Refine closure extractor to handle Typed trees

Author: liufengyun

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -527,6 +527,7 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
     def unapply(tree: Tree): Option[(List[Tree], Tree, Tree)] = tree match {
       case Block(_, expr) => unapply(expr)
       case Closure(env, meth, tpt) => Some(env, meth, tpt)
+      case Typed(expr, _)  => unapply(expr)
       case _ => None
     }
   }

tests/pos/i3246.scala

@@ -0,0 +1,8 @@
+class Test {
+  class A {
+    type T = Int
+    def f(x: T): T = ???
+  }
+  def a: A = new A
+  val f = a.f _
+}