' or `custom-autoload'), or
+\(3) it is an alias for another user variable.
+Return nil if VARIABLE is an alias and there is a loop in the
+chain of symbols.  */)
      (variable)
      Lisp_Object variable;
@@ -904,21 +916,35 @@
       return Qnil;
 
-  documentation = Fget (variable, Qvariable_documentation);
-  if (INTEGERP (documentation) && XINT (documentation) < 0)
-    return Qt;
-  if (STRINGP (documentation)
-      && ((unsigned char) SREF (documentation, 0) == '*'))
-    return Qt;
-  /* If it is (STRING . INTEGER), a negative integer means a user variable.  */
-  if (CONSP (documentation)
-      && STRINGP (XCAR (documentation))
-      && INTEGERP (XCDR (documentation))
-      && XINT (XCDR (documentation)) < 0)
-    return Qt;
-  /* Customizable?  See `custom-variable-p'. */
-  if ((!NILP (Fget (variable, intern ("standard-value"))))
-      || (!NILP (Fget (variable, intern ("custom-autoload")))))
-    return Qt;
-  return Qnil;
+  /* If indirect and there's an alias loop, don't check anything else.  */
+  if (XSYMBOL (variable)->indirect_variable
+      && NILP (internal_condition_case_1 (indirect_variable, variable,
+                                          Qt, user_variable_p_eh)))
+    return Qnil;
+
+  while (1)
+    {
+      documentation = Fget (variable, Qvariable_documentation);
+      if (INTEGERP (documentation) && XINT (documentation) < 0)
+        return Qt;
+      if (STRINGP (documentation)
+          && ((unsigned char) SREF (documentation, 0) == '*'))
+        return Qt;
+      /* If it is (STRING . INTEGER), a negative integer means a user
variable.  */
+      if (CONSP (documentation)
+          && STRINGP (XCAR (documentation))
+          && INTEGERP (XCDR (documentation))
+          && XINT (XCDR (documentation)) < 0)
+        return Qt;
+      /* Customizable?  See `custom-variable-p'.  */
+      if ((!NILP (Fget (variable, intern ("standard-value"))))
+          || (!NILP (Fget (variable, intern ("custom-autoload")))))
+        return Qt;
+
+      if (!XSYMBOL (variable)->indirect_variable)
+        return Qnil;
+
+      /* An indirect variable?  Let's follow the chain.  */
+      variable = XSYMBOL (variable)->value;
+    }
 }