From: Elijah Newren <newren@gmail.com>
Date: Fri, 23 Oct 2020 17:40:28 GMT
Subject: Re: [PATCH 2/9] merge tests: expect improved directory/file conflict handling in ort
Message-ID: <CABPp-BEhjecB7_juP3cSuF7MUHKbPXqAxKgKstPZw2ezHXputw@mail.gmail.com>
In-Reply-To: <9394d526f1425fcf6b8865b53b737ba81c11dd80.1603468885.git.gitgitgadget@gmail.com>

On Fri, Oct 23, 2020 at 9:01 AM Elijah Newren via GitGitGadget
<gitgitgadget@gmail.com> wrote:
>
> From: Elijah Newren <newren@gmail.com>
>
> merge-recursive.c is built on the idea of running unpack_trees() and
> then "doing minor touch-ups" to get the result.  Unfortunately,
> unpack_trees() was run in an update-as-it-goes mode, leading
> merge-recursive.c to follow suit and end up with an immediate evaluation
> and fix-it-up-as-you-go design.  Some things like directory/file
> conflicts are not well representable in the index data structure, and
> required special extra code to handle.  But then when it was discovered
> that rename/delete conflicts could also be involved in directory/file
> conflicts, the special directory/file conflict handling code had to be
> copied to the rename/delete codepath.  ...and then it had to be copied
> for modify/delete, and for rename/rename(1to2) conflicts, ...and yet it
> still missed some.  Further, when it was discovered that there were also
> file/submodule conflicts and submodule/directory conflicts, we needed to
> copy the special submodule handling code to all the special cases
> throughout the codebase.
>
> And then it was discovered that our handling of directory/file conflicts
> was suboptimal because it would create untracked files to store the
> contents of the conflicting file, which would not be cleaned up if
> someone were to run a 'git merge --abort' or 'git rebase --abort'.  It
> was also difficult or scary to try to add or remove the index entries
> corresponding to these files given the directory/file conflict in the
> index.  But changing merge-recursive.c to handle these correctly was a
> royal pain because there were so many sites in the code with similar but
> not identical code for handling directory/file/submodule conflicts that
> would all need to be updated.
>
> I have worked hard to push all directory/file/submodule conflict
> handling in merge-ort through a single codepath, and avoid creating
> untracked files for storing tracked content (it does record things at
> alternate paths, but makes sure they have higher-order stages in the
> index).
>
> Since updating merge-recursive is too much work and we don't want to
> destabilize it, instead update the testsuite to have different
> expectations for relevant directory/file/submodule conflict tests.
>
> Signed-off-by: Elijah Newren <newren@gmail.com>

Perhaps I should also mention that these changes to directory/file
conflict handling were discussed previously in the thread at
https://lore.kernel.org/git/xmqqbmabcuhf.fsf@gitster-ct.c.googlers.com/.
I just never got around to a complete implementation within
merge-recursive.c, but did implement it in merge-ort.c

I still haven't gotten around to fixing up git-mv and git-rm as
suggested by Junio in that thread; but at least I've finally gotten
the merge machinery side written...