Re: git submodules implementation question

[Junio C Hamano <gitster@pobox.com>]

Uma Srinivasan <usrinivasan@twitter.com> writes:

>> I might suggest to update prepare_submodule_repo_env() so that the
>> spawned process will *NOT* have to guess where the working tree and
>> repository by exporting GIT_DIR (set to "git_dir" we discover above)
>> and GIT_WORK_TREE (set to "." as cp.dir is set to the path to the
>> working tree of the submodule).  That would stop the "git status" to
>> guess (and fooled by a corrupted dir/.git that is not a git
>> repository).
>
> Here's where I am struggling with my lack of knowledge of git
> internals and the implementation particularly in the context of how
> environment variables are passed from the parent to the child process.

Ah, I was primarily addressing Jacob in the latter part of my
message, as he's looked at similar things in his recent topic.

> Are you suggesting that we set up the child process environment array
> (the "out" argument) in prepare_submodule_repo_env() to include
> GIT_DIR_ENVIRONMENT and GIT_WORK_TREE_ENVIRONMENT in addition to
> CONFIG_DATA_ENVIRONMENT that is there now?

I was wondering if we should unconditionally stuff GIT_DIR=<the
repository location for the submodule> in the cp.env_array passed to
the function prepare_submodule_repo_env().  As cp.dir will be set to
the submodule's working tree, there is no need to set GIT_WORK_TREE
and export it, I think, although it would not hurt.

After all, we _are_ going into a separate and different project's
repository (that is what a submodule is), and we _know_ where its
repository data (i.e. GIT_DIR) and the location of its working tree
(i.e. GIT_WORK_TREE).  There is no reason for the process that will
work in the submodule to go through the usual "do we have .git in
our $cwd that is a repository?  if not how about the parent directory
of $cwd?  go up until we find one and that directory is the top of
the working tree" discovery.

More importantly, this matters when your GIT_DIR for the submodule
is somehow corrupt.  The discovery process would say "there is .git
in $cwd but that is not a repository" and continue upwards, which
likely would find the repository for the top-level superproject,
which definitely is _not_ want you want to happen.  And one way to
avoid it is to tell the setup.c code that it should not do the
discovery by being explicit.