builtin/apply: add 'lock_file' pointer into 'struct apply_state'

We cannot have a 'struct lock_file' allocated on the stack, as lockfile.c
keeps a linked list of all created lock_file structures.

Also 'struct apply_state' users might later want the same 'struct lock_file'
instance to be reused by different series of calls to the apply api.

So let's add a 'struct lock_file *lock_file' pointer into 'struct apply_state'
and have the user of 'struct apply_state' allocate memory for the actual
'struct lock_file' instance.

Let's also add an argument to init_apply_state(), so that the caller can
easily supply a pointer to the allocated instance.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/apply.c

@@ -52,6 +52,12 @@ struct apply_state {
 	const char *prefix;
 	int prefix_length;
 
+	/*
+	 * Since lockfile.c keeps a linked list of all created
+	 * lock_file structures, it isn't safe to free(lock_file).
+	 */
+	struct lock_file *lock_file;
+
 	/* These control what gets looked at and modified */
 	int apply; /* this is not a dry-run */
 	int cached; /* apply to the index only */
@@ -4547,7 +4553,7 @@ static int apply_patch(struct apply_state *state,
 
 	state->update_index = state->check_index && state->apply;
 	if (state->update_index && newfd < 0)
-		newfd = hold_locked_index(&lock_file, 1);
+		newfd = hold_locked_index(state->lock_file, 1);
 
 	if (state->check_index) {
 		if (read_cache() < 0)
@@ -4648,11 +4654,14 @@ static int option_parse_directory(const struct option *opt,
 	return 0;
 }
 
-static void init_apply_state(struct apply_state *state, const char *prefix)
+static void init_apply_state(struct apply_state *state,
+			     const char *prefix,
+			     struct lock_file *lock_file)
 {
 	memset(state, 0, sizeof(*state));
 	state->prefix = prefix;
 	state->prefix_length = state->prefix ? strlen(state->prefix) : 0;
+	state->lock_file = lock_file;
 	state->apply = 1;
 	state->line_termination = '\n';
 	state->p_value = 1;
@@ -4705,6 +4714,8 @@ static void check_apply_state(struct apply_state *state, int force_apply)
 	}
 	if (state->check_index)
 		state->unsafe_paths = 0;
+	if (!state->lock_file)
+		die("BUG: state->lock_file should not be NULL");
 }
 
 static int apply_all_patches(struct apply_state *state,
@@ -4769,7 +4780,7 @@ static int apply_all_patches(struct apply_state *state,
 	}
 
 	if (state->update_index) {
-		if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
+		if (write_locked_index(&the_index, state->lock_file, COMMIT_LOCK))
 			die(_("Unable to write new index file"));
 	}
 
@@ -4852,7 +4863,7 @@ int cmd_apply(int argc, const char **argv, const char *prefix)
 		OPT_END()
 	};
 
-	init_apply_state(&state, prefix);
+	init_apply_state(&state, prefix, &lock_file);
 
 	argc = parse_options(argc, argv, state.prefix, builtin_apply_options,
 			apply_usage, 0);