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

From: Phil Hord <phil.hord@gmail.com>
Date: Jul 8, 2015, 20:52 UTC
Message-ID: <CABURp0pyYcKvmbEeDSYqm15DtXvH7g_UXASR3utGco+=D95bOA@mail.gmail.com>
In-Reply-To: <ef740bdea9af35564c75efd2a6daae65f3108df5.1434400625.git.hvoigt@hvoigt.net>

On Mon, Jun 15, 2015 at 5:06 PM, Heiko Voigt <hvoigt@hvoigt.net> wrote:

Show 55 quoted lines

> 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?