Share a working tree with git submodules

Suppose I have a library Common that may be used stand-alone, and is used by projects P1 and P2, so the tree I want looks 开发者_如何学编程like

/Common/.git
        ...
/P1/.git
    .gitmodules  # points to remote server
    Common/
    ...
/P2/.git
    .gitmodules  # points to remote server
    Common/
    ...

When I make a change in /Common, I would like to be able to test it using P1 and P2 before committing. With the usual git submodule command set, I would have to commit from /Common, push to remote, then pull from both /P1/Common and /P2/Common. If the commit breaks something, it cannot be amended because the bad change has already been published. Alternatively, I could git remote add quicktest /Common from /P?/Common to be able to pull without touching the remote server. But this has lots of opportunities for inconsistency and it is dirty to strip broken commits from /P?/Common so that they can be amended in /Common.

I would rather that, during development, the working tree from /Common be used by P1 and P2, but I can't make /P1/Common a symlink to /Common because git submodule recognizes the symlink as different from a directory. Hardlinking directories is not allowed by most file systems. I can hardlink all the files using

rm -rf /P1/Common
cp -rl /Common /P1/Common

which works quite well until a new file is added to /Common in which case this process needs to be repeated. Is there an elegant way to both

1. keep git clone --recursive git://remote/P1.git working for the end user, and
2. allow me to easily test that changes in /Common work with P1 and P2?

Try git worktree feature since git 2.5.

1. Delete /P1/Common
2. cd /Common
3. Create P1 branch for the coming /P1/Common working tree
4. run git worktree add ../P1/Common P1

Do the same thing on /P2.

Then, /P1/Common, /P2/Common and/Commonworking trees share the same repository/Common/.git`.

And you can easily just checkout any commit which is commit in another working tree.

P.S. you can still use git submodule command for daily work with this git worktree feature.

I would rather establish an intermediate bare repo where to:

• push Common new commits
• pull from for P1/Common and P2/Common

At least, if commits are amended/removed later, that intermediate repo has never been published outside and you still can reset your P1/Common and P2/Common submodules to that intermediate repo content.

Update: if you are using git worktree, since Git 2.5 (July 2015, 5 years after writing this answer), make sure to use Git 2.25 (Q1 2020).
Before that, "git worktree add" internally calls "reset --hard", which affected submodules.