oidtree: avoid nested struct oidtree_node

92d8ed8 (oidtree: a crit-bit tree for odb_loose_cache, 2021-07-07)
adds a struct oidtree_node that contains only an n field with a
struct cb_node.

unfortunately, while building in pedantic mode witch clang 12 (as well
as a similar error from gcc 11) it will show:

  oidtree.c:11:17: error: 'n' may not be nested in a struct due to flexible array member [-Werror,-Wflexible-array-extensions]
          struct cb_node n;
                         ^

because of a constrain coded in ISO C 11 6.7.2.1¶3 that forbids using
structs that contain a flexible array as part of another struct.

use a strict cb_node directly instead.

Signed-off-by: Carlo Marcelo Arenas Belón <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: carenas

oidtree.c

@@ -6,11 +6,6 @@
 #include "alloc.h"
 #include "hash.h"
 
-struct oidtree_node {
-	/* n.k[] is used to store "struct object_id" */
-	struct cb_node n;
-};
-
 struct oidtree_iter_data {
 	oidtree_iter fn;
 	void *arg;
@@ -35,21 +30,21 @@ void oidtree_clear(struct oidtree *ot)
 
 void oidtree_insert(struct oidtree *ot, const struct object_id *oid)
 {
-	struct oidtree_node *on;
+	struct cb_node *on;
 
 	if (!oid->algo)
 		BUG("oidtree_insert requires oid->algo");
 
 	on = mem_pool_alloc(&ot->mem_pool, sizeof(*on) + sizeof(*oid));
-	oidcpy_with_padding((struct object_id *)on->n.k, oid);
+	oidcpy_with_padding((struct object_id *)on->k, oid);
 
 	/*
 	 * n.b. Current callers won't get us duplicates, here.  If a
 	 * future caller causes duplicates, there'll be a a small leak
 	 * that won't be freed until oidtree_clear.  Currently it's not
 	 * worth maintaining a free list
 	 */
-	cb_insert(&ot->tree, &on->n, sizeof(*oid));
+	cb_insert(&ot->tree, on, sizeof(*oid));
 }