5 files changed, 105 insertions, 16 deletions

diff --git a/builtin/read-tree.c b/builtin/read-tree.c
index ca5e655d2f..af7424b94c 100644
--- a/builtin/read-tree.c
+++ b/builtin/read-tree.c
@@ -185,7 +185,7 @@ int cmd_read_tree(int argc, const char **argv, const char *cmd_prefix)
 
 	if (opts.reset || opts.merge || opts.prefix) {
 		if (read_cache_unmerged() && (opts.prefix || opts.merge))
-			die("You need to resolve your current index first");
+			die(_("You need to resolve your current index first"));
 		stage = opts.merge = 1;
 	}
 	resolve_undo_clear();
diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 55b337ad8e..a5d32e4702 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -7,6 +7,11 @@
 #include "run-command.h"
 #include "strbuf.h"
 #include "string-list.h"
+#include "cache.h"
+#include "cache-tree.h"
+#include "lockfile.h"
+#include "resolve-undo.h"
+#include "unpack-trees.h"
 
 static char const * const builtin_sparse_checkout_usage[] = {
 	N_("git sparse-checkout (init|list|set|disable) <options>"),
@@ -60,18 +65,54 @@ static int sparse_checkout_list(int argc, const char **argv)
 	return 0;
 }
 
-static int update_working_directory(void)
+static int update_working_directory(struct pattern_list *pl)
 {
-	struct argv_array argv = ARGV_ARRAY_INIT;
 	int result = 0;
-	argv_array_pushl(&argv, "read-tree", "-m", "-u", "HEAD", NULL);
+	struct unpack_trees_options o;
+	struct lock_file lock_file = LOCK_INIT;
+	struct object_id oid;
+	struct tree *tree;
+	struct tree_desc t;
+	struct repository *r = the_repository;
 
-	if (run_command_v_opt(argv.argv, RUN_GIT_CMD)) {
-		error(_("failed to update index with new sparse-checkout patterns"));
-		result = 1;
-	}
+	if (repo_read_index_unmerged(r))
+		die(_("you need to resolve your current index first"));
+
+	if (get_oid("HEAD", &oid))
+		return 0;
+
+	tree = parse_tree_indirect(&oid);
+	parse_tree(tree);
+	init_tree_desc(&t, tree->buffer, tree->size);
+
+	memset(&o, 0, sizeof(o));
+	o.verbose_update = isatty(2);
+	o.merge = 1;
+	o.update = 1;
+	o.fn = oneway_merge;
+	o.head_idx = -1;
+	o.src_index = r->index;
+	o.dst_index = r->index;
+	o.skip_sparse_checkout = 0;
+	o.pl = pl;
+	o.keep_pattern_list = !!pl;
+
+	resolve_undo_clear_index(r->index);
+	setup_work_tree();
+
+	cache_tree_free(&r->index->cache_tree);
+
+	repo_hold_locked_index(r, &lock_file, LOCK_DIE_ON_ERROR);
+
+	core_apply_sparse_checkout = 1;
+	result = unpack_trees(1, &t, &o);
+
+	if (!result) {
+		prime_cache_tree(r, r->index, tree);
+		write_locked_index(r->index, &lock_file, COMMIT_LOCK);
+	} else
+		rollback_lock_file(&lock_file);
 
-	argv_array_clear(&argv);
 	return result;
 }
 
@@ -129,6 +170,15 @@ static int write_patterns_and_update(struct pattern_list *pl)
 {
 	char *sparse_filename;
 	FILE *fp;
+	int result;
+
+	result = update_working_directory(pl);
+
+	if (result) {
+		clear_pattern_list(pl);
+		update_working_directory(NULL);
+		return result;
+	}
 
 	sparse_filename = get_sparse_checkout_filename();
 	fp = fopen(sparse_filename, "w");
@@ -139,9 +189,11 @@ static int write_patterns_and_update(struct pattern_list *pl)
 		write_patterns_to_file(fp, pl);
 
 	fclose(fp);
+
 	free(sparse_filename);
+	clear_pattern_list(pl);
 
-	return update_working_directory();
+	return 0;
 }
 
 enum sparse_checkout_mode {
@@ -199,7 +251,11 @@ static int sparse_checkout_init(int argc, const char **argv)
 			     builtin_sparse_checkout_init_options,
 			     builtin_sparse_checkout_init_usage, 0);
 
-	mode = init_opts.cone_mode ? MODE_CONE_PATTERNS : MODE_ALL_PATTERNS;
+	if (init_opts.cone_mode) {
+		mode = MODE_CONE_PATTERNS;
+		core_sparse_checkout_cone = 1;
+	} else
+		mode = MODE_ALL_PATTERNS;
 
 	if (set_config(mode))
 		return 1;
@@ -230,7 +286,8 @@ static int sparse_checkout_init(int argc, const char **argv)
 	}
 
 reset_dir:
-	return update_working_directory();
+	core_apply_sparse_checkout = 1;
+	return update_working_directory(NULL);
 }
 
 static void insert_recursive_pattern(struct pattern_list *pl, struct strbuf *path)
@@ -311,6 +368,7 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 
 		hashmap_init(&pl.recursive_hashmap, pl_hashmap_cmp, NULL, 0);
 		hashmap_init(&pl.parent_hashmap, pl_hashmap_cmp, NULL, 0);
+		pl.use_cone_patterns = 1;
 
 		if (set_opts.use_stdin) {
 			while (!strbuf_getline(&line, stdin))
@@ -365,7 +423,8 @@ static int sparse_checkout_disable(int argc, const char **argv)
 	fprintf(fp, "/*\n");
 	fclose(fp);
 
-	if (update_working_directory())
+	core_apply_sparse_checkout = 1;
+	if (update_working_directory(NULL))
 		die(_("error while refreshing working directory"));
 
 	unlink(sparse_filename);
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index b88d08da98..53aeb5980f 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -248,4 +248,32 @@ test_expect_success 'cone mode: set with nested folders' '
 	test_cmp repo/.git/info/sparse-checkout expect
 '
 
+test_expect_success 'revert to old sparse-checkout on bad update' '
+	echo update >repo/deep/deeper2/a &&
+	cp repo/.git/info/sparse-checkout expect &&
+	test_must_fail git -C repo sparse-checkout set deep/deeper1 2>err &&
+	test_i18ngrep "Cannot update sparse checkout" err &&
+	test_cmp repo/.git/info/sparse-checkout expect &&
+	ls repo/deep >dir &&
+	cat >expect <<-EOF &&
+		a
+		deeper1
+		deeper2
+	EOF
+	test_cmp dir expect
+'
+
+test_expect_success 'revert to old sparse-checkout on empty update' '
+	git init empty-test &&
+	(
+		echo >file &&
+		git add file &&
+		git commit -m "test" &&
+		test_must_fail git sparse-checkout set nothing 2>err &&
+		test_i18ngrep "Sparse checkout leaves no entry on working directory" err &&
+		test_i18ngrep ! ".git/index.lock" err &&
+		git sparse-checkout set file
+	)
+'
+
 test_done
diff --git a/unpack-trees.c b/unpack-trees.c
index 8bb684ad62..3789a22cf0 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1511,7 +1511,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	memset(&pl, 0, sizeof(pl));
 	if (!core_apply_sparse_checkout || !o->update)
 		o->skip_sparse_checkout = 1;
-	if (!o->skip_sparse_checkout) {
+	if (!o->skip_sparse_checkout && !o->pl) {
 		char *sparse = git_pathdup("info/sparse-checkout");
 		pl.use_cone_patterns = core_sparse_checkout_cone;
 		if (add_patterns_from_file_to_list(sparse, "", 0, &pl, NULL) < 0)
@@ -1684,7 +1684,8 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 
 done:
 	trace_performance_leave("unpack_trees");
-	clear_pattern_list(&pl);
+	if (!o->keep_pattern_list)
+		clear_pattern_list(&pl);
 	return ret;
 
 return_failed:
diff --git a/unpack-trees.h b/unpack-trees.h
index f2eee0c7c5..ca94a421a5 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -59,7 +59,8 @@ struct unpack_trees_options {
 		     quiet,
 		     exiting_early,
 		     show_all_errors,
-		     dry_run;
+		     dry_run,
+		     keep_pattern_list;
 	const char *prefix;
 	int cache_bottom;
 	struct dir_struct *dir;