Re: Failure to fetch submodule with --depth=1 parameter

[Jeff King <peff@peff.net>]

On Tue, Sep 03, 2019 at 05:30:02PM +0200, Grigory Yakushev wrote:

> $ git --version
> git version 2.17.1
> 
> Repro:
> $ git clone https://github.com/PX4/Firmware.git
> $ cd Firmware
> $ git submodule update --init --recursive --depth=1
> ...
> error: Server does not allow request for unadvertised object
> 22df9475ca0d157e2db066a20f64c35906bf7f25
> Fetched in submodule path 'Tools/sitl_gazebo', but it did not contain
> 22df9475ca0d157e2db066a20f64c35906bf7f25. Direct fetching of that
> commit failed.
> 
> The same line without --depth=1 flag works fine:
> $ git submodule update --init --recursive

I think what's happening is this: the super-project (PX4/Firmware)
points to a specific sha1 in the submodule (Tools/sitl_gazebo). But
there's no branch pointing at that sha1, so the client cannot ask for it
directly.

As a fallback we instead fetch HEAD from the submodule and hope that we
got the sha1 we needed. But because we pass along "--depth=1", that
fallback is not likely to work.

IMHO one obvious improvement on the client side is to have a third-level
fallback to do a full clone, and hope we get it then.

However, there may a be an easier solution. In the v2 protocol, Git does
not enforce any advertisement or reachability properties for items the
client asks for. So the client would be free to just ask for the sha1
directly, no fallback required.

Try setting:

  git config --global protocol.version 2

which seems to make it work.

-Peff