feat: look inside :ref when searching for default for :map child

When a default value gets produced up via the normal transformer
pipeline, the -transform method of -ref-schema will delegate to the
child schema. However, when we're building up the default values for a
:map in add-defaults, we're not using the transformer pipeline, but
calling get-default manually. Thus, we need to manually deref.

fixes #1145

src/malli/transform.cljc

@@ -486,7 +486,9 @@
                                                                (when (or (not optional) add-optional-keys)
                                                                  (let [e (find p key)]
                                                                    (when-some [f (if e (constantly (val e))
-                                                                                       (get-default v))]
+                                                                                       (or (get-default v)
+                                                                                           (when (m/-ref-schema? v)
+                                                                                             (get-default (m/-deref v)))))]
                                                                      [k (fn [] (default-fn schema (f)))])))))
                                                        (m/children schema))]
                                     (when (seq defaults)

test/malli/transform_test.cljc

@@ -1042,11 +1042,9 @@
       (is (= 7 (m/decode [:ref "bing"] nil opts transformer)))
       (is (= [7] (m/decode [:vector [:ref "bing"]] [nil] opts transformer)))
       (is (= {:a 7} (m/decode [:map [:a [:ref "bing"]]] {:a nil} opts transformer)))
-      ;; TODO fails
-      #_(is (= {:a 7} (m/decode [:map [:a [:ref "bing"]]] {} opts transformer)))
+      (is (= {:a 7} (m/decode [:map [:a [:ref "bing"]]] {} opts transformer)))
       (is (= {:a 8} (m/decode [:map [:a [:ref {:default 8} "bing"]]] {:a nil} opts transformer)))
-      ;; TODO fails
-      #_(is (= {:a 8} (m/decode [:map [:a [:ref {:default 8} "bing"]]] {} opts transformer))))))
+      (is (= {:a 8} (m/decode [:map [:a [:ref {:default 8} "bing"]]] {} opts transformer))))))
 
 (deftest type-properties-based-transformations
   (is (= 12 (m/decode malli.core-test/Over6 "12" mt/string-transformer))))