Re: [PATCHv2 0/6] git clone: Marry --recursive and --reference

On Tue, Aug 9, 2016 at 2:45 PM, Junio C Hamano [off-list ref] wrote:

becomes easily doable (i.e. subsequent "submodule update" can realize
that the submodule does not have alternates but it could borrow from
the submodule in the other-super-project-location).

I would suggest to postpone this to a later time once the need arises.

I rather imagine that once you clone from "other-super-project-location"
and get the warning about no alternates borrowing, you can decide if you want
to set it up and link the submodule manually to that alternate, or if you just
don't care about this one repository being duplicated.

For now I plan to introduce 2 options, as these are 2 different things, that
can be extended independently of each other:

submodule.alternateLocation::
    Specifies how the submodules obtain alternates when submodules are
    cloned. Possible values are `no`, `superproject`.
    By default `no` is assumed, which doesn't add references. When the
    value is set to `superproject` the submodule to be cloned computes
    its alternates location relative to the superprojects alternate.

submodule.alternateErrorStrategy::
    Specifies how to treat errors with the alternates for a submodule
    as computed via `submodule.alternateLocation`. Possible values are
    `ignore`, `info`, `die`.

*1* Rather, I meant: clone has a very intimate knowledge on what and
    what cannot be borrowed from and it is not just "is there a
    directory?", so "git submodule update --init" is not in a good
    position to decide if it wants to add --reference to the
    invocation of "git clone" it makes internally, and introducing
    an "if-able" variant to "clone" is one way to relieve it from
    having to make that decision.

That is how I first understood the design as well.

    I could have suggested an alternative: because the submodule
    machinery is gettting moved to C the "update --init" code that
    drives the internal invocation of "git clone" could share the
    the logic in "git clone --reference" that determines if a local
    repository can be used as an alternate by small refactoring of
    builtin/clone.c::add_one_reference().

I see. I might actually need to do this anyway as the helper is a place
to act on the submodule.alternateErrorStrategy.