Changing branches in supermodule does not affect submodule?

Hi!

If I have a repository with submodules that is in a clean state, and switch branches in the super repository, the submodules are left in the state they were in before I switched branches (with 1.6.4, at least). Is this the expected behaviour?

--->8--8<--- #!/bin/bash # Create supermodule. mkdir super-$$ cd super-$$ git init

# Create submodule with commit. mkdir sub cd sub git init echo C > c.txt echo D > d.txt git add c.txt d.txt git commit -m Created. cd ..

# Create commit and branch in supermodule. echo A > a.txt echo B > b.txt git add a.txt b.txt sub git commit -m Created. git tag branchpoint git checkout -b branch1

# Create branch1 in submodule and commit. cd sub git checkout -b branch1 echo E > c.txt echo F > d.txt git add c.txt d.txt git commit -m Branched. cd ..

# Commit to a branch in the supermodule. git add sub git commit -m Sub-update.

# Status should now be clean. git status

# Create a new branch in supermodule, from the original commit. git checkout -b branch2 branchpoint

# I now expect the submodule to be up-to-date and the state clean. git status --->8--8<---

Peter Krefting schrieb:

Yup, submodules have to be updated separatly.

When they are cloned from a remote with "git submodule add" followed by a "git submodule init", just calling "git submodule update" every time you want the submodule to be updated according to the state committed in the superproject will do the trick (but keep in mind that all referenced commits have to be accessible in the local clone of your submodule, so you might have to do a fetch there once in a while).

Jens

Jens Lehmann:

Is it possible to automate this from a hook or something else? Basically, I would like it to update all the submodules to the state recorded in the commit I move to, if they were in a clean state before I moved. I do not want it to change states if I do something like

   cd submodule
   # do some changes
   git commit
   cd ..
   git checkout -b newbranch

because there I want the commit I made to the submodule to be recorded on the new branch I created. But then it was in a dirty state before I created the branch anyway, so that shouldn't be a problem.

Peter Krefting schrieb:

BTW: unless you use the -N or --no-fetch option, git submodule update
will do the fetch for you.

Yep, you can use the post-checkout hook for that, just put a "git submodule update" in it.

*But*: If you do a checkout in the superproject while the submodule has new commits not contained in any branch (remember submodules often have a detached head) you'll silently lose these commits! Then only the reflog can help you ...

Currently gits default behaviour is not to recursively update submodules when they are unchanged in the working copy. This hook implements this by comparing whether the current HEAD in the submodule is the same as recorded in the commit we are coming from. It then initializes or updates the submodule as necessary.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
---

On Wed, Oct 14, 2009 at 05:39:29PM +0200, Jens Lehmann wrote:

Incidentially I have just been working on such a hook. Here is a patch that implements it as a sample hook.

I tested most cases, but I have not worked with it productively so it might have strange results in some cases. One I already found is that post-checkout is not called after a merge so you need to add a submodule update there as well.

cheers Heiko

 templates/hooks--post-checkout.sample |   50 +++++++++++++++++++++++++++++++++
 1 files changed, 50 insertions(+), 0 deletions(-)
 create mode 100644 templates/hooks--post-checkout.sample

Peter Krefting <peter@softwolves.pp.se> writes:

My understanding is that the primary reason "git checkout $another_branch" does not touch submodules (other than updating the commit object name bound in the index in the superproject) is because we did not know what people would want to happen when submodule support was introduced.

Now people have used submodules for a while, we can update this. I think modelling the behaviour after how normal blobs are updated upon branch switching would make sense.

So let's step back a bit and review what happens to a normal blob upon branch switching. There are three cases for a path while switching branches from A to B:

 #1 The path is the same between A and B.  In this case, whatever you have
    for path in the index and in the work tree stay the same.  Your local
    modification is carried across branch switching.

    This is already what we do with submodules.  In cases #2 and #3 below,
    path is different between A and B.

 #2 You do not have any change to the path in either the index nor in the
    work tree.  The path is updated to B's version in the index and also
    what you have in the work tree matches it.

    Note that if B lacks the path, it is _removed_ from both the index and
    the work tree.

 #3 You have a change to the path in the index or in the work tree.  The
    branch switch is refused if the index does not match what is in B.

    I think this also is already what we do with submodules.

With a reasonable definition of "have a change in the work tree" for a submodule path, we can define a reasonable behaviour for updating the submodules when a different branch is checked out in the superproject.

For a regular blob, having a change in the work tree is that the object recorded in HEAD (in the superproject) is different from what you have in the work tree. What should the definition be for a submodule?

The HEAD (in the submodule), the index (in the submodule) and the work tree (in the submodule) form the "state" of what you have in the path, and that corresponds to the "work tree state". So I think we can say that there is no change in the work tree for a submodule at path P if all of the following holds:

    - the HEAD in the submodule matches the commit recorded for the path P
      in the HEAD in the superproject;

    - the index in the submodule matches the HEAD in the submodule; and

    - the work tree in the submodule matches the index in the submodule.

With this definition, you should be able to patch "git checkout" to recurse into the submodule directory for case #2.

As to the implementation, I'd suggest:

 - the check between the submodule HEAD and what the superproject records
   in the HEAD (the first condition above) be done inside the main process
   (because we already have a working check for #3 to refuse branch
   switching, I think it would be easier to implement this check by
   comparison between the submodule HEAD and the superproject index).

 - the check between the index and the HEAD in the submodule and the check
   between the index and the work tree in the submodule (the second and
   the third conditions above) be done in a subprocess that runs something
   like "git status" via the run_command() interface; and

 - the actual recursive checkout to happen in a subprocess that runs
   another instance of "git checkout" via the run_command() interface.

There is one caveat. The potential removal of the work tree path in #2 may not be desirable for a submodule path, even if you do not have any change to it (i.e. both the index and the work tree in the submodule match the HEAD in the submodule), as you may have untracked files you would rather want to keep in the submodule work tree.