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copy a directory and its git history

This article outlines the cherry-picking approach.

1. Create a new git repo, git init
2. Set original repo as a remote, git remote add hmwk file://path/to/original/repo
3. Download history from original repo, git remote update
4. List commits that change this directory, git log -- day2009-bouncing-discs. Or use helper in IDE.
5. Cherry-pick commits from remote, git cherry-pick f1a6884d^..5dfa0336 if commits are consecutive. Or cherry-pick them one by one.

However, cherry-pick will throw fatal error if specified hash range contains merge commit. And commits from another branch will be “merged” to HEAD which is a very undesirable behaviour.

Subtree merging approach preserves merge commits and full commit history, see this link. Excerpt:

Here is the command sequence you need:

$ git remote add -f Bproject /path/to/B <1>
$ git merge -s ours --no-commit --allow-unrelated-histories Bproject/master <2>
$ git read-tree --prefix=dir-B/ -u Bproject/master <3>
$ git commit -m "Merge B project as our subdirectory" <4>
$ git pull -s subtree Bproject master <5>

1. name the other project “Bproject”, and fetch.
2. prepare for the later step to record the result as a merge.
3. read “master” branch of Bproject to the subdirectory “dir-B”.
4. record the merge result.
5. maintain the result with subsequent merges using “subtree”

The first four commands are used for the initial merge, while the last one is to merge updates from B project.