From: Derrick Stolee <redacted>

The 'git sparse-checkout set' subcommand takes a list of patterns
as arguments and writes them to the sparse-checkout file. Then, it
updates the working directory using 'git read-tree -mu HEAD'.

The 'set' subcommand will replace the entire contents of the
sparse-checkout file. The write_patterns_and_update() method is
extracted from cmd_sparse_checkout() to make it easier to implement
'add' and/or 'remove' subcommands in the future.

Signed-off-by: Derrick Stolee <redacted>
---
 Documentation/git-sparse-checkout.txt |  5 ++++
 builtin/sparse-checkout.c             | 35 ++++++++++++++++++++++++++-
 t/t1091-sparse-checkout-builtin.sh    | 19 +++++++++++++++
 3 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-sparse-checkout.txt b/Documentation/git-sparse-checkout.txt
index e095c4a98b..f4bd951550 100644
--- a/Documentation/git-sparse-checkout.txt
+++ b/Documentation/git-sparse-checkout.txt

@@ -39,6 +39,11 @@ and sets the `core.sparseCheckout` setting in the worktree-specific config
 file. This prevents the sparse-checkout feature from interfering with other
 worktrees.

+'set'::
+       Write a set of patterns to the sparse-checkout file, as given as
+       a list of arguments following the 'set' subcommand. Update the
+       working directory to match the new patterns.
+
 SPARSE CHECKOUT
 ----------------

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 3ecb7ac2e7..52d4f832f3 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c

@@ -8,7 +8,7 @@
 #include "strbuf.h"

 static char const * const builtin_sparse_checkout_usage[] = {
-       N_("git sparse-checkout [init|list]"),
+       N_("git sparse-checkout [init|list|set] <options>"),
        NULL
 };

@@ -140,6 +140,37 @@ static int sparse_checkout_init(int argc, const char **argv)
        return update_working_directory();
 }

+static int write_patterns_and_update(struct pattern_list *pl)
+{
+       char *sparse_filename;
+       FILE *fp;
+
+       sparse_filename = get_sparse_checkout_filename();
+       fp = fopen(sparse_filename, "w");
+       write_patterns_to_file(fp, pl);
+       fclose(fp);
+       free(sparse_filename);
+
+       return update_working_directory();
+}
+
+static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
+{
+       static const char *empty_base = "";
+       int i;
+       struct pattern_list pl;
+       int result;
+       memset(&pl, 0, sizeof(pl));
+
+       for (i = 1; i < argc; i++)
+               add_pattern(argv[i], empty_base, 0, &pl, 0);
+
+       result = write_patterns_and_update(&pl);
+
+       clear_pattern_list(&pl);
+       return result;
+}
+
 int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
 {
        static struct option builtin_sparse_checkout_options[] = {

@@ -162,6 +193,8 @@ int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
                        return sparse_checkout_list(argc, argv);
                if (!strcmp(argv[0], "init"))
                        return sparse_checkout_init(argc, argv);
+               if (!strcmp(argv[0], "set"))
+                       return sparse_checkout_set(argc, argv, prefix);
        }

        usage_with_options(builtin_sparse_checkout_usage,

diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index d4c145a3af..19e8673c6b 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh

@@ -101,4 +101,23 @@ test_expect_success 'clone --sparse' '
        test_cmp expect dir
 '

+test_expect_success 'set sparse-checkout using builtin' '
+       git -C repo sparse-checkout set "/*" "!/*/" "*folder*" &&
+       cat >expect <<-EOF &&
+               /*
+               !/*/
+               *folder*
+       EOF
+       git -C repo sparse-checkout list >actual &&
+       test_cmp expect actual &&
+       test_cmp expect repo/.git/info/sparse-checkout &&
+       ls repo >dir  &&
+       cat >expect <<-EOF &&
+               a
+               folder1
+               folder2
+       EOF
+       test_cmp expect dir
+'
+
 test_done
--