fix #1096

CHANGELOG.md

@@ -19,6 +19,7 @@ Malli is in well matured [alpha](README.md#alpha).
 * Fix ClojureScript [arithmetic warning](https://github.com/metosin/malli/issues/1093)
 * Distribute `:merge` over `:multi` [#1086](https://github.com/metosin/malli/pull/1086), see [documentation](README.md#distributive-schemas)
 * allow `m/-proxy-schema` child to be a `delay`
+* Fix `malli.dev.pretty` throws when explaining errors in nested maps [#1094](https://github.com/metosin/malli/issues/1096)
 
 ## 0.16.3 (2024-08-05)
 

src/malli/error.cljc

@@ -193,7 +193,7 @@
     (reduce (fn [acc error] (cond-> acc (accept error) (-replace-in value (:in error) (wrap error) mask))) acc errors)))
 
 (defn -masked [mask x y]
-  (cond (map? x) (reduce-kv (fn [acc k v] (let [e (find y k)] (assoc acc k (if e (-masked mask v (val e)) mask)))) y x)
+  (cond (and (map? x) (or (nil? y) (map? y))) (reduce-kv (fn [acc k v] (let [e (find y k)] (assoc acc k (if e (-masked mask v (val e)) mask)))) y x)
         (set? x) (cond-> y (not= (count x) (count y)) (conj mask))
         (sequential? x) (-fill y (count x) mask)
         :else y))

test/malli/error_test.cljc

@@ -758,6 +758,11 @@
                (for [error (:errors explain)]
                  (me/error-value (assoc explain :errors [error]) {::me/mask-valid-values '...}))))))
 
+    (testing "masked nested maps #1096"
+      (is (= {"foo" "foo"}
+             (-> (m/explain [:map-of :keyword [:map-of :keyword :any]] {"foo" {:bar 1}})
+                 (me/error-value {::me/mask-valid-values '...})))))
+
     (testing "custom painting of errors"
       (is (= {:EXTRA {:value "KEY", :type :malli.core/extra-key}
               :tags #{{:value "ground"} {:value "coffee"}}