Don't make AndTypes Singletons

Author: odersky

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -248,7 +248,7 @@ object Types {
       case _ => NoType
     }
 
-    /** Is this type a (possibly aliased or intersected) singleton type? */
+    /** Is this type a (possibly aliased) singleton type? */
     def isSingleton(implicit ctx: Context) = SingletonType.unapply(this).isDefined
 
     /** Is this type guaranteed not to have `null` as a value? */
@@ -1501,11 +1501,10 @@ object Types {
   }
 
   /** An extractor that returns the underlying singleton type of a
-   *  (possibly annotated, aliased, or intersected) type
+   *  (possibly annotated or aliased) type
    */
   object SingletonType {
     def unapply(tp: Type)(implicit ctx: Context): Option[SingletonType] = tp.dealias match {
-      case AndType(tp1, tp2) => unapply(tp1).orElse(unapply(tp2))
       case tp: SingletonType => Some(tp)
       case _ => None
     }

tests/neg/i830.scala renamed to tests/pos/i830.scala

@@ -2,5 +2,5 @@ object C {
   trait X[T]
   implicit def u[A, B]: X[A | B] = new X[A | B] {}
   def y[T](implicit x: X[T]): T = ???
-  val x: 1 & 2 | 2 & 3 = y // error: singleton is not allowed in a union type
+  val x: 1 & 2 | 2 & 3 = y
 }

tests/pos/i864.scala

@@ -6,5 +6,5 @@ object C {
   trait X[T]
   implicit def u[A, B]: X[A | B] = new X[A | B] {}
   def y[T](implicit x: X[T]): T = ???
-  // val x: a.type & b.type | b.type & c.type = y  // no longer allowed, singletons cannot be in union types
+  val x: a.type & b.type | b.type & c.type = y  // no longer allowed, singletons cannot be in union types
 }