Define USE_LISP_UNION_TYPE using autoconf.

* configure.in (--enable-use-lisp-union-type): New flag.
* src/lisp.h: Document that USE_LISP_UNION_TYPE is now enabled using autoconf.

3 files changed, 8 insertions, 4 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 45d8bf3fc4f..46d41bf24bd 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,7 @@
 2010-07-02  Dan Nicolaescu  <dann@ics.uci.edu>
 
+        * lisp.h: Document that USE_LISP_UNION_TYPE is now enabled using autoconf.
+
         Cleanup old code.
         * dired.c (BSD4_3): Remove all uses, redundant with BSD4_2.
         * syssignal.h: Remove code for Lynx, not supported anymore.
diff --git a/src/config.in b/src/config.in
index 962edf62571..b1370dcbb95 100644
--- a/src/config.in
+++ b/src/config.in
@@ -933,6 +933,9 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 /* Define to 1 if using GTK. */
 #undef USE_GTK
 
+/* Define this to use a lisp union for the Lisp_Object data type. */
+#undef USE_LISP_UNION_TYPE
+
 /* Define to 1 if using the Lucid X toolkit. */
 #undef USE_LUCID
 
diff --git a/src/lisp.h b/src/lisp.h
index 1941a2471a4..0da668bb87f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -95,10 +95,9 @@ extern void die P_((const char *, const char *, int)) NO_RETURN;
 #endif
 #endif /* ENABLE_CHECKING */
 
-/* Define this to make Lisp_Object use a union type instead of the
-   default int.  FIXME: It might be better to add a flag to configure
-   to do this.  */
-/* #define USE_LISP_UNION_TYPE */
+/* Use the configure flag --enable-use-lisp-union-type to make
+   Lisp_Object use a union type instead of the default int.  The flag
+   causes USE_LISP_UNION_TYPE to be defined.  */
 
 /***** Select the tagging scheme.  *****/
 /* There are basically two options that control the tagging scheme: