db: remove manual db_migration_count function.

More efficient to measure the ARRAY_SIZE(), which is a runtime
constant.  We move it into the unit test.

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

wallet/db.c

@@ -1,5 +1,6 @@
 #include "db.h"
 
+#include <ccan/array_size/array_size.h>
 #include <ccan/tal/str/str.h>
 #include <common/json_escaped.h>
 #include <common/version.h>
@@ -600,20 +601,6 @@ static int db_get_version(struct db *db)
 	}
 }
 
-/**
- * db_migration_count - Count how many migrations are available
- *
- * Returns the maximum migration index, i.e., the version number of an
- * up-to-date database schema.
- */
-static int db_migration_count(void)
-{
-	int count = 0;
-	while (dbmigrations[count] != NULL)
-		count++;
-	return count - 1;
-}
-
 /**
  * db_migrate - Apply all remaining migrations from the current version
  */
@@ -625,7 +612,7 @@ static void db_migrate(struct db *db, struct log *log)
 	db_begin_transaction(db);
 
 	orig = current = db_get_version(db);
-	available = db_migration_count();
+	available = ARRAY_SIZE(dbmigrations) - 2;
 
 	if (current == -1)
 		log_info(log, "Creating database");

wallet/test/run-db.c

@@ -51,6 +51,14 @@ static struct db *create_test_db(void)
 	return db;
 }
 
+static int db_migration_count(void)
+{
+	int count = 0;
+	while (dbmigrations[count] != NULL)
+		count++;
+	return count - 1;
+}
+
 static bool test_empty_db_migrate(void)
 {
 	struct db *db = create_test_db();
@@ -61,6 +69,7 @@ static bool test_empty_db_migrate(void)
 	db_migrate(db, NULL);
 	db_begin_transaction(db);
 	CHECK(db_get_version(db) == db_migration_count());
+	CHECK(db_get_version(db) == ARRAY_SIZE(dbmigrations) - 2);
 	db_commit_transaction(db);
 
 	tal_free(db);