commit-reach: move ref_newer from remote.c

There are several commit walks in the codebase. Group them together into
a new commit-reach.c file and corresponding header. After we group these
walks into one place, we can reduce duplicate logic by calling
equivalent methods.

The ref_newer() method is used by 'git push -f' to check if a force-push
is necessary. By making the method public, we make it possible to test
the method directly without setting up an envieronment where a 'git
push' call makes sense.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 54 insertions, 1 deletions

diff --git a/commit-reach.c b/commit-reach.c
index 8ab6044..a6bc478 100644
--- a/commit-reach.c
+++ b/commit-reach.c
@@ -1,6 +1,10 @@
 #include "cache.h"
-#include "prio-queue.h"
 #include "commit.h"
+#include "decorate.h"
+#include "prio-queue.h"
+#include "tree.h"
+#include "revision.h"
+#include "tag.h"
 #include "commit-reach.h"
 
 /* Remember to update object flag allocation in object.h */
@@ -358,3 +362,52 @@ void reduce_heads_replace(struct commit_list **heads)
 	free_commit_list(*heads);
 	*heads = result;
 }
+
+static void unmark_and_free(struct commit_list *list, unsigned int mark)
+{
+	while (list) {
+		struct commit *commit = pop_commit(&list);
+		commit->object.flags &= ~mark;
+	}
+}
+
+int ref_newer(const struct object_id *new_oid, const struct object_id *old_oid)
+{
+	struct object *o;
+	struct commit *old_commit, *new_commit;
+	struct commit_list *list, *used;
+	int found = 0;
+
+	/*
+	 * Both new_commit and old_commit must be commit-ish and new_commit is descendant of
+	 * old_commit.  Otherwise we require --force.
+	 */
+	o = deref_tag(the_repository, parse_object(the_repository, old_oid),
+		      NULL, 0);
+	if (!o || o->type != OBJ_COMMIT)
+		return 0;
+	old_commit = (struct commit *) o;
+
+	o = deref_tag(the_repository, parse_object(the_repository, new_oid),
+		      NULL, 0);
+	if (!o || o->type != OBJ_COMMIT)
+		return 0;
+	new_commit = (struct commit *) o;
+
+	if (parse_commit(new_commit) < 0)
+		return 0;
+
+	used = list = NULL;
+	commit_list_insert(new_commit, &list);
+	while (list) {
+		new_commit = pop_most_recent_commit(&list, TMP_MARK);
+		commit_list_insert(new_commit, &used);
+		if (new_commit == old_commit) {
+			found = 1;
+			break;
+		}
+	}
+	unmark_and_free(list, TMP_MARK);
+	unmark_and_free(used, TMP_MARK);
+	return found;
+}