Re: [PATCH v5 1/4] implement submodule config API for lookup of .gitmodules values

[Heiko Voigt <hvoigt@hvoigt.net>]

On Wed, Jul 08, 2015 at 04:52:14PM -0400, Phil Hord wrote:
> On Mon, Jun 15, 2015 at 5:06 PM, Heiko Voigt <hvoigt@hvoigt.net> wrote:
> > In a superproject some commands need to interact with submodules. They
> > need to query values from the .gitmodules file either from the worktree
> > of from certain revisions. At the moment this is quite hard since a
> > caller would need to read the .gitmodules file from the history and then
> > parse the values. We want to provide an API for this so we have one
> > place to get values from .gitmodules from any revision (including the
> > worktree).
> >
> > The API is realized as a cache which allows us to lazily read
> > .gitmodules configurations by commit into a runtime cache which can then
> > be used to easily lookup values from it. Currently only the values for
> > path or name are stored but it can be extended for any value needed.
> >
> > It is expected that .gitmodules files do not change often between
> > commits. Thats why we lookup the .gitmodules sha1 from a commit and then
> > either lookup an already parsed configuration or parse and cache an
> > unknown one for each sha1. The cache is lazily build on demand for each
> > requested commit.
> >
> > This cache can be used for all purposes which need knowledge about
> > submodule configurations. Example use cases are:
> >
> >  * Recursive submodule checkout needs to lookup a submodule name from
> >    its path when a submodule first appears. This needs be done before
> >    this configuration exists in the worktree.
> >
> >  * The implementation of submodule support for 'git archive' needs to
> >    lookup the submodule name to generate the archive when given a
> >    revision that is not checked out.
> >
> >  * 'git fetch' when given the --recurse-submodules=on-demand option (or
> >    configuration) needs to lookup submodule names by path from the
> >    database rather than reading from the worktree. For new submodule it
> >    needs to lookup the name from its path to allow cloning new
> >    submodules into the .git folder so they can be checked out without
> >    any network interaction when the user does a checkout of that
> >    revision.
> >
> > Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
> > ---
> >  .gitignore                                       |   1 +
> >  Documentation/technical/api-submodule-config.txt |  46 +++
> >  Makefile                                         |   2 +
> >  submodule-config.c                               | 445 +++++++++++++++++++++++
> >  submodule-config.h                               |  27 ++
> >  submodule.c                                      |   1 +
> >  submodule.h                                      |   1 +
> >  t/t7411-submodule-config.sh                      |  85 +++++
> >  test-submodule-config.c                          |  66 ++++
> >  9 files changed, 674 insertions(+)
> >  create mode 100644 Documentation/technical/api-submodule-config.txt
> >  create mode 100644 submodule-config.c
> >  create mode 100644 submodule-config.h
> >  create mode 100755 t/t7411-submodule-config.sh
> >  create mode 100644 test-submodule-config.c
> 
> 
> Instead of test-submodule-config.c to test this new module, it could
> be useful to implement these as extensions to rev-parse:
> 
>     git rev-parse --submodule-name [<ref>:]<path>
>     git rev-parse --submodule-path [<ref>:]<name>
>     git rev-parse --submodule-url [<ref>:]<name>
>     git rev-parse --submodule-ignore [<ref>:]<name>
>     git rev-parse --submodule-recurse [<ref>:]<name>
> 
> Has this already been considered and rejected for some reason?

No that has not been considered. But I am open to it if others agree
that this is a sensible thing to do. We should be able to adapt the
existing tests right?

Cheers Heiko