checkout: factor out functions to new lib file

Factor the functions out, so they can be re-used from other places.  In
particular these functions will be re-used in builtin/worktree.c to make
git worktree add dwim more.

While there add some docs to the function.

Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/checkout.c b/checkout.c
new file mode 100644
index 0000000000..ac42630f74
--- /dev/null
+++ b/checkout.c
@@ -0,0 +1,43 @@
+#include "cache.h"
+#include "remote.h"
+#include "checkout.h"
+
+struct tracking_name_data {
+	/* const */ char *src_ref;
+	char *dst_ref;
+	struct object_id *dst_oid;
+	int unique;
+};
+
+static int check_tracking_name(struct remote *remote, void *cb_data)
+{
+	struct tracking_name_data *cb = cb_data;
+	struct refspec query;
+	memset(&query, 0, sizeof(struct refspec));
+	query.src = cb->src_ref;
+	if (remote_find_tracking(remote, &query) ||
+	    get_oid(query.dst, cb->dst_oid)) {
+		free(query.dst);
+		return 0;
+	}
+	if (cb->dst_ref) {
+		free(query.dst);
+		cb->unique = 0;
+		return 0;
+	}
+	cb->dst_ref = query.dst;
+	return 0;
+}
+
+const char *unique_tracking_name(const char *name, struct object_id *oid)
+{
+	struct tracking_name_data cb_data = { NULL, NULL, NULL, 1 };
+	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
+	cb_data.dst_oid = oid;
+	for_each_remote(check_tracking_name, &cb_data);
+	free(cb_data.src_ref);
+	if (cb_data.unique)
+		return cb_data.dst_ref;
+	free(cb_data.dst_ref);
+	return NULL;
+}