revwalk: port over the topological sorting

After porting over the commit hiding and selection we were still left
with mistmaching output due to the topologial sort.

This ports the topological sorting code to make us match with our
equivalent of `--date-order` and `--topo-order` against the output
from `rev-list`.

src/revwalk.c

@@ -357,39 +357,16 @@ static int revwalk_next_unsorted(git_commit_list_node **object_out, git_revwalk
 
 static int revwalk_next_toposort(git_commit_list_node **object_out, git_revwalk *walk)
 {
-	git_commit_list_node *next;
-	unsigned short i, max;
-
-	for (;;) {
-		next = git_commit_list_pop(&walk->iterator_topo);
-		if (next == NULL) {
-			giterr_clear();
-			return GIT_ITEROVER;
-		}
+	git_commit_list_node *node;
 
-		if (next->in_degree > 0) {
-			next->topo_delay = 1;
-			continue;
-		}
-
-
-		max = next->out_degree;
-		if (walk->first_parent && next->out_degree)
-			max = 1;
-
-		for (i = 0; i < max; ++i) {
-			git_commit_list_node *parent = next->parents[i];
-
-			if (--parent->in_degree == 0 && parent->topo_delay) {
-				parent->topo_delay = 0;
-				if (git_commit_list_insert(parent, &walk->iterator_topo) == NULL)
-					return -1;
-			}
-		}
-
-		*object_out = next;
+	node = git_commit_list_pop(&walk->iterator_topo);
+	if (node) {
+		*object_out = node;
 		return 0;
 	}
+
+	giterr_clear();
+	return GIT_ITEROVER;
 }
 
 static int revwalk_next_reverse(git_commit_list_node **object_out, git_revwalk *walk)
@@ -453,8 +430,6 @@ static int add_parents_to_list(git_revwalk *walk, git_commit_list_node *commit,
 
 	commit->added = 1;
 
-	/* TODO: add the insertion callback here as well */
-
 	/*
 	 * Go full on in the uninteresting case as we want to include
 	 * as many of these as we can.
@@ -578,10 +553,104 @@ static int limit_list(git_commit_list **out, git_revwalk *walk, git_commit_list
 		p = &git_commit_list_insert(commit, p)->next;
 	}
 
+	git_commit_list_free(&list);
 	*out = newlist;
 	return 0;
 }
 
+static int sort_in_topological_order(git_commit_list **out, git_revwalk *walk)
+{
+	git_commit_list *list = NULL, *ll = NULL, *newlist, **pptr;
+	git_commit_list_node *next;
+	git_pqueue queue;
+	git_vector_cmp queue_cmp = NULL;
+	unsigned short i;
+	int error;
+
+	if (walk->sorting & GIT_SORT_TIME)
+		queue_cmp = git_commit_list_time_cmp;
+
+	if ((error = git_pqueue_init(&queue, 0, 8, queue_cmp)))
+		return error;
+
+	/*
+	 * Start by resetting the in-degree to 1 for the commits in
+	 * our list. We want to go through this list again, so we
+	 * store it in the commit list as we extract it from the lower
+	 * machinery.
+	 */
+	while ((error = walk->get_next(&next, walk)) == 0) {
+		next->in_degree = 1;
+		git_commit_list_insert(next, &list);
+	}
+
+	if (error != GIT_ITEROVER)
+		goto cleanup;
+
+	error = 0;
+
+	/*
+	 * Count up how many children each commit has. We limit
+	 * ourselves to those commits in the original list (in-degree
+	 * of 1) avoiding setting it for any parent that was hidden.
+	 */
+	for(ll = list; ll; ll = ll->next) {
+		for (i = 0; i < ll->item->out_degree; ++i) {
+			git_commit_list_node *parent = ll->item->parents[i];
+			if (parent->in_degree)
+				parent->in_degree++;
+		}
+	}
+
+	/*
+	 * Now we find the tips i.e. those not reachable from any other node
+	 * i.e. those which still have an in-degree of 1.
+	 */
+	for(ll = list; ll; ll = ll->next) {
+		if (ll->item->in_degree == 1) {
+			if ((error = git_pqueue_insert(&queue, ll->item)))
+				goto cleanup;
+		}
+	}
+
+	/*
+	 * We need to output the tips in the order that they came out of the
+	 * traversal, so if we're not doing time-sorting, we need to reverse the
+	 * pqueue in order to get them to come out as we inserted them.
+	 */
+	if ((walk->sorting & GIT_SORT_TIME) == 0)
+		git_pqueue_reverse(&queue);
+
+
+	pptr = &newlist;
+	newlist = NULL;
+	while ((next = git_pqueue_pop(&queue)) != NULL) {
+		for (i = 0; i < next->out_degree; ++i) {
+			git_commit_list_node *parent = next->parents[i];
+			if (parent->in_degree == 0)
+				continue;
+
+			if (--parent->in_degree == 1) {
+				if ((error = git_pqueue_insert(&queue, parent)))
+					goto cleanup;
+			}
+		}
+
+		/* All the children of 'item' have been emitted (since we got to it via the priority queue) */
+		next->in_degree = 0;
+
+		pptr = &git_commit_list_insert(next, pptr)->next;
+	}
+
+	*out = newlist;
+	error = 0;
+
+cleanup:
+	git_commit_list_free(&list);
+	git_pqueue_free(&queue);
+	return error;
+}
+
 static int prepare_walk(git_revwalk *walk)
 {
 	int error;
@@ -615,25 +684,16 @@ static int prepare_walk(git_revwalk *walk)
 		if (list->item->uninteresting)
 			continue;
 
-		if ((error = walk->enqueue(walk, list->item)) < 0)
+		if ((error = walk->enqueue(walk, list->item)) < 0) {
+			git_commit_list_free(&commits);
 			return error;
 		}
-
-
-	if (walk->sorting & GIT_SORT_TOPOLOGICAL) {
-		unsigned short i;
-
-		while ((error = walk->get_next(&next, walk)) == 0) {
-			for (i = 0; i < next->out_degree; ++i) {
-				git_commit_list_node *parent = next->parents[i];
-				parent->in_degree++;
 	}
 
-			if (git_commit_list_insert(next, &walk->iterator_topo) == NULL)
-				return -1;
-		}
+	git_commit_list_free(&commits);
 
-		if (error != GIT_ITEROVER)
+	if (walk->sorting & GIT_SORT_TOPOLOGICAL) {
+		if ((error = sort_in_topological_order(&walk->iterator_topo, walk)))
 			return error;
 
 		walk->get_next = &revwalk_next_toposort;

tests/revwalk/hidecb.c

@@ -158,7 +158,7 @@ void test_revwalk_hidecb__hide_some_commits(void)
 
 	cl_git_pass(git_revwalk_new(&walk, _repo));
 	cl_git_pass(git_revwalk_push(walk, &_head_id));
-	git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL | GIT_SORT_TIME);
+	git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL);
 
 	/* Add hide callback */
 	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_commit_cb, NULL));
@@ -183,7 +183,7 @@ void test_revwalk_hidecb__test_payload(void)
 
 	cl_git_pass(git_revwalk_new(&walk, _repo));
 	cl_git_pass(git_revwalk_push(walk, &_head_id));
-	git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL | GIT_SORT_TIME);
+	git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL);
 
 	/* Add hide callback, pass id of parent of initial commit as payload data */
 	cl_git_pass(git_revwalk_add_hide_cb(walk, hide_commit_use_payload_cb, &commit_ids[5]));