Don't treat non-capturechecked classes are pure.

If they have a self type, it would not mention a capture set anyway.

Author: odersky

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

@@ -256,10 +256,11 @@ extension (cls: ClassSymbol)
   def pureBaseClass(using Context): Option[Symbol] =
     cls.baseClasses.find: bc =>
       defn.pureBaseClasses.contains(bc)
-      || bc.givenSelfType.dealiasKeepAnnots.match
-          case CapturingType(_, refs) => refs.isAlwaysEmpty
-          case RetainingType(_, refs) => refs.isEmpty
-          case selfType => selfType.exists && selfType.captureSet.isAlwaysEmpty
+      || bc.is(CaptureChecked)
+          && bc.givenSelfType.dealiasKeepAnnots.match
+            case CapturingType(_, refs) => refs.isAlwaysEmpty
+            case RetainingType(_, refs) => refs.isEmpty
+            case selfType => selfType.exists && selfType.captureSet.isAlwaysEmpty
 
 extension (sym: Symbol)
 

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

@@ -1,4 +1,11 @@
--- 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 Fuzz
+-- [E058] Type Mismatch Error: tests/neg-custom-args/captures/leaked-curried.scala:15:10 -------------------------------
+15 |    class Foo extends Box, Pure: // error
+   |          ^
+   |          illegal inheritance: self type Foo^{io} of class Foo does not conform to self type Pure
+   |          of parent trait Pure
+   |
+   | longer explanation available when compiling with `-explain`

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

@@ -8,8 +8,12 @@ trait Box:
 
 def main(): Unit =
   val leaked = withCap: (io: Cap^) =>
-    class Foo extends Box, Pure:
+    class Fuzz extends Box, Pure:
+      self =>
       val get: () ->{} () ->{io} Cap^ =
         () => () => io // error
+    class Foo extends Box, Pure: // error
+      val get: () ->{} () ->{io} Cap^ =
+        () => () => io
     new Foo
   val bad = leaked.get()().use()  // using a leaked capability

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