Fix issue with GADT not typechecking without bind in match

Author: felixmulder

src/dotty/tools/dotc/typer/Typer.scala

@@ -1605,7 +1605,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
           }
           tree
         }
-        else if (tree.tpe <:< pt) tree
+        else if (tree.tpe.<:<(pt)(ctx.addMode(Mode.GADTflexible))) tree
         else if (wtp.isInstanceOf[MethodType]) missingArgs
         else {
           typr.println(i"adapt to subtype ${tree.tpe} !<:< $pt")

tests/pos/i1307.scala

@@ -0,0 +1,7 @@
+class Term[A]
+class Number(val n: Int) extends Term[Int]
+object Test {
+  def f[B](t: Term[B]): B = t match {
+    case y: Number => y.n
+  }
+}