Follow upper bounds of type variables when computing dcs

Author: odersky

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

@@ -1120,13 +1120,17 @@ object CaptureSet:
    */
   def ofTypeDeeply(tp: Type)(using Context): CaptureSet =
     val collect = new TypeAccumulator[CaptureSet]:
+      val seen = util.HashSet[Symbol]()
       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: TypeRef if t.symbol.isAbstractOrParamType && !seen.contains(t.symbol) =>
+            seen += t.symbol
+            this(cs, t.info.bounds.hi)
           case t @ FunctionOrMethod(args, res @ Existential(_, _))
           if args.forall(_.isAlwaysPure) =>
             this(cs, Existential.toCap(res))

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

@@ -655,7 +655,7 @@ class CheckCaptures extends Recheck, SymTransformer:
           for (getterName, argType) <- mt.paramNames.lazyZip(argTypes) do
             val getter = cls.info.member(getterName).suchThat(_.isRefiningParamAccessor).symbol
             if !getter.is(Private) && getter.hasTrackedParts then
-              refined = RefinedType(refined, getterName, argType)
+              refined = RefinedType(refined, getterName, argType.unboxed)
               allCaptures ++= argType.captureSet
           (refined, allCaptures)
 

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

@@ -73,11 +73,15 @@ class Setup extends PreRecheck, SymTransformer, SetupAPI:
   private def newFlagsFor(symd: SymDenotation)(using Context): FlagSet =
 
     object containsCovarRetains extends TypeAccumulator[Boolean]:
+      val seen = util.HashSet[Symbol]()
       def apply(x: Boolean, tp: Type): Boolean =
         if x then true
         else if tp.derivesFromCapability && variance >= 0 then true
         else tp match
           case AnnotatedType(_, ann) if ann.symbol.isRetains && variance >= 0 => true
+          case t: TypeRef if t.symbol.isAbstractOrParamType && !seen.contains(t.symbol) =>
+            seen += t.symbol
+            apply(x, t.info.bounds.hi)
           case _ => foldOver(x, tp)
       def apply(tp: Type): Boolean = apply(false, tp)
 

tests/neg-custom-args/captures/dcs-tvar.check

@@ -0,0 +1,10 @@
+-- Error: tests/neg-custom-args/captures/dcs-tvar.scala:6:15 -----------------------------------------------------------
+6 |  () => runOps(xs) // error
+  |               ^^
+  |               reference xs* is not included in the allowed capture set {}
+  |               of an enclosing function literal with expected type () -> Unit
+-- Error: tests/neg-custom-args/captures/dcs-tvar.scala:9:15 -----------------------------------------------------------
+9 |  () => runOps(xs) // error
+  |               ^^
+  |               reference xs* is not included in the allowed capture set {}
+  |               of an enclosing function literal with expected type () -> Unit

tests/neg-custom-args/captures/dcs-tvar.scala

@@ -0,0 +1,9 @@
+import caps.use
+
+def runOps(@use xs: List[() => Unit]): Unit = ???
+
+def f[T <: List[() => Unit]](xs: T): () -> Unit =
+  () => runOps(xs) // error
+
+def g[T <: List[U], U <: () => Unit](xs: T): () -> Unit =
+  () => runOps(xs) // error

tests/neg-custom-args/captures/i21646.scala

@@ -9,5 +9,5 @@ class Resource[T <: Capability](gen: T):
 
 @main def run =
   val myFile: File = ???
-  val r = Resource(myFile) // error
+  val r = Resource(myFile) // now ok, was error
   ()

tests/neg-custom-args/captures/unsound-reach-6.scala

@@ -0,0 +1,22 @@
+class IO
+
+def f(xs: List[() => Unit]): () => Unit = () =>
+  println(xs.head) // error
+
+def test(io: IO^)(ys: List[() ->{io} Unit]) =
+  val x = () =>
+    val z = f(ys)
+    z()
+  val _: () -> Unit = x // !!! ys* gets lost
+  ()
+
+def test(io: IO^) =
+  def ys: List[() ->{io} Unit] = ???
+  val x = () =>
+    val z = f(ys)
+    z()
+  val _: () -> Unit = x // !!! io gets lost
+  ()
+
+
+

tests/neg-custom-args/captures/use-override.scala

@@ -0,0 +1,15 @@
+import caps.use
+
+def test(io: Object^, async: Object^) =
+
+  trait A:
+    def f(@use x: List[() ->{io} Unit]): Unit
+
+  class B extends A:
+    def f(@use x: List[() => Unit]): Unit =  // error, would be unsound if allowed
+      x.foreach(_())
+
+  class C extends A:
+    def f(@use x: List[() ->{io, async} Unit]): Unit =  // error, this one could be soundly allowed actually
+      x.foreach(_())
+

tests/pos-custom-args/captures/i21646.scala

@@ -0,0 +1,13 @@
+import language.experimental.captureChecking
+import caps.Capability
+
+trait File extends Capability
+
+class Resource[T <: Capability](gen: T):
+  def use[U](f: T => U): U =
+    f(gen) // OK, was error under unsealed
+
+@main def run =
+  val myFile: File = ???
+  val r = Resource(myFile) // error
+  ()