Add scala.language.experimental.matchWithSubCases

Author: EugeneFlesselle

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -37,6 +37,7 @@ object Feature:
   val modularity = experimental("modularity")
   val quotedPatternsWithPolymorphicFunctions = experimental("quotedPatternsWithPolymorphicFunctions")
   val packageObjectValues = experimental("packageObjectValues")
+  val matchWithSubCases = experimental("matchWithSubCases")
 
   def experimentalAutoEnableFeatures(using Context): List[TermName] =
     defn.languageExperimentalFeatures

library/src/scala/runtime/stdLibPatches/language.scala

@@ -154,6 +154,11 @@ object language:
      */
     @compileTimeOnly("`packageObjectValues` can only be used at compile time in import statements")
     object packageObjectValues
+
+    /** Experimental support for match expressions with sub-cases.
+     */
+    @compileTimeOnly("`matchWithSubCases` can only be used at compile time in import statements")
+    object matchWithSubCases
   end experimental
 
   /** The deprecated object contains features that are no longer officially suypported in Scala.