[PATCH 0/6] Teach fetch/pull the on-demand mode and make it the default

So here is my patch series to implement the new default "on-demand" fetch mode and let "git submodule update" only fetch submodules when the commit to check out is not already present in the submodule. This is only done for populated submodules and prepares them for disconnected operation without having to think about doing a recursive fetch before going on a plane and having to add the '-N' option to "git submodule update" while on it. Also merging submodule commits in the superproject and "git diff --submodule" (which is used by git gui and gitk) depend on the presence of those commits referenced by the superproject to work.

The last commit is slightly orthogonal as it would be useful without on-demand fetch too. With it rewinding a submodule to a commit that is already present (e.g. because it was checked out earlier) will be done without issuing a fetch even in current git. Together with the other patches "git submodule update" won't have to fetch a submodule at all anymore (at least unless the new "on-demand" default is disabled through the also added configuration options).

Changes since the last version: (see http://article.gmane.org/gmane.comp.version-control.git/163429)

*) Added the "on-demand" value to the "--recurse-submodules" command
   line option and the "submodule.<name>.fetchRecurseSubmodules" and
   "fetch.recurseSubmodules" config options.
*) The fetch is only done when the recorded submodule commit isn't
   already present.
*) Added test cases.

There are two things that could be optimized, but that can be the topic of other patches:

*) The submodule fetches could be done in parallel.
*) It might be expensive to compute the newly fetched commits. If
   the transport helper could be asked for the list commits it just
   fetched that would go away.

I tend to think that this is suited for 1.7.5 but don't have any objections against holding it back until 1.8.0 either. What do others think?

Jens Lehmann (6):
  fetch/pull: recurse into submodules when necessary
  fetch/pull: Add the 'on-demand' value to the --recurse-submodules
    option
  config: teach the fetch.recurseSubmodules option the 'on-demand'
    value
  Submodules: Add 'on-demand' value for the 'fetchRecurseSubmodule'
    option
  fetch/pull: Don't recurse into a submodule when commits are already
    present
  submodule update: Don't fetch when the submodule commit is already
    present

 Documentation/config.txt        |   12 ++-
 Documentation/fetch-options.txt |   24 +++-
 Documentation/git-pull.txt      |    2 +-
 Documentation/gitmodules.txt    |    4 +-
 builtin/fetch.c                 |   49 ++++++--
 git-pull.sh                     |    3 +
 git-submodule.sh                |    2 +-
 submodule.c                     |  124 +++++++++++++++++--
 submodule.h                     |   11 ++-
 t/t5526-fetch-submodules.sh     |  255 +++++++++++++++++++++++++++++++++++++++
 t/t7403-submodule-sync.sh       |    2 +-
 t/t7406-submodule-update.sh     |   20 +++
 12 files changed, 471 insertions(+), 37 deletions(-)