From 571119a06939b0a111a7ca9320ffce2ca42223f3 Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Sun, 3 Nov 2024 23:54:44 +0100
Subject: [PATCH] Fix toFunctionType for methods containing reach capabilities
 in the result type

---
 .../src/dotty/tools/dotc/core/Types.scala     |  7 +++++--
 .../captures/depfun-reach.check               | 14 +++++++++++++
 .../captures/depfun-reach.scala               | 20 +++++++++++++++++++
 .../captures/gears-problem.scala              |  7 ++++++-
 4 files changed, 45 insertions(+), 3 deletions(-)
 create mode 100644 tests/neg-custom-args/captures/depfun-reach.check
 create mode 100644 tests/neg-custom-args/captures/depfun-reach.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 0c1d542bd6fc..612769616ac8 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/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
@@ -4074,6 +4073,10 @@ 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
diff --git a/tests/neg-custom-args/captures/depfun-reach.check b/tests/neg-custom-args/captures/depfun-reach.check
new file mode 100644
index 000000000000..c1d7d05dc8d6
--- /dev/null
+++ b/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`
diff --git a/tests/neg-custom-args/captures/depfun-reach.scala b/tests/neg-custom-args/captures/depfun-reach.scala
new file mode 100644
index 000000000000..94b10f7dbcdb
--- /dev/null
+++ b/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
diff --git a/tests/pos-custom-args/captures/gears-problem.scala b/tests/pos-custom-args/captures/gears-problem.scala
index c6ef72bc421e..531c59d9fe7d 100644
--- a/tests/pos-custom-args/captures/gears-problem.scala
+++ b/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}
\ No newline at end of file
+    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
\ No newline at end of file