handle nullability check before true magicasting

clj/src/cljd/compiler.cljc

@@ -1534,7 +1534,7 @@
    (cond
      (= 'dc.dynamic (:canon-qname expected-type)) dart-expr ; TODO: should be covered by is-assignable?
      (is-assignable? expected-type actual-type) dart-expr   ; <1>
-     (and (nullable-type? expected-type) (nullable-type? actual-type))
+     (and (nullable-type? expected-type) (nullable-type? actual-type)) ; <2>
      (if-some [expected-type+ (positive-type expected-type)]
        (with-once [dart-expr dart-expr] env
          `(dart/if (dart/. nil "!=" ~dart-expr)
@@ -1543,6 +1543,13 @@
             ~(magicast dart-expr expected-type+ actual-type env)
             nil))
        (list 'dart/let [[nil dart-expr]] nil))
+     (and
+       (not= 'dc.dynamic (:canon-qname actual-type))
+       (nullable-type? actual-type))
+     ; expected-type is not nullable because of the previous check <2>
+     (if-some [actual-type+ (positive-type actual-type)]
+       (recur (list 'dart/as dart-expr actual-type+) expected-type actual-type+ env)
+       (throw (Exception. "Can't cast a null expression to something non-nullable.")))
      ;; When inlined #dart[], we keep it inlines
      ;; TODO: don't like the (vector? dart-expr) check, it smells bad
      (and (= 'dc.List (:canon-qname expected-type) (:canon-qname actual-type))

clj/test/cljd/test_clojure/core_test_cljd.cljd

@@ -923,7 +923,8 @@
 (deftest nil-as-test-expression-in-when-some
   (is (nil? (when-some [x nil] 42))))
 
-(deftest nametobedefined
-  (let [f (fn [^Function? f ^Iterable l]
+(deftest throw-when-passing-a-nullable-fn-instead-of-a-non-nullable-fn
+  (let [f (fn [^^{:fn-type {:fixed-params-types [dynamic]
+                            :ret-type bool}} Function? f ^Iterable l]
             (.any l f))]
-    (is (thrown? Exception (f nil [1])))))
+    (is (thrown? Error (f nil [1])))))