commit-graph: check mixed generation validation when loading chain file

In read_commit_graph_one(), we call validate_mixed_generation_chain()
after loading the graph. Even though we don't check the return value,
this has the side effect of clearing the read_generation_data flag,
which is important when working with mixed generation numbers.

But doing this in load_commit_graph_chain_fd_st() makes more sense:

  1. We are calling it even when we did not load a chain at all, which
     is pointless (you cannot have mixed generations in a single file).

  2. For now, all callers load the graph via read_commit_graph_one().
     But the point of factoring out the open/load in the previous commit
     was to let "commit-graph verify" call them separately. So it needs
     to trigger this function as part of the load.

     Without this patch, the mixed-generation tests in t5324 would start
     failing on "git commit-graph verify" calls, once we switch to using
     a separate open/load call there.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

commit-graph.c

@@ -473,6 +473,31 @@ static struct commit_graph *load_commit_graph_v1(struct repository *r,
 	return g;
 }
 
+/*
+ * returns 1 if and only if all graphs in the chain have
+ * corrected commit dates stored in the generation_data chunk.
+ */
+static int validate_mixed_generation_chain(struct commit_graph *g)
+{
+	int read_generation_data = 1;
+	struct commit_graph *p = g;
+
+	while (read_generation_data && p) {
+		read_generation_data = p->read_generation_data;
+		p = p->base_graph;
+	}
+
+	if (read_generation_data)
+		return 1;
+
+	while (g) {
+		g->read_generation_data = 0;
+		g = g->base_graph;
+	}
+
+	return 0;
+}
+
 static int add_graph_to_chain(struct commit_graph *g,
 			      struct commit_graph *chain,
 			      struct object_id *oids,
@@ -581,6 +606,8 @@ struct commit_graph *load_commit_graph_chain_fd_st(struct repository *r,
 		}
 	}
 
+	validate_mixed_generation_chain(graph_chain);
+
 	free(oids);
 	fclose(fp);
 	strbuf_release(&line);
@@ -605,31 +632,6 @@ static struct commit_graph *load_commit_graph_chain(struct repository *r,
 	return g;
 }
 
-/*
- * returns 1 if and only if all graphs in the chain have
- * corrected commit dates stored in the generation_data chunk.
- */
-static int validate_mixed_generation_chain(struct commit_graph *g)
-{
-	int read_generation_data = 1;
-	struct commit_graph *p = g;
-
-	while (read_generation_data && p) {
-		read_generation_data = p->read_generation_data;
-		p = p->base_graph;
-	}
-
-	if (read_generation_data)
-		return 1;
-
-	while (g) {
-		g->read_generation_data = 0;
-		g = g->base_graph;
-	}
-
-	return 0;
-}
-
 struct commit_graph *read_commit_graph_one(struct repository *r,
 					   struct object_directory *odb)
 {
@@ -638,8 +640,6 @@ struct commit_graph *read_commit_graph_one(struct repository *r,
 	if (!g)
 		g = load_commit_graph_chain(r, odb);
 
-	validate_mixed_generation_chain(g);
-
 	return g;
 }