Refactor CaptureParam Flag Set

Author: noti0na1

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

@@ -433,11 +433,13 @@ object Flags {
   /** A denotation that is valid in all run-ids */
   val (Permanent @ _, _, _) = newFlags(61, "<permanent>")
 
-  /** Symbol is a constructor proxy (either companion, or apply method) */
+  /** A phantom symbol made up by the compiler to achieve special typing rules.
+   *  Phantom symbols cannot be used as regular values, and will be erased after erasure phase.
+   *  - For constructor proxies (companion or apply method).
+   *  - For dummy capture parameters in capture sets (variables or fields).
+   */
   val (PhantomSymbol @ _, _, _) = newFlags(62, "<phantom symbol>") // (could be merged with Lifted)
 
-  val CaptureParam = PhantomSymbol
-
 // --------- Combined Flag Sets and Conjunctions ----------------------
 
   /** All possible flags */
@@ -569,6 +571,7 @@ object Flags {
   val ContravariantLocal: FlagSet            = Contravariant | Local                          // A contravariant type parameter
   val EffectivelyErased                      = PhantomSymbol | Erased
   val ConstructorProxyModule: FlagSet        = PhantomSymbol | Module
+  val CaptureParam: FlagSet                  = PhantomSymbol | StableRealizable | Synthetic
   val DefaultParameter: FlagSet              = HasDefault | Param                             // A Scala 2x default parameter
   val DeferredInline: FlagSet                = Deferred | Inline
   val DeferredMethod: FlagSet                = Deferred | Method

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

@@ -324,7 +324,7 @@ object NamerOps:
    */
   def addDummyTermCaptureParam(param: Symbol)(using Context): Unit =
     val name = param.name.toTermName
-    val flags = (param.flagsUNSAFE & AccessFlags).toTermFlags | CaptureParam | StableRealizable | Synthetic
+    val flags = (param.flagsUNSAFE & AccessFlags).toTermFlags | CaptureParam
     val dummy = newSymbol(param.owner, name, flags, param.typeRef)
     typr.println(i"Adding dummy term symbol $dummy for $param, flags = $flags")
     ctx.enter(dummy)

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

@@ -91,7 +91,7 @@ class SymUtils:
       self.is(Synthetic) && self.infoOrCompleter.typeSymbol == defn.CBCompanion
 
     def isDummyCaptureParam(using Context): Boolean =
-      self.is(Synthetic) && self.is(CaptureParam) && !(self.isClass || self.is(Method))
+      self.isAllOf(CaptureParam) && !(self.isClass || self.is(Method))
 
     /** Is this a case class for which a product mirror is generated?
     *  Excluded are value classes, abstract classes and case classes with more than one

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2533,7 +2533,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
 
   def typedSingletonTypeTree(tree: untpd.SingletonTypeTree)(using Context): Tree = {
     val ref1 = typedExpr(tree.ref, SingletonTypeProto)
-    if ctx.mode.is(Mode.InCaptureSet) && ref1.symbol.is(Flags.CaptureParam) then
+    if ctx.mode.is(Mode.InCaptureSet) && ref1.symbol.isDummyCaptureParam then
       // When a dummy term capture variable is found, it is replaced with
       // the corresponding type references (stored in the underling types).
       return Ident(ref1.tpe.widen.asInstanceOf[TypeRef]).withSpan(tree.span)