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

[Johannes Altmanninger <aclopte@gmail.com>]

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?