Bring Mayby back

Author: noti0na1

compiler/src/dotty/tools/dotc/cc/Capability.scala

@@ -599,7 +599,7 @@ object Capabilities:
         c match
           case _: ReadOnly => ReadOnlyCapability(c1)
           case _: Reach => ReachCapability(c1)
-          // TODO: do we need to handle Maybe here?
+          case _: Maybe => MaybeCapability(c1)
           case _ => c1
 
     def toText(printer: Printer): Text = printer.toTextCapability(this)

compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -50,28 +50,6 @@ def ccState(using Context): CCState =
 
 extension (tree: Tree)
 
-  /** Map tree with a Capability type to the corresponding capability,
-   *  map CapSet^{refs} to the `refs` references,
-   *  throw IllegalCaptureRef otherwise
-   */
-  // def toCapabilities(using Context): List[Capability] = tree match
-  //   case ReachCapabilityApply(arg) =>
-  //     arg.toCapabilities.map(_.reach)
-  //   case ReadOnlyCapabilityApply(arg) =>
-  //     arg.toCapabilities.map(_.readOnly)
-  //   case CapsOfApply(arg) =>
-  //     arg.toCapabilities
-  //   case _ => tree.tpe.dealiasKeepAnnots match
-  //     case ref: TermRef if ref.isCapRef =>
-  //       GlobalCap :: Nil
-  //     case ref: Capability if ref.isTrackableRef =>
-  //       ref :: Nil
-  //     case AnnotatedType(parent, ann)
-  //     if ann.symbol.isRetains && parent.derivesFrom(defn.Caps_CapSet) =>
-  //       ann.tree.toCaptureSet.elems.toList
-  //     case tpe =>
-  //       throw IllegalCaptureRef(tpe) // if this was compiled from cc syntax, problem should have been reported at Typer
-
   /** Convert a @retains or @retainsByName annotation tree to the capture set it represents.
    *  For efficience, the result is cached as an Attachment on the tree.
    */
@@ -82,6 +60,7 @@ extension (tree: Tree)
         val refs = CaptureSet(tree.retainedSet.retainedElements*)
         tree.putAttachment(Captures, refs)
         refs
+
   /** The type representing the capture set of retains annotation.
     */
   def retainedSet(using Context): Type =
@@ -584,11 +563,16 @@ end AnnotatedCapability
  */
 object ReadOnlyCapability extends AnnotatedCapability(defn.ReadOnlyCapabilityAnnot)
 
-/** An extractor for `ref @annotation.internal.reachCapability`, which is used to express
+/** An extractor for `ref @reachCapability`, which is used to express
  *  the reach capability `ref*` as a type.
  */
 object ReachCapability extends AnnotatedCapability(defn.ReachCapabilityAnnot)
 
+/** An extractor for `ref @amaybeCapability`, which is used to express
+ *  the maybe capability `ref?` as a type.
+ */
+object MaybeCapability extends AnnotatedCapability(defn.MaybeCapabilityAnnot)
+
 /** An extractor for all kinds of function types as well as method and poly types.
  *  It includes aliases of function types such as `=>`. TODO: Can we do without?
  *  @return  1st half: The argument types or empty if this is a type function

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

@@ -549,6 +549,10 @@ class Definitions {
     cls
   @tu lazy val SingletonType: TypeRef = SingletonClass.typeRef
 
+  @tu lazy val MaybeCapabilityAnnot: ClassSymbol =
+     completeClass(enterCompleteClassSymbol(
+       ScalaPackageClass, tpnme.maybeCapability, Final, List(StaticAnnotationClass.typeRef)))
+
   @tu lazy val CollectionSeqType: TypeRef  = requiredClassRef("scala.collection.Seq")
   @tu lazy val SeqType: TypeRef            = requiredClassRef("scala.collection.immutable.Seq")
   @tu lazy val SeqModule: Symbol           = requiredModule("scala.collection.immutable.Seq")
@@ -2224,7 +2228,8 @@ class Definitions {
       NullClass,
       NothingClass,
       SingletonClass,
-      CBCompanion)
+      CBCompanion,
+      MaybeCapabilityAnnot)
 
   @tu lazy val syntheticCoreClasses: List[Symbol] = syntheticScalaClasses ++ List(
     EmptyPackageVal,

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

@@ -551,6 +551,7 @@ object StdNames {
     val materializeClassTag: N  = "materializeClassTag"
     val materializeWeakTypeTag: N = "materializeWeakTypeTag"
     val materializeTypeTag: N   = "materializeTypeTag"
+    val maybeCapability: N      = "maybeCapability"
     val mirror : N              = "mirror"
     val moduleClass : N         = "moduleClass"
     val mut: N                  = "mut"