Make formalCaptures use the spanCaptureSet

Author: odersky

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

@@ -341,7 +341,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
    *  the latter contains a cap.
    */
   private def formalCaptures(arg: Tree)(using Context): Refs =
-    arg.formalType.orElse(arg.nuType).deepCaptureSet.elems
+    arg.formalType.orElse(arg.nuType).spanCaptureSet.elems
 
    /** The span capture set if the type of `tree` */
   private def spanCaptures(tree: Tree)(using Context): Refs =
@@ -402,7 +402,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
       if clashIdx == 0 && !isShowableMethod then "" // we already mentioned the type in `funStr`
       else i" with type  ${clashing.nuType}"
     val hiddenSet = formalCaptures(polyArg).transHiddenSet
-    val clashSet = deepCaptures(clashing)
+    val clashSet = if clashIdx == -1 then deepCaptures(clashing) else spanCaptures(clashing)
     val hiddenFootprint = hiddenSet.directFootprint
     val clashFootprint = clashSet.directFootprint
     report.error(
@@ -891,10 +891,11 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
     val resultType = mtpe.finalResultType
     val resultCaptures =
       (resultArgCaptures(resultType) ++ resultType.deepCaptureSet.elems).filter(!isLocalRef(_))
+      // See i23726.scala why deepCaptureSet is needed here.
     val resultPeaks = resultCaptures.allPeaks
     capt.println(i"deps for $app = ${deps.toList}")
     (deps, resultPeaks)
-
+  end dependencies
 
   /** Decompose an application into a function prefix and a list of argument lists.
    *  If some of the arguments need a separation check because they are capture polymorphic,

tests/neg-custom-args/captures/sepchecks2.check

@@ -1,19 +1,3 @@
--- Error: tests/neg-custom-args/captures/sepchecks2.scala:13:7 ---------------------------------------------------------
-13 |  foo((() => println(c)) :: Nil, c) // error
-   |       ^^^^^^^^^^^^^^^^^^^^^^^^
-   |Separation failure: argument of type  List[() ->{c} Unit]
-   |to method foo: (xs: List[() => Unit], y: Object^): Nothing
-   |corresponds to capture-polymorphic formal parameter xs of type  List[() => Unit]
-   |and hides capabilities  {c}.
-   |Some of these overlap with the captures of the second argument with type  (c : Object^).
-   |
-   |  Hidden set of current argument        : {c}
-   |  Hidden footprint of current argument  : {c}
-   |  Capture set of second argument        : {c}
-   |  Footprint set of second argument      : {c}
-   |  The two sets overlap at               : {c}
-   |
-   |where:    => refers to a fresh root capability created in method Test2 when checking argument to parameter xs of method foo
 -- Error: tests/neg-custom-args/captures/sepchecks2.scala:14:10 --------------------------------------------------------
 14 |  val x1: (Object^, Object^) = (c, c) // error
    |          ^^^^^^^^^^^^^^^^^^

tests/neg-custom-args/captures/sepchecks2.scala

@@ -10,7 +10,7 @@ def Test(consume c: Object^) =
   println(c)
 
 def Test2(c: Object^, d: Object^): Unit =
-  foo((() => println(c)) :: Nil, c) // error
+  foo((() => println(c)) :: Nil, c) // ok
   val x1: (Object^, Object^) = (c, c) // error
   val x2: (Object^, Object^{d}) = (d, d) // error