Re: [PATCH v3 04/20] repository: introduce the repository object

> Introduce the repository object 'struct repository' which can be used to
> hold all state pertaining to a git repository.
> 
> Some of the benefits of object-ifying a repository are:
> 
>   1. Make the code base more readable and easier to reason about.
> 
>   2. Allow for working on multiple repositories, specifically
>      submodules, within the same process.  Currently the process for
>      working on a submodule involves setting up an argv_array of options
>      for a particular command and then launching a child process to
>      execute the command in the context of the submodule.  This is
>      clunky and can require lots of little hacks in order to ensure
>      correctness.  Ideally it would be nice to simply pass a repository
>      and an options struct to a command.
> 
>   3. Eliminating reliance on global state will make it easier to
>      enable the use of threading to improve performance.

> +/* called after setting gitdir */
> +static void repo_setup_env(struct repository *repo)
> +{
> +	struct strbuf sb = STRBUF_INIT;
> +
> +	if (!repo->gitdir)
> +		BUG("gitdir wasn't set before setting up the environment");
> +
> +	repo->different_commondir = find_common_dir(&sb, repo->gitdir,
> +						    !repo->ignore_env);
> +	repo->commondir = strbuf_detach(&sb, NULL);
> +	repo->objectdir = git_path_from_env(DB_ENVIRONMENT, repo->commondir,
> +					    "objects", !repo->ignore_env);
> +	repo->graft_file = git_path_from_env(GRAFT_ENVIRONMENT, repo->commondir,
> +					     "info/grafts", !repo->ignore_env);
> +	repo->index_file = git_path_from_env(INDEX_ENVIRONMENT, repo->gitdir,
> +					     "index", !repo->ignore_env);
> +}

> +static int verify_repo_format(struct repository_format *format,
> +			      const char *commondir)
> +{
> +	int ret = 0;
> +	struct strbuf sb = STRBUF_INIT;
> +
> +	strbuf_addf(&sb, "%s/config", commondir);
> +	read_repository_format(format, sb.buf);
> +	strbuf_reset(&sb);
> +
> +	if (verify_repository_format(format, &sb) < 0) {
> +		warning("%s", sb.buf);
> +		ret = -1;
> +	}
> +
> +	strbuf_release(&sb);
> +	return ret;
> +}

> +void repo_clear(struct repository *repo)
> +{
> +	free(repo->gitdir);
> +	repo->gitdir = NULL;
> +	free(repo->commondir);
> +	repo->commondir = NULL;
> +	free(repo->objectdir);
> +	repo->objectdir = NULL;
> +	free(repo->graft_file);
> +	repo->graft_file = NULL;
> +	free(repo->index_file);
> +	repo->index_file = NULL;
> +	free(repo->worktree);
> +	repo->worktree = NULL;
> +
> +	memset(repo, 0, sizeof(*repo));
> +}

> +	/* Configurations */
> +	/*
> +	 * Bit used during initialization to indicate if repository state (like
> +	 * the location of the 'objectdir') should be read from the
> +	 * environment.  By default this bit will be set at the begining of
> +	 * 'repo_init()' so that all repositories will ignore the environment.
> +	 * The exception to this is 'the_repository', which doesn't go through
> +	 * the normal 'repo_init()' process.
> +	 */
> +	unsigned ignore_env:1;