Merge branch 'jk/commit-graph-lazy-load-fallback'

The logic to lazy-load trees from the commit-graph has been made
more robust by falling back to reading the commit object when
the commit-graph is no longer available.

* jk/commit-graph-lazy-load-fallback:
  commit: fall back to full read when maybe_tree is NULL

1 files changed, 32 insertions, 1 deletions

diff --git a/commit.c b/commit.c
index e3e7352e69..fd8723502e 100644
--- a/commit.c
+++ b/commit.c
@@ -434,6 +434,27 @@ static inline void set_commit_tree(struct commit *c, struct tree *t)
 	c->maybe_tree = t;
 }
 
+static void load_tree_from_commit_contents(struct repository *r, struct commit *commit)
+{
+	enum object_type type;
+	unsigned long size;
+	char *buf;
+	const char *p;
+	struct object_id tree_oid;
+
+	buf = odb_read_object(r->objects, &commit->object.oid, &type, &size);
+	if (!buf)
+		return;
+
+	if (type == OBJ_COMMIT &&
+	    skip_prefix(buf, "tree ", &p) &&
+	    !parse_oid_hex_algop(p, &tree_oid, &p, r->hash_algo) &&
+	    *p == '\n')
+		set_commit_tree(commit, lookup_tree(r, &tree_oid));
+
+	free(buf);
+}
+
 struct tree *repo_get_commit_tree(struct repository *r,
 				  const struct commit *commit)
 {
@@ -443,7 +464,17 @@ struct tree *repo_get_commit_tree(struct repository *r,
 	if (commit_graph_position(commit) != COMMIT_NOT_FROM_GRAPH)
 		return get_commit_tree_in_graph(r, commit);
 
-	return NULL;
+	/*
+	 * This is either a corrupt commit, or one which we partially loaded
+	 * from a graph file but then subsequently threw away the graph data.
+	 *
+	 * Optimistically assume it's the latter and try to reload from
+	 * scratch. This gives a performance penalty if it really is a corrupt
+	 * commit, but presumably that happens rarely (and only once per
+	 * process).
+	 */
+	load_tree_from_commit_contents(r, (struct commit *)commit);
+	return commit->maybe_tree;
 }
 
 struct object_id *get_commit_tree_oid(const struct commit *commit)