Drop @unbox

Convert remaining occurrences in tests to @use

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

@@ -402,15 +402,16 @@ class CheckCaptures extends Recheck, SymTransformer:
                   && (!ccConfig.useSealed || refSym.is(Param))
                   && refOwner == env.owner
               then
-                if refSym.hasAnnotation(defn.UnboxAnnot)
-                  || ref.info.hasAnnotation(defn.UseAnnot)
-                  || c.isUnderUse
-                then
+                if ref.info.hasAnnotation(defn.UseAnnot)|| c.isUnderUse then
                   capt.println(i"exempt: $ref in $refOwner")
                 else
                   // Reach capabilities that go out of scope have to be approximated
                   // by their underlying capture set, which cannot be universal.
-                  // Reach capabilities of @unboxed parameters are exempted.
+                  // Reach capabilities are exempted if
+                  //  - they are under-use capabilties that were generated from a cap
+                  //    appearing under a @use, or
+                  //  - their reference has a type thar carries a @use annotation. In that
+                  //    case callers will charge the deep capture set of the argument.
                   val cs = CaptureSet.ofInfo(c)
                   cs.disallowRootCapability: () =>
                     def kind = if c.isReach then "reach capability" else "capture set variable"
@@ -428,48 +429,14 @@ class CheckCaptures extends Recheck, SymTransformer:
     end markFree
 
     /** Include references captured by the called method in the current environment stack */
-    def includeCallCaptures(sym: Symbol, pos: SrcPos)(using Context): Unit =
-      if sym.exists && curEnv.isOpen then markFree(capturedVars(sym), pos)
-
-    private val prefixCalls = util.EqHashSet[GenericApply]()
-    private val unboxedArgs = util.EqHashSet[Tree]()
-
-    def handleCall(meth: Symbol, call: GenericApply, eval: () => Type)(using Context): Type =
-      if prefixCalls.remove(call) then return eval()
-
-      val unboxedParamNames =
-        meth.rawParamss.flatMap: params =>
-          params.collect:
-            case param if param.hasAnnotation(defn.UnboxAnnot) =>
-              param.name
-        .toSet
-
-      def markUnboxedArgs(call: GenericApply): Unit = call.fun.tpe.widen match
-        case MethodType(pnames) =>
-          for (pname, arg) <- pnames.lazyZip(call.args) do
-            if unboxedParamNames.contains(pname) then
-              unboxedArgs.add(arg)
-        case _ =>
-
-      def markPrefixCalls(tree: Tree): Unit = tree match
-        case tree: GenericApply =>
-          prefixCalls.add(tree)
-          markUnboxedArgs(tree)
-          markPrefixCalls(tree.fun)
-        case _ =>
-
-      markUnboxedArgs(call)
-      markPrefixCalls(call.fun)
-      val res = eval()
-      includeCallCaptures(meth, call.srcPos)
-      res
-    end handleCall
+    def includeCallCaptures(sym: Symbol, resType: Type, pos: SrcPos)(using Context): Unit = resType match
+      case _: MethodOrPoly => // wait until method is fully applied
+      case _ =>
+        if sym.exists && curEnv.isOpen then markFree(capturedVars(sym), pos)
 
     override def recheckIdent(tree: Ident, pt: Type)(using Context): Type =
       if tree.symbol.is(Method) then
-        if tree.symbol.info.isParameterless then
-          // there won't be an apply; need to include call captures now
-          includeCallCaptures(tree.symbol, tree.srcPos)
+        includeCallCaptures(tree.symbol, tree.symbol.info, tree.srcPos)
       else if !tree.symbol.isStatic then
         //debugShowEnvs()
         def addSelects(ref: TermRef, pt: Type): TermRef = pt match
@@ -574,16 +541,15 @@ class CheckCaptures extends Recheck, SymTransformer:
             tp.derivedCapturingType(forceBox(parent), refs)
         mapArgUsing(forceBox)
       else
-        handleCall(meth, tree, () => super.recheckApply(tree, pt))
+        val res = super.recheckApply(tree, pt)
+        includeCallCaptures(meth, res, tree.srcPos)
+        res
     end recheckApply
 
     protected override
     def recheckArg(arg: Tree, formal: Type)(using Context): Type =
       val argType = recheck(arg, formal)
       accountForUses(arg, argType, formal)
-      if unboxedArgs.contains(arg) then
-        capt.println(i"charging deep capture set of $arg: ${argType} = ${argType.deepCaptureSet}")
-        markFree(argType.deepCaptureSet, arg.srcPos)
       argType
 
     class MapUses(deep: Boolean)(using Context) extends TypeMap:
@@ -620,27 +586,18 @@ class CheckCaptures extends Recheck, SymTransformer:
      *  ---------------------
      *  E |- f(a): Tr^C
      *
-     *  If the function `f` does not have an `@unboxed` parameter, then
-     *  any unboxing it does would be charged to the environment of the function
-     *  so they have to appear in Cq. Since any capabilities of the result of the
-     *  application must already be present in the application, an upper
-     *  approximation of the result capture set is Cq \union Ca, where `Ca`
-     *  is the capture set of the argument.
-     *  If the function `f` does have an `@unboxed` parameter, then it could in addition
-     *  unbox reach capabilities over its formal parameter. Therefore, the approximation
-     *  would be `Cq \union dcs(Ca)` instead.
+     *  If the type of the function `f` does not mention any formal parameters
+     *  any capabilities of the result of the application must already be present in
+     *  the application. So an upper approximation of the result capture set is Cq \union Ca,
+     *  where `Ca` is the capture set of the argument.
      *  If the approximation is known to subcapture the declared result Cr, we pick it for C
      *  otherwise we pick Cr.
      */
     protected override
     def recheckApplication(tree: Apply, qualType: Type, funType: MethodType, argTypes: List[Type])(using Context): Type =
       val appType = Existential.toCap(super.recheckApplication(tree, qualType, funType, argTypes))
       val qualCaptures = qualType.captureSet
-      val argCaptures =
-        for (arg, argType) <- tree.args.lazyZip(argTypes) yield
-          if unboxedArgs.remove(arg) // need to ensure the remove happens, that's why argCaptures is computed even if not needed.
-          then argType.deepCaptureSet
-          else argType.captureSet
+      val argCaptures = argTypes.map(_.captureSet)
       appType match
         case appType @ CapturingType(appType1, refs)
         if qualType.exists
@@ -735,8 +692,10 @@ class CheckCaptures extends Recheck, SymTransformer:
               i"Sealed type variable $pname", "be instantiated to",
               i"This is often caused by a local capability$where\nleaking as part of its result.",
               tree.srcPos)
-      try handleCall(meth, tree, () => Existential.toCap(super.recheckTypeApply(tree, pt)))
-      finally checkContains(tree)
+      val res = Existential.toCap(super.recheckTypeApply(tree, pt))
+      includeCallCaptures(meth, res, tree.srcPos)
+      checkContains(tree)
+      res
     end recheckTypeApply
 
     /** Faced with a tree of form `caps.contansImpl[CS, r.type]`, check that `R` is a tracked
@@ -1423,21 +1382,6 @@ class CheckCaptures extends Recheck, SymTransformer:
           !setup.isPreCC(overriding) && !setup.isPreCC(overridden)
 
         override def checkInheritedTraitParameters: Boolean = false
-
-        /** Check that overrides don't change the @unbox status of their parameters */
-        override def additionalChecks(member: Symbol, other: Symbol)(using Context): Unit =
-          for
-            (params1, params2) <- member.rawParamss.lazyZip(other.rawParamss)
-            (param1, param2) <- params1.lazyZip(params2)
-          do
-            if param1.hasAnnotation(defn.UnboxAnnot) != param2.hasAnnotation(defn.UnboxAnnot) then
-              report.error(
-                OverrideError(
-                    i"has a parameter ${param1.name} with different @unbox status than the corresponding parameter in the overridden definition",
-                    self, member, other, self.memberInfo(member), self.memberInfo(other)
-                  ),
-                if member.owner == clazz then member.srcPos else clazz.srcPos
-              )
       end OverridingPairsCheckerCC
 
       def traverse(t: Tree)(using Context) =

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

@@ -552,7 +552,7 @@ class Definitions {
       ScalaPackageClass, tpnme.maybeCapability, Final, List(StaticAnnotationClass.typeRef)))
 
   /** A type `type <use>[+T] <: T` used locally in capture checking. At certain points
-   *  `T @use` types are converted to `<use>[T]` types. These types are handled as 
+   *  `T @use` types are converted to `<use>[T]` types. These types are handled as
    *  compile-time applied types by TypeComparer.
    */
   @tu lazy val UseType: TypeSymbol =
@@ -1068,7 +1068,6 @@ class Definitions {
   @tu lazy val ExperimentalAnnot: ClassSymbol = requiredClass("scala.annotation.experimental")
   @tu lazy val ThrowsAnnot: ClassSymbol = requiredClass("scala.throws")
   @tu lazy val TransientAnnot: ClassSymbol = requiredClass("scala.transient")
-  @tu lazy val UnboxAnnot: ClassSymbol = requiredClass("scala.caps.unbox")
   @tu lazy val UncheckedAnnot: ClassSymbol = requiredClass("scala.unchecked")
   @tu lazy val UncheckedStableAnnot: ClassSymbol = requiredClass("scala.annotation.unchecked.uncheckedStable")
   @tu lazy val UncheckedVarianceAnnot: ClassSymbol = requiredClass("scala.annotation.unchecked.uncheckedVariance")

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

@@ -1796,7 +1796,7 @@ object Types extends TypeUtils {
 
     /** Is this either not a method at all, or a parameterless method? */
     final def isParameterless(using Context): Boolean = stripPoly match {
-      case mt: MethodType => false
+      case mt: MethodOrPoly => false
       case _ => true
     }
 

library/src/scala/caps.scala

@@ -55,7 +55,6 @@ import annotation.{experimental, compileTimeOnly, retainsCap}
   /** This should go into annotations. For now it is here, so that we
    *  can experiment with it quickly between minor releases
    */
-  final class unbox extends annotation.StaticAnnotation
   final class use extends annotation.StaticAnnotation
 
   object unsafe:

tests/neg-custom-args/captures/spread-problem.scala

@@ -2,7 +2,7 @@ import language.experimental.captureChecking
 
 trait Source[+T]
 
-def race[T](@caps.unbox sources: (Source[T]^)*): Source[T]^{sources*} = ???
+def race[T](sources: (Source[T]^ @caps.use)*): Source[T]^{sources*} = ???
 
 def raceTwo[T](src1: Source[T]^, src2: Source[T]^): Source[T]^{} =
   race(Seq(src1, src2)*) // error

tests/pos-custom-args/captures/Buffer.scala

@@ -8,10 +8,8 @@ trait Buffer[A]:
   def flatMapInPlace(f: A => IterableOnce[A]^): this.type = {
     val g = f
     val s = 10
-     // capture checking: we need the copy since we box/unbox on g* on the next line
+      // capture checking: we need the copy since we box/unbox on g* on the next line
       // TODO: This looks fishy, need to investigate
-      // Alternative would be to mark `f` as @unbox. It's not inferred
-      // since `^ appears in a function result, not under a box.
     val newElems = new Array[(IterableOnce[A]^{f})](s)
     var i = 0
     while i < s do

tests/pos-custom-args/captures/dep-reach.scala

@@ -1,10 +1,10 @@
-import caps.unbox
+import caps.use
 object Test:
   class C
   type Proc = () => Unit
 
   def f(c: C^, d: C^): () ->{c, d} Unit =
-    def foo(@unbox xs: Proc*): () ->{xs*} Unit =
+    def foo(xs: Proc @use *): () ->{xs*} Unit =
       xs.head
     val a: () ->{c} Unit = () => ()
     val b: () ->{d} Unit = () => ()
@@ -13,7 +13,7 @@ object Test:
 
   def g(c: C^, d: C^): () ->{c, d} Unit =
 
-    def foo(@unbox xs: Seq[() => Unit]): () ->{xs*} Unit =
+    def foo(xs: Seq[(() => Unit) @use]): () ->{xs*} Unit =
       xs.head
 
     val a: () ->{c} Unit = () => ()

tests/pos-custom-args/captures/reaches.scala

@@ -1,4 +1,4 @@
-import caps.unbox
+import caps.use
 
 class C
 def f(xs: List[C^]) =
@@ -22,7 +22,7 @@ extension [A](x: A) def :: (xs: List[A]): List[A] = ???
 
 object Nil extends List[Nothing]
 
-def runAll(@unbox xs: List[Proc]): Unit =
+def runAll(xs: List[Proc] @use): Unit =
   var cur: List[() ->{xs*} Unit] = xs  // OK, by revised VAR
   while cur.nonEmpty do
     val next: () ->{xs*} Unit = cur.head

tests/pos/cc-poly-source-capability.scala

@@ -1,7 +1,7 @@
 import language.experimental.captureChecking
 import annotation.experimental
 import caps.{CapSet, Capability}
-import caps.unbox
+import caps.use
 
 @experimental object Test:
 
@@ -18,7 +18,7 @@ import caps.unbox
 
     def allListeners: Set[Listener^{X^}] = listeners
 
-  def test1(async1: Async, @unbox others: List[Async]) =
+  def test1(async1: Async, others: List[Async @use]) =
     val src = Source[CapSet^{async1, others*}]
     val lst1 = listener(async1)
     val lsts = others.map(listener)

tests/pos/cc-poly-source.scala

@@ -1,7 +1,7 @@
 import language.experimental.captureChecking
 import annotation.experimental
 import caps.{CapSet, Capability}
-import caps.unbox
+import caps.use
 
 @experimental object Test:
 
@@ -25,7 +25,7 @@ import caps.unbox
     val ls = src.allListeners
     val _: Set[Listener^{lbl1, lbl2}] = ls
 
-  def test2(@unbox lbls: List[Label^]) =
+  def test2(lbls: List[Label^ @use]) =
     def makeListener(lbl: Label^): Listener^{lbl} = ???
     val listeners = lbls.map(makeListener)
     val src = Source[CapSet^{lbls*}]

tests/pos/gears-probem-1.scala

@@ -1,5 +1,5 @@
 import language.experimental.captureChecking
-import caps.unbox
+import caps.use
 
 trait Future[+T]:
   def await: T
@@ -17,7 +17,7 @@ class Result[+T, +E]:
 case class Err[+E](e: E) extends Result[Nothing, E]
 case class Ok[+T](x: T) extends Result[T, Nothing]
 
-extension [T](@unbox fs: Seq[Future[T]^])
+extension [T](fs: Seq[Future[T]^ @use])
   def awaitAll =
     val collector//: Collector[T]{val futures: Seq[Future[T]^{fs*}]}
        = Collector(fs)

tests/pos/i18699.scala

@@ -1,9 +1,9 @@
 import language.experimental.captureChecking
-import caps.unbox
+import caps.use
 
 trait Cap:
   def use: Int = 42
 
-def test2(@unbox cs: List[Cap^]): Unit =
+def test2(cs: List[Cap^] @use): Unit =
   val t0: Cap^{cs*} = cs.head  // error
   var t1: Cap^{cs*} = cs.head  // error

tests/pos/reach-capability.scala

@@ -1,7 +1,7 @@
 import language.experimental.captureChecking
 import annotation.experimental
 import caps.Capability
-import caps.unbox
+import caps.use
 
 @experimental object Test2:
 
@@ -12,7 +12,7 @@ import caps.unbox
 
   class Listener
 
-  def test2(@unbox lbls: List[Label]) =
+  def test2(lbls: List[Label] @use) =
     def makeListener(lbl: Label): Listener^{lbl} = ???
     val listeners = lbls.map(makeListener) // should work
 

tests/pos/reach-problem.scala

@@ -1,11 +1,11 @@
 import language.experimental.captureChecking
-import caps.unbox
+import caps.use
 
 class Box[T](items: Seq[T^]):
   def getOne: T^{items*} = ???
 
 object Box:
-  def getOne[T](@unbox items: Seq[T^]): T^{items*} =
+  def getOne[T](items: Seq[T^ @use]): T^{items*} =
     val bx = Box(items)
     bx.getOne
 /*