How do I change a file's path in git's history?

Question

Here is what I have - a git repo of my code:

projects
       |-proj1 (no git repo here yet)
             |-subproj1 <- current git repo here

Here is what I want - a git repo which is now tracking a new project that uses my code:

projects
       |-proj1 <-git repo moved to here, but still tracking files in subproj1
             |-subproj1 (no git repo here)

I'd like to keep the history intact and therefore the new repository will be referring to files that are one level deeper than the original. What is the most pain free way to do this?

Answer 1

Rewriting history can be done with the git filter-branch command. In fact, moving a directory tree into a subdirectory is one of the cut&paste-ready examples given in the git filter-branch manpage:

git filter-branch --index-filter '
  git ls-files -s |
  sed "s-\t\"*-&subproj1/-" |
  GIT_INDEX_FILE=$GIT_INDEX_FILE.new git update-index --index-info &&
  mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE
' HEAD