Address review comments

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

@@ -508,7 +508,7 @@ extension (tp: Type)
     case _ =>
       ReadOnlyCapability(tp)
 
-  /** If `x` is a capture ref, replacxe all no-flip covariant occurrences of `cap`
+  /** If `x` is a capture ref, replace all no-flip covariant occurrences of `cap`
    *  in type `tp` with `x*`.
    */
   def withReachCaptures(ref: Type)(using Context): Type =
@@ -758,7 +758,7 @@ object MaybeCapability extends AnnotatedCapability(defn.MaybeCapabilityAnnot):
   protected def unwrappable(using Context) = Set()
 
 /** An extractor for `ref @readOnlyCapability`, which is used to express
- *  the rad-only capability `ref.rd` as a type.
+ *  the read-only capability `ref.rd` as a type.
  */
 object ReadOnlyCapability extends AnnotatedCapability(defn.ReadOnlyCapabilityAnnot):
   protected def unwrappable(using Context) = Set(defn.MaybeCapabilityAnnot)

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

@@ -116,13 +116,13 @@ trait CaptureRef extends TypeProxy, ValueType:
     case _ => false
 
   /** An exclusive capability is a capability that derives
-   *  indirectly from a maximal capability without goinh through
+   *  indirectly from a maximal capability without going through
    *  a read-only capability first.
    */
   final def isExclusive(using Context): Boolean =
     !isReadOnly && (isMaxCapability || captureSetOfInfo.isExclusive)
 
-  // With the support of pathes, we don't need to normalize the `TermRef`s anymore.
+  // With the support of paths, we don't need to normalize the `TermRef`s anymore.
   // /** Normalize reference so that it can be compared with `eq` for equality */
   // final def normalizedRef(using Context): CaptureRef = this match
   //   case tp @ AnnotatedType(parent: CaptureRef, annot) if tp.isTrackableRef =>
@@ -242,7 +242,7 @@ trait CaptureRef extends TypeProxy, ValueType:
         case _ => false
   end subsumes
 
-  /** This is a maximal capabaility that subsumes `y` in given context and VarState.
+  /** This is a maximal capability that subsumes `y` in given context and VarState.
    *  @param canAddHidden  If true we allow maximal capabilities to subsume all other capabilities.
    *                       We add those capabilities to the hidden set if this is Fresh.Cap
    *                       If false we only accept `y` elements that are already in the

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

@@ -227,11 +227,7 @@ sealed abstract class CaptureSet extends Showable:
     elems.forall(that.mightAccountFor)
     && !that.elems.forall(this.mightAccountFor)
 
-  /** The subcapturing test.
-   *  @param frozen   if true, no new variables or dependent sets are allowed to
-   *                  be added when making this test. An attempt to add either
-   *                  will result in failure.
-   */
+  /** The subcapturing test, taking an explicit VarState. */
   final def subCaptures(that: CaptureSet, vs: VarState)(using Context): CompareResult =
     subCaptures(that)(using ctx, vs)
 
@@ -392,7 +388,7 @@ sealed abstract class CaptureSet extends Showable:
   override def toText(printer: Printer): Text =
     printer.toTextCaptureSet(this) ~~ description
 
-  /** Apply function `f` to the elements. Typcially used for printing.
+  /** Apply function `f` to the elements. Typically used for printing.
    *  Overridden in HiddenSet so that we don't run into infinite recursions
    */
   def processElems[T](f: Refs => T): T = f(elems)
@@ -407,10 +403,10 @@ object CaptureSet:
   /** If set to `true`, capture stack traces that tell us where sets are created */
   private final val debugSets = false
 
-  val emptySet = SimpleIdentitySet.empty
+  val emptyRefs: Refs = SimpleIdentitySet.empty
 
   /** The empty capture set `{}` */
-  val empty: CaptureSet.Const = Const(emptySet)
+  val empty: CaptureSet.Const = Const(emptyRefs)
 
   /** The universal capture set `{cap}` */
   def universal(using Context): CaptureSet =
@@ -466,7 +462,7 @@ object CaptureSet:
    *  nulls, this provides more lenient checking against compilation units that
    *  were not yet compiled with capture checking on.
    */
-  object Fluid extends Const(emptySet):
+  object Fluid extends Const(emptyRefs):
     override def isAlwaysEmpty = false
     override def addThisElem(elem: CaptureRef)(using Context, VarState) = CompareResult.OK
     override def accountsFor(x: CaptureRef)(using Context, VarState): Boolean = true
@@ -475,7 +471,7 @@ object CaptureSet:
   end Fluid
 
   /** The subclass of captureset variables with given initial elements */
-  class Var(override val owner: Symbol = NoSymbol, initialElems: Refs = emptySet, val level: Level = undefinedLevel, underBox: Boolean = false)(using @constructorOnly ictx: Context) extends CaptureSet:
+  class Var(override val owner: Symbol = NoSymbol, initialElems: Refs = emptyRefs, val level: Level = undefinedLevel, underBox: Boolean = false)(using @constructorOnly ictx: Context) extends CaptureSet:
 
     /** A unique identification number for diagnostics */
     val id =
@@ -493,7 +489,7 @@ object CaptureSet:
     /** The sets currently known to be dependent sets (i.e. new additions to this set
      *  are propagated to these dependent sets.)
      */
-    var deps: Deps = emptySet
+    var deps: Deps = SimpleIdentitySet.empty
 
     def isConst = isSolved
     def isAlwaysEmpty = isSolved && elems.isEmpty
@@ -927,16 +923,16 @@ object CaptureSet:
     cs1.elems.filter(cs2.mightAccountFor) ++ cs2.elems.filter(cs1.mightAccountFor)
 
   /** A capture set variable used to record the references hidden by a Fresh.Cap instance */
-  class HiddenSet(initialHidden: Refs = emptySet)(using @constructorOnly ictx: Context)
+  class HiddenSet(initialHidden: Refs = emptyRefs)(using @constructorOnly ictx: Context)
   extends Var(initialElems = initialHidden):
 
     /** Apply function `f` to `elems` while setting `elems` to empty for the
-     *  duration. This is used to escape infinite recursions if two Frash.Caps
+     *  duration. This is used to escape infinite recursions if two Fresh.Caps
      *  refer to each other in their hidden sets.
      */
     override def processElems[T](f: Refs => T): T =
       val savedElems = elems
-      elems = emptySet
+      elems = emptyRefs
       try f(savedElems)
       finally elems = savedElems
   end HiddenSet

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

@@ -622,7 +622,7 @@ class CheckCaptures extends Recheck, SymTransformer:
         case _ => denot
 
       // Don't allow update methods to be called unless the qualifier captures
-      // contain an exclusive referenece. TODO This should probabkly rolled into
+      // an exclusive reference. TODO This should probably rolled into
       // qualifier logic once we have it.
       if tree.symbol.isUpdateMethod && !qualType.captureSet.isExclusive then
         report.error(

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

@@ -13,7 +13,7 @@ import NameKinds.ExistentialBinderName
 import NameOps.isImpureFunction
 import reporting.Message
 import util.SimpleIdentitySet.empty
-import CaptureSet.{Refs, emptySet, NarrowingCapabilityMap}
+import CaptureSet.{Refs, emptyRefs, NarrowingCapabilityMap}
 import dotty.tools.dotc.util.SimpleIdentitySet
 
 /** A module for handling Fresh types. Fresh.Cap instances are top type that keep
@@ -43,14 +43,14 @@ object Fresh:
   private def ownerToHidden(owner: Symbol, reach: Boolean)(using Context): Refs =
     val ref = owner.termRef
     if reach then
-      if ref.isTrackableRef then SimpleIdentitySet(ref.reach) else emptySet
+      if ref.isTrackableRef then SimpleIdentitySet(ref.reach) else emptyRefs
     else
-      if ref.isTracked then SimpleIdentitySet(ref) else emptySet
+      if ref.isTracked then SimpleIdentitySet(ref) else emptyRefs
 
   /** An extractor for "fresh" capabilities */
   object Cap:
 
-    def apply(initialHidden: Refs = emptySet)(using Context): CaptureRef =
+    def apply(initialHidden: Refs = emptyRefs)(using Context): CaptureRef =
       if ccConfig.useSepChecks then
         AnnotatedType(defn.captureRoot.termRef, Annot(CaptureSet.HiddenSet(initialHidden)))
       else

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

@@ -7,7 +7,7 @@ import collection.mutable
 import core.*
 import Symbols.*, Types.*, Flags.*
 import Contexts.*, Names.*, Flags.*, Symbols.*, Decorators.*
-import CaptureSet.{Refs, emptySet, HiddenSet}
+import CaptureSet.{Refs, emptyRefs, HiddenSet}
 import config.Printers.capt
 import StdNames.nme
 import util.{SimpleIdentitySet, EqHashMap, SrcPos}
@@ -149,7 +149,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
   /** The set of capabilities that are hidden by a polymorphic result type
    *  of some previous definition.
    */
-  private var defsShadow: Refs = emptySet
+  private var defsShadow: Refs = emptyRefs
 
   /** A map from definitions to their internal result types.
    *  Populated during separation checking traversal.
@@ -243,10 +243,10 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
       def hiddenByElem(elem: CaptureRef): Refs = elem match
         case Fresh.Cap(hcs) => hcs.elems.filter(!_.isRootCapability) ++ recur(hcs.elems)
         case ReadOnlyCapability(ref1) => hiddenByElem(ref1).map(_.readOnly)
-        case _ => emptySet
+        case _ => emptyRefs
 
       def recur(refs: Refs): Refs =
-        (emptySet /: refs): (elems, elem) =>
+        (emptyRefs /: refs): (elems, elem) =>
           if seen.add(elem) then elems ++ hiddenByElem(elem) else elems
 
       recur(refs)
@@ -335,7 +335,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
     def hiddenCaptures = formalCaptures(arg).hidden
     def clashFootprint = clashCaptures.footprint
     def hiddenFootprint = hiddenCaptures.footprint
-    def declaredFootprint = deps(arg).map(captures(_)).foldLeft(emptySet)(_ ++ _).footprint
+    def declaredFootprint = deps(arg).map(captures(_)).foldLeft(emptyRefs)(_ ++ _).footprint
     def footprintOverlap = hiddenFootprint.overlapWith(clashFootprint).deduct(declaredFootprint)
     report.error(
       em"""Separation failure: argument of type  ${arg.nuType}
@@ -500,7 +500,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
     case AnnotatedType(parent, _) => explicitRefs(parent)
     case AndType(tp1, tp2) => explicitRefs(tp1) ++ explicitRefs(tp2)
     case OrType(tp1, tp2) => explicitRefs(tp1) ** explicitRefs(tp2)
-    case _ => emptySet
+    case _ => emptyRefs
 
   /** Deduct some elements from `refs` according to the role of the checked type `tpe`:
    *   - If the the type apears as a (result-) type of a definition of `x`, deduct
@@ -593,8 +593,8 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
      *  be explicitly referenced or hidden in some other part.
      */
     def checkParts(parts: List[Type]): Unit =
-      var footprint: Refs = emptySet
-      var hiddenSet: Refs = emptySet
+      var footprint: Refs = emptyRefs
+      var hiddenSet: Refs = emptyRefs
       var checked = 0
       for part <- parts do