Exclude AnyVal from set of pure base classes

User-defined value classes should be able to capture capabilities

Author: odersky

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

@@ -1388,11 +1388,12 @@ class Definitions {
   /** Base classes that are assumed to be pure for the purposes of capture checking.
    *  Every class inheriting from a pure baseclass is pure.
    */
-  @tu lazy val pureBaseClasses = Set(defn.AnyValClass, defn.ThrowableClass)
+  @tu lazy val pureBaseClasses = Set(defn.ThrowableClass)
 
   /** Non-inheritable lasses that are assumed to be pure for the purposes of capture checking,
    */
-  @tu lazy val pureSimpleClasses = Set(StringClass, NothingClass, NullClass)
+  @tu lazy val pureSimpleClasses =
+    Set(StringClass, NothingClass, NullClass) ++ ScalaValueClasses()
 
   @tu lazy val AbstractFunctionType: Array[TypeRef] = mkArityArray("scala.runtime.AbstractFunction", MaxImplementedFunctionArity, 0).asInstanceOf[Array[TypeRef]]
   val AbstractFunctionClassPerRun: PerRun[Array[Symbol]] = new PerRun(AbstractFunctionType.map(_.symbol.asClass))

tests/neg-custom-args/captures/exception-definitions.check

@@ -3,10 +3,6 @@
   |^
   |reference (caps.cap : Any) is not included in allowed capture set {} of pure base class class Throwable
 3 |  self: Err^ =>
--- Error: tests/neg-custom-args/captures/exception-definitions.scala:10:6 ----------------------------------------------
-10 |class Err4(c: Any^) extends AnyVal // error
-   |^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |reference (Err4.this.c : Any^) is not included in allowed capture set {} of pure base class class AnyVal
 -- Error: tests/neg-custom-args/captures/exception-definitions.scala:7:12 ----------------------------------------------
 7 |    val x = c  // error
   |            ^

tests/neg-custom-args/captures/exception-definitions.scala

@@ -7,6 +7,6 @@ def test(c: Any^) =
     val x = c  // error
   class Err3(c: Any^) extends Exception // error
 
-class Err4(c: Any^) extends AnyVal // error
+class Err4(c: Any^) extends AnyVal // was error, now ok