On 2019-08-15 at 22:10:29, Junio C Hamano wrote: > Junio C Hamano <gits...@pobox.com> writes: > > > "brian m. carlson" <sand...@crustytoothpaste.net> writes: > > > >> When applying multiple patches with git am, or when rebasing using the > >> am backend, it's possible that one of our patches has updated a > >> gitattributes file. Currently, we cache this information, so if a > >> file in a subsequent patch has attributes applied, the file will be > >> written out with the attributes in place as of the time we started the > >> rebase or am operation, not with the attributes applied by the previous > >> patch. This problem does not occur when using the -m or -i flags to > >> rebase. > > ... > > "rebase -m" and "rebase -i" are not repeated run_command() calls > > that invoke "git cherry-pick" or "git merge" these days, either, so > > I am somewhat curious how they avoid fallilng into the same trap. > > > > Thanks for the fix. Will queue. > > Actually there still is one more thing I wasn't clear about the > change. > > > To ensure we write the correct data into the working tree, expire the > > cache after each patch that touches a path ending in ".gitattributes". > > ... > > + if (!flush_attributes && patch->new_name && > > + ends_with_path_components(patch->new_name, > > GITATTRIBUTES_FILE)) > > + flush_attributes = 1; > > When an attribute file is removed by a patch, we should forget what > we read earlier from the file before it got removed. Would such a > case, where patch->new_name would be NULL, be handled correctly?
That's a good question. I don't think we handle that case, so I'll include that (and an appropriate test) with my reroll. I suspect we probably want something like: if ((patch->new_name && ends_with_path_components(patch->new_name, GITATTRIBUTES_FILE)) || (patch->old_name && ends_with_path_components(patch->old_name, GITATTRIBUTES_FILE))) This should cause at most one flush per patch, and I think this should cover both cases, as well as any we haven't thought of. It's also possible that we could get a copy or rename that causes a false positive, but considering the contents of a .gitattributes file, that seems unlikely enough in practice that it's probably not worth worrying about for now. > The call to ends_with_path_components() is almost no cost, and I > would suspect that this call is easier to reason about without the > "!flush_attributes &&" in the conditional part, by the way. Yeah, it probably is. It was added to avoid the allocation, but now that we don't have one, it shouldn't be a problem. -- brian m. carlson: Houston, Texas, US OpenPGP: https://keybase.io/bk2204
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