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

["W. Trevor King" <wking@tremily.us>]

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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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