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.

4 files changed, 41 insertions, 16 deletions

diff --git a/lib-src/ChangeLog b/lib-src/ChangeLog
index 8d2c95e671c..534d253cabb 100644
--- a/lib-src/ChangeLog
+++ b/lib-src/ChangeLog
@@ -1,3 +1,13 @@
+2015-02-13  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Better support for future plugins
+	See the thread containing:
+	http://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00720.html
+	* 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.
+
 2015-01-24  Paul Eggert  <eggert@cs.ucla.edu>
 
 	Fix a couple of AM_V_GEN bugs
diff --git a/lib-src/make-docfile.c b/lib-src/make-docfile.c
index 79d421a0a8e..a7943e3118c 100644
--- a/lib-src/make-docfile.c
+++ b/lib-src/make-docfile.c
@@ -707,12 +707,9 @@ write_globals (void)
 		  globals[i].name, globals[i].name);
 	}
       else if (globals[i].type == SYMBOL)
-	printf (("DEFINE_LISP_SYMBOL_BEGIN (%s)\n"
-		 "#define i%s %d\n"
-		 "#define %s builtin_lisp_symbol (i%s)\n"
-		 "DEFINE_LISP_SYMBOL_END (%s)\n\n"),
-		globals[i].name, globals[i].name, symnum++,
-		globals[i].name, globals[i].name, globals[i].name);
+	printf (("#define i%s %d\n"
+		 "DEFINE_LISP_SYMBOL (%s)\n"),
+		globals[i].name, symnum++, globals[i].name);
       else
 	{
 	  if (globals[i].flags & DEFUN_noreturn)
@@ -740,15 +737,19 @@ write_globals (void)
   puts ("#ifdef DEFINE_SYMBOLS");
   puts ("static char const *const defsym_name[] = {");
   for (int i = 0; i < num_globals; i++)
-    {
-      if (globals[i].type == SYMBOL)
-	printf ("\t\"%s\",\n", globals[i].v.svalue);
-      while (i + 1 < num_globals
-	     && strcmp (globals[i].name, globals[i + 1].name) == 0)
-	i++;
-    }
+    if (globals[i].type == SYMBOL)
+      printf ("\t\"%s\",\n", globals[i].v.svalue);
   puts ("};");
   puts ("#endif");
+
+  puts ("#define Qnil builtin_lisp_symbol (0)");
+  puts ("#if DEFINE_NONNIL_Q_SYMBOL_MACROS");
+  num_symbols = 0;
+  for (int i = 0; i < num_globals; i++)
+    if (globals[i].type == SYMBOL && num_symbols++ != 0)
+      printf ("# define %s builtin_lisp_symbol (%d)\n",
+	      globals[i].name, num_symbols - 1);
+  puts ("#endif");
 }
 
 
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.