On 06/02, Elijah Newren wrote: > On Fri, Jun 1, 2018 at 10:03 PM, Duy Nguyen <pclo...@gmail.com> wrote: > > On Fri, Jun 1, 2018 at 8:34 PM, Elijah Newren <new...@gmail.com> wrote: > >> On Fri, Jun 1, 2018 at 9:11 AM, Nguyễn Thái Ngọc Duy <pclo...@gmail.com> > >> wrote: > >>> This is more of a bug report than an actual fix because I'm not sure > >>> if "o->src_index" is always the correct answer instead of "the_index" > >>> here. But this is very similar to 7db118303a (unpack_trees: fix > >>> breakage when o->src_index != o->dst_index - 2018-04-23) and could > >>> potentially break things again... > > I'm pretty sure your patch is correct. Adding Brandon Williams to the > cc for comment since his patches came up in the analysis below... > > >> Actually, I don't think the patch will break anything in the current > >> code. Currently, all callers of unpack_trees() (even merge recursive > >> which uses different src_index and dst_index now) set src_index = > >> &the_index. So, these changes should continue to work as before (with > >> a minor possible exception of merge-recursive calling into other > >> functions from unpack-trees.c after unpack_trees() has finished..). > >> That's not to say that your patch is bug free, just that I think any > >> bugs shouldn't be triggerable from the current codebase. > > > > Ah.. I thought merge-recursive would do fancier things and used some > > temporary index. Good to know. > > Well, it does does use a temporary index, but for dst_index rather > than src_index. It then does some fancier things, but not until the > call to unpack_trees() is over. In particular, at that point, it > swaps the_index and tmp_index, reversing their roles so that now > tmp_index is the original index and the_index becomes the result after > unpack_trees() is run. That's done because I later want to use the > original index for calling verify_uptodate(). verify_uptodate() is > then used for was_tracked_and_matches() and was_tracked(). > > Anyway, the whole upshot of this is: > * merge-recursive uses src_index == &the_index for the unpack_trees() call. > * merge-recursive uses src_index == o->orig_index for subsequent > calls to verify_uptodate(), but verify_uptodate() doesn't call into > any of the sites you have modified. > > Further: > * Every other existing caller of unpack-trees in the code sets > src_index == &the_index, so this won't break any of them. > * There are only two callers in the codebase that set dst_index to > something other than &the_index -- diff-lib.c (which sets it to NULL) > and merge-recursive (which does the stuff described above). > > So, having done that analysis, I am now pretty convinced your patch > won't break anything. That's one half... > > >> Also, if any of the changes you made are wrong, what was there before > >> was also clearly wrong. So I think we're at least no worse off. > >> > >> But, I agree, it's not easy to verify what the correct thing should be > >> in all cases. I'll try to take a closer look in the next couple days. > > > > Thanks. I will also stare at this code some more in the next couple > > days trying to remember what these functions do. > > Your patch has two divisible parts: > > 1) Your modifications to > * clear_ce_flags_1() > * clear_ce_flags_dir() > * clear_ce_flags() > * mark_new_skip_worktree() > The clear_ce_flags*() functions are only called by each other and by > mark_new_skip_worktree(), which in turn is only called from > unpack_trees(). Also, in all of these, your change ends up only > modifying what index_state is passed to is_excluded_from_list(). > > 2) Your modifications to > * verify_clean_subdirectory() > * check_ok_to_remove() > In this case, the former is only called by the latter, and the latter > ends up only being called (via verify_absent_1()) from verify_absent() > and verify_absent_sparse(). > > I'll address each, in reverse order. > > 2) The stuff that affects verify_absent() > > While verify_absent() is not called from merge-recursive right now, it > was something I wanted to use in the future for very similar reasons > that verify_uptodate() started being called directly from > merge-recursive. In particular, if the rewrite of merge-recursive[A] > I want to do sets index_only when calling unpack_trees(), then does > the whole merge without touching the worktree, then at the end goes to > update the working tree, it will need to do extra checks. > verify_absent() will come in handy as one of those extra checks. For > that case, using the_index (the new index just created with lots of > changes) would be wrong in all the same ways that using the_index > caused massive problems for was_tracked() in merge-recursive (e.g. the > blow up of when Junio merged the original directory rename detection > series into master and subsequently reverted it); we'd instead want > src_index (which was the index that existed when merge was called) > instead. So, with this patch you've fixed some important bugs that I > would have hit later. > > [A] sidenote: see > https://public-inbox.org/git/xmqqk1ydkbx0....@gitster.mtv.corp.google.com/ > for more details > > 1) mark_new_skip_worktree() ... is_excluded_from_list(). > > Sadly, I'm not very familiar with the skip_worktree and sparse > checkout stuff. However, the fact that mark_new_skip_worktree() > explicitly takes an index_state (and a different one is passed to it > the two different times it is called), and that it is the only caller > of the clear_ce_flags*() family of functions, and that those function > use the cache entries from the index passed to them in all cases other > than the calls to is_excluded_from_list() makes those two look like > oversights. In fact, a little more digging turns up commit > fba92be8f7 ("dir: convert is_excluded_from_list to take an index", > 2017-05-05) > and before then, those functions didn't use the_index directly. But > they did use it indirectly, because they called a function in dir.c > that had it hardcoded. So it looks like Brandon fixed part of the bug > for us, but moved the incorrect hardcoding from dir.c to > unpack-trees.c. Your patch is just fixing it up. In fact, a little > more digging turns up: > > 2c1eb10454 ("dir: convert read_directory to take an index", 2017-05-05) > a0bba65b10 ("dir: convert is_excluded to take an index", 2017-05-05) > > which appear to be the culprits behind the other two uses of the_index > called from verify_absent(). It looks like before these commits that > unpack_trees() was carefully using the appropriate index, except that > functions in dir.c had use of the_index hardcoded. Brandon fix the > functions in dir.c for us, but ended up still hardcoding the_index in > unpack-trees.c. Basically, he did most of the necessary lifting, and > your patch just finally changes them over to use the correct index. > > Brandon: Does anything look off in my analysis above?
Nope your analysis is correct with regards to the changes I made to dir. Back when I was converting ls-files and grep to recursively work on submodules I needed to make it so that some of the dir functions explicitly accepted an index parameter instead of implicitly relying on the_index. So I bubbled up the hardcoded the_index to the places I wasn't passing in a specific index (which would be when the_index appeared in unpack-trees.c) and allowed for arbitrary index's to be passed in like in ls-files. This is one of the larger issues with working in our codebase, implicitly relying on global state. It makes it very difficult to reason if a section of code is correct or not, as is in this case. Is it a bug that we use o->src_index in some places and the_index in others? Well maybe not, but that's because they usually are the same thing in the few cases that it matters (at least now its a bit more explicit to see this, whereas before it was very implicit). Of course I know stefan has done work with making unpack-trees recursive so maybe it can be a bug in the recursive case. -- Brandon Williams
