A dyn value into a written type has a checker row that compiles.

test/test_flan.ml

@@ -7717,8 +7717,8 @@ let () =
     "(defn f [x dyn] str (the str x))"
     ~needle:"a dyn becomes a str where a str is passed";
   accepts "a dyn becomes a slice, an array and a struct where passed"
-    "(defstruct P [x i32]) (defn f [a [const i64] b [2 f32] c P s str] () ()) \
-     (defn g [d dyn] () (f d d d d))";
+    "(defstruct P [x i32]) (defn f [a [const i64] b [2 f32] c P s str] i64 (length a)) \
+     (defn g [d dyn] i64 (f d d d d))";
   rejects_check "a dyn does not become an array of Vecs"
     "(defn f [d dyn] [2 (Vec i64)] d)"
     ~needle:"it holds a Vec, which owns its storage";