Re: [PATCH 1/1] builtin/checkout: simplify metadata initialization

From: Junio C Hamano <gitster@pobox.com>
Date: May 20, 2020, 15:17 UTC
Message-ID: <xmqqmu62ws88.fsf@gitster.c.googlers.com>
In-Reply-To: <20200520014156.1570124-1-sandals@crustytoothpaste.net>

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

Show 12 quoted lines

> When we call init_checkout_metadata in reset_tree, we want to pass the
> object ID of the commit in question so that it can be passed to filters,
> or if there is no commit, the tree.  We anticipated this latter case,
> which can occur elsewhere in the checkout code, but it cannot occur
> here, since reset_tree is called only (indirectly) via switch_branches,
> which requires that we have a valid commit.  switch_branches dies if we
> lack a name and cannot produce a commit from HEAD, and its caller dies
> if we do have a branch name but still lack a commit pointer.
>
> Since we know we must always have a valid commit structure in this case,
> let's remove the dead code paths and just refer to the commit structure.
> This simplifies the code and makes it easier for the reader.

builtin/checkout.c::merge_working_tree() has these lines in its earlier part:

	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
		if (new_branch_info->commit)
			BUG("'switch --orphan' should never acc...");
		new_tree = parse_tree_indirect(the_hash_algo->empty_tree);
	} else
		new_tree = get_commit_tree(new_branch_info->commit);
	if (opts->discard_changes) {
		ret = reset_tree(new_tree, opts, 1, writeout_error, new_branch_info);
		if (ret)
			return ret;
	...

So, when orphan && orphan-from-empty are both set, we must not have commit, and then if discard is also there, we end up passing new_brnach_info that has NULL in its commit.

There are few more callers of reset_tree() in this function, which I did not trace.

Perhaps the "orphan && orphan-from-empty" is a dead combination and we won't hit the codepath and that is why this change is safe? I dunno.

Show 22 quoted lines

> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
>  builtin/checkout.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
>
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index e9d111bb83..e53bdab5b8 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -620,11 +620,7 @@ static int reset_tree(struct tree *tree, const struct checkout_opts *o,
>  	opts.verbose_update = o->show_progress;
>  	opts.src_index = &the_index;
>  	opts.dst_index = &the_index;
> -	init_checkout_metadata(&opts.meta, info->refname,
> -			       info->commit ? &info->commit->object.oid :
> -			       is_null_oid(&info->oid) ? &tree->object.oid :
> -			       &info->oid,
> -			       NULL);
> +	init_checkout_metadata(&opts.meta, info->refname, &info->commit->object.oid, NULL);
>  	parse_tree(tree);
>  	init_tree_desc(&tree_desc, tree->buffer, tree->size);
>  	switch (unpack_trees(1, &tree_desc, &opts)) {