Re: Feature Request: Branch-Aware Submodules

["Hedges Alexander" <ahedges@student.ethz.ch>]

> On 25 Aug 2016, at 19:45, Stefan Beller <sbeller@google.com> wrote:
> 
> +cc Jacob and Lars who work with submodules as well.
> 
> On Thu, Aug 25, 2016 at 2:00 AM, Hedges  Alexander
> <ahedges@student.ethz.ch> wrote:
>> 
>> Right now updating a submodule in a topic branch and merging it into master
>> will not change the submodule index in master leading to at least two commit
>> for the same change (one in any active branch). This happened to me quite a few
>> times. To a newcomer this behavior is confusing and it leads to unnecessary
>> commits.
> 
> So you roughly do
> 
>   git checkout -b new-topic
>   # change the submodule to point at the latest upstream version:
>   git submodule update --remote <submodule-path>
>   git commit -a -m "update submodule"
>   git checkout master
>   git merge new-topic
>   # here seems to be your point of critic?
>   # now the submodule pointer would still point to the latest
> upstream version?
> 

Excuse my poor wording above. The problem is the following:

# assume a repo with a few branches and one submodules
git checkout -b new_feature
git commit -am "some new commits"
cd submodule/path
git commit -am "dirty hacking on a library"
cd ../..
git commit -am "changes and update library"
git status
# all is well
git checkout master
git status
# it says new submodule commits ??
git commit -am "update library again…"
git merge new_feature
git checkout old_feature_that_never_made_it
git status
# still ???
git commit -am …

Now reading the comments below, I overlooked git submodule update. I used update
only the first time after a clone with the init flag. As a remedy I could just
run git submodule update after every merge, but then I always get a detached
head which is also not ideal.
The second thing I overlooked is just merging without worrying about the git
status telling me the repository is dirty. But here my muscle memory does a
commit when the repository is dirty, before running any other git commands.

Obviously, its confusing to people without a certain amount of experience.

>> The proposed change would be to have a submodule either ignored or tracked by
>> the .gitmodules file.
>> If it is ignored, as for instance after a clone of the superproject, git simply
>> ignores all files in the submodule directory. The content of the gitmodules
>> file is then also not updated by git.
>> If it is not ignored, the .gitmodules is updated every time a commit happens in
>> the submodule.
> 
> So
> 
>   git -C <submodule-path> commit
> 
> should trigger a commit in the superproject as well, that changes the gitmodules
> file? What do you record in the git modules file that needs updating?
> As the version is tracked via the gitlink entry, I do not see the
> information that
> needs tracking here?

I guess nothing has to be done here. I mistakenly thought the .gitmodules stores
the SHA.

> 
>> On branch switches the revision shown in the gitmodules from
>> that branch is checked out.
> 
> So you are proposing to put the revision into the gitmodules file?
> That would be redundant with the actual gitlink entry in your tree.
> (as shown via `git submodule status`)
> What would happen if the recorded revision in the gitmodules file and the
> gitlink are out of sync?
> 
> Oh, are you just proposing to actually make `git checkout` aware of the
> submodules? See[1]. I would welcome such a change and be happy th
> 
> [1] https://github.com/jlehmann/git-submod-enhancements
> which has some attempts for checkout including the submodules.
> I also tried writing some patches which integrate checking out submodules
> via checkout as well. A quicker `solution` would be a config option that
> just runs `git submodule update` after each checkout/pull etc.
> 

I see. The quick fix is almost what I’m looking for, except that it leaves
the repo in a detached head state. Could the submodule update be made 
automatically and intelligently pick the branch?

> 
>> This change would have submodules conceptually behave more like files to the
>> superproject.
>> 
>> 
>> Like current behavior, git status would display whether the submodule has
>> uncommitted changes or is at a new commit.
> 
> See config options diff.submodule and status.submoduleSummary.
> 

I meant that git status works fine the way it is implemented right now.

> 
>> 
>> I couldn't find any discussions on the initial implementation of git-submodule
>> or any previous proposals related to this in nature due to gmane being down
>> right now and the mailing list archives on the other sites are not great for
>> searching. So please excuse me if I'm bringing up already discussed stuff.
> 
> https://public-inbox.org/git for reading on the web, or
> 
>   git clone https://public-inbox.org/git
> 
> for reading offline.
> 

Thanks.

Best Regards,
Alexander Hedges