Drop mayBeTypePat

It does not seem to serve a purpose. The only test where it was used does
not really make sense.

Author: odersky

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

@@ -1440,7 +1440,7 @@ object desugar {
     def collect(tree: Tree): Unit = tree match {
       case Bind(nme.WILDCARD, tree1) =>
         collect(tree1)
-      case tree @ Bind(_, Typed(tree1, tpt)) if !mayBeTypePat(tpt) =>
+      case tree @ Bind(_, Typed(tree1, tpt)) =>
         add(tree, tpt)
         collect(tree1)
       case tree @ Bind(_, tree1) =>

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

@@ -164,15 +164,6 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
   /** Is name a left-associative operator? */
   def isLeftAssoc(operator: Name): Boolean = !operator.isEmpty && (operator.toSimpleName.last != ':')
 
-  /** can this type be a type pattern? */
-  def mayBeTypePat(tree: Tree): Boolean = unsplice(tree) match {
-    case RefinedTypeTree(tpt, refinements) => mayBeTypePat(tpt) || refinements.exists(_.isInstanceOf[Bind])
-    case AppliedTypeTree(tpt, args) => mayBeTypePat(tpt) || args.exists(_.isInstanceOf[Bind])
-    case Select(tpt, _) => mayBeTypePat(tpt)
-    case Annotated(tpt, _) => mayBeTypePat(tpt)
-    case _ => false
-  }
-
   /** Is this argument node of the form <expr> : _*, or is it a reference to
    *  such an argument ? The latter case can happen when an argument is lifted.
    */

tests/neg/patvars.scala

@@ -0,0 +1,12 @@
+object Test {
+
+  (??? : Any) match {
+
+    case x1 | y1 => ???  // error // error
+
+    case _: List[t2] | y2 => ??? // error // error
+
+    case x3: Int | y3: String => ??? // error // error
+
+  }
+}