Re: Why we should avoid new submodules if possible

[Peter Maydell]

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