Improve checking for C99-style varargs macros.

[sod] / lib / sod.h

diff --git a/lib/sod.h b/lib/sod.h
index dc85843..360afa8 100644 (file)
--- a/lib/sod.h
+++ b/lib/sod.h
@@ -34,6 +34,49 @@
 
 /*----- Preliminary utilities ---------------------------------------------*/
 
+/* --- @SOD__HAVE_VARARGS_MACROS@ --- *
+ *
+ * Use:                Defined if the compiler supports C99-style variadic macros.
+ *
+ *             This is more complicated than just checking the value of
+ *             @__STDC_VERSION__@ because GCC has traditionally claimed C89
+ *             by default, but provides the functionality anyway unless it's
+ *             been explicitly turned off.
+ */
+
+#if __STDC_VERSION__ >= 199901
+   /* The feature exists.  All is well with the world. */
+
+#  define SOD__HAVE_VARARGS_MACROS
+
+#elif __GNUC__ >= 3
+   /* We're using GCC, which is trying to deny it but we don't believe it.
+    * Unfortunately there's a fly in the ointment: if `-pedantic' -- or,
+    * worse, `-pedantic-errors' -- is set, then GCC will warn about these
+    * macros being defined, and there isn't a way to detect pedantry from the
+    * preprocessor.
+    *
+    * We must deploy bodges.  There doesn't seem to be a good way to suppress
+    * particular warnings from the preprocessor: in particular, messing about
+    * with `pragma GCC diagnostic' doesn't help.  So we're left with this
+    * hack: just declare all Sod-generated header files which try to do
+    * varargs macro things to be `system headers', which means that GCC's
+    * preprocessor will let them get away with all manner of nefarious stuff.
+    */
+
+#  define SOD__HAVE_VARARGS_MACROS
+#  define SOD__VARARGS_MACROS_PREAMBLE _Pragma("GCC system_header")
+
+#endif
+
+/* Make sure this gratuitous hack is understood, at least vacuously. */
+#ifndef SOD__VARARGS_MACROS_PREAMBLE
+#  define SOD__VARARGS_MACROS_PREAMBLE
+#endif
+
+/* We're going to want to make use of this ourselves. */
+SOD__VARARGS_MACROS_PREAMBLE
+
 /* --- @SOD__CAR@ --- *
  *
  * Arguments:  @...@ = a nonempty list of arguments
@@ -41,7 +84,7 @@
  * Returns:    The first argument only.
  */
 
-#if __STDC_VERSION__ >= 199901
+#ifdef SOD__HAVE_VARARGS_MACROS
 #  define SOD__CAR(...) SOD__CARx(__VA_LIST__, _)
 #  define SOD__CARx(a, ...) a
 #endif