From: Rusty Russell <rusty@rustcorp.com.au>
Date: Mon, 9 Jan 2023 02:06:22 +0000 (+1030)
Subject: tcon: fix warning when it's used with NULL on some gcc versions.
X-Git-Url: http://git.ozlabs.org/?p=ccan;a=commitdiff_plain;h=5c6a0ad7a9260c4cb02c707a0d813d17b23d9289

tcon: fix warning when it's used with NULL on some gcc versions.

Seems to be happening with gcc 12.2.0-3ubuntu1:

```
lightningd/jsonrpc.c: In function ‘destroy_json_command’:
lightningd/jsonrpc.c:1180:63: error: the comparison will always evaluate as ‘false’ for the address of ‘canary’ will never be NULL [-Werror=address]
lightningd/jsonrpc.c:108:53: note: ‘canary’ declared here
```

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

diff --git a/ccan/tcon/tcon.h b/ccan/tcon/tcon.h
index e0f84b38..df3aac88 100644
--- a/ccan/tcon/tcon.h
+++ b/ccan/tcon/tcon.h
@@ -147,8 +147,7 @@
  * It evaluates to @x so you can chain it.
  */
 #define tcon_check_ptr(x, canary, expr)				\
-	(sizeof(&(x)->_tcon[0].canary == (expr)) ? (x) : (x))
-
+	(sizeof((expr) ? (expr) : &(x)->_tcon[0].canary) ? (x) : (x))
 
 /**
  * tcon_type - the type within a container (or void *)