unpack-trees: expand conditions for sparse result index

After `unpack-trees` processing, the index would only be considered "sparse" if
it contains any sparse directories. That condition missed the case where the
index contains only files inside the sparse checkout definition. By explicitly
checking for that condition and setting `sparse_index` accordingly, later
processing to ensure the index "remains" full can be avoided.

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

unpack-trees.c

@@ -1945,6 +1945,30 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 		}
 	}
 
+	/*
+	 * After unpacking trees, the index will be marked "sparse" if any sparse
+	 * directories have been encountered. However, the index may still be
+	 * sparse if there are no sparse directories. To make sure the index is
+	 * marked "sparse" as often as possible, the index is marked sparse if
+	 * all of the following are true:
+	 * - the command in progress allows use of a sparse index
+	 * - the index is not already sparse
+	 * - cone-mode sparse checkout with sparse index is enabled for the repo
+	 * - all index entries are inside of the sparse checkout cone
+	 */
+	if (!repo->settings.command_requires_full_index && !o->result.sparse_index &&
+	    core_apply_sparse_checkout && core_sparse_checkout_cone && repo->settings.sparse_index) {
+		o->result.sparse_index = COLLAPSED;
+		for (i = 0; i < o->result.cache_nr; i++) {
+			struct cache_entry *ce = o->result.cache[i];
+
+			if (!path_in_cone_modesparse_checkout(ce->name, &o->result)) {
+				o->result.sparse_index = COMPLETELY_FULL;
+				break;
+			}
+		}
+	}
+
 	ret = check_updates(o, &o->result) ? (-2) : 0;
 	if (o->dst_index) {
 		move_index_extensions(&o->result, o->src_index);