Re: [PATCH] git-submodule add: Record branch name in .gitmodules

On Mon, Oct 22, 2012 at 06:03:53PM -0400, Phil Hord wrote:

Some projects now use the 'branch' config value to record the tracking
branch for the submodule.  Some ascribe different meaning to the
configuration if the value is given vs. undefined.  For example, see
the Gerrit submodule-subscription mechanism.  This change will cause
those workflows to behave differently than they do now.

For those to lazy to hunt down a reference, Gerrit uses
submodule.$name.branch to

  “indicate the branch of a submodule project that when updated will
  trigger automatic update of its registered gitlink.” [1]

They also have some extra sauce:

  “The branch value could be '.' if the submodule project branch has
  the same name as the destination branch of the commit having
  gitlinks/.gitmodules file.
  …
  Any git submodules which are added and not have the branch field
  available in the .gitmodules file will not be subscribed by Gerrit
  to automatically update the superproject.”

I do like the idea, but I wish it had a different name for the
recording.  Maybe --record-branch=${BRANCH} as an extra switch so the
action is explicitly requested.

  git submodule add --branch=master --record-branch=master foo bar

Ugh, I don't want to retype the branch name whenever I do this.

<brainstorming>

How about -r/--record, with the recorded name being optional?

  --record-branch[=<recorded_name>]

This would satisfy Gerrit users that wanted to use '.', but also
satisfy me with:

  git submodule add -rb=master foo bar

However, there is a change that people would see that, and then use

  git submodule add -r -b=master foo bar

which would checkout the HEAD from foo and store `-b=master` in
submodule.$name.branch.

A more verbose, but less dangerous, option would be a boolean
-r/--record that enables the recording of whatever was passed to
-b/--branch.  This looses the flexibility of running something like

  git submodule add --branch=master --record-branch=. foo bar

but the Gerrit folks have gotten along OK without any branch recording
so far ;).  They can keep setting '.' the same way they always have.

</brainstorming>

On a tangentially related note, it would be nice to set environment
variables for each of the settings in submodule.$name during a foreach
call.  Then you could use

  git submodule foreach 'git checkout $branch && git pull'

Perhaps you'd want to blacklist/whitelist or downcase settings names
to avoid things like

  [submodule "foo"]
        PATH = /my/rootkit/

but the update line is much cleaner.

Cheers,
Trevor

[1]: https://gerrit.googlesource.com/gerrit/+/master/Documentation/user-submodules.txt

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