Add NameBasedPattern

Author: OlivierBlanvillain

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

@@ -507,6 +507,7 @@ class Definitions {
   def DynamicClass(implicit ctx: Context) = DynamicType.symbol.asClass
   lazy val OptionType: TypeRef                  = ctx.requiredClassRef("scala.Option")
   def OptionClass(implicit ctx: Context) = OptionType.symbol.asClass
+  lazy val NameBasedPatternType: TypeRef        = ctx.requiredClassRef("scala.NameBasedPattern")
   lazy val ProductType: TypeRef                 = ctx.requiredClassRef("scala.Product")
   def ProductClass(implicit ctx: Context) = ProductType.symbol.asClass
     lazy val Product_canEqualR = ProductClass.requiredMethodRef(nme.canEqual_)

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

@@ -184,6 +184,7 @@ object StdNames {
     final val Function: N            = "Function"
     final val ImplicitFunction: N    = "ImplicitFunction"
     final val Mirror: N              = "Mirror"
+    final val NameBasedPattern: N    = "NameBasedPattern"
     final val Nothing: N             = "Nothing"
     final val Null: N                = "Null"
     final val Object: N              = "Object"

library/src/scala/NameBasedPattern.scala

@@ -0,0 +1,4 @@
+package scala
+
+/** Class extending this trait are eligible for name based pattern matching. */
+trait NameBasedPattern