git-filter [FreeBSD WIKI]

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===== GIT Filter =====

Using git filters to extract or separate %%FreeBSD%% components into their own git repos.

This is still a work in progress. Two examples will be provided.

==== git-filter-repo ====

[[https://github.com/newren/git-filter-repo|git-filter-repo]] is a handy [[https://www.freshports.org/devel/git-filter-repo/|port]] that will rewrite git history, including separating %%FreeBSD%% components from the tree. Following is how I separated telnet (telnetd, libtelnet, and telnet) into its own repo.

  - git clone a fresh copy of src.
  - git filter-repo --path contrib/telnet --path lib/libtelnet --path libexec/telnetd --path usr.bin/telnet
  - git reflog expire --all --expire-unreachable=0
  - git repack -A -d
  - git prune

This resulted in a 1 MB git repo containing only telnet.

git-filter-repo is recommended by the authors of git. git-filter-branch displays a message suggesting that git-filter-repo be used.

==== git-filter-branch ====

As efficient as git-filter-repo is, I discovered it deleted files that should not have been deleted when extracting ftpd into its own repo. The other tool at our disposal is git-filter-branch, which is already packaged with git. Though git warns about git-filter-branch caveats and the possibility of repo corruption, it was the only solution to separate ftpd into its own repo. The steps I used are:

  - git clone a fresh copy of src.
  - git filter-branch --subdirectory-filter libexec/ftpd
  - git filter-branch --tag-name-filter cat --index-filter 'git rm -r --cached --ignore-unmatch filename' --prune-empty -f -- --all
  - rm -r .git/refs/original
  - git reflog expire --expire=now --all
  - git gc --prune=now
  - git gc --aggressive

This resulted in a 448KB git repo only containing ftpd.

Hopefully this will be of use to someone. I will expound on the above at a later date as time permits.