On Mon, Mar 04, 2019 at 11:19:32AM -0800, Jonathan Tan wrote: > > - some callers of has_sha1_file() might care about durability between > > processes. Because it's baked in, the empty tree is safe for that > > (whatever follow-on process runs, it will also be baked in there). > > But that's not necessarily true for other "cached" objects. I'm not > > really that worried about it because we use it sparingly (the only > > call to pretend_sha1_file() is in git-blame, and if it ever did ask > > "do we have this object", I actually think the right answer would be > > "yes"). > > > > But if this is a concern, we could perhaps have two levels of flags: > > SKIP_CACHED and SKIP_INTERNAL. > > Or teach git-blame to have its own pretend mechanism, and remove the > pretend mechanism from sha1-file.c. I think that would be ideal, but I'm not sure if it's feasible due to the layering of the various modules. IOW, the blame code isn't just pretending a fake object file for _itself_, it needs to then call into the diff code, which must be able to then find that content in order to produce a diff. But maybe it is not so bad. Our diff_filespec struct does represent working-tree files (as it must, since we diff them!). So it may be possible to feed it to the diff code at the right spot. I haven't looked closely enough to say for sure whether it's feasible or not. But it does imply to me that we should go with this regression fix in the near-term and think about building bigger changes separately on master. > The last time I deeply thought of this was during the partial clone > implementation, so I am probably not completely up-to-date, but it seems > to me that ideally, for reading, we would remove SKIP_CACHED completely > (and always consult the cache), and also remove completely the ability > to pretend (blame will have to do it by itself); and for writing, we > would write the empty tree whenever we do now (for backwards > compatibility with old versions of Git that read what we write). Both > the approach in this patch and making has_object_file() respect cached > objects are steps in that direction, so I'm OK with both. Yeah, I think our world-views are in accord. :) -Peff
