Merge pull request libgit2#5766 from lhchavez/cgraph-generation-cmp

commit-graph: Introduce `git_commit_list_generation_cmp`

Author: ethomson

src/commit_list.c

@@ -12,6 +12,24 @@
 #include "odb.h"
 #include "commit.h"
 
+int git_commit_list_generation_cmp(const void *a, const void *b)
+{
+	uint32_t generation_a = ((git_commit_list_node *) a)->generation;
+	uint32_t generation_b = ((git_commit_list_node *) b)->generation;
+
+	if (!generation_a || !generation_b) {
+		/* Fall back to comparing by timestamps if at least one commit lacks a generation. */
+		return git_commit_list_time_cmp(a, b);
+	}
+
+	if (generation_a < generation_b)
+		return 1;
+	if (generation_a > generation_b)
+		return -1;
+
+	return 0;
+}
+
 int git_commit_list_time_cmp(const void *a, const void *b)
 {
 	int64_t time_a = ((git_commit_list_node *) a)->time;

src/commit_list.h

@@ -46,6 +46,7 @@ typedef struct git_commit_list {
 } git_commit_list;
 
 git_commit_list_node *git_commit_list_alloc_node(git_revwalk *walk);
+int git_commit_list_generation_cmp(const void *a, const void *b);
 int git_commit_list_time_cmp(const void *a, const void *b);
 void git_commit_list_free(git_commit_list **list_p);
 git_commit_list *git_commit_list_insert(git_commit_list_node *item, git_commit_list **list_p);

src/graph.c

@@ -43,7 +43,7 @@ static int mark_parents(git_revwalk *walk, git_commit_list_node *one,
 		return 0;
 	}
 
-	if (git_pqueue_init(&list, 0, 2, git_commit_list_time_cmp) < 0)
+	if (git_pqueue_init(&list, 0, 2, git_commit_list_generation_cmp) < 0)
 		return -1;
 
 	if (git_commit_list_parse(walk, one) < 0)

src/merge.c

@@ -387,7 +387,7 @@ static int paint_down_to_common(
 	int error;
 	unsigned int i;
 
-	if (git_pqueue_init(&list, 0, twos->length * 2, git_commit_list_time_cmp) < 0)
+	if (git_pqueue_init(&list, 0, twos->length * 2, git_commit_list_generation_cmp) < 0)
 		return -1;
 
 	one->flags |= PARENT1;