fixes #4766

tests/errmsgs/tnested_generic_instantiation.nim

@@ -0,0 +1,19 @@
+discard """
+errormsg: "generic instantiation too nested"
+file: "system.nim"
+"""
+
+# bug #4766
+
+type
+  Plain = ref object
+    discard
+
+  Wrapped[T] = object
+    value: T
+
+converter toWrapped[T](value: T): Wrapped[T] =
+  Wrapped[T](value: value)
+
+let result = Plain()
+discard $result