[Bug #21669] Implement void value expression check for `case`/`when`

If the all `when` and `else` branches are void, the `case` is also
void.

1 files changed, 12 insertions, 0 deletions

diff --git a/parse.y b/parse.y
index 7efc7a7ea5..63b6ab9b16 100644
--- a/parse.y
+++ b/parse.y
@@ -13864,6 +13864,18 @@ value_expr_check(struct parser_params *p, NODE *node)
           case NODE_RETRY:
             goto found;
 
+          case NODE_CASE:
+          case NODE_CASE2:
+            for (node = RNODE_CASE(node)->nd_body;
+                 node && nd_type_p(node, NODE_WHEN);
+                 node = RNODE_WHEN(node)->nd_next) {
+                if (!(vn = value_expr_check(p, RNODE_WHEN(node)->nd_body))) {
+                    return NULL;
+                }
+                if (!void_node) void_node = vn;
+            }
+            break;
+
           case NODE_CASE3:
             if (!RNODE_CASE3(node)->nd_body || !nd_type_p(RNODE_CASE3(node)->nd_body, NODE_IN)) {
                 compile_error(p, "unexpected node");