sparse-checkout: add sanity-checks on initial sparsity state

Most sparse-checkout subcommands (list, add, reapply) only make sense
when already in a sparse state.  Add a quick check that will error out
early if this is not the case.

Also document with a comment why we do not exit early in `disable` even
when core.sparseCheckout starts as false.

Reviewed-by: Derrick Stolee <[email protected]>
Reviewed-by: Victoria Dye <[email protected]>
Signed-off-by: Elijah Newren <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: newren

builtin/sparse-checkout.c

@@ -56,6 +56,9 @@ static int sparse_checkout_list(int argc, const char **argv)
 	char *sparse_filename;
 	int res;
 
+	if (!core_apply_sparse_checkout)
+		die(_("this worktree is not sparse"));
+
 	argc = parse_options(argc, argv, NULL,
 			     builtin_sparse_checkout_list_options,
 			     builtin_sparse_checkout_list_usage, 0);
@@ -671,6 +674,9 @@ static int sparse_checkout_add(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	if (!core_apply_sparse_checkout)
+		die(_("no sparse-checkout to add to"));
+
 	repo_read_index(the_repository);
 
 	argc = parse_options(argc, argv, prefix,
@@ -719,6 +725,9 @@ static int sparse_checkout_reapply(int argc, const char **argv)
 		OPT_END(),
 	};
 
+	if (!core_apply_sparse_checkout)
+		die(_("must be in a sparse-checkout to reapply sparsity patterns"));
+
 	argc = parse_options(argc, argv, NULL,
 			     builtin_sparse_checkout_reapply_options,
 			     builtin_sparse_checkout_reapply_usage, 0);
@@ -740,6 +749,17 @@ static int sparse_checkout_disable(int argc, const char **argv)
 	struct pattern_list pl;
 	struct strbuf match_all = STRBUF_INIT;
 
+	/*
+	 * We do not exit early if !core_apply_sparse_checkout; due to the
+	 * ability for users to manually muck things up between
+	 *   direct editing of .git/info/sparse-checkout
+	 *   running read-tree -m u HEAD or update-index --skip-worktree
+	 *   direct toggling of config options
+	 * users might end up with an index with SKIP_WORKTREE bit set on
+	 * some files and not know how to undo it.  So, here we just
+	 * forcibly return to a dense checkout regardless of initial state.
+	 */
+
 	argc = parse_options(argc, argv, NULL,
 			     builtin_sparse_checkout_disable_options,
 			     builtin_sparse_checkout_disable_usage, 0);

t/t1091-sparse-checkout-builtin.sh

@@ -41,7 +41,15 @@ test_expect_success 'setup' '
 	)
 '
 
-test_expect_success 'git sparse-checkout list (empty)' '
+test_expect_success 'git sparse-checkout list (not sparse)' '
+	test_must_fail git -C repo sparse-checkout list >list 2>err &&
+	test_must_be_empty list &&
+	test_i18ngrep "this worktree is not sparse" err
+'
+
+test_expect_success 'git sparse-checkout list (not sparse)' '
+	git -C repo sparse-checkout set &&
+	rm repo/.git/info/sparse-checkout &&
 	git -C repo sparse-checkout list >list 2>err &&
 	test_must_be_empty list &&
 	test_i18ngrep "this worktree is not sparse (sparse-checkout file may not exist)" err