[PATCH 2/4] reset: use "unpack_trees()" directly instead of "git read-tree"

@@ -18,6 +18,8 @@
 #include "tree.h"
 #include "branch.h"
 #include "parse-options.h"
+#include "unpack-trees.h"
+#include "cache-tree.h"
 
 static const char * const git_reset_usage[] = {
 	"git reset [--mixed | --soft | --hard | --merge] [-q] [<commit>]",

@@ -52,29 +54,56 @@ static inline int is_merge(void)
 	return !access(git_path("MERGE_HEAD"), F_OK);
 }
 
+static int parse_and_init_tree_desc(const unsigned char *sha1,
+					     struct tree_desc *desc)
+{
+	struct tree *tree = parse_tree_indirect(sha1);
+	if (!tree)
+		return 1;
+	init_tree_desc(desc, tree->buffer, tree->size);
+	return 0;
+}
+
 static int reset_index_file(const unsigned char *sha1, int reset_type, int quiet)
 {
-	int i = 0;
-	const char *args[6];
+	int nr = 1;
+	int newfd;
+	struct tree_desc desc[2];
+	struct unpack_trees_options opts;
+	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 
-	args[i++] = "read-tree";
+	memset(&opts, 0, sizeof(opts));
+	opts.head_idx = 1;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+	opts.fn = oneway_merge;
+	opts.merge = 1;
 	if (!quiet)
-		args[i++] = "-v";
+		opts.verbose_update = 1;
 	switch (reset_type) {
 	case MERGE:
-		args[i++] = "-u";
-		args[i++] = "-m";
+		opts.update = 1;
 		break;
 	case HARD:
-		args[i++] = "-u";
+		opts.update = 1;
 		/* fallthrough */
 	default:
-		args[i++] = "--reset";
+		opts.reset = 1;
 	}
-	args[i++] = sha1_to_hex(sha1);
-	args[i] = NULL;
 
-	return run_command_v_opt(args, RUN_GIT_CMD);
+	newfd = hold_locked_index(lock, 1);
+
+	read_cache_unmerged();
+
+	if (parse_and_init_tree_desc(sha1, desc + nr - 1))
+		return error("Failed to find tree of %s.", sha1_to_hex(sha1));
+	if (unpack_trees(nr, desc, &opts))
+		return -1;
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_locked_index(lock))
+		return error("Could not write new index file.");
+
+	return 0;
 }
 
 static void print_new_head_line(struct commit *commit)