Should "git submodule update" accepts --init?

Should "git submodule update" accepts --init?

[Nazri Ramliy]

Hi,

The command "git submodule update" accepts an "--init" flag to
initialize an uninitialized submodules.

Shouldn't it also accept "--sync" flag in order to sync and unsync'd submodule?

Otherwise it seems like I'll have to do "git submodule update" twice
in order to update an already initialized submodule whose upstream
repo url has been updated in .gitmodules to point to somewhere new,
like so:

$ cd superproject
$ git pull
$ git submodule update --init --recursive
fatal: reference is not a tree: c21784553dcd15e1534773fe3177f39cbb93be65
Unable to checkout 'c21784553dcd15e1534773fe3177f39cbb93be65' in
submodule path 'path/to/submodule'
Failed to recurse into submodule path 'path/to/submodule'
$ git submodule sync
$ git submodule update --init --recursive

If the submodule update subcommand accepts the "--sync" flag then
above can then be simplified to this:

$ cd superproject
$ git pull
$ git submodule update --init --sync --recursive

So the "--init" and "--sync" flags tells git to initialize an
uninitialized submodule, and syncs any out-of-sync submodules.

nazri

Re: Should "git submodule update" accepts --init?

[Junio C Hamano]

Nazri Ramliy <ayiehere@gmail.com> writes:

> Otherwise it seems like I'll have to do "git submodule update" twice
> in order to update an already initialized submodule whose upstream
> repo url has been updated in .gitmodules to point to somewhere new,

I am not a heavy submodule user so what I think may not count, but I
think the "upstream" changing the URL of the submodule should be a
rare and notable event.  Making it easy to automatically run "sync"
without thinking would be a huge mistake---it will make it likely
for users to blindly follow what the upstream has in .gitmodules
without checking if the new URL is sensible.

Also doesn't "submodule sync" blindly overwrite URL, even the ones
that you tweaked in your configuration to override to point at a
mirror that is closer to you than the one suggested in .gitmodules?
If that is the case, sucn a change to make it easier to run "sync"
without thinking is doubly bad, I would think.

Re: Should "git submodule update" accepts --init?

[Nazri Ramliy]

On Thu, May 11, 2017 at 2:42 PM, Junio C Hamano <gitster@pobox.com> wrote:
> I am not a heavy submodule user so what I think may not count, but I
> think the "upstream" changing the URL of the submodule should be a
> rare and notable event.  Making it easy to automatically run "sync"
> without thinking would be a huge mistake---it will make it likely
> for users to blindly follow what the upstream has in .gitmodules
> without checking if the new URL is sensible.

Yes that would be a mistake for the case when we don't trust upstream.
But for the case that we do trust upstream, I would argue that we should
always follow what upstream told us to use when it comes to getting the
content of the submodule.

> Also doesn't "submodule sync" blindly overwrite URL, even the ones
> that you tweaked in your configuration to override to point at a
> mirror that is closer to you than the one suggested in .gitmodules?
> If that is the case, sucn a change to make it easier to run "sync"
> without thinking is doubly bad, I would think.

For such use cases I would suggest using url.<pattern>.insteadOf, instead
of changing what submodule.<name>.url.

My recent use case that prompted this question (I just realized that I typo'ed
the mail subject s/--init/--sync/) is this:

We are using git submodule for vendoring our Go dependencies. We've been using
it since 2015 and it has been great for this role. There comes a time when we
have to patch the vendored version so we do what is normally done - we fork the
code at github and made a pull request. This pull request may get rejected, or
accepted. For the latter case it may take some time for the acceptance to
happen - upstream owner may be away, or there are some cosmetic changes needed
etc, while on our side we need the changes in place for our build (and on
developer machines) to succeed so that it can be used in production (after
testing it in our staging). It is during this time that we want to switch the
submodule url (upstream github repo) to point to another submodule url (our
github repo)

Hmm after writing all of the above I wonder if we can't just use
url.<pattern>.insteadOf
to achieve this. But then url.<pattern>.insteadOf feels less official than
submodule.name.<url> so that's another point to think about.

nazri