fixes #4124

tests/types/typeof_produces_alias.nim

@@ -0,0 +1,25 @@
+
+# bug #4124
+
+import sequtils
+
+type
+    Foo = distinct string
+
+var
+  foo: Foo
+
+type
+    Alias = (type(foo))
+var
+  a: Alias
+
+a = foo
+
+when true:
+  var xs = @[1,2,3]
+
+  proc asFoo(i: string): Foo =
+      Foo(i)
+
+  var xx = xs.mapIt(asFoo($(it + 5)))