checkout-index: perform lazy index expansion for --sparse

When `--sparse` is specified for `checkout-index` but no sparse directory
entries exist outside the sparse checkout definition, the index does not need
to be expanded. For this case, moving the index expansion into an explicit
check for a sparse directory entry prevents unnecessary expansion.

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

Author: vdye

builtin/checkout-index.c

@@ -128,11 +128,18 @@ static int checkout_all(const char *prefix, int prefix_length, int include_spars
 	int i, errs = 0;
 	struct cache_entry *last_ce = NULL;
 
-	if (include_sparse)
-		ensure_full_index(&the_index);
-
 	for (i = 0; i < active_nr ; i++) {
 		struct cache_entry *ce = active_cache[i];
+		if (include_sparse && S_ISSPARSEDIR(ce->ce_mode)) {
+			/*
+			 * If the current entry is a sparse directory (and entries outside the
+			 * sparse checkout definition are included), expand the index and
+			 * continue the loop on the current index position (now pointing to the
+			 * first entry inside the expanded sparse directory).
+			 */
+			ensure_full_index(&the_index);
+			ce = active_cache[i];
+		}
 		if (!include_sparse && !path_in_sparse_checkout(ce->name, &the_index))
 			continue;
 		if (ce_stage(ce) != checkout_stage