checkout-index: integrate with sparse index

Add repository settings to allow usage of the sparse index.

When using the `--all` option, sparse directories are ignored by default due
to the `skip-worktree` flag, so there is no need to expand the index. If
`--ignore-skip-worktree-bits` is specified, the index is expanded in order
to check out all files.

When checking out individual files, existing behavior in a full index is to
exit with an error if a directory is specified (as the directory name will
not match an index entry). However, it is possible in a sparse index to
match a directory name to a sparse directory index entry, but checking out
that sparse directory still results in an error on checkout. To reduce some
potential confusion for users, `checkout_file(...)` explicitly exits with an
informative error if provided with a sparse directory name. The test
corresponding to this scenario verifies the error message, which now differs
between sparse index and non-sparse index checkouts.

Signed-off-by: Victoria Dye <vdye@github.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout-index.c

@@ -67,6 +67,7 @@ static int checkout_file(const char *name, const char *prefix)
 	int namelen = strlen(name);
 	int pos = cache_name_pos(name, namelen);
 	int has_same_name = 0;
+	int is_file = 0;
 	int is_skipped = 1;
 	int did_checkout = 0;
 	int errs = 0;
@@ -81,6 +82,9 @@ static int checkout_file(const char *name, const char *prefix)
 			break;
 		has_same_name = 1;
 		pos++;
+		if (S_ISSPARSEDIR(ce->ce_mode))
+			break;
+		is_file = 1;
 		if (!ignore_skip_worktree && ce_skip_worktree(ce))
 			break;
 		is_skipped = 0;
@@ -112,6 +116,8 @@ static int checkout_file(const char *name, const char *prefix)
 		fprintf(stderr, "git checkout-index: %s ", name);
 		if (!has_same_name)
 			fprintf(stderr, "is not in the cache");
+		else if (!is_file)
+			fprintf(stderr, "is a sparse directory");
 		else if (is_skipped)
 			fprintf(stderr, "has skip-worktree enabled; "
 					"use '--ignore-skip-worktree-bits' to checkout");
@@ -130,10 +136,25 @@ static int checkout_all(const char *prefix, int prefix_length)
 	int i, errs = 0;
 	struct cache_entry *last_ce = NULL;
 
-	/* TODO: audit for interaction with sparse-index. */
-	ensure_full_index(&the_index);
 	for (i = 0; i < active_nr ; i++) {
 		struct cache_entry *ce = active_cache[i];
+
+		if (S_ISSPARSEDIR(ce->ce_mode)) {
+			if (!ce_skip_worktree(ce))
+				BUG("sparse directory '%s' does not have skip-worktree set", ce->name);
+
+			/*
+			 * If the current entry is a sparse directory and skip-worktree
+			 * entries are being checked out, expand the index and continue
+			 * the loop on the current index position (now pointing to the
+			 * first entry inside the expanded sparse directory).
+			 */
+			if (ignore_skip_worktree) {
+				ensure_full_index(&the_index);
+				ce = active_cache[i];
+			}
+		}
+
 		if (!ignore_skip_worktree && ce_skip_worktree(ce))
 			continue;
 		if (ce_stage(ce) != checkout_stage
@@ -225,6 +246,9 @@ int cmd_checkout_index(int argc, const char **argv, const char *prefix)
 	git_config(git_default_config, NULL);
 	prefix_length = prefix ? strlen(prefix) : 0;
 
+	prepare_repo_settings(the_repository);
+	the_repository->settings.command_requires_full_index = 0;
+
 	if (read_cache() < 0) {
 		die("invalid cache");
 	}

t/t1092-sparse-checkout-compatibility.sh

@@ -801,7 +801,14 @@ test_expect_success 'checkout-index with folders' '
 	test_all_match test_must_fail git checkout-index -f -- deep/ &&
 
 	# Outside checkout definition
-	test_all_match test_must_fail git checkout-index -f -- folder1/
+	# Note: although all tests fail (as expected), the messaging differs. For
+	# non-sparse index checkouts, the error is that the "file" does not appear
+	# in the index; for sparse checkouts, the error is explicitly that the
+	# entry is a sparse directory.
+	run_on_all test_must_fail git checkout-index -f -- folder1/ &&
+	test_cmp full-checkout-err sparse-checkout-err &&
+	! test_cmp full-checkout-err sparse-index-err &&
+	grep "is a sparse directory" sparse-index-err
 '
 
 test_expect_success 'checkout-index --all' '
@@ -972,6 +979,8 @@ test_expect_success 'sparse-index is not expanded' '
 	echo >>sparse-index/untracked.txt &&
 	ensure_not_expanded add . &&
 
+	ensure_not_expanded checkout-index -f a &&
+	ensure_not_expanded checkout-index -f --all &&
 	for ref in update-deep update-folder1 update-folder2 update-deep
 	do
 		echo >>sparse-index/README.md &&