Align deep capture sets with reach capabilities

Count in dcs exactly those locations where a cap gets replaced by a reach capability.

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

@@ -1064,7 +1064,7 @@ object CaptureSet:
  case ref: (TermRef | TermParamRef) if ref.isMaxCapability =>
  if ref.isTrackableRef then ref.singletonCaptureSet
  else CaptureSet.universal
- case ReachCapability(ref1) => deepCaptureSet(ref1.widen)
+ case ReachCapability(ref1) => ref1.widen.deepCaptureSet
  .showing(i"Deep capture set of $ref: ${ref1.widen} = $result", capt)
  case _ => ofType(ref.underlying, followResult = true)
 
@@ -1115,17 +1115,25 @@ object CaptureSet:
 
  /** The deep capture set of a type is the union of all covariant occurrences of
  * capture sets. Nested existential sets are approximated with `cap`.
+ * NOTE: The traversal logic needs to be in sync with narrowCaps in CaptureOps, which
+ * replaces caps with reach capabilties.
  */
  def ofTypeDeeply(tp: Type)(using Context): CaptureSet =
  val collect = new TypeAccumulator[CaptureSet]:
- def apply(cs: CaptureSet, t: Type) = t.dealias match
- case t @ CapturingType(p, cs1) =>
- val cs2 = apply(cs, p)
- if variance > 0 then cs2 ++ cs1 else cs2
- case t @ Existential(_, _) =>
- apply(cs, Existential.toCap(t))
- case _ =>
- foldOver(cs, t)
+ def apply(cs: CaptureSet, t: Type) =
+ if variance <= 0 then cs
+ else t.dealias match
+ case t @ CapturingType(p, cs1) =>
+ this(cs, p) ++ cs1
+ case t @ AnnotatedType(parent, ann) =>
+ this(cs, parent)
+ case t @ FunctionOrMethod(args, res @ Existential(_, _))
+ if args.forall(_.isAlwaysPure) =>
+ this(cs, Existential.toCap(res))
+ case t @ Existential(_, _) =>
+ cs
+ case _ =>
+ foldOver(cs, t)
  collect(CaptureSet.empty, tp)
 
  type AssumedContains = immutable.Map[TypeRef, SimpleIdentitySet[CaptureRef]]

tests/neg-custom-args/captures/reaches.check

@@ -30,7 +30,7 @@
  | ^^^^^^^^^^^^^^^^^^^
  | Local reach capability id* leaks into capture scope of method test
 -- [E007] Type Mismatch Error: tests/neg-custom-args/captures/reaches.scala:62:27 --------------------------------------
-62 | val f1: File^{id*} = id(f) // error, since now id(f): File^
+62 | val f1: File^{id*} = id(f) // error, since now id(f): File^ // error
  | ^^^^^
  | Found: File^{f}
  | Required: File^{id*}
@@ -50,3 +50,11 @@
  | Type argument () -> Unit does not conform to lower bound () => Unit
  |
  | longer explanation available when compiling with `-explain`
+-- Error: tests/neg-custom-args/captures/reaches.scala:61:31 -----------------------------------------------------------
+61 | val leaked = usingFile[File^{id*}]: f => // error
+ | ^^^
+ | id* cannot be tracked since its capture set is empty
+-- Error: tests/neg-custom-args/captures/reaches.scala:62:18 -----------------------------------------------------------
+62 | val f1: File^{id*} = id(f) // error, since now id(f): File^ // error
+ | ^^^
+ | id* cannot be tracked since its capture set is empty

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

@@ -58,8 +58,8 @@ def attack2 =
  val id: File^ -> File^ = x => x
  // val id: File^ -> EX C.File^C
 
- val leaked = usingFile[File^{id*}]: f =>
- val f1: File^{id*} = id(f) // error, since now id(f): File^
+ val leaked = usingFile[File^{id*}]: f => // error
+ val f1: File^{id*} = id(f) // error, since now id(f): File^ // error
  f1
 
 class List[+A]:

tests/neg-custom-args/captures/refine-reach-shallow.scala

@@ -5,14 +5,15 @@ def test1(): Unit =
  val g: IO^ => IO^{f*} = f // error
 def test2(): Unit =
  val f: [R] -> (IO^ => R) -> R = ???
- val g: [R] -> (IO^{f*} => R) -> R = f // error
+ val ff = f
+ val g: [R] -> (IO^{f*} => R) -> R = f // error // error
 def test3(): Unit =
  val f: [R] -> (IO^ -> R) -> R = ???
- val g: [R] -> (IO^{f*} -> R) -> R = f // error
+ val g: [R] -> (IO^{f*} -> R) -> R = f // error // error
 def test4(): Unit =
  val xs: List[IO^] = ???
  val ys: List[IO^{xs*}] = xs // ok
 def test5(): Unit =
  val f: [R] -> (IO^ -> R) -> IO^ = ???
- val g: [R] -> (IO^ -> R) -> IO^{f*} = f // error
- val h: [R] -> (IO^{f*} -> R) -> IO^ = f // error
+ val g: [R] -> (IO^ -> R) -> IO^{f*} = f // error // error
+ val h: [R] -> (IO^{f*} -> R) -> IO^ = f // error // error

tests/neg-custom-args/captures/refine-withFile.scala

@@ -4,5 +4,5 @@ trait File
 val useFile: [R] -> (path: String) -> (op: File^ -> R) -> R = ???
 def main(): Unit =
  val f: [R] -> (path: String) -> (op: File^ -> R) -> R = useFile
- val g: [R] -> (path: String) -> (op: File^{f*} -> R) -> R = f // error
- val leaked = g[File^{f*}]("test")(f => f) // boom
+ val g: [R] -> (path: String) -> (op: File^{f*} -> R) -> R = f // error // error
+ val leaked = g[File^{f*}]("test")(f => f) // error