Test case for issue 16311 (#16317)

Closes #16311

Author: odersky

tests/pos-deep-subtype/i16311.scala

@@ -0,0 +1,17 @@
+trait Tagged[U]
+type WithTag[+T, U] = T & Tagged[U]
+
+trait FromInput[Val]
+implicit def coercedScalaInput[T]: FromInput[WithTag[T, Int]] = ???
+implicit def optionInput[T](implicit ev: FromInput[T]): FromInput[Option[T]] = ???
+
+trait WithoutInputTypeTags[T]
+implicit def coercedOptArgTpe[T]: WithoutInputTypeTags[Option[WithTag[T, Int]]] = ???
+
+trait InputType[+T]
+class OptionInputType[T](ofType: InputType[T]) extends InputType[Option[T]]
+
+type Argument[T]
+def argument[T](argumentType: InputType[T])(implicit fromInput: FromInput[T], res: WithoutInputTypeTags[T]): Argument[Option[T]] = ???
+
+def test = argument(OptionInputType(??? : InputType[WithTag[Boolean, Int]]))