* lisp/custom.el: Avoid adding vars to load-history multiple times

Avoid the abuse of (eval `(defvar ...)) which tends to end up
adding redundant entries in `load-history`, as discussed in
https://lists.gnu.org/r/help-gnu-emacs/2019-03/msg00237.html

(custom-initialize-default): Don't add to load-history.
(custom-declare-variable): Use internal--define-uninitialized-variable
and only add the var to load-history once.  Do it before calling
`initialize` so the special-variable-p flag is set.

* src/eval.c (Finternal__define_uninitialized_variable): New function.
(Fdefvar, Fdefconst): Use it.
(syms_of_eval): Defsubr' it.

1 files changed, 28 insertions, 22 deletions

diff --git a/src/eval.c b/src/eval.c
index 3fd9a40a3a2..567c32e0d75 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -715,6 +715,25 @@ DEFUN ("set-default-toplevel-value", Fset_default_toplevel_value,
   return Qnil;
 }
 
+DEFUN ("internal--define-uninitialized-variable",
+       Finternal__define_uninitialized_variable,
+       Sinternal__define_uninitialized_variable, 1, 2, 0,
+       doc: /* Define SYMBOL as a variable, with DOC as its docstring.
+This is like `defvar' and `defconst' but without affecting the variable's
+value.  */)
+  (Lisp_Object symbol, Lisp_Object doc)
+{
+  XSYMBOL (symbol)->u.s.declared_special = true;
+  if (!NILP (doc))
+    {
+      if (!NILP (Vpurify_flag))
+	doc = Fpurecopy (doc);
+      Fput (symbol, Qvariable_documentation, doc);
+    }
+  LOADHIST_ATTACH (symbol);
+  return Qnil;
+}
+
 DEFUN ("defvar", Fdefvar, Sdefvar, 1, UNEVALLED, 0,
        doc: /* Define SYMBOL as a variable, and return SYMBOL.
 You are not required to define a variable in order to use it, but
@@ -754,32 +773,25 @@ usage: (defvar SYMBOL &optional INITVALUE DOCSTRING)  */)
     {
       if (!NILP (XCDR (tail)) && !NILP (XCDR (XCDR (tail))))
 	error ("Too many arguments");
+      Lisp_Object exp = XCAR (tail);
 
       tem = Fdefault_boundp (sym);
+      tail = XCDR (tail);
 
       /* Do it before evaluating the initial value, for self-references.  */
-      XSYMBOL (sym)->u.s.declared_special = true;
+      Finternal__define_uninitialized_variable (sym, CAR (tail));
 
       if (NILP (tem))
-	Fset_default (sym, eval_sub (XCAR (tail)));
+	Fset_default (sym, eval_sub (exp));
       else
 	{ /* Check if there is really a global binding rather than just a let
 	     binding that shadows the global unboundness of the var.  */
 	  union specbinding *binding = default_toplevel_binding (sym);
 	  if (binding && EQ (specpdl_old_value (binding), Qunbound))
 	    {
-	      set_specpdl_old_value (binding, eval_sub (XCAR (tail)));
+	      set_specpdl_old_value (binding, eval_sub (exp));
 	    }
 	}
-      tail = XCDR (tail);
-      tem = Fcar (tail);
-      if (!NILP (tem))
-	{
-	  if (!NILP (Vpurify_flag))
-	    tem = Fpurecopy (tem);
-	  Fput (sym, Qvariable_documentation, tem);
-	}
-      LOADHIST_ATTACH (sym);
     }
   else if (!NILP (Vinternal_interpreter_environment)
 	   && (SYMBOLP (sym) && !XSYMBOL (sym)->u.s.declared_special))
@@ -827,19 +839,12 @@ usage: (defconst SYMBOL INITVALUE [DOCSTRING])  */)
       docstring = XCAR (XCDR (XCDR (args)));
     }
 
+  Finternal__define_uninitialized_variable (sym, docstring);
   tem = eval_sub (XCAR (XCDR (args)));
   if (!NILP (Vpurify_flag))
     tem = Fpurecopy (tem);
-  Fset_default (sym, tem);
-  XSYMBOL (sym)->u.s.declared_special = true;
-  if (!NILP (docstring))
-    {
-      if (!NILP (Vpurify_flag))
-	docstring = Fpurecopy (docstring);
-      Fput (sym, Qvariable_documentation, docstring);
-    }
-  Fput (sym, Qrisky_local_variable, Qt);
-  LOADHIST_ATTACH (sym);
+  Fset_default (sym, tem);      /* FIXME: set-default-toplevel-value? */
+  Fput (sym, Qrisky_local_variable, Qt); /* FIXME: Why?  */
   return sym;
 }
 
@@ -4198,6 +4203,7 @@ alist of active lexical bindings.  */);
   defsubr (&Sdefvaralias);
   DEFSYM (Qdefvaralias, "defvaralias");
   defsubr (&Sdefconst);
+  defsubr (&Sinternal__define_uninitialized_variable);
   defsubr (&Smake_var_non_special);
   defsubr (&Slet);
   defsubr (&SletX);