Re: [PATCH 4/8] merge-tree: implement real merges

[Elijah Newren <newren@gmail.com>]

On Sat, Jan 1, 2022 at 12:08 PM Johannes Altmanninger <aclopte@gmail.com> wrote:
>
> On Fri, Dec 31, 2021 at 05:04:00AM +0000, Elijah Newren via GitGitGadget wrote:
> > From: Elijah Newren <newren@gmail.com>
> >
> > This adds the ability to perform real merges rather than just trivial
> > merges (meaning handling three way content merges, recursive ancestor
> > consolidation, renames, proper directory/file conflict handling, and so
> > forth).  However, unlike `git merge`, the working tree and index are
> > left alone and no branch is updated.
> >
> > The only output is:
> >   - the toplevel resulting tree printed on stdout
> >   - exit status of 0 (clean) or 1 (conflicts present)
> >
> > This output is mean to be used by some higher level script, perhaps in a
> > sequence of steps like this:
> >
> >    NEWTREE=$(git merge-tree --real $BRANCH1 $BRANCH2)
> >    test $? -eq 0 || die "There were conflicts..."
> >    NEWCOMMIT=$(git commit-tree $NEWTREE -p $BRANCH1 $BRANCH2)
> >    git update-ref $BRANCH1 $NEWCOMMIT
> >
> > Note that higher level scripts may also want to access the
> > conflict/warning messages normally output during a merge, or have quick
> > access to a list of files with conflicts.  That is not available in this
> > preliminary implementation, but subsequent commits will add that
> > ability.
> >
> > Signed-off-by: Elijah Newren <newren@gmail.com>
> > ---
> >  Documentation/git-merge-tree.txt | 28 +++++++----
> >  builtin/merge-tree.c             | 55 +++++++++++++++++++++-
> >  t/t4301-merge-tree-real.sh       | 81 ++++++++++++++++++++++++++++++++
> >  3 files changed, 153 insertions(+), 11 deletions(-)
> >  create mode 100755 t/t4301-merge-tree-real.sh
> >
> > diff --git a/Documentation/git-merge-tree.txt b/Documentation/git-merge-tree.txt
> > index 58731c19422..5823938937f 100644
> > --- a/Documentation/git-merge-tree.txt
> > +++ b/Documentation/git-merge-tree.txt
> > @@ -3,26 +3,34 @@ git-merge-tree(1)
> >
> >  NAME
> >  ----
> > -git-merge-tree - Show three-way merge without touching index
> > +git-merge-tree - Perform merge without touching index or working tree
> >
> >
> >  SYNOPSIS
> >  --------
> >  [verse]
> > +'git merge-tree' --real <branch1> <branch2>
> >  'git merge-tree' <base-tree> <branch1> <branch2>
>
> This is really exciting. It could replace the merge-machinery of git-revise
> (which is a "fast rebase" tool).
> I think for cherry-pick/rebase we need to specify a custom merge base,
> would that suit the new form?

I'm glad you're excited about it.  :-)

I think having a server side tool for replaying commits (which can
double as a fast rebase/cherry-pick tool on the client side) is also
important, but I think it should be part of a proper builtin, not some
script that calls out to `merge-tree --real`.

`merge-tree --real` is simpler, though, so I implemented and submitted it first.