Re: git push failing when push.recurseSubmodules on-demand and git commit --amend was used in submodule.

[Stefan Beller <sbeller@google.com>]

On Sun, Jan 29, 2017 at 5:00 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Carlo Wood <carlo@alinoe.com> writes:
>
>> there seems to be a problem with using 'git commit --amend' in
>> git submodules when using 'git push --recurse-submodules=on-demand'
>> in the parent.
>>
>> The latter fails, saying "The following submodule paths contain changes
>> that can not be found on any remote:" for such submodule, even though
>> the submodule is clean, pushed and reports 'Everything up-to-date'
>> when trying to push it.
>>
>> I believe that the reason has to be that the parent repository thinks
>> that the comment that was amended, but not pushed, must be on the remote
>> too, while the whole point of amend is that this commit is not pushed.
>
> I am not super familiar with the actualy implementation of the
> codepaths involved in this, so CC'ed the folks who can help you
> better.
>
> I suspect the submodule folks would say it is working as intended,
> if \
>
>  - you made a commit in the submodule;
>  - recorded the resulting commit in the superproject;
>  - you amended the commit in the submodule; and then
>  - you did "push, while pushing out in the submodule as needed" from
>    the superproject.

Yes, for the current state of affairs, this is it.

>
> There are two commits in the submodule that are involved in the
> above scenario, and the first one before amending is needed by the
> other participants of the project in order for them to check out
> what you are trying to push in the superproject, because that is
> what the superproject's tree records.  You somehow need to make that
> commit available to them, but after you amended, the original commit
> may no longer be reachable from any branch in your submodule, so
> even if you (or the "on-demand" mechanism) pushed any and all
> branches out, that would not make the needed commit available to
> others.  If you push your top-level superproject out in such a
> situation, you would break others.

In the long term future, we may want to reject non-fastforward
submodule updates. (Not sure if that is feasible)

>
> I think you have two options.
>
>  1. If the amend was done to improve things in submodule but is not
>     quite ready, then get rid of that amended commit and restore the
>     branch in the submodule to the state before you amended, i.e.
>     the tip of the branch will become the same commit as the one
>     that is recorded in the superproject.  Then push the submodule
>     and the superproject out.  After that, move the submodule branch
>     to point at the amended commit (or record the amended commit as
>     a child of the commit you pushed out).
>
>  2. If the amend is good and ready to go, "git add" to update the
>     superproject to make that amended result the one that is needed
>     in the submodule.

yup.