Simplify

Removes ad-hoc CapSet detection and capture set computation

Author: bracevac

Diff for: compiler/src/dotty/tools/dotc/cc/CaptureOps.scala

@@ -170,32 +170,6 @@ extension (tree: Tree)
 
 extension (tp: Type)
 
-  /**
-   * Is the type `tp` a `CapSet` type, i.e., a capture variable?
-   *
-   * @param tp The type to check
-   * @param includeCapSet Whether to include the bare `CapSet` type itself in the check, false at the top level
-   */
-  final def isCapSet(includeCapSet: Boolean = false)(using Context): Boolean = tp match
-    case tp: TypeRef => (includeCapSet && (tp.symbol eq defn.Caps_CapSet)) || {
-      tp.underlying match
-        case TypeBounds(lo, hi) => lo.isCapSet(true) && hi.isCapSet(true)
-        case TypeAlias(alias)   => alias.isCapSet() // TODO: test cases involving type aliases
-        case _                  => false
-    }
-    case tp: SingletonType => tp.underlying.isCapSet()
-    case CapturingType(parent, _) => parent.isCapSet(true)
-    case _ => false
-
-  /**
-   * The capture set of a capture variable. Assumes that tp.isCapSet() is true.
-   */
-  final def captureSetOfCapSet(using Context): CaptureSet = tp match
-    case CapturingType(_,c) => c
-    case tp: TypeRef if tp.symbol eq defn.Caps_CapSet => CaptureSet.empty
-    case tp: SingletonType => tp.underlying.captureSetOfCapSet
-    case tp: CaptureRef => CaptureSet(tp)
-
   /** Is this type a CaptureRef that can be tracked?
    *  This is true for
    *    - all ThisTypes and all TermParamRef,

Diff for: compiler/src/dotty/tools/dotc/cc/CaptureSet.scala

@@ -1073,9 +1073,6 @@ object CaptureSet:
     case ReachCapability(ref1) =>
       ref1.widen.deepCaptureSet(includeTypevars = true)
         .showing(i"Deep capture set of $ref: ${ref1.widen} = ${result}", capt)
-    case tp : TypeRef if tp.isCapSet() => tp.underlying match
-      case TypeBounds(lo, hi) if hi.isCapSet() => hi.captureSetOfCapSet
-      case _ => ofType(ref.underlying, followResult = true)
     case _ =>
       if ref.isMaxCapability then ref.singletonCaptureSet
       else ofType(ref.underlying, followResult = true)
@@ -1088,10 +1085,9 @@ object CaptureSet:
           tp.captureSet
         case tp: TermParamRef =>
           tp.captureSet
-        case _: TypeRef =>
-          empty
-        case _: TypeParamRef =>
-          empty
+        case tp: (TypeRef | TypeParamRef) =>
+          if tp.derivesFrom(defn.Caps_CapSet) then tp.captureSet
+          else empty
         case CapturingType(parent, refs) =>
           recur(parent) ++ refs
         case tp @ AnnotatedType(parent, ann) if ann.hasSymbol(defn.ReachCapabilityAnnot) =>

Diff for: compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -307,8 +307,8 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
      *           0 if both tp1 and tp2 are capture variables but tp1 is not a subcapture of tp2.
      */
     inline def tryHandleCaptureVars: Int =
-      if !(isCaptureCheckingOrSetup && tp1.isCapSet() && tp2.isCapSet()) then -1
-      else if (subCaptures(tp1.captureSetOfCapSet, tp2.captureSetOfCapSet, frozenConstraint).isOK) then 1
+      if !(isCaptureCheckingOrSetup && tp1.derivesFrom(defn.Caps_CapSet) && tp1.derivesFrom(defn.Caps_CapSet)) then -1
+      else if (subCaptures(tp1.captureSet, tp2.captureSet, frozenConstraint).isOK) then 1
       else 0
 
     def firstTry: Boolean = tp2 match {