Space: Fix decomposable prefixes of TermRefs

Author: dwijnand

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

@@ -2182,14 +2182,16 @@ object Types {
 
 // --- NamedTypes ------------------------------------------------------------------
 
-  abstract class NamedType extends CachedProxyType, ValueType { self =>
+  abstract class NamedType extends CachedProxyType, ValueType, Product { self =>
 
     type ThisType >: this.type <: NamedType
     type ThisName <: Name
 
     val prefix: Type
     def designator: Designator
     protected def designator_=(d: Designator): Unit
+    def _1: Type
+    def _2: Designator
 
     assert(NamedType.validPrefix(prefix), s"invalid prefix $prefix")
 
@@ -2905,6 +2907,7 @@ object Types {
     def apply(prefix: Type, designator: Name, denot: Denotation)(using Context): NamedType =
       if (designator.isTermName) TermRef.apply(prefix, designator.asTermName, denot)
       else TypeRef.apply(prefix, designator.asTypeName, denot)
+    def unapply(tp: NamedType): NamedType = tp
 
     def validPrefix(prefix: Type): Boolean = prefix.isValueType || (prefix eq NoPrefix)
   }

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -611,11 +611,11 @@ object SpaceEngine {
           case tp if !TypeComparer.provablyDisjoint(tp, tpB) => AndType(tp, tpB)
 
       case OrType(tp1, tp2)                            => List(tp1, tp2)
-      case _: SingletonType                            => ListOfNoType
       case tp if tp.isRef(defn.BooleanClass)           => List(ConstantType(Constant(true)), ConstantType(Constant(false)))
       case tp if tp.isRef(defn.UnitClass)              => ConstantType(Constant(())) :: Nil
       case tp if tp.classSymbol.isAllOf(JavaEnumTrait) => tp.classSymbol.children.map(_.termRef)
-      case tp @ TypeRef(Parts(parts), _)               => parts.map(tp.derivedSelect)
+      case tp @ NamedType(Parts(parts), _)             => parts.map(tp.derivedSelect)
+      case _: SingletonType                            => ListOfNoType
 
       case tp @ AppliedType(Parts(parts), targs) if tp.classSymbol.children.isEmpty =>
         // It might not obvious that it's OK to apply the type arguments of a parent type to child types.