wt-status: fix leaking buffer with sparse directories

When hitting a sparse directory in `wt_status_collect_changes_initial()`
we use a `struct strbuf` to assemble the directory's name. We never free
that buffer though, causing a memory leak.

Fix the leak by releasing the buffer. While at it, move the buffer
outside of the loop and reset it to save on some wasteful allocations.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/t1092-sparse-checkout-compatibility.sh

@@ -5,6 +5,7 @@ test_description='compare full workdir to sparse workdir'
 GIT_TEST_SPLIT_INDEX=0
 GIT_TEST_SPARSE_INDEX=
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '

wt-status.c

@@ -717,6 +717,7 @@ static int add_file_to_list(const struct object_id *oid,
 static void wt_status_collect_changes_initial(struct wt_status *s)
 {
 	struct index_state *istate = s->repo->index;
+	struct strbuf base = STRBUF_INIT;
 	int i;
 
 	for (i = 0; i < istate->cache_nr; i++) {
@@ -735,17 +736,18 @@ static void wt_status_collect_changes_initial(struct wt_status *s)
 			 * expanding the trees to find the elements that are new in this
 			 * tree and marking them with DIFF_STATUS_ADDED.
 			 */
-			struct strbuf base = STRBUF_INIT;
 			struct pathspec ps = { 0 };
 			struct tree *tree = lookup_tree(istate->repo, &ce->oid);
 
 			ps.recursive = 1;
 			ps.has_wildcard = 1;
 			ps.max_depth = -1;
 
+			strbuf_reset(&base);
 			strbuf_add(&base, ce->name, ce->ce_namelen);
 			read_tree_at(istate->repo, tree, &base, 0, &ps,
 				     add_file_to_list, s);
+
 			continue;
 		}
 
@@ -772,6 +774,8 @@ static void wt_status_collect_changes_initial(struct wt_status *s)
 			s->committable = 1;
 		}
 	}
+
+	strbuf_release(&base);
 }
 
 static void wt_status_collect_untracked(struct wt_status *s)