An OUTARG() macro for optional return values

The OUTARG() macro avoids a fair amount of tedious boilerplate.
I have included a Coccinelle semantic patch to use OUTARG()
where appropriate. The patch needs a #include in `openssl_shim.c`
in order to work.

cocci/outarg.spatch

@@ -0,0 +1,14 @@
+@@
+type T;
+identifier fun;
+identifier arg;
+expression val;
+@@
+	fun(..., T *arg, ...) {
+		...
+-		if (arg != NULL) {
+-				*arg = val;
+-		}
++		OUTARG(arg, val);
+		...
+	}

lib/dns/openssl_shim.c

@@ -13,6 +13,8 @@
 
 #include "openssl_shim.h"
 
+#include <isc/util.h>
+
 #if !HAVE_RSA_SET0_KEY && OPENSSL_VERSION_NUMBER < 0x30000000L
 /* From OpenSSL 1.1.0 */
 int

lib/isc/histo.c

@@ -34,16 +34,6 @@
 #define STRUCT_FLEX_SIZE(pointer, member, count) \
 	(sizeof(*(pointer)) + sizeof(*(pointer)->member) * (count))
 
-/*
- * XXXFANF this should probably be in <isc/util.h> too
- */
-#define OUTARG(ptr, val)                \
-	({                              \
-		if ((ptr) != NULL) {    \
-			*(ptr) = (val); \
-		}                       \
-	})
-
 #define HISTO_MAGIC	    ISC_MAGIC('H', 's', 't', 'o')
 #define HISTO_VALID(p)	    ISC_MAGIC_VALID(p, HISTO_MAGIC)
 #define HISTOMULTI_MAGIC    ISC_MAGIC('H', 'g', 'M', 't')

lib/isc/include/isc/util.h

@@ -96,6 +96,16 @@
 
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
 
+/*
+ * Optional return values, or out-arguments
+ */
+#define OUTARG(ptr, val)                \
+	({                              \
+		if ((ptr) != NULL) {    \
+			*(ptr) = (val); \
+		}                       \
+	})
+
 /*%
  * Use this in translation units that would otherwise be empty, to
  * suppress compiler warnings.