[PATCH v2 18/18] sparse-checkout: provide a new reapply subcommand

["Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Elijah Newren <newren@gmail.com>

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.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 Documentation/git-sparse-checkout.txt | 10 ++++++++++
 builtin/sparse-checkout.c             | 10 +++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-sparse-checkout.txt b/Documentation/git-sparse-checkout.txt
index c0342e53938..1a3ace60820 100644
--- a/Documentation/git-sparse-checkout.txt
+++ b/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
diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index aa81199f85d..95d08824172 100644
--- a/builtin/sparse-checkout.c
+++ b/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);
 	}
-- 
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