Patch pure base classes for FunctionN

Author: nicolasstucki

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

@@ -256,7 +256,8 @@ extension (cls: ClassSymbol)
   def pureBaseClass(using Context): Option[Symbol] =
     cls.baseClasses.find: bc =>
       defn.pureBaseClasses.contains(bc)
-      || bc.givenSelfType.dealiasKeepAnnots.match
+      || bc.is(CaptureChecked)
+         && bc.givenSelfType.dealiasKeepAnnots.match
           case CapturingType(_, refs) => refs.isAlwaysEmpty
           case RetainingType(_, refs) => refs.isEmpty
           case selfType => selfType.exists && selfType.captureSet.isAlwaysEmpty

tests/neg-custom-args/captures/leaked-curried.check

@@ -1,4 +1,4 @@
--- Error: tests/neg-custom-args/captures/leaked-curried.scala:13:20 ----------------------------------------------------
-13 |        () => () => io // error
+-- Error: tests/neg-custom-args/captures/leaked-curried.scala:14:20 ----------------------------------------------------
+14 |        () => () => io // error
    |                    ^^
-   |(io : Cap^) cannot be referenced here; it is not included in the allowed capture set {} of pure base class trait Pure
+   |(io : Cap^) cannot be referenced here; it is not included in the allowed capture set {} of the self type of class Foo

tests/neg-custom-args/captures/leaked-curried.scala

@@ -9,6 +9,7 @@ trait Box:
 def main(): Unit =
   val leaked = withCap: (io: Cap^) =>
     class Foo extends Box, Pure:
+      self =>
       val get: () ->{} () ->{io} Cap^ =
         () => () => io // error
     new Foo

tests/neg-custom-args/captures/outer-var.check

@@ -36,7 +36,7 @@
 16 |  var finalizeActions = collection.mutable.ListBuffer[() => Unit]() // error
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |                        Found:    scala.collection.mutable.ListBuffer[box () => Unit]
-   |                        Required: scala.collection.mutable.ListBuffer[box () ->? Unit]
+   |                        Required: scala.collection.mutable.ListBuffer[box () ->? Unit]^?
    |
    |                        Note that the universal capability `cap`
    |                        cannot be included in capture set ? of variable finalizeActions