sparse-checkout: create builtin with 'list' subcommand

The sparse-checkout feature is mostly hidden to users, as its
only documentation is supplementary information in the docs for
'git read-tree'. In addition, users need to know how to edit the
.git/info/sparse-checkout file with the right patterns, then run
the appropriate 'git read-tree -mu HEAD' command. Keeping the
working directory in sync with the sparse-checkout file requires
care.

Begin an effort to make the sparse-checkout feature a porcelain
feature by creating a new 'git sparse-checkout' builtin. This
builtin will be the preferred mechanism for manipulating the
sparse-checkout file and syncing the working directory.

The documentation provided is adapted from the "git read-tree"
documentation with a few edits for clarity in the new context.
Extra sections are added to hint toward a future change to
a more restricted pattern set.

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

1 files changed, 86 insertions, 0 deletions

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
new file mode 100644
index 0000000000..5717c9b2cb
--- /dev/null
+++ b/builtin/sparse-checkout.c
@@ -0,0 +1,86 @@
+#include "builtin.h"
+#include "config.h"
+#include "dir.h"
+#include "parse-options.h"
+#include "pathspec.h"
+#include "repository.h"
+#include "run-command.h"
+#include "strbuf.h"
+
+static char const * const builtin_sparse_checkout_usage[] = {
+	N_("git sparse-checkout list"),
+	NULL
+};
+
+static char *get_sparse_checkout_filename(void)
+{
+	return git_pathdup("info/sparse-checkout");
+}
+
+static void write_patterns_to_file(FILE *fp, struct pattern_list *pl)
+{
+	int i;
+
+	for (i = 0; i < pl->nr; i++) {
+		struct path_pattern *p = pl->patterns[i];
+
+		if (p->flags & PATTERN_FLAG_NEGATIVE)
+			fprintf(fp, "!");
+
+		fprintf(fp, "%s", p->pattern);
+
+		if (p->flags & PATTERN_FLAG_MUSTBEDIR)
+			fprintf(fp, "/");
+
+		fprintf(fp, "\n");
+	}
+}
+
+static int sparse_checkout_list(int argc, const char **argv)
+{
+	struct pattern_list pl;
+	char *sparse_filename;
+	int res;
+
+	memset(&pl, 0, sizeof(pl));
+
+	sparse_filename = get_sparse_checkout_filename();
+	res = add_patterns_from_file_to_list(sparse_filename, "", 0, &pl, NULL);
+	free(sparse_filename);
+
+	if (res < 0) {
+		warning(_("this worktree is not sparse (sparse-checkout file may not exist)"));
+		return 0;
+	}
+
+	write_patterns_to_file(stdout, &pl);
+	clear_pattern_list(&pl);
+
+	return 0;
+}
+
+int cmd_sparse_checkout(int argc, const char **argv, const char *prefix)
+{
+	static struct option builtin_sparse_checkout_options[] = {
+		OPT_END(),
+	};
+
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage_with_options(builtin_sparse_checkout_usage,
+				   builtin_sparse_checkout_options);
+
+	argc = parse_options(argc, argv, prefix,
+			     builtin_sparse_checkout_options,
+			     builtin_sparse_checkout_usage,
+			     PARSE_OPT_STOP_AT_NON_OPTION);
+
+	git_config(git_default_config, NULL);
+
+	if (argc > 0) {
+		if (!strcmp(argv[0], "list"))
+			return sparse_checkout_list(argc, argv);
+	}
+
+	usage_with_options(builtin_sparse_checkout_usage,
+			   builtin_sparse_checkout_options);
+}