Move required... calls from Space to Definitions

That way they are cached for the whole run, and not recomputed for each
exhaustivity match.

Author: odersky

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

@@ -431,8 +431,11 @@ class Definitions {
     methodNames.map(getWrapVarargsArrayModule.requiredMethod(_))
   })
 
-  @tu lazy val ListModule: Symbol = requiredModule("scala.collection.immutable.List")
-  @tu lazy val NilModule: Symbol = requiredModule("scala.collection.immutable.Nil")
+  @tu lazy val ListClass: Symbol       = requiredClass("scala.collection.immutable.List")
+  @tu lazy val ListModule: Symbol      = requiredModule("scala.collection.immutable.List")
+  @tu lazy val NilModule: Symbol       = requiredModule("scala.collection.immutable.Nil")
+  @tu lazy val ConsClass: Symbol       = requiredClass("scala.collection.immutable.::")
+  @tu lazy val SeqFactoryClass: Symbol = requiredClass("scala.collection.SeqFactory")
 
   @tu lazy val SingletonClass: ClassSymbol =
     // needed as a synthetic class because Scala 2.x refers to it in classfiles

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

@@ -317,10 +317,10 @@ class SpaceEngine(using Context) extends SpaceLogic {
   import tpd._
   import SpaceEngine._
 
-  private val scalaSeqFactoryClass = requiredClass("scala.collection.SeqFactory")
-  private val scalaListType        = requiredClassRef("scala.collection.immutable.List")
-  private val scalaNilType         = requiredModuleRef("scala.collection.immutable.Nil")
-  private val scalaConsType        = requiredClassRef("scala.collection.immutable.::")
+  private val scalaSeqFactoryClass = defn.SeqFactoryClass
+  private val scalaListType        = defn.ListClass.typeRef
+  private val scalaNilType         = defn.NilModule.termRef
+  private val scalaConsType        = defn.ConsClass.typeRef
 
   private val constantNullType     = ConstantType(Constant(null))
   private val constantNullSpace    = Typ(constantNullType)