git - setting a commit's parent without rebase

问题

I used git-svn to create a git mirror of an SVN repository. The structure inside the SVN was a little off-standard, so git created a branch that has no common commit with the master branch.

      A---B---C topic

D---E---F---G master

I know that commit A is based off commit E and I'm pretty positive that I've fixed the issues causing git not to recognize that fact (using filter-branch). What I want to do is re-attach topic to the master branch, setting E as the parent of A:

      A---B---C topic
     /
D---E---F---G master

git-rebase doesn't seem to work for me because the diff for commit A lists the creation of a whole lot of files that already exist in master, resulting in a huge number of conflicts.
From my understanding of git just setting E as the parent of A should be enough to solve all problems.
Is this possible? If it is, how can I do it?

回答1:

Have a look at grafts (the graft file can be found in .git/info/grafts). The format is pretty simple:

<commit sha1> <parent1 sha1> <parent2 sha1> … <parentN sha1>

This makes git believe that a commit has different parents than it actually has. Use filter-branch to make grafts permanent (so the grafts file can be removed):

git filter-branch --tag-name-filter cat -- --all

Note that this rewrites history of the repository, so should not be used on shared repos!

If you only want to rewrite the history of the commits that are being grafted onto the master branch, for example, use this command:

git filter-branch --tag-name-filter cat -- master..

回答2:

Based on your diagrams (although I'm concerned about what you mean by "I'm pretty positive that I've fixed the issues causing git not to recognize that fact (using filter-branch)."), you should be able to do something like the following.

# checkout A
git checkout A

# Reset the branch pointer to E so that E is the parent of the next commit
# --soft ensures that the index stays the same
git reset --soft E

# Remake the commit with the E as the parent, re-using the old commit metadata
git commit -C HEAD@{1}

# Rebase the topic branch onto the modified A commit (current HEAD)
git rebase --onto HEAD A topic

回答3:

All you need is this:

git rebase --root --onto master^^ topic^^ topic

the root option lets you include A.

UPDATE:

Add the --preserve-merges option if you want to retain the branching and merging of the part that you are rebasing.

来源：https://stackoverflow.com/questions/4163895/git-setting-a-commits-parent-without-rebase

标签

git

rebase