Guard .tag; it helps keep structs tidy.

src/libfsm/clone.c

@@ -118,7 +118,9 @@ copy_capture_actions(struct fsm *dst, const struct fsm *src)
 }
 
 struct copy_end_ids_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	struct fsm *dst;
 	const struct fsm *src;
 	bool ok;

src/libfsm/consolidate.c

@@ -36,7 +36,9 @@ struct mapping_closure {
 };
 
 struct consolidate_copy_capture_actions_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	struct fsm *dst;
 	size_t mapping_count;
 	const fsm_state_t *mapping;

src/libfsm/determinise_internal.h

@@ -83,7 +83,9 @@ struct reverse_mapping {
 };
 
 struct det_copy_capture_actions_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	struct fsm *dst;
 	struct reverse_mapping *reverse_mappings;
 	bool ok;

src/libfsm/endids.c

@@ -753,7 +753,9 @@ fsm_endid_get(const struct fsm *fsm, fsm_state_t end_state,
 }
 
 struct carry_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	struct fsm *dst;
 	fsm_state_t dst_state;
 	bool ok;

src/libfsm/epsilons.c

@@ -28,7 +28,9 @@
 #define DEF_CARRY_ENDIDS_COUNT 2
 
 struct remap_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	bool ok;
 	const struct fsm_alloc *alloc;
 	struct state_set **rmap;

src/libfsm/merge.c

@@ -26,7 +26,9 @@
 #define LOG_MERGE_ENDIDS 0
 
 struct copy_capture_env {
+#ifndef NDEBUG
 	char tag;
+#endif
 	bool ok;
 	struct fsm *dst;
 };