Easy one-time git subtree merge

The situation:

• Have a git project (A)
• Have a second git project (B) that I want to merge to A under a directory
• This needs to be done once. After that, project B will not be re-sync to A’s subdirectory
• Need to preserve history

The actual situation: I have a git project that is named “drlaunch” and another git project that is named “debian”. “debian” is the packaging directory for drlaunch. The problem occurred because I used to have two svn trees, one for the project and one for the debian/ directory for making this a package for maemo.

I found a number of related things but all of them were complicated because they were doing more than I wanted. Finally, I came to this simple solution:

Under project drlaunch, there is a subdir drlaunch. I want to include the project debian under a directory named debian in the drlaunch project. The tree looks like this:

drlaunch (project)
-- drlaunch (dir)

debian (project)

And at the end I want it to look like this:

drlaunch (project)
|-- drlaunch (dir)
-- debian (dir)

The solution is as simple as this:

1. Go to the debian’s project dir and export all changes with format-patch:[shell]
   cd debian/
   mkdir ../1
   git format-patch –root -o ../1/
   rm ../1/0000-*
   [/shell]

   (Note: The removal of the first file is required. The file should be empty and for me it triggers a git bug causing it to use 100% cpu indefinitely. Feel free to check it yourself)

2. Go to the drlaunch’s project dir and import all changes to a directory:
   [shell]
   cd drlaunch/
   git am –directory=debian/ ../1/*
   [/shell]
3. Ta-da! Ready! Now compare the tree to be sure that nothing bad happend:
   [shell]
   diff -uR debian ../debian/
   [/shell]

Don’t forget to commit your changes.

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