NAME

git-nullmerge - Find and merge a commit with a tree that matches an ancestor exactly.

SYNOPSIS

git nullmerge [OPTIONS] <commit>

DESCRIPTION

When a branch has undergone extensive history rewriting, attempting to merge it can result in many false and unnecessary merge conflicts. If such history rewriting has preserved the entire tree at some points along the history, a so-called null merge can be justified. git-nullmerge can automatically find the correct point in history and create a null merge. The message will include a justification with an overview of the relavant part of the commit graph.

Technically, git nullmerge will:

• Find the latest commit THEIR such that
  • THEIR is in <commit>
  • THEIR is not in OUR (where OUR is HEAD at start of execution)
  • There exists a commit IDENTICAL such that
    • IDENTICAL is in OUR
    • IDENTICAL is not in THEIR
    • IDENTICAL and THEIR point to identical trees.
• Make a merge commit with OUR and THEIR as parents and with a tree identical to OUR.
• Optionally update HEAD to point to the newly created merge commit.

INSTALLATION

Place git-nullmerge somewhere in your $PATH.

EXAMPLE

Suppose a remote repository has altered all commit messages, and also diverged. It will then appear like an unrelated history, and git merge will refuse to merge it.

  * (remote) E
  * C'
  * B'
  * A'
*   (HEAD) D
*   C
*   B
*   A

Using git nullmerge remote, the actual fork point will be identified and merged:

  * (remote) E
* | (HEAD) Null merge
|\|
| * C'
| * B'
| * A'
*   D
*   C
*   B
*   A

After this, git merge can do a correct merge.

*   (HEAD) Merge
|\
| * (remote) E
* | Null merge
|\|
* | D
| * C'
| * B'
| * A'
*   C
*   B
*   A

SEE ALSO

git replace: Replace objects in the git graph at the interpretation level.

git-reparent: Create a commit with the same tree but different parents.