[Git] Introduction of llvm-project-subtree.git

Hello guys,

I made the "subtree" all-in-one LLVM, clang, dragonegg &c repository.

https://github.com/chapuni/llvm-project

* How to play

  1) git clone git://github.com/chapuni/llvm-project.git

  2) (Optional) Add the line in [remote "origin"], .git/config

    [remote "origin"]
        fetch = +refs/notes/commits:refs/notes/commits

    And "git fetch origin"

You can see like below;

commit a2010a39da6a56317fda432954aadafb8241e1a4
Author: NAKAMURA Takumi <geek4civic@gmail.com>

    Prune more RALinScan. RALinScan was also here!

Notes:
    git-svn-rev: 144487

* What would be made happier with it?

  - Fast pulling and checking-out
  - Work with traditional llvm.git, clang.git &c. llvm-project.git
shares each root commit of subproject.
  - Ability to bisect inter projects (eg. tracking clang-llvm
bi-dependent issues)
  - (for developers) See below

* How to commit my changes via git-svn?

  [Stupid way] On your clone of {llvm.git | clang.git &c),

    $ git fetch /path/to/your/clone/of/llvm-project your-branch
    $ git cherry-pick --strategy subtree FETCH_HEAD

  [Smarter way] On your clone of {llvm.git | clang.git &c),

    - add "/path/to/your/clone/of/llvm-project/.git/objects to
.git/objects/info/alternates
    - git cherry-pick --strategy subtree (sha1 of commits on your branch)

* (WIP) Can I commit my inter-project changes?

  Yes. For now, you can do manually.

  1) Create temporary branch (may be detached)
  2) Create a commit, that moves directory structure.
    $ git mv llvm trunk; mkdir llvm; git mv trunk llvm
    $ mkdir cfe; git mv clang cfe/trunk
    $ git commit
  3) $ git cherry-pick --strategy subtree (a commit of your branch)
  4) $ git commit-diff -r HEAD HEAD^ HEAD https://llvm.org/svn/llvm-project/

* TODO
  - Provide the script who commits llvm-project to
llvm.org/svn/llvm-project/ directly.
  - Managing refs/tags/rXXXXXX corresponding to git-notes.

Happy happy hacking,
...Takumi