Better support for future plugins

See the thread containing:
http://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00720.html
* lib-src/make-docfile.c (write_globals): Generate code that #defines
Qxxx macros other than Qnil only if DEFINE_NONNIL_Q_SYMBOL_MACROS.
Qnil is safe to define even in plugins, since it must be zero for
other reasons.
* src/lisp.h (DEFINE_LISP_SYMBOL): New macro, replacing and simplifying
DEFINE_LISP_SYMBOL_BEGIN / DEFINE_LISP_SYMBOL_END.  All uses changed.
(DEFINE_NONNIL_Q_SYMBOL_MACROS): New macro, defaulting to true.

2 files changed, 17 insertions, 3 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index f8e65d5d91d..6d246fb52c6 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,10 @@
+2015-02-13  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Better support for future plugins
+        * lisp.h (DEFINE_LISP_SYMBOL): New macro, replacing and simplifying
+        DEFINE_LISP_SYMBOL_BEGIN / DEFINE_LISP_SYMBOL_END.  All uses changed.
+        (DEFINE_NONNIL_Q_SYMBOL_MACROS): New macro, defaulting to true.
+
 2015-02-11  Martin Rudalics  <rudalics@gmx.at>
 
         * w32term.c (w32_read_socket): In SIZE_MAXIMIZED and
diff --git a/src/lisp.h b/src/lisp.h
index 6c7b51fea06..7795c90e5cc 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -740,11 +740,18 @@ struct Lisp_Symbol
 /* Declare extern constants for Lisp symbols.  These can be helpful
    when using a debugger like GDB, on older platforms where the debug
    format does not represent C macros.  */
-#define DEFINE_LISP_SYMBOL_BEGIN(name) \
-  DEFINE_GDB_SYMBOL_BEGIN (Lisp_Object, name)
-#define DEFINE_LISP_SYMBOL_END(name) \
+#define DEFINE_LISP_SYMBOL(name) \
+  DEFINE_GDB_SYMBOL_BEGIN (Lisp_Object, name) \
   DEFINE_GDB_SYMBOL_END (LISP_INITIALLY (XLI_BUILTIN_LISPSYM (i##name)))
 
+/* By default, define macros for Qt, etc., as this leads to a bit
+   better performance in the core Emacs interpreter.  A plugin can
+   define DEFINE_NONNIL_Q_SYMBOL_MACROS to be false, to be portable to
+   other Emacs instances that assign different values to Qt, etc.  */
+#ifndef DEFINE_NONNIL_Q_SYMBOL_MACROS
+# define DEFINE_NONNIL_Q_SYMBOL_MACROS true
+#endif
+
 #include "globals.h"
 
 /* Convert a Lisp_Object to the corresponding EMACS_INT and vice versa.