fix: explain :path of ref schemas

The path from a [:ref ::kw] or a [:ref #'Var] to the referred schema
is [0 0] due to the intermediate -pointer. See additions to
get-in-test. Thus the -explainer of a -ref-schema needs to add [0 0]
to the path, instead of the previous [0]. This mirrors the [0 0]
already present in the -walk of -ref-schema.

fixes #1106

src/malli/core.cljc

@@ -1709,7 +1709,7 @@
              (let [validator (-memoize (fn [] (-validator (rf))))]
                (fn [x] ((validator) x))))
            (-explainer [_ path]
-             (let [explainer (-memoize (fn [] (-explainer (rf) (conj path 0))))]
+             (let [explainer (-memoize (fn [] (-explainer (rf) (into path [0 0]))))]
                (fn [x in acc] ((explainer) x in acc))))
            (-parser [_] (->parser -parser))
            (-unparser [_] (->parser -unparser))

test/malli/core_test.cljc

@@ -624,6 +624,19 @@
 
   (testing "ref schemas"
 
+    (let [schema [:ref {:registry {::referred [:map [:foo :int]]}} ::referred]]
+      (is (nil? (m/explain schema {:foo 2})))
+      (testing "explain path"
+        (let [exp (m/explain schema {:foo "2"})]
+          (is (results= {:value {:foo "2"}
+                         :schema schema
+                         :errors [{:in [:foo]
+                                   :path [0 0 :foo]
+                                   :schema :int
+                                   :value "2"}]}
+                        exp))
+          (is (form= :int (mu/get-in schema (-> exp :errors first :path)))))))
+
     (testing "invalid refs fail"
       (is (thrown?
            #?(:clj Exception, :cljs js/Error)
@@ -640,7 +653,7 @@
         (is (results= {:schema ConsCell
                        :value [1 [2]]
                        :errors [{:in [1]
-                                 :path [0 0 0 1 0 0]
+                                 :path [0 0 0 1 0 0 0]
                                  :schema (mu/get-in ConsCell [0 0 0])
                                  :type :malli.core/tuple-size
                                  :value [2]}]}
@@ -3333,7 +3346,28 @@
 
     (testing "it works"
       (is (= User (m/form schema)))
-      (is (every? (m/validator schema) (mg/sample schema {:seed 100}))))))
+      (is (every? (m/validator schema) (mg/sample schema {:seed 100}))))
+
+    (testing "explain path"
+      (let [exp (m/explain schema {:id 1})]
+        (is (results= {:value {:id 1}
+                       :schema User
+                       :errors [{:in [:id]
+                                 :path [:id 0]
+                                 :schema :string
+                                 :value 1}]}
+                      exp))
+        (is (form= :string (mu/get-in schema (-> exp :errors first :path)))))
+      (let [explicit-ref [:ref #'UserId]
+            exp (m/explain explicit-ref 1)]
+        (is (results= {:value 1
+                       :schema explicit-ref
+                       :errors [{:in []
+                                 :path [0 0]
+                                 :schema :string
+                                 :value 1}]}
+                      exp))
+        (is (form= :string (mu/get-in explicit-ref (-> exp :errors first :path))))))))
 
 #?(:clj
    (deftest roundrobin-var-references

test/malli/error_test.cljc

@@ -545,6 +545,8 @@
              (m/explain [1 2 :foo])
              (me/humanize)))))
 
+(def VarSchema [:map [:foo :int]])
+
 (deftest error-definion-lookup-test
   (is (= {:foo ["should be an integer"]}
          (-> [:map
@@ -629,7 +631,17 @@
                     (= password password2))]]
                (m/explain {:password "secret"
                            :password2 "faarao"})
-               (me/humanize {:resolve me/-resolve-root-error}))))))
+               (me/humanize {:resolve me/-resolve-root-error})))))
+
+  (testing "refs #1106"
+    (is (= {:foo ["should be an integer"]}
+           (me/humanize
+            (m/explain [:ref #'VarSchema] {:foo "2"})
+            {:resolve me/-resolve-direct-error})))
+    (is (= {:foo ["should be an integer"]}
+           (me/humanize
+            (m/explain [:ref #'VarSchema] {:foo "2"})
+            {:resolve me/-resolve-root-error})))))
 
 (deftest limits
   (is (= {:a [["should be an int"]]

test/malli/util_test.cljc

@@ -276,6 +276,8 @@
 ;; LensSchemas
 ;;
 
+(def Var :string)
+
 (deftest basic-lens-schema-test
   (let [re #"kikka"
         int? (m/schema int?)]
@@ -333,6 +335,8 @@
 
         [:ref {:registry {::a int?, ::b string?}} ::a] 0 ::a
         [:ref {:registry {::a int?, ::b string?}} ::a] 1 nil
+        [:ref #'Var] 0 #'Var
+        [:ref #'Var] 1 nil
 
         [:schema int?] 0 int?
         [:schema int?] 1 nil)
@@ -439,7 +443,12 @@
   (is (form= (mu/get-in (m/schema [:ref {:registry {::a int?, ::b string?}} ::a]) [0]) ::a))
   (is (mu/equals (mu/get-in (m/schema [:ref {:registry {::a int?, ::b string?}} ::a]) [0 0]) int?))
   (is (form= (mu/get-in (m/schema [:schema {:registry {::a int?, ::b string?}} ::a]) [0]) ::a))
-  (is (mu/equals (mu/get-in (m/schema [:schema {:registry {::a int?, ::b string?}} ::a]) [0 0]) int?)))
+  (is (mu/equals (mu/get-in (m/schema [:schema {:registry {::a int?, ::b string?}} ::a]) [0 0]) int?))
+
+  (is (form= (mu/get-in (m/schema [:ref #'Var]) [0]) #'Var))
+  (is (form= (mu/get-in (m/schema [:ref #'Var]) [0 0]) :string))
+  (is (form= (mu/get-in (m/schema [:schema #'Var]) [0]) #'Var))
+  (is (form= (mu/get-in (m/schema [:schema #'Var]) [0 0]) :string)))
 
 (deftest dissoc-test
   (let [schema [:map {:title "map"}