Re: [PATCH v3 6/8] read-tree: narrow scope of index expansion for '--prefix'

[Glen Choo <chooglen@google.com>]

"Victoria Dye via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Victoria Dye <vdye@github.com>
> +static void update_sparsity_for_prefix(const char *prefix,
> +				       struct index_state *istate)
> +{
> +	int prefix_len = strlen(prefix);
> +	struct strbuf ce_prefix = STRBUF_INIT;
> +
> +	if (!istate->sparse_index)
> +		return;
> +
> +	while (prefix_len > 0 && prefix[prefix_len - 1] == '/')
> +		prefix_len--;
> +
> +	if (prefix_len <= 0)
> +		BUG("Invalid prefix passed to update_sparsity_for_prefix");
> +
> +	strbuf_grow(&ce_prefix, prefix_len + 1);
> +	strbuf_add(&ce_prefix, prefix, prefix_len);
> +	strbuf_addch(&ce_prefix, '/');
> +
> +	/*
> +	 * If the prefix points to a sparse directory or a path inside a sparse
> +	 * directory, the index should be expanded. This is accomplished in one
> +	 * of two ways:
> +	 * - if the prefix is inside a sparse directory, it will be expanded by
> +	 *   the 'ensure_full_index(...)' call in 'index_name_pos(...)'.
> +	 * - if the prefix matches an existing sparse directory entry,
> +	 *   'index_name_pos(...)' will return its index position, triggering
> +	 *   the 'ensure_full_index(...)' below.
> +	 */
> +	if (!path_in_cone_mode_sparse_checkout(ce_prefix.buf, istate) &&
> +	    index_name_pos(istate, ce_prefix.buf, ce_prefix.len) >= 0)
> +		ensure_full_index(istate);
> +
> +	strbuf_release(&ce_prefix);
> +}

Hm, I don't think I follow the rationale for having two different ways
of expanding the index:

- If the prefix is inside a sparse directory, we should expand the
  index.
- If the prefix matches a sparse directory entry, we should expand the
  index.

So it seems like distinguishing between the two cases with
index_name_pos(...) isn't necessary. I've attached a diff that does
exactly this, and it passes t1092-sparse-checkout-compatibility.sh as
far as I can tell. I've also amended the comment in a way that makes
more sense to me, but I'm not 100% sure if it's accurate.

I'm also a little averse to using a side effect of index_name_pos() to
achieve what we really want, so I'd prefer to get rid of the call if we
can :)

----- >8 --------- >8 --------- >8 --------- >8 --------- >8 ----

diff --git a/unpack-trees.c b/unpack-trees.c
index b876caca0d..5b07055605 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1749,17 +1749,11 @@ static void update_sparsity_for_prefix(const char *prefix,
 	strbuf_addch(&ce_prefix, '/');
 
 	/*
-	 * If the prefix points to a sparse directory or a path inside a sparse
-	 * directory, the index should be expanded. This is accomplished in one
-	 * of two ways:
-	 * - if the prefix is inside a sparse directory, it will be expanded by
-	 *   the 'ensure_full_index(...)' call in 'index_name_pos(...)'.
-	 * - if the prefix matches an existing sparse directory entry,
-	 *   'index_name_pos(...)' will return its index position, triggering
-	 *   the 'ensure_full_index(...)' below.
+	 * If the prefix points to a sparse directory or a path inside a
+	 * sparse directory (not within the sparse patterns), the index
+	 * should be expanded.
 	 */
-	if (!path_in_cone_mode_sparse_checkout(ce_prefix.buf, istate) &&
-	    index_name_pos(istate, ce_prefix.buf, ce_prefix.len) >= 0)
+	if (!path_in_cone_mode_sparse_checkout(ce_prefix.buf, istate))
 		ensure_full_index(istate);
 
 	strbuf_release(&ce_prefix);