git submodule update - reset instead of checkout?

git submodule update - reset instead of checkout?

[Andreas Krey]

Hi everyone,

I've been reading up on the current state of git submodules
(our customer's customers want to use them, causing a slight
groan from our customer).

The usability thing I wonder about - with git submodule update,
is it necessary to detach the head to the current (or upstream)
head, instead of resetting the current branch to that state?

Primary interest in the question: Seeing 'detached head' scares
almost everybody. To brainstorm:

- as we can already use 'submodule update --remote' to update
  to the remote head of a branch, it would be logical to have
  that branch checked out locally (and unfortunately, potentially
  have that branch's name conflict with the remote branch setup).

- when developers more or less accidentally commit on the detached
  head, all is not lost yet (I remember this being differently),
  but if the next 'submodule update' just resets again, the commit
  just made is still dropped, just as in the detached head state.

- So, we'd need to have 'submodule update' act closer to the pull or
  rebase counterparts and refuse to just lose commits (or uncommitted
  changes).

Having a checked-out branch in the submodule would have the advantage
that I can 'just' push local commits. At the moment, doing that requires
a relatively intricate dance, not at all similar to working in the
base (parent) module.

I'm working on hooks that automatically update the submodules after
a commit change (merge, pull, checkout) in the parent module, but
with the additional feature of (a) keeping a branch checked out
and (b) avoid discarding local changes. Probably means I shouldn't
invoke 'submodule update' at all, and deal with everyting myself.

Any thoughs/comments/helpful hints?

(Addional complexity: egit/jgit is in use as well, and the work model
we will arrive at probabaly needs to work with the current egit.)

- Andreas

-- 
"Totally trivial. Famous last words."
From: Linus Torvalds <torvalds@*.org>
Date: Fri, 22 Jan 2010 07:29:21 -0800

Re: git submodule update - reset instead of checkout?

[Stefan Beller]

On Fri, Mar 9, 2018 at 7:07 AM Andreas Krey <a.krey@gmx.de> wrote:

> Hi everyone,

> I've been reading up on the current state of git submodules
> (our customer's customers want to use them, causing a slight
> groan from our customer).

> The usability thing I wonder about - with git submodule update,
> is it necessary to detach the head to the current (or upstream)
> head, instead of resetting the current branch to that state?

Try "git checkout --recurse-submodules" or
"git reset --recurse-submodules"  (there is also the
submodule.recurse option in case you don't want to type
the option all the time)


> Primary interest in the question: Seeing 'detached head' scares
> almost everybody. To brainstorm:

I agree on that. That is what we are trying to work out
eventually, too.

One idea is to "reattach the submodule branch if it fits"
another idea would be a submodule ref store that is
(partially) tied to the superproject, such that the HEAD
of the submodule is non-existent for most of the time.
https://public-inbox.org/git/cover.1512168087.git.jonathantanmy@google.com/

> - as we can already use 'submodule update --remote' to update
>    to the remote head of a branch, it would be logical to have
>    that branch checked out locally (and unfortunately, potentially
>    have that branch's name conflict with the remote branch setup).

> - when developers more or less accidentally commit on the detached
>    head, all is not lost yet (I remember this being differently),
>    but if the next 'submodule update' just resets again, the commit
>    just made is still dropped, just as in the detached head state.

> - So, we'd need to have 'submodule update' act closer to the pull or
>    rebase counterparts and refuse to just lose commits (or uncommitted
>    changes).

> Having a checked-out branch in the submodule would have the advantage
> that I can 'just' push local commits. At the moment, doing that requires
> a relatively intricate dance, not at all similar to working in the
> base (parent) module.

> I'm working on hooks that automatically update the submodules after
> a commit change (merge, pull, checkout) in the parent module, but
> with the additional feature of (a) keeping a branch checked out
> and (b) avoid discarding local changes. Probably means I shouldn't
> invoke 'submodule update' at all, and deal with everyting myself.

> Any thoughs/comments/helpful hints?

Our plan is to deprecate "git submodule" just like "git remote" is not
a well known tool any more. (e.g. Instead of git remote update, use
git fetch, that learned about updating the remote tracking branches
on its own)


> (Addional complexity: egit/jgit is in use as well, and the work model
> we will arrive at probabaly needs to work with the current egit.)

That sounds familiar, we also have JGit/Gerrit in the setup.

Stefan