[PATCH v5 02/17] sparse-checkout: create 'init' subcommand

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

Getting started with a sparse-checkout file can be daunting. Help
users start their sparse enlistment using 'git sparse-checkout init'.
This will set 'core.sparseCheckout=true' in their config, write
an initial set of patterns to the sparse-checkout file, and update
their working directory.

Make sure to use the `extensions.worktreeConfig` setting and write
the sparse checkout config to the worktree-specific config file.
This avoids confusing interactions with other worktrees.

The use of running another process for 'git read-tree' is sub-
optimal. This will be removed in a later change.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-sparse-checkout.txt | 11 ++++
 builtin/sparse-checkout.c             | 79 ++++++++++++++++++++++++++-
 t/t1091-sparse-checkout-builtin.sh    | 41 ++++++++++++++
 3 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/Documentation/git-sparse-checkout.txt b/Documentation/git-sparse-checkout.txt
index 9d6ca22917..930a361567 100644
--- a/Documentation/git-sparse-checkout.txt
+++ b/Documentation/git-sparse-checkout.txt
@@ -30,6 +30,17 @@ COMMANDS
 'list'::
 	Provide a list of the contents in the sparse-checkout file.
 
+'init'::
+	Enable the `core.sparseCheckout` setting. If the
+	sparse-checkout file does not exist, then populate it with
+	patterns that match every file in the root directory and
+	no other directories, then will remove all directories tracked
+	by Git. Add patterns to the sparse-checkout file to
+	repopulate the working directory.
++
+To avoid interfering with other worktrees, it first enables the
+`extensions.worktreeConfig` setting and makes sure to set the
+`core.sparseCheckout` setting in the worktree-specific config file.
 
 SPARSE CHECKOUT
 ---------------
diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 5717c9b2cb..77aa52ca01 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 list"),
+	N_("git sparse-checkout (init|list)"),
 	NULL
 };
 
@@ -59,6 +59,81 @@ static int sparse_checkout_list(int argc, const char **argv)
 	return 0;
 }
 
+static int update_working_directory(void)
+{
+	struct argv_array argv = ARGV_ARRAY_INIT;
+	int result = 0;
+	argv_array_pushl(&argv, "read-tree", "-m", "-u", "HEAD", NULL);
+
+	if (run_command_v_opt(argv.argv, RUN_GIT_CMD)) {
+		error(_("failed to update index with new sparse-checkout paths"));
+		result = 1;
+	}
+
+	argv_array_clear(&argv);
+	return result;
+}
+
+enum sparse_checkout_mode {
+	MODE_NO_PATTERNS = 0,
+	MODE_ALL_PATTERNS = 1,
+};
+
+static int sc_set_config(enum sparse_checkout_mode mode)
+{
+	struct argv_array argv = ARGV_ARRAY_INIT;
+
+	if (git_config_set_gently("extensions.worktreeConfig", "true")) {
+		error(_("failed to set extensions.worktreeConfig setting"));
+		return 1;
+	}
+
+	argv_array_pushl(&argv, "config", "--worktree", "core.sparseCheckout", NULL);
+
+	if (mode)
+		argv_array_pushl(&argv, "true", NULL);
+	else
+		argv_array_pushl(&argv, "false", NULL);
+
+	if (run_command_v_opt(argv.argv, RUN_GIT_CMD)) {
+		error(_("failed to enable core.sparseCheckout"));
+		return 1;
+	}
+
+	return 0;
+}
+
+static int sparse_checkout_init(int argc, const char **argv)
+{
+	struct pattern_list pl;
+	char *sparse_filename;
+	FILE *fp;
+	int res;
+
+	if (sc_set_config(MODE_ALL_PATTERNS))
+		return 1;
+
+	memset(&pl, 0, sizeof(pl));
+
+	sparse_filename = get_sparse_checkout_filename();
+	res = add_patterns_from_file_to_list(sparse_filename, "", 0, &pl, NULL);
+
+	/* If we already have a sparse-checkout file, use it. */
+	if (res >= 0) {
+		free(sparse_filename);
+		goto reset_dir;
+	}
+
+	/* initial mode: all blobs at root */
+	fp = xfopen(sparse_filename, "w");
+	free(sparse_filename);
+	fprintf(fp, "/*\n!/*/\n");
+	fclose(fp);
+
+reset_dir:
+	return update_working_directory();
+}
+
 int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
 {
 	static struct option builtin_sparse_checkout_options[] = {
@@ -79,6 +154,8 @@ int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
 	if (argc > 0) {
 		if (!strcmp(argv[0], "list"))
 			return sparse_checkout_list(argc, argv);
+		if (!strcmp(argv[0], "init"))
+			return sparse_checkout_init(argc, argv);
 	}
 
 	usage_with_options(builtin_sparse_checkout_usage,
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index 9b73d44907..cd56cc384b 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -42,4 +42,45 @@ test_expect_success 'git sparse-checkout list (populated)' '
 	test_cmp expect list
 '
 
+test_expect_success 'git sparse-checkout init' '
+	git -C repo sparse-checkout init &&
+	cat >expect <<-EOF &&
+		/*
+		!/*/
+	EOF
+	test_cmp expect repo/.git/info/sparse-checkout &&
+	git -C repo config --list >config &&
+	test_i18ngrep "core.sparsecheckout=true" config &&
+	ls repo >dir  &&
+	echo a >expect &&
+	test_cmp expect dir
+'
+
+test_expect_success 'git sparse-checkout list after init' '
+	git -C repo sparse-checkout list >actual &&
+	cat >expect <<-EOF &&
+		/*
+		!/*/
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'init with existing sparse-checkout' '
+	echo "*folder*" >> repo/.git/info/sparse-checkout &&
+	git -C repo sparse-checkout init &&
+	cat >expect <<-EOF &&
+		/*
+		!/*/
+		*folder*
+	EOF
+	test_cmp expect repo/.git/info/sparse-checkout &&
+	ls repo >dir  &&
+	cat >expect <<-EOF &&
+		a
+		folder1
+		folder2
+	EOF
+	test_cmp expect dir
+'
+
 test_done
-- 
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