git: How to split off library from project? filter-branch, subtree?

Question

So, I\'ve a bigger (closed source) project, and in the context of this project created a library which could also be useful elsewhere, I think.

I now want to split o

Answer 1

Splitting a subtree mixed with files from the parent project

This seems to be a common request, however I don't think there's a simple answer, when the folders are mixed together like that.

The general method I suggest to split out the library mixed in with other folders is this:

1. Make a branch with the new root for the library:

   git subtree split -P src/de/fencing_game -b temp-br
   git checkout temp-br
   
   # -or-, if you really want to keep the full path:
   
   git checkout -b temp-br
   cd src/de/fencing_game
   

2. Then use something to re-write history to remove the parts that aren't part of the library. I'm not expert on this but I was able to experiment and found something like this to work:

   git filter-branch --tag-name-filter cat --prune-empty --index-filter 'git rm -rf --cached --ignore-unmatch client server otherstuff' HEAD
   
   # also clear out stuff from the sub dir
   cd transport 
   git filter-branch --tag-name-filter cat --prune-empty --index-filter 'git rm -rf --cached --ignore-unmatch fencing client server' HEAD
   

   Note: You might need to delete the back-up made by filter-branch between successive commands.

   git update-ref -d refs/original/refs/heads/temp-br
   

3. Lastly, just create a new repo for the library and pull in everything that's left:

   cd 
   git init
   git pull  temp-br
   

I recommend that your final library path be more like /transport/protocol instead of the full parent project path since that seems kind of tied to the project.