type_to_string: return const char *.

Always be const if you can.

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

common/type_to_string.c

@@ -13,10 +13,10 @@ REGISTER_TYPE_TO_HEXSTR(ripemd160);
 /* This one in bitcoin/ but doesn't have its own C file */
 REGISTER_TYPE_TO_HEXSTR(preimage);
 
-char *type_to_string_(const tal_t *ctx,  const char *typename,
+const char *type_to_string_(const tal_t *ctx,  const char *typename,
 			    union printable_types u)
 {
-	char *s = NULL;
+	const char *s = NULL;
 	size_t i;
 	static size_t num_p;
 	static struct type_to_string **t = NULL;

common/type_to_string.h

@@ -38,11 +38,11 @@ union printable_types {
 			((void)sizeof((ptr) == (type *)NULL),		\
 			 ((union printable_types)((const type *)ptr))))
 
-char *type_to_string_(const tal_t *ctx, const char *typename,
+const 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,		\
+	static const char *fmt_##typename##_(const tal_t *ctx,		\
 					     union printable_types u)	\
 	{								\
 		return fmtfn(ctx, u.typename);				\
@@ -53,7 +53,7 @@ char *type_to_string_(const tal_t *ctx, const char *typename,
 	AUTODATA(type_to_string, &ttos_##typename)
 
 #define REGISTER_TYPE_TO_HEXSTR(typename)				\
-	static char *fmt_##typename##_(const tal_t *ctx,		\
+	static const char *fmt_##typename##_(const tal_t *ctx,		\
 					     union printable_types u)	\
 	{								\
 		return tal_hexstr(ctx, u.typename, sizeof(*u.typename)); \
@@ -65,7 +65,7 @@ char *type_to_string_(const tal_t *ctx, const char *typename,
 
 struct type_to_string {
 	const char *typename;
-	char *(*fmt)(const tal_t *ctx, union printable_types u);
+	const char *(*fmt)(const tal_t *ctx, union printable_types u);
 };
 AUTODATA_TYPE(type_to_string, struct type_to_string);
 #endif /* LIGHTNING_COMMON_TYPE_TO_STRING_H */

lightningd/channel.c

@@ -195,7 +195,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 	if (!log) {
 		/* FIXME: update log prefix when we get scid */
 		/* FIXME: Use minimal unique pubkey prefix for logs! */
-		char *idname = type_to_string(peer, struct pubkey, &peer->id);
+		const char *idname = type_to_string(peer, struct pubkey, &peer->id);
 		channel->log = new_log(channel,
 				       peer->log_book, "%s chan #%"PRIu64":",
 				       idname, dbid);

lightningd/opening_control.c

@@ -604,7 +604,7 @@ new_uncommitted_channel(struct peer *peer)
 {
 	struct lightningd *ld = peer->ld;
 	struct uncommitted_channel *uc = tal(ld, struct uncommitted_channel);
-	char *idname;
+	const char *idname;
 
 	uc->peer = peer;
 	assert(!peer->uncommitted_channel);