commit-graph: always load commit-graph information

Most code paths load commits using lookup_commit() and then
parse_commit(). In some cases, including some branch lookups, the commit
is parsed using parse_object_buffer() which side-steps parse_commit() in
favor of parse_commit_buffer().

With generation numbers in the commit-graph, we need to ensure that any
commit that exists in the commit-graph file has its generation number
loaded.

Create new load_commit_graph_info() method to fill in the information
for a commit that exists only in the commit-graph file. Call it from
parse_commit_buffer() after loading the other commit information from
the given buffer. Only fill this information when specified by the
'check_graph' parameter.

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

commit-graph.c

@@ -245,6 +245,13 @@ static struct commit_list **insert_parent_or_die(struct commit_graph *g,
 	return &commit_list_insert(c, pptr)->next;
 }
 
+static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, uint32_t pos)
+{
+	const unsigned char *commit_data = g->chunk_commit_data + GRAPH_DATA_WIDTH * pos;
+	item->graph_pos = pos;
+	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
+}
+
 static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t pos)
 {
 	uint32_t edge_value;
@@ -292,31 +299,40 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
 	return 1;
 }
 
+static int find_commit_in_graph(struct commit *item, struct commit_graph *g, uint32_t *pos)
+{
+	if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
+		*pos = item->graph_pos;
+		return 1;
+	} else {
+		return bsearch_graph(g, &(item->object.oid), pos);
+	}
+}
+
 int parse_commit_in_graph(struct commit *item)
 {
+	uint32_t pos;
+
 	if (!core_commit_graph)
 		return 0;
 	if (item->object.parsed)
 		return 1;
-
 	prepare_commit_graph();
-	if (commit_graph) {
-		uint32_t pos;
-		int found;
-		if (item->graph_pos != COMMIT_NOT_FROM_GRAPH) {
-			pos = item->graph_pos;
-			found = 1;
-		} else {
-			found = bsearch_graph(commit_graph, &(item->object.oid), &pos);
-		}
-
-		if (found)
+	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
 		return fill_commit_in_graph(item, commit_graph, pos);
-	}
-
 	return 0;
 }
 
+void load_commit_graph_info(struct commit *item)
+{
+	uint32_t pos;
+	if (!core_commit_graph)
+		return;
+	prepare_commit_graph();
+	if (commit_graph && find_commit_in_graph(item, commit_graph, &pos))
+		fill_commit_graph_info(item, commit_graph, pos);
+}
+
 static struct tree *load_tree_for_commit(struct commit_graph *g, struct commit *c)
 {
 	struct object_id oid;

commit-graph.h

@@ -17,6 +17,14 @@ char *get_commit_graph_filename(const char *obj_dir);
  */
 int parse_commit_in_graph(struct commit *item);
 
+/*
+ * It is possible that we loaded commit contents from the commit buffer,
+ * but we also want to ensure the commit-graph content is correctly
+ * checked and filled. Fill the graph_pos and generation members of
+ * the given commit.
+ */
+void load_commit_graph_info(struct commit *item);
+
 struct tree *get_commit_tree_in_graph(const struct commit *c);
 
 struct commit_graph {

commit.c

@@ -331,7 +331,7 @@ const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
 	return ret;
 }
 
-int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size)
+int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph)
 {
 	const char *tail = buffer;
 	const char *bufptr = buffer;
@@ -386,6 +386,9 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
 	}
 	item->date = parse_commit_date(bufptr, tail);
 
+	if (check_graph)
+		load_commit_graph_info(item);
+
 	return 0;
 }
 
@@ -412,7 +415,7 @@ int parse_commit_gently(struct commit *item, int quiet_on_missing)
 		return error("Object %s not a commit",
 			     oid_to_hex(&item->object.oid));
 	}
-	ret = parse_commit_buffer(item, buffer, size);
+	ret = parse_commit_buffer(item, buffer, size, 0);
 	if (save_commit_buffer && !ret) {
 		set_commit_buffer(item, buffer, size);
 		return 0;

commit.h

@@ -72,7 +72,7 @@ struct commit *lookup_commit_reference_by_name(const char *name);
  */
 struct commit *lookup_commit_or_die(const struct object_id *oid, const char *ref_name);
 
-int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
+int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size, int check_graph);
 int parse_commit_gently(struct commit *item, int quiet_on_missing);
 static inline int parse_commit(struct commit *item)
 {

object.c

@@ -207,7 +207,7 @@ struct object *parse_object_buffer(const struct object_id *oid, enum object_type
 	} else if (type == OBJ_COMMIT) {
 		struct commit *commit = lookup_commit(oid);
 		if (commit) {
-			if (parse_commit_buffer(commit, buffer, size))
+			if (parse_commit_buffer(commit, buffer, size, 1))
 				return NULL;
 			if (!get_cached_commit_buffer(commit, NULL)) {
 				set_commit_buffer(commit, buffer, size);

sha1_file.c

@@ -1755,7 +1755,7 @@ static void check_commit(const void *buf, size_t size)
 {
 	struct commit c;
 	memset(&c, 0, sizeof(c));
-	if (parse_commit_buffer(&c, buf, size))
+	if (parse_commit_buffer(&c, buf, size, 0))
 		die("corrupt commit");
 }