Don't store elements in hidden sets under CCState.collapseFresh

Author: odersky

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

@@ -1392,7 +1392,7 @@ object CaptureSet:
     def addHidden(hidden: HiddenSet, elem: Capability)(using Context): Boolean =
       if hidden.isConst then false
       else
-        hidden.add(elem)(using ctx, this)
+        if !CCState.collapseFresh then hidden.add(elem)(using ctx, this)
         true
 
     /** If root1 and root2 belong to the same binder but have different originalBinders

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

@@ -923,6 +923,9 @@ object Types extends TypeUtils {
           else
             val isRefinedMethod = rinfo.isInstanceOf[MethodOrPoly]
             val joint = CCState.withCollapsedFresh:
+                // We have to do a collapseFresh here since `pdenot` will see the class
+                // view and a fresh in the class will not be able to subsume a
+                // refinement from outside since level checking would fail.
                 pdenot.meet(
                   new JointRefDenotation(NoSymbol, rinfo, Period.allInRun(ctx.runId), pre, isRefinedMethod),
                   pre,

tests/neg-custom-args/captures/cc-poly-varargs.check

@@ -15,7 +15,3 @@
 19 |  class C4(val f: () => Int) extends C3 // error
    |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |reference (C4.this.f : () => Int) captured by this self type is not included in the allowed capture set {} of pure base class class C3
--- Error: tests/neg-custom-args/captures/cc-this.scala:33:8 ------------------------------------------------------------
-33 |  def c3 = c2.y // error
-   |        ^
-   |        Separation failure: method c3's inferred result type C{val x: () => Int}^ hides non-local parameter cc

tests/neg-custom-args/captures/cc-this.check

@@ -30,6 +30,6 @@ def test2(using consume cc: Cap) =
 
   def c1 = new C(f)
   def c2 = c1
-  def c3 = c2.y // error
+  def c3 = c2.y // was error, now OK
   val c4: C^ = c3
   val _ = c3: C^

tests/neg-custom-args/captures/cc-this.scala

@@ -8,6 +8,6 @@ def race[T, Cap^](sources: Source[T, {Cap}]^{Cap}*): Source[T, {Cap}]^{Cap} = ??
 def either[T1, T2, Cap^](
     src1: Source[T1, {Cap}]^{Cap},
     src2: Source[T2, {Cap}]^{Cap}): Source[Either[T1, T2], {Cap}]^{Cap} =
-  val left = src1.transformValuesWith(Left(_))    // error
-  val right = src2.transformValuesWith(Right(_))  // error
+  val left = src1.transformValuesWith(Left(_))    // was error, now OK
+  val right = src2.transformValuesWith(Right(_))  // was error, now OK
   race(left, right)