Re: [PATCH 00/30] Add directory rename detection to git

From: Elijah Newren <newren@gmail.com>
Date: Nov 10, 2017, 23:26 UTC
Message-ID: <CABPp-BE1+32fQQdYuwP-7m+GXqyhoUpHKgMM6SCcW4e9geutvw@mail.gmail.com>
In-Reply-To: <3076EE0E678D43B286F86E622CB9F06E@PhilipOakley>

On Fri, Nov 10, 2017 at 2:27 PM, Philip Oakley <philipoakley@iee.org> wrote:

Show 25 quoted lines

> From: "Elijah Newren" <newren@gmail.com>
>>
>> In this patchset, I introduce directory rename detection to
>> merge-recursive,
>> predominantly so that when files are added to directories on one side of
>> history and those directories are renamed on the other side of history,
>> the
>> files will end up in the proper location after a merge or cherry-pick.
>>
>> However, this isn't limited to that simplistic case.  More interesting
>> possibilities exist, such as:
>>
>>  * a file being renamed into a directory which is renamed on the other
>>    side of history, causing the need for a transitive rename.
>>
>
> How does this cope with the case insensitive case preserving file systems on
> Mac and Windows, esp when core.ignorecase is true. If it's a bigger problem
> that the series already covers, would the likely changes be reasonably
> localised?
>
> This came up recently on GfW for `git checkout` of a branch where the case
> changed ("Test" <-> "test"), but git didn't notice that it needed to rename
> the directories on such an file system.
> https://github.com/git-for-windows/git/issues/1333

I wasn't aware there were problems with git on case insensitive case preserving filesystems; fixing them wasn't something I had in mind when writing this series. However, the particular bug you mention is actually completely orthogonal to this series; it talks about git-checkout without the -m/--merge option, which doesn't touch any code path I modified in my series, so my series can't really fix or worsen that particular issue.

But, if there are further issues with such filesystems that also affect merges/cherry-picks/rebases, then I don't think my series will either help or hurt there either. The recursive merge machinery already has remove_file() and update_file() wrappers that it uses whenever it needs to remove/add/update a file in the working directory and/or index, and I have simply continued using those, so the number of places you'd need to modify to fix issues would remain just as localized as before. Also, I continue to depend on the reading of the index & trees that unpack_trees() does, which I haven't modified, so again it'd be the same number of places that someone would need to fix. (However, the whole design to have unpack_trees() do the initial work and then have recursive merge try to "fix it up" is really starting to strain. I'm starting to think, again, that merge recursive needs a redesign, and have some arguments I wanted to float out there...but I've dumped enough on the list for a day.)

It's possible that this series fixes one particular issue -- namely when merging, if the merge-base contained a "Test" directory, one side added a file to that directory, and the other side renamed "Test" to "test", and if the presence of both "Test" and "test" directories in the merge result is problematic, then at least with my fixes you wouldn't end up with both directories and could thus avoid that problem in a narrow set of cases.

Sorry that I don't have any better news than that for you.

Elijah