Re: Why we should avoid new submodules if possible

[Michael S. Tsirkin]

On Wed, Sep 28, 2022 at 04:07:40PM +0100, Peter Maydell wrote:
> On Wed, 28 Sept 2022 at 15:29, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Wed, Sep 28, 2022 at 11:18:18AM +0100, Daniel P. Berrangé wrote:
> > > On Wed, Sep 28, 2022 at 06:13:45AM -0400, Michael S. Tsirkin wrote:
> > > > On Wed, Sep 28, 2022 at 10:37:14AM +0100, Daniel P. Berrangé wrote:
> > > > > There's also the perenial problem that developers frequently send
> > > > > patches that mistakenly include submodule changes, which is related 
> > > > > to the
> > > > > way that 'git checkout' doesn't sync submodule state when switching 
> > > > > branches.
> > > >
> > > > Do you happen to know how exactly that happens?
> > >
> > > For any given branch the submodule is synced to a given git commit hash.
> > > If the submodule checkout is not synced to the same commit hash it will
> > > show as dirty, and if you git add this pending change, it'll record that
> > > new submodule commit hash.  Seeing dirty state is common when you switch
> > > between branches, either side of a git master change that updated a
> > > submodule.
> > I see. It is interesting.
> >
> > So apparently what you want is ignore submodule
> > changes, right? If yes this is close to what we want:
> >
> > git submodule update --checkout testsub
> > git update-index --skip-worktree testsub
> >
> > A script checking out the submodule can just run this
> > command.
> 
> The problem happens not when you check out the submodule, but when
> you do basic not-submodule-related git operations like
> "git checkout my-working-branch". The fix would be if git itself
> automatically kept submodule state in sync with the main repo's
> branch. But it doesn't, so the UI is a massive beartrap.
> 
> -- PMM

If this is what you want, you can make it do that too:

$ cat .gitmodules 
[submodule "testsub"]
        path = testsub
        recurse = true
        url = /tmp/testsub/


git checkout (and a bunch of other commands) will now recurse into this
submodule.


-- 
MST