Address review comments

Author: odersky

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

@@ -53,7 +53,7 @@ object ccConfig:
     Feature.sourceVersion.stable != SourceVersion.`3.5`
 
   /** If true, turn on separation checking */
-  def useFresh(using Context): Boolean =
+  def useSepChecks(using Context): Boolean =
     Feature.sourceVersion.stable.isAtLeast(SourceVersion.`3.7`)
 
 end ccConfig

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

@@ -17,7 +17,7 @@ import CaptureSet.VarState
 
 /** A trait for references in CaptureSets. These can be NamedTypes, ThisTypes or ParamRefs,
  *  as well as three kinds of AnnotatedTypes representing readOnly, reach, and maybe capabilities.
- *  If there are several annotations they come with an orderL
+ *  If there are several annotations they come with an order:
  *  `*` first, `.rd` next, `?` last.
  */
 trait CaptureRef extends TypeProxy, ValueType:

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

@@ -1487,7 +1487,7 @@ class CheckCaptures extends Recheck, SymTransformer:
      *  The unboxed condition ensures that the expected is not a type variable
      *  that's upper bounded by a read-only type. In this case it would not be sound
      *  to narrow to the read-only set, since that set can be propagated
-     *  by the type variable instantiatiin.
+     *  by the type variable instantiation.
      */
     private def improveReadOnly(actual: Type, expected: Type)(using Context): Type = actual match
       case actual @ CapturingType(parent, refs)
@@ -1816,7 +1816,7 @@ class CheckCaptures extends Recheck, SymTransformer:
       end checker
 
       checker.traverse(unit)(using ctx.withOwner(defn.RootClass))
-      if ccConfig.useFresh then SepChecker(this).traverse(unit)
+      if ccConfig.useSepChecks then SepChecker(this).traverse(unit)
       if !ctx.reporter.errorsReported then
         // We dont report errors here if previous errors were reported, because other
         // errors often result in bad applied types, but flagging these bad types gives

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

@@ -42,7 +42,7 @@ object Fresh:
   object Cap:
 
     def apply(initialHidden: Refs = emptySet)(using Context): CaptureRef =
-      if ccConfig.useFresh then
+      if ccConfig.useSepChecks then
         AnnotatedType(defn.captureRoot.termRef, Annot(CaptureSet.HiddenSet(initialHidden)))
       else
         defn.captureRoot.termRef
@@ -61,20 +61,13 @@ object Fresh:
   class FromCap(owner: Symbol)(using Context) extends BiTypeMap, FollowAliasesMap:
     thisMap =>
 
-    var reach = false
-
-    private def initHidden =
-      val ref = owner.termRef
-      if reach then
-        if ref.isTrackableRef then SimpleIdentitySet(ref.reach) else emptySet
-      else
-        if ref.isTracked then SimpleIdentitySet(ref) else emptySet
+    private var reach = false
 
     override def apply(t: Type) =
       if variance <= 0 then t
       else t match
         case t: CaptureRef if t.isCap =>
-          Cap(initHidden)
+          Cap(ownerToHidden(owner, reach))
         case t @ CapturingType(_, refs) =>
           val savedReach = reach
           if t.isBoxed then reach = true
@@ -103,11 +96,11 @@ object Fresh:
 
   /** Maps cap to fresh */
   def fromCap(tp: Type, owner: Symbol = NoSymbol)(using Context): Type =
-    if ccConfig.useFresh then FromCap(owner)(tp) else tp
+    if ccConfig.useSepChecks then FromCap(owner)(tp) else tp
 
   /** Maps fresh to cap */
   def toCap(tp: Type)(using Context): Type =
-    if ccConfig.useFresh then FromCap(NoSymbol).inverse(tp) else tp
+    if ccConfig.useSepChecks then FromCap(NoSymbol).inverse(tp) else tp
 
   /** If `refs` contains an occurrence of `cap` or `cap.rd`, the current context
    *  with an added property PrintFresh. This addition causes all occurrences of

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

@@ -432,7 +432,7 @@ class Setup extends PreRecheck, SymTransformer, SetupAPI:
 
     private val paramSigChange = util.EqHashSet[Tree]()
 
-    /** Transform type of tree, and remember the transformed type as the type the tree
+    /** Transform type of tree, and remember the transformed type as the type of the tree
      *  @pre !(boxed && sym.exists)
      */
     private def transformTT(tree: TypeTree, sym: Symbol, boxed: Boolean)(using Context): Unit =

library/src/scala/annotation/internal/freshCapability.scala

@@ -1,7 +1,10 @@
 package scala.annotation
 package internal
 
-/** An annotation used internally for fresh capability wrappers of `cap`
+/** An annotation used internally for fresh capability wrappers of `cap`.
+ *  A fresh capability is encoded as `caps.cap @freshCapability(...)` where
+ *  `freshCapability(...)` is a special kind of annotation of type `Fresh.Annot`
+ *  that contains a hidden set.
  */
 class freshCapability extends StaticAnnotation
 

library/src/scala/caps.scala

@@ -43,9 +43,9 @@ import annotation.{experimental, compileTimeOnly, retainsCap}
    */
   extension (x: Any) def reachCapability: Any = x
 
-  /** Unique capabilities x! which appear as terms in @retains annotations are encoded
-   *  as `caps.uniqueCapability(x)`. When converted to CaptureRef types in capture sets
-   *  they are  represented as `x.type @annotation.internal.uniqueCapability`.
+  /** Read-only capabilities x.rd which appear as terms in @retains annotations are encoded
+   *  as `caps.readOnlyCapability(x)`. When converted to CaptureRef types in capture sets
+   *  they are  represented as `x.type @annotation.internal.readOnlyCapability`.
    */
   extension (x: Any) def readOnlyCapability: Any = x