type_to_string: make type printing dynamic.

The union still contains all the types, but we can only print
the ones which are linked in.

This makes it much easier to use type_to_string in different binaries
without pulling in the world.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

type_to_string.c

@@ -11,6 +11,8 @@
 #include <ccan/tal/str/str.h>
 #include <inttypes.h>
 
+REGISTER_TYPE_TO_STRING(netaddr, netaddr_name);
+
 char *type_to_string_(const tal_t *ctx,  const char *typename,
 		      union printable_types u)
 {
@@ -78,9 +80,26 @@ char *type_to_string_(const tal_t *ctx,  const char *typename,
 					   &u.cstate->side[LOCAL]),
 			    type_to_string(ctx, struct channel_oneside,
 					   &u.cstate->side[REMOTE]));
-	} else if (streq(typename, "struct netaddr")) {
-		s = netaddr_name(ctx, u.netaddr);
-	}
+	} else {
+		size_t i;
+		static size_t num_p;
+		static struct type_to_string **t = NULL;
+
+		if (!t)
+			t = autodata_get(type_to_string, &num_p);
 
+		/* Typenames in registrations don't include "struct " */
+		if (strstarts(typename, "struct "))
+			typename += strlen("struct ");
+
+		for (i = 0; i < num_p; i++) {
+			if (streq(t[i]->typename, typename)) {
+				s = t[i]->fmt(ctx, u);
+				break;
+			}
+		}
+		if (!s)
+			s = tal_fmt(ctx, "UNKNOWN TYPE %s", typename);
+	}
 	return s;
 }

type_to_string.h

@@ -1,7 +1,8 @@
 #ifndef LIGHTNING_TYPE_TO_STRING_H
 #define LIGHTNING_TYPE_TO_STRING_H
 #include "config.h"
-#include <ccan/tal/tal.h>
+#include "utils.h"
+#include <ccan/autodata/autodata.h>
 
 /* This must match the type_to_string_ cases. */
 union printable_types {
@@ -27,4 +28,31 @@ union printable_types {
 char *type_to_string_(const tal_t *ctx, const char *typename,
 		      union printable_types u);
 
+#define REGISTER_TYPE_TO_STRING(typename, fmtfn)			\
+	static char *fmt_##typename##_(const tal_t *ctx,		\
+				       union printable_types u)		\
+	{								\
+		return fmtfn(ctx, u.typename);				\
+	}								\
+	static struct type_to_string ttos_##typename = {		\
+		#typename, fmt_##typename##_				\
+	};								\
+	AUTODATA(type_to_string, &ttos_##typename)
+
+#define REGISTER_TYPE_TO_HEXSTR(typename)				\
+	static char *fmt_##typename##_(const tal_t *ctx,		\
+				       union printable_types u)		\
+	{								\
+		return tal_hexstr(ctx, u.typename, sizeof(*u.typename)); \
+	}								\
+	static struct type_to_string ttos_##typename = {		\
+		#typename, fmt_##typename##_				\
+	};								\
+	AUTODATA(type_to_string, &ttos_##typename)
+
+struct type_to_string {
+	const char *typename;
+	char *(*fmt)(const tal_t *ctx, union printable_types u);
+};
+AUTODATA_TYPE(type_to_string, struct type_to_string);
 #endif /* LIGHTNING_UTILS_H */