Fix toFunctionType for methods containing reach capabilities in the r…

…esult type

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

@@ -38,8 +38,7 @@ import config.Printers.{core, typr, matchTypes}
 import reporting.{trace, Message}
 import java.lang.ref.WeakReference
 import compiletime.uninitialized
-import cc.{CapturingType, CaptureRef, CaptureSet, SingletonCaptureRef, isTrackableRef,
-           derivedCapturingType, isBoxedCapturing, isCaptureChecking, isRetains, isRetainsLike}
+import cc.*
 import CaptureSet.{CompareResult, IdempotentCaptRefMap, IdentityCaptRefMap}
 
 import scala.annotation.internal.sharable
@@ -4070,6 +4069,10 @@ object Types extends TypeUtils {
               range(defn.NothingType, atVariance(1)(apply(tp.underlying)))
             case CapturingType(_, _) =>
               mapOver(tp)
+            case ReachCapability(tp1) =>
+              apply(tp1) match
+                case tp1a: CaptureRef if tp1a.isTrackableRef => tp1a.reach
+                case _ => defn.captureRoot.termRef
             case AnnotatedType(parent, ann) if ann.refersToParamOf(thisLambdaType) =>
               val parent1 = mapOver(parent)
               if ann.symbol.isRetainsLike then

tests/neg-custom-args/captures/depfun-reach.check

@@ -0,0 +1,14 @@
+-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/depfun-reach.scala:13:4 ----------------------------------
+13 |    op // error
+   |    ^^
+   |    Found:    (xs: List[(X, box () ->{io} Unit)]) ->{op} List[box () ->{xs*} Unit]
+   |    Required: (xs: List[(X, box () ->{io} Unit)]) => List[() -> Unit]
+   |
+   | longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/depfun-reach.scala:20:60 ---------------------------------
+20 |  val b: (xs: List[() ->{io} Unit]) => List[() ->{} Unit] = a // error
+   |                                                            ^
+   |                                        Found:    (xs: List[box () ->{io} Unit]) ->{a} List[box () ->{xs*} Unit]
+   |                                        Required: (xs: List[box () ->{io} Unit]) => List[() -> Unit]
+   |
+   | longer explanation available when compiling with `-explain`

tests/neg-custom-args/captures/depfun-reach.scala

@@ -0,0 +1,20 @@
+import language.experimental.captureChecking
+import caps.cap
+
+def test(io: Object^, async: Object^) =
+  def compose(op: List[(() ->{cap} Unit, () ->{cap} Unit)]): List[() ->{op*} Unit] =
+    List(() => op.foreach((f,g) => { f(); g() }))
+
+  def compose1(op: List[(() ->{async} Unit, () ->{io} Unit)]): List[() ->{op*} Unit] =
+    compose(op)
+
+  def foo[X](op: (xs: List[(X, () ->{io} Unit)]) => List[() ->{xs*} Unit])
+               : (xs: List[(X, () ->{io} Unit)]) => List[() ->{} Unit] =
+    op // error
+
+  def boom(op: List[(() ->{async} Unit, () ->{io} Unit)]): List[() ->{} Unit] =
+    foo(compose1)(op)
+
+def test2(io: Object^) =
+  val a: (xs: List[() ->{io} Unit]) => List[() ->{xs*} Unit] = ???
+  val b: (xs: List[() ->{io} Unit]) => List[() ->{} Unit] = a // error

tests/pos-custom-args/captures/gears-problem.scala

@@ -16,4 +16,9 @@ extension [T](@use fs: Seq[Future[T]^])
     val collector: Collector[T]{val futures: Seq[Future[T]^{fs*}]}
        = Collector(fs)
     // val ch = collector.results // also errors
-    val fut: Future[T]^{fs*} = collector.results.read().right.get // found ...^{caps.cap}
+    val fut: Future[T]^{fs*} = collector.results.read().right.get // found ...^{caps.cap}
+
+    val ch = collector.results
+    val item = ch.read()
+    val r = item.right
+    val fut2: Future[T]^{fs*} = r.get