The good and the bad of git subtree.

• Atlassian -- Git subtree: the alternative to Git submodule

NAME
       git-subtree - Merge subtrees together and split repository into subtrees

SYNOPSIS
       git subtree add   -P <prefix> <commit>
       git subtree add   -P <prefix> <repository> <ref>
       git subtree pull  -P <prefix> <repository> <ref>
       git subtree push  -P <prefix> <repository> <ref>
       git subtree merge -P <prefix> <commit>
       git subtree split -P <prefix> [OPTIONS] [<commit>]

$ git checkout -b subtree

$ git subtree add \
  --prefix .vim/bundle/tpope-vim-surround \
  https://bitbucket.org/vim-plugins-mirror/vim-surround.git \
  master \
  --squash
git fetch https://bitbucket.org/vim-plugins-mirror/vim-surround.git master
warning: no common commits
remote: Counting objects: 338, done.
remote: Compressing objects: 100% (133/133), done.
remote: Total 338 (delta 101), reused 338 (delta 101)
Receiving objects: 100% (338/338), 71.46 KiB | 46.00 KiB/s, done.
Resolving deltas: 100% (101/101), done.
From https://bitbucket.org/vim-plugins-mirror/vim-surround
 * branch            master     -> FETCH_HEAD
Added dir '.vim/bundle/tpope-vim-surround'
$

$ tree .vim
.vim
└── bundle
    └── tpope-vim-surround
        ├── doc
        │   └── surround.txt
        ├── plugin
        │   └── surround.vim
        └── README.markdown

4 directories, 3 files
$

$ git log --oneline
cc770c1 (HEAD -> subtree) Merge commit 'bd61f717bcc5d8569846d875952d6aefab987dd1' as '.vim/bundle/tpope-vim-surround'
bd61f71 Squashed '.vim/bundle/tpope-vim-surround/' content from commit 02199ea
... snip ...
$

$ git subtree pull \
  --prefix .vim/bundle/tpope-vim-surround \
  https://bitbucket.org/vim-plugins-mirror/vim-surround.git \
  master \
  --squash
$