Move Pure to caps and make it non-experimental (#23745)

natsukagami · web-flow · commit 25aadca2b7c9 · 2025-08-15T22:30:12.000+01:00
This PR consists of two commits: 
- The first one moves `scala.Pure` to `scala.caps.Pure`, updating all
relevant references and tests
- The second one drops `@experimental`, marking it stable in accordance
with the status of `scala.caps`'s other non-experimental symbols.

Pure has always been a capture-checking only class.
diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
@@ -1020,7 +1020,7 @@ class Definitions {
     @tu lazy val Caps_ContainsModule: Symbol = requiredModule("scala.caps.Contains")
     @tu lazy val Caps_containsImpl: TermSymbol = Caps_ContainsModule.requiredMethod("containsImpl")
 
-  @tu lazy val PureClass: ClassSymbol = requiredClass("scala.Pure")
+  @tu lazy val PureClass: ClassSymbol = requiredClass("scala.caps.Pure")
 
   // Annotation base classes
   @tu lazy val AnnotationClass: ClassSymbol = requiredClass("scala.annotation.Annotation")
diff --git a/compiler/src/dotty/tools/dotc/core/TypeErasure.scala b/compiler/src/dotty/tools/dotc/core/TypeErasure.scala
@@ -109,9 +109,9 @@ object TypeErasure {
         case _ => -1
 
   def normalizeClass(cls: ClassSymbol)(using Context): ClassSymbol = {
+    if (defn.specialErasure.contains(cls))
+      return defn.specialErasure(cls).uncheckedNN
     if (cls.owner == defn.ScalaPackageClass) {
-      if (defn.specialErasure.contains(cls))
-        return defn.specialErasure(cls).uncheckedNN
       if (cls == defn.UnitClass)
         return defn.BoxedUnitClass
     }
diff --git a/compiler/src/dotty/tools/dotc/transform/Erasure.scala b/compiler/src/dotty/tools/dotc/transform/Erasure.scala
@@ -191,7 +191,7 @@ class Erasure extends Phase with DenotTransformer {
       || isAllowed(defn.TupleClass, "Tuple.scala")
       || isAllowed(defn.NonEmptyTupleClass, "Tuple.scala")
       || isAllowed(defn.PairClass, "Tuple.scala")
-      || isAllowed(defn.PureClass, "Pure.scala"),
+      || isAllowed(defn.PureClass, /* caps/ */ "Pure.scala"),
       i"The type $tp - ${tp.toString} of class ${tp.getClass} of tree $tree : ${tree.tpe} / ${tree.getClass} is illegal after erasure, phase = ${ctx.phase.prev}")
   }
 }
diff --git a/library/src/scala/caps/Pure.scala b/library/src/scala/caps/Pure.scala
@@ -1,9 +1,9 @@
 package scala
-import annotation.experimental
+package caps
 
 /** A marker trait that declares that all inheriting classes are "pure" in the
  *  sense that their values retain no capabilities including capabilities needed
  *  to perform effects. This has formal meaning only under capture checking.
  */
-@experimental trait Pure:
+trait Pure:
   this: Pure =>
diff --git a/project/Build.scala b/project/Build.scala
@@ -1100,7 +1100,6 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/CanEqual.scala"),
         file(s"${baseDirectory.value}/src/scala/Conversion.scala"),
         file(s"${baseDirectory.value}/src/scala/PolyFunction.scala"),
-        file(s"${baseDirectory.value}/src/scala/Pure.scala"),
         file(s"${baseDirectory.value}/src/scala/IArray.scala"),
         file(s"${baseDirectory.value}/src/scala/CanThrow.scala"),
         file(s"${baseDirectory.value}/src/scala/Tuple.scala"),
@@ -1113,6 +1112,7 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/util/NotGiven.scala"),
         file(s"${baseDirectory.value}/src/scala/util/boundary.scala"),
         file(s"${baseDirectory.value}/src/scala/caps/package.scala"),
+        file(s"${baseDirectory.value}/src/scala/caps/Pure.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/TypeTest.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/Selectable.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/Typeable.scala"),
@@ -1238,7 +1238,6 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/CanEqual.scala"),
         file(s"${baseDirectory.value}/src/scala/Conversion.scala"),
         file(s"${baseDirectory.value}/src/scala/PolyFunction.scala"),
-        file(s"${baseDirectory.value}/src/scala/Pure.scala"),
         file(s"${baseDirectory.value}/src/scala/IArray.scala"),
         file(s"${baseDirectory.value}/src/scala/CanThrow.scala"),
         file(s"${baseDirectory.value}/src/scala/Tuple.scala"),
@@ -1251,6 +1250,7 @@ object Build {
         file(s"${baseDirectory.value}/src/scala/util/NotGiven.scala"),
         file(s"${baseDirectory.value}/src/scala/util/boundary.scala"),
         file(s"${baseDirectory.value}/src/scala/caps/package.scala"),
+        file(s"${baseDirectory.value}/src/scala/caps/Pure.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/TypeTest.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/Selectable.scala"),
         file(s"${baseDirectory.value}/src/scala/reflect/Typeable.scala"),
diff --git a/scala2-library-cc/src/scala/collection/Factory.scala b/scala2-library-cc/src/scala/collection/Factory.scala
@@ -31,7 +31,7 @@ import caps.unsafe.unsafeAssumePure
   * @tparam A Type of elements (e.g. `Int`, `Boolean`, etc.)
   * @tparam C Type of collection (e.g. `List[Int]`, `TreeMap[Int, String]`, etc.)
   */
-trait Factory[-A, +C] extends Pure {
+trait Factory[-A, +C] extends caps.Pure {
 
   /**
     * @return A collection of type `C` containing the same elements
@@ -82,7 +82,7 @@ object Factory {
   * @define coll collection
   * @define Coll `Iterable`
   */
-trait IterableFactory[+CC[_]] extends Serializable, Pure {
+trait IterableFactory[+CC[_]] extends Serializable, caps.Pure {
 
   /** Creates a target $coll from an existing source collection
     *
@@ -389,7 +389,7 @@ trait SpecificIterableFactory[-A, +C] extends Factory[A, C] {
   * @define coll collection
   * @define Coll `Iterable`
   */
-trait MapFactory[+CC[_, _]] extends Serializable, Pure {
+trait MapFactory[+CC[_, _]] extends Serializable, caps.Pure {
 
   /**
    * An empty Map
@@ -462,7 +462,7 @@ object MapFactory {
   * @define coll collection
   * @define Coll `Iterable`
   */
-trait EvidenceIterableFactory[+CC[_], Ev[_]] extends Serializable, Pure {
+trait EvidenceIterableFactory[+CC[_], Ev[_]] extends Serializable, caps.Pure {
 
   def from[E : Ev](it: IterableOnce[E]^): CC[E]
 
diff --git a/scala2-library-cc/src/scala/collection/Map.scala b/scala2-library-cc/src/scala/collection/Map.scala
@@ -26,7 +26,7 @@ trait Map[K, +V]
     with MapOps[K, V, Map, Map[K, V]]
     with MapFactoryDefaults[K, V, Map, Iterable]
     with Equals
-    with Pure {
+    with caps.Pure {
 
   def mapFactory: scala.collection.MapFactory[Map] = Map
 
diff --git a/scala2-library-cc/src/scala/collection/Set.scala b/scala2-library-cc/src/scala/collection/Set.scala
@@ -26,7 +26,7 @@ trait Set[A]
     with SetOps[A, Set, Set[A]]
     with Equals
     with IterableFactoryDefaults[A, Set]
-    with Pure {
+    with caps.Pure {
   self: Set[A] =>
 
   def canEqual(that: Any) = true
diff --git a/scala2-library-cc/src/scala/collection/SortedMap.scala b/scala2-library-cc/src/scala/collection/SortedMap.scala
@@ -51,7 +51,7 @@ trait SortedMap[K, +V]
 trait SortedMapOps[K, +V, +CC[X, Y] <: Map[X, Y] with SortedMapOps[X, Y, CC, _], +C <: SortedMapOps[K, V, CC, C]]
   extends MapOps[K, V, Map, C]
      with SortedOps[K, C]
-     with Pure {
+     with caps.Pure {
 
   /** The companion object of this sorted map, providing various factory methods.
     *
diff --git a/scala2-library-cc/src/scala/collection/StepperShape.scala b/scala2-library-cc/src/scala/collection/StepperShape.scala
@@ -20,7 +20,7 @@ import scala.collection.Stepper.EfficientSplit
 /** An implicit StepperShape instance is used in the [[IterableOnce.stepper]] to return a possibly
   * specialized Stepper `S` according to the element type `T`.
   */
-sealed trait StepperShape[-T, S <: Stepper[_]^] extends Pure {
+sealed trait StepperShape[-T, S <: Stepper[_]^] extends caps.Pure {
   /** Return the Int constant (as defined in the `StepperShape` companion object) for this `StepperShape`. */
   def shape: StepperShape.Shape
 
diff --git a/scala2-library-cc/src/scala/collection/StrictOptimizedMapOps.scala b/scala2-library-cc/src/scala/collection/StrictOptimizedMapOps.scala
@@ -24,7 +24,7 @@ import language.experimental.captureChecking
 trait StrictOptimizedMapOps[K, +V, +CC[_, _] <: IterableOps[_, AnyConstr, _], +C]
   extends MapOps[K, V, CC, C]
     with StrictOptimizedIterableOps[(K, V), Iterable, C]
-    with Pure {
+    with caps.Pure {
 
   override def map[K2, V2](f: ((K, V)) => (K2, V2)): CC[K2, V2] =
     strictOptimizedMap(mapFactory.newBuilder, f)
diff --git a/scala2-library-cc/src/scala/collection/View.scala b/scala2-library-cc/src/scala/collection/View.scala
@@ -99,7 +99,7 @@ object View extends IterableFactory[View] {
 
   /** A view with given elements */
   @SerialVersionUID(3L)
-  class Elems[A](xs: A*) extends AbstractView[A], Pure {
+  class Elems[A](xs: A*) extends AbstractView[A], caps.Pure {
     def iterator = xs.iterator
     override def knownSize = xs.knownSize
     override def isEmpty: Boolean = xs.isEmpty
diff --git a/scala2-library-cc/src/scala/collection/immutable/ArraySeq.scala b/scala2-library-cc/src/scala/collection/immutable/ArraySeq.scala
@@ -40,7 +40,7 @@ sealed abstract class ArraySeq[+A]
     with StrictOptimizedSeqOps[A, ArraySeq, ArraySeq[A]]
     with EvidenceIterableFactoryDefaults[A, ArraySeq, ClassTag]
     with Serializable
-    with Pure {
+    with caps.Pure {
 
   /** The tag of the element type. This does not have to be equal to the element type of this ArraySeq. A primitive
     * ArraySeq can be backed by an array of boxed values and a reference ArraySeq can be backed by an array of a supertype
diff --git a/scala2-library-cc/src/scala/collection/immutable/Map.scala b/scala2-library-cc/src/scala/collection/immutable/Map.scala
@@ -314,7 +314,7 @@ object Map extends MapFactory[Map] {
       override protected def nextResult(k: K, v: V): V = v
     }
 
-    private abstract class Map2Iterator[A] extends AbstractIterator[A], Pure {
+    private abstract class Map2Iterator[A] extends AbstractIterator[A], caps.Pure {
       private[this] var i = 0
       override def hasNext: Boolean = i < 2
       override def next(): A = {
@@ -417,7 +417,7 @@ object Map extends MapFactory[Map] {
       override protected def nextResult(k: K, v: V): V = v
     }
 
-    private abstract class Map3Iterator[A] extends AbstractIterator[A], Pure {
+    private abstract class Map3Iterator[A] extends AbstractIterator[A], caps.Pure {
       private[this] var i = 0
       override def hasNext: Boolean = i < 3
       override def next(): A = {
@@ -537,7 +537,7 @@ object Map extends MapFactory[Map] {
       override protected def nextResult(k: K, v: V): V = v
     }
 
-    private abstract class Map4Iterator[A] extends AbstractIterator[A], Pure {
+    private abstract class Map4Iterator[A] extends AbstractIterator[A], caps.Pure {
       private[this] var i = 0
       override def hasNext: Boolean = i < 4
       override def next(): A = {
diff --git a/scala2-library-cc/src/scala/collection/immutable/Set.scala b/scala2-library-cc/src/scala/collection/immutable/Set.scala
@@ -129,7 +129,7 @@ object Set extends IterableFactory[Set] {
   private[collection] def emptyInstance: Set[Any] = EmptySet
 
   @SerialVersionUID(3L)
-  private abstract class SetNIterator[A](n: Int) extends AbstractIterator[A], Serializable, Pure {
+  private abstract class SetNIterator[A](n: Int) extends AbstractIterator[A], Serializable, caps.Pure {
     private[this] var current = 0
     private[this] var remainder = n
     override def knownSize: Int = remainder
diff --git a/scala2-library-cc/src/scala/collection/immutable/WrappedString.scala b/scala2-library-cc/src/scala/collection/immutable/WrappedString.scala
@@ -36,7 +36,7 @@ import language.experimental.captureChecking
 final class WrappedString(private val self: String) extends AbstractSeq[Char] with IndexedSeq[Char]
   with IndexedSeqOps[Char, IndexedSeq, WrappedString]
   with Serializable
-  with Pure {
+  with caps.Pure {
 
   def apply(i: Int): Char = self.charAt(i)
 
diff --git a/scala2-library-cc/src/scala/collection/mutable/ArrayBuffer.scala b/scala2-library-cc/src/scala/collection/mutable/ArrayBuffer.scala
@@ -359,7 +359,7 @@ object ArrayBuffer extends StrictOptimizedSeqFactory[ArrayBuffer] {
 
 // TODO: use `CheckedIndexedSeqView.Id` once we can change the return type of `ArrayBuffer#view`
 final class ArrayBufferView[A] private[mutable](underlying: ArrayBuffer[A], mutationCount: () -> Int)
-  extends AbstractIndexedSeqView[A], Pure {
+  extends AbstractIndexedSeqView[A], caps.Pure {
   /* Removed since it poses problems for capture checking
   @deprecated("never intended to be public; call ArrayBuffer#view instead", since = "2.13.7")
   def this(array: Array[AnyRef], length: Int) = {
diff --git a/scala2-library-cc/src/scala/collection/mutable/ArraySeq.scala b/scala2-library-cc/src/scala/collection/mutable/ArraySeq.scala
@@ -41,7 +41,7 @@ sealed abstract class ArraySeq[T]
     with IndexedSeqOps[T, ArraySeq, ArraySeq[T]]
     with StrictOptimizedSeqOps[T, ArraySeq, ArraySeq[T]]
     with Serializable
-    with Pure {
+    with caps.Pure {
 
   override def iterableFactory: scala.collection.SeqFactory[ArraySeq] = ArraySeq.untagged
 
diff --git a/scala2-library-cc/src/scala/collection/mutable/Map.scala b/scala2-library-cc/src/scala/collection/mutable/Map.scala
@@ -71,7 +71,7 @@ trait MapOps[K, V, +CC[X, Y] <: MapOps[X, Y, CC, _], +C <: MapOps[K, V, CC, C]]
     with Builder[(K, V), C]
     with Growable[(K, V)]
     with Shrinkable[K]
-    with Pure {
+    with caps.Pure {
 
   def result(): C = coll
 
diff --git a/tests/neg-custom-args/captures/leaked-curried-shared.scala b/tests/neg-custom-args/captures/leaked-curried-shared.scala
@@ -8,11 +8,11 @@ trait Box:
 
 def main(): Unit =
   val leaked = withCap: (io: Cap) =>
-    class Fuzz extends Box, Pure:
+    class Fuzz extends Box, caps.Pure:
       self =>
       val get: () ->{} () ->{io} Cap =
         () => () => io // error
-    class Foo extends Box, Pure:
+    class Foo extends Box, caps.Pure:
       val get: () ->{} () ->{io} Cap =
         () => () => io // error
     new Foo
diff --git a/tests/neg-custom-args/captures/leaked-curried.scala b/tests/neg-custom-args/captures/leaked-curried.scala
@@ -8,11 +8,11 @@ trait Box:
 
 def main(): Unit =
   val leaked = withCap: (io: Cap^) =>
-    class Fuzz extends Box, Pure:
+    class Fuzz extends Box, caps.Pure:
       self =>
       val get: () ->{} () ->{io} Cap^ = // error
         () => () => io // error
-    class Foo extends Box, Pure:
+    class Foo extends Box, caps.Pure:
       val get: () ->{} () ->{io} Cap^ = // error
         () => () => io // error
     new Foo
diff --git a/tests/neg-custom-args/captures/selftype.scala b/tests/neg-custom-args/captures/selftype.scala
@@ -1,4 +1,4 @@
-@annotation.experimental class C(x: () => Unit) extends Pure // error
+@annotation.experimental class C(x: () => Unit) extends caps.Pure // error
 
-@annotation.experimental class D(@annotation.constructorOnly x: () => Unit) extends Pure // ok
+@annotation.experimental class D(@annotation.constructorOnly x: () => Unit) extends caps.Pure // ok
 
diff --git a/tests/pos-custom-args/captures/cc-experimental.scala b/tests/pos-custom-args/captures/cc-experimental.scala
@@ -5,9 +5,9 @@ package scala.runtime
 import language.experimental.captureChecking
 
 object test:
-  type T = Pure
+  type T = caps.Pure
 
-class Foo extends Object, Pure:
-  val x: Pure = ???
+class Foo extends Object, caps.Pure:
+  val x: caps.Pure = ???
   def foo() = ()
 
diff --git a/tests/pos-custom-args/captures/dependent-pure.scala b/tests/pos-custom-args/captures/dependent-pure.scala
@@ -2,4 +2,4 @@ import language.experimental.captureChecking
 class ContextCls
 type Context = ContextCls^
 
-class Filtered(p: (c: Context) ?-> () ->{c} Boolean) extends Pure
+class Filtered(p: (c: Context) ?-> () ->{c} Boolean) extends caps.Pure
diff --git a/tests/pos-custom-args/captures/invariant-cc.scala b/tests/pos-custom-args/captures/invariant-cc.scala
@@ -1,7 +1,7 @@
 import language.experimental.captureChecking
 import scala.annotation.unchecked.uncheckedVariance
 
-trait IterableFactory[+CC[_]] extends Pure:
+trait IterableFactory[+CC[_]] extends caps.Pure:
 
   def fill[A](n: Int)(elem: => A): CC[A]^{elem} = ???
   def fill[A](n1: Int, n2: Int)(elem: => A): CC[(CC[A]^{elem}) @uncheckedVariance]^{elem} =
diff --git a/tests/pos-custom-args/captures/steppers.scala b/tests/pos-custom-args/captures/steppers.scala
@@ -4,12 +4,12 @@ trait Stepper[+A]
 object Stepper:
   trait EfficientSplit
 
-sealed trait StepperShape[-T, S <: Stepper[_]^] extends Pure
+sealed trait StepperShape[-T, S <: Stepper[_]^] extends caps.Pure
 
 trait IterableOnce[+A] extends Any:
   def stepper[S <: Stepper[_]^{this}](implicit shape: StepperShape[A, S]): S = ???
 
-sealed abstract class ArraySeq[T] extends IterableOnce[T], Pure:
+sealed abstract class ArraySeq[T] extends IterableOnce[T], caps.Pure:
   def array: Array[_]
 
   def sorted[B >: T](implicit ord: Ordering[B]): ArraySeq[T] =
@@ -20,6 +20,6 @@ object ArraySeq:
 
   def make[T](x: Array[T]): ArraySeq[T] = ???
 
-  final class ofRef[T <: AnyRef](val array: Array[T]) extends ArraySeq[T], Pure:
+  final class ofRef[T <: AnyRef](val array: Array[T]) extends ArraySeq[T], caps.Pure:
     override def stepper[S <: Stepper[_]](implicit shape: StepperShape[T, S]): S & Stepper.EfficientSplit = ???
 
diff --git a/tests/run-custom-args/captures/minicheck.scala b/tests/run-custom-args/captures/minicheck.scala
@@ -3,7 +3,7 @@ import compiletime.uninitialized
 import annotation.{experimental, tailrec, constructorOnly}
 import collection.mutable
 
-case class Symbol(name: String, initOwner: Symbol | Null) extends Pure:
+case class Symbol(name: String, initOwner: Symbol | Null) extends caps.Pure:
   def owner = initOwner.nn
   private var myInfo: Type = uninitialized
   def infoOrCompleter: Type = myInfo
@@ -27,7 +27,7 @@ object NoSymbol extends Symbol("", null):
   override def exists: Boolean = false
   override def orElse(alt: => Symbol): Symbol = alt
 
-abstract class Type extends Pure:
+abstract class Type extends caps.Pure:
   def exists = true
   def show: String
 case class IntType()(using @constructorOnly c: Context) extends Type:
diff --git a/tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala b/tests/run-tasty-inspector/stdlibExperimentalDefinitions.scala
@@ -30,7 +30,6 @@ val experimentalDefinitionInLibrary = Set(
   "scala.annotation.retains",
   "scala.annotation.retainsByName",
   "scala.annotation.retainsCap",
-  "scala.Pure",
   "scala.caps.CapSet",
   "scala.caps.Contains",
   "scala.caps.Contains$",

Original file line number	Diff line number	Diff line change
`@@ -191,7 +191,7 @@ class Erasure extends Phase with DenotTransformer {`
`191`	`191`	`\|\| isAllowed(defn.TupleClass, "Tuple.scala")`
`192`	`192`	`\|\| isAllowed(defn.NonEmptyTupleClass, "Tuple.scala")`
`193`	`193`	`\|\| isAllowed(defn.PairClass, "Tuple.scala")`
`194`		`- \|\| isAllowed(defn.PureClass, "Pure.scala"),`
	`194`	`+ \|\| isAllowed(defn.PureClass, /* caps/ */ "Pure.scala"),`
`195`	`195`	`i"The type $tp - ${tp.toString} of class ${tp.getClass} of tree $tree : ${tree.tpe} / ${tree.getClass} is illegal after erasure, phase = ${ctx.phase.prev}")`
`196`	`196`	`}`
`197`	`197`	`}`
Original file line number	Diff line number	Diff line change
`@@ -51,7 +51,7 @@ trait SortedMap[K, +V]`
`51`	`51`	`trait SortedMapOps[K, +V, +CC[X, Y] <: Map[X, Y] with SortedMapOps[X, Y, CC, _], +C <: SortedMapOps[K, V, CC, C]]`
`52`	`52`	`extends MapOps[K, V, Map, C]`
`53`	`53`	`with SortedOps[K, C]`
`54`		`- with Pure {`
	`54`	`+ with caps.Pure {`
`55`	`55`
`56`	`56`	`/** The companion object of this sorted map, providing various factory methods.`
`57`	`57`	`*`