• Junio C Hamano's avatar
    merge-base: teach "--fork-point" mode · d96855ff
    Junio C Hamano authored
    The "git pull --rebase" command computes the fork point of the
    branch being rebased using the reflog entries of the "base" branch
    (typically a remote-tracking branch) the branch's work was based on,
    in order to cope with the case in which the "base" branch has been
    rewound and rebuilt.  For example, if the history looked like this:
    
                         o---B1
                        /
        ---o---o---B2--o---o---o---Base
                \
                 B3
                  \
                   Derived
    
    where the current tip of the "base" branch is at Base, but earlier
    fetch observed that its tip used to be B3 and then B2 and then B1
    before getting to the current commit, and the branch being rebased
    on top of the latest "base" is based on commit B3, it tries to find
    B3 by going through the output of "git rev-list --reflog base" (i.e.
    Base, B1, B2, B3) until it finds a commit that is an ancestor of the
    current tip "Derived".
    
    Internally, we have get_merge_bases_many() that can compute this
    with one-go.  We would want a merge-base between Derived and a
    fictitious merge commit that would result by merging all the
    historical tips of "base".  When such a commit exist, we should get
    a single result, which exactly match one of the reflog entries of
    "base".
    
    Teach "git merge-base" a new mode, "--fork-point", to compute
    exactly that.
    Helped-by: default avatarMartin von Zweigbergk <martinvonz@gmail.com>
    Helped-by: John Keeping's avatarJohn Keeping <john@keeping.me.uk>
    Signed-off-by: default avatarJunio C Hamano <gitster@pobox.com>
    d96855ff
git-merge-base.txt 5.55 KB