tal_tmpctx: keep information around so we can find leaks.

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

common/utils.c

@@ -1,5 +1,7 @@
 #include "utils.h"
+#include <ccan/list/list.h>
 #include <ccan/str/hex/hex.h>
+#include <ccan/tal/str/str.h>
 
 secp256k1_context *secp256k1_ctx;
 
@@ -22,3 +24,35 @@ u8 *tal_hexdata(const tal_t *ctx, const void *str, size_t len)
 		return NULL;
 	return data;
 }
+
+struct tmpctx {
+	struct list_node list;
+	const char *file;
+	unsigned int line;
+};
+
+static struct list_head tmpctxs = LIST_HEAD_INIT(tmpctxs);
+
+static void destroy_tmpctx(struct tmpctx *t)
+{
+	list_del_from(&tmpctxs, &t->list);
+}
+
+tal_t *tal_tmpctx_(const tal_t *ctx, const char *file, unsigned int line)
+{
+	struct tmpctx *t = tal(ctx, struct tmpctx);
+	t->file = file;
+	t->line = line;
+	list_add_tail(&tmpctxs, &t->list);
+	tal_add_destructor(t, destroy_tmpctx);
+	return t;
+}
+
+const char *tmpctx_any(void)
+{
+	struct tmpctx *t = list_top(&tmpctxs, struct tmpctx, list);
+
+	if (t)
+		return tal_fmt(t, "%s:%u", t->file, t->line);
+	return NULL;
+}