Re: [PATCH 10/15] update submodules: add submodule_move_head

> In later patches we introduce the options and flag for commands
> that modify the working directory, e.g. git-checkout.
> 
> This piece of code will be used universally for
> all these working tree modifications as it
> * supports dry run to answer the question:
>   "Is it safe to change the submodule to this new state?"
>   e.g. is it overwriting untracked files or are there local
>   changes that would be overwritten?
> * supports a force flag that can be used for resetting
>   the tree.
> 
> Signed-off-by: Stefan Beller <sbeller@google.com>
> ---
>  submodule.c | 135 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  submodule.h |   7 ++++
>  2 files changed, 142 insertions(+)
> 
> diff --git a/submodule.c b/submodule.c
> index 0b2596e88a..a2cf8c9376 100644
> --- a/submodule.c
> +++ b/submodule.c
> @@ -1239,6 +1239,141 @@ int bad_to_remove_submodule(const char *path, unsigned flags)
>  	return ret;
>  }
>  
> +static int submodule_has_dirty_index(const struct submodule *sub)
> +{
> +	struct child_process cp = CHILD_PROCESS_INIT;
> +
> +	prepare_submodule_repo_env_no_git_dir(&cp.env_array);
> +
> +	cp.git_cmd = 1;
> +	argv_array_pushl(&cp.args, "diff-index", "--quiet", \
> +					"--cached", "HEAD", NULL);
> +	cp.no_stdin = 1;
> +	cp.no_stdout = 1;
> +	cp.dir = sub->path;
> +	if (start_command(&cp))
> +		die("could not recurse into submodule '%s'", sub->path);
> +
> +	return finish_command(&cp);
> +}
> +
> +void submodule_reset_index(const char *path)