On Sun, Dec 09, 2018 at 09:51:28AM +0900, Junio C Hamano wrote: > > -static int parse_commit_in_graph_one(struct commit_graph *g, struct commit > > *item) > > +static struct commit *parse_commit_in_graph_one(struct repository *r, > > + struct commit_graph *g, > > + struct commit *shell, > > + const struct object_id *oid) > > Now the complexity of the behaviour of this function deserves to be > documented in a comment in front. Let me see if I can get it > correctly without such a comment by explaining the function aloud. > > The caller may or may not have already obtained an in-core commit > object for a given object name, so shell could be NULL but otherwise > it could be used for optimization. When shell==NULL, the function > looks up the commit object using the oid parameter instead. The > returned in-core commit has the parents etc. filled as if we ran > parse_commit() on it. If the commit is not yet in the graph, the > caller may get a NULL even if the commit exists.
Yeah, this was the part that took me a bit to figure out, as well. The optimization here is really just avoiding a call to lookup_commit(), which will do a single hash-table lookup. I wonder if that's actually worth this more complex interface (as opposed to just always taking an oid and then always returning a "struct commit", which could be old or new). -Peff
