Merge pull request #1309 from felixmulder/topic/fix#1307

Fix issue with GADT not typechecking without bind in match

Author: DarkDimius

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

@@ -448,6 +448,10 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
                 return typed(untpd.Apply(untpd.TypedSplice(arg), tree.expr), pt)
               case _ =>
             }
+          case tref: TypeRef if tref.symbol.isClass && !ctx.isAfterTyper =>
+            val setBefore = ctx.mode is Mode.GADTflexible
+            tpt1.tpe.<:<(pt)(ctx.addMode(Mode.GADTflexible))
+            if (!setBefore) ctx.retractMode(Mode.GADTflexible)
           case _ =>
         }
         ascription(tpt1, isWildcard = true)

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
+  }
+}