sparse-checkout: provide a new reapply subcommand

If commands like merge or rebase materialize files as part of their work,
or a previous sparse-checkout command failed to update individual files
due to dirty changes, users may want a command to simply 'reapply' the
sparsity rules.  Provide one.

Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-sparse-checkout.txt

@@ -70,6 +70,16 @@ C-style quoted strings.
 	`core.sparseCheckoutCone` is enabled, the given patterns are interpreted
 	as directory names as in the 'set' subcommand.
 
+'reapply::
+	Reapply the sparsity pattern rules to paths in the working tree.
+	Commands like merge or rebase can materialize paths to do their
+	work (e.g. in order to show you a conflict), and other
+	sparse-checkout commands might fail to sparsify an individual file
+	(e.g. because it has unstaged changes or conflicts).  In such
+	cases, it can make sense to run `git sparse-checkout reapply` later
+	after cleaning up affected paths (e.g. resolving conflicts, undoing
+	or committing changes, etc.).
+
 'disable'::
 	Disable the `core.sparseCheckout` config setting, and restore the
 	working directory to include all files. Leaves the sparse-checkout

builtin/sparse-checkout.c

@@ -18,7 +18,7 @@
 static const char *empty_base = "";
 
 static char const * const builtin_sparse_checkout_usage[] = {
-	N_("git sparse-checkout (init|list|set|add|disable) <options>"),
+	N_("git sparse-checkout (init|list|set|add|reapply|disable) <options>"),
 	NULL
 };
 
@@ -554,6 +554,12 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix,
 	return modify_pattern_list(argc, argv, m);
 }
 
+static int sparse_checkout_reapply(int argc, const char **argv)
+{
+	repo_read_index(the_repository);
+	return update_working_directory(NULL);
+}
+
 static int sparse_checkout_disable(int argc, const char **argv)
 {
 	struct pattern_list pl;
@@ -603,6 +609,8 @@ int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
 			return sparse_checkout_set(argc, argv, prefix, REPLACE);
 		if (!strcmp(argv[0], "add"))
 			return sparse_checkout_set(argc, argv, prefix, ADD);
+		if (!strcmp(argv[0], "reapply"))
+			return sparse_checkout_reapply(argc, argv);
 		if (!strcmp(argv[0], "disable"))
 			return sparse_checkout_disable(argc, argv);
 	}

t/t1091-sparse-checkout-builtin.sh

@@ -370,6 +370,47 @@ test_expect_success 'sparse-checkout (init|set|disable) warns with unmerged stat
 	git -C unmerged sparse-checkout disable
 '
 
+test_expect_success 'sparse-checkout reapply' '
+	git clone repo tweak &&
+
+	echo dirty >tweak/deep/deeper2/a &&
+
+	cat >input <<-EOF &&
+	0 0000000000000000000000000000000000000000	folder1/a
+	100644 $(git -C tweak rev-parse HEAD:folder1/a) 1	folder1/a
+	EOF
+	git -C tweak update-index --index-info <input &&
+
+	git -C tweak sparse-checkout init --cone 2>err &&
+	test_i18ngrep "warning.*The following paths are not up to date" err &&
+	test_i18ngrep "warning.*The following paths are unmerged" err &&
+
+	git -C tweak sparse-checkout set folder2 deep/deeper1 2>err &&
+	test_i18ngrep "warning.*The following paths are not up to date" err &&
+	test_i18ngrep "warning.*The following paths are unmerged" err &&
+
+	git -C tweak sparse-checkout reapply 2>err &&
+	test_i18ngrep "warning.*The following paths are not up to date" err &&
+	test_path_is_file tweak/deep/deeper2/a &&
+	test_i18ngrep "warning.*The following paths are unmerged" err &&
+	test_path_is_file tweak/folder1/a &&
+
+	git -C tweak checkout HEAD deep/deeper2/a &&
+	git -C tweak sparse-checkout reapply 2>err &&
+	test_i18ngrep ! "warning.*The following paths are not up to date" err &&
+	test_path_is_missing tweak/deep/deeper2/a &&
+	test_i18ngrep "warning.*The following paths are unmerged" err &&
+	test_path_is_file tweak/folder1/a &&
+
+	git -C tweak add folder1/a &&
+	git -C tweak sparse-checkout reapply 2>err &&
+	test_must_be_empty err &&
+	test_path_is_missing tweak/deep/deeper2/a &&
+	test_path_is_missing tweak/folder1/a &&
+
+	git -C tweak sparse-checkout disable
+'
+
 test_expect_success 'cone mode: set with core.ignoreCase=true' '
 	rm repo/.git/info/sparse-checkout &&
 	git -C repo sparse-checkout init --cone &&