bug 343640 - error out when building using --enable-calendar with a nice error message. r=dmose,sr=bsmedberg

configure.in

@@ -4760,10 +4760,21 @@ AC_SUBST(MOZ_UI_LOCALE)
 dnl =========================================================
 dnl = Calendar client
 dnl =========================================================
-MOZ_ARG_ENABLE_BOOL(calendar,
-[  --enable-calendar       Enable building of the calendar client],
-    MOZ_CALENDAR=1,
-    MOZ_CALENDAR= )
+MOZ_ARG_ENABLE_BOOL(calendar,,
+    MOZ_OLD_CALENDAR=1,
+    MOZ_OLD_CALENDAR= )
+
+if test "$MOZ_OLD_CALENDAR"; then
+    AC_MSG_WARN([Building with the calendar extension is no longer supported.])
+    if test "$MOZ_THUNDERBIRD"; then
+        AC_MSG_WARN([Since you're trying to build mail, you could try adding])
+        AC_MSG_WARN(['--enable-extensions=default,lightning' to your mozconfig])
+        AC_MSG_WARN([and building WITH A FRESH TREE.])
+    fi
+    AC_MSG_WARN([For more information, please visit:])
+    AC_MSG_ERROR([http://www.mozilla.org/projects/calendar/])
+fi
+
 AC_SUBST(MOZ_CALENDAR)
 
 dnl =========================================================