commit-graph: use corrected commit dates for comparision

With corrected commit dates implemented, we no longer have to rely on
commit date as a heuristic in paint_down_to_common().

t6024-recursive-merge setups a unique repository where all commits have
the same committer date. As such, using committer date for priority
queue essentially transforms it to a FIFO queue. As we use corrected
commit date, this is no longer true and effects the order in which
commits are merged (A and B, then B and C instead of B and C, then A
and B). As such, we need to update oid for intermediate stage commit
which fails to be merged.

TODO: Update intermediate stage commit oid for sha256 as well.

Signed-off-by: Abhishek Kumar <[email protected]>

Author: abhishekkumar2718

commit-graph.c

@@ -690,6 +690,17 @@ int generation_numbers_enabled(struct repository *r)
 	return !!first_generation;
 }
 
+int corrected_commit_dates_enabled(struct repository *r)
+{
+	struct commit_graph *g;
+	if (!prepare_commit_graph(r))
+		return 0;
+
+	g = r->objects->commit_graph;
+
+	return !!g->chunk_generation_data;
+}
+
 static void close_commit_graph_one(struct commit_graph *g)
 {
 	if (!g)

commit-graph.h

@@ -88,6 +88,12 @@ struct commit_graph *parse_commit_graph(void *graph_map, size_t graph_size);
  */
 int generation_numbers_enabled(struct repository *r);
 
+/*
+ * Return 1 if and only if the repository has a commit-graph
+ * file and corrected commit date offsets are computed in that file.
+ */
+int corrected_commit_dates_enabled(struct repository *r);
+
 enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_APPEND     = (1 << 0),
 	COMMIT_GRAPH_WRITE_PROGRESS   = (1 << 1),

commit-reach.c

@@ -39,7 +39,7 @@ static struct commit_list *paint_down_to_common(struct repository *r,
 	int i;
 	timestamp_t last_gen = GENERATION_NUMBER_V2_INFINITY;
 
-	if (!min_generation)
+	if (!min_generation && !corrected_commit_dates_enabled(r))
 		queue.compare = compare_commits_by_commit_date;
 
 	one->object.flags |= PARENT1;

t/t6024-recursive-merge.sh

@@ -60,7 +60,7 @@ test_expect_success 'setup tests' '
 	GIT_AUTHOR_DATE="2006-12-12 23:00:08" git commit -m F &&
 
 	test_oid_cache <<-EOF
-	idxstage1 sha1:ec3fe2a791706733f2d8fa7ad45d9a9672031f5e
+	idxstage1 sha1:35e1b0dd0fcb603a1b74f9e651a7069e4dedfd48
 	idxstage1 sha256:b3c8488929903aaebdeb22270cb6d36e5b8724b01ae0d4da24632f158c99676f
 	EOF
 '