Enhancement: Move unsafe box/unbox ops into separate caps.unsafe module

Author: odersky

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

@@ -961,10 +961,11 @@ class Definitions {
   def RuntimeTupleFunctionsModule(using Context): Symbol = requiredModule("scala.runtime.TupledFunctions")
 
   @tu lazy val CapsModule: Symbol = requiredModule("scala.caps")
-    @tu lazy val Caps_unsafeBox: Symbol = CapsModule.requiredMethod("unsafeBox")
-    @tu lazy val Caps_unsafeUnbox: Symbol = CapsModule.requiredMethod("unsafeUnbox")
-    @tu lazy val Caps_unsafeBoxFunArg: Symbol = CapsModule.requiredMethod("unsafeBoxFunArg")
     @tu lazy val captureRoot: TermSymbol = CapsModule.requiredValue("*")
+    @tu lazy val CapsUnsafeModule: Symbol = requiredModule("scala.caps.unsafe")
+    @tu lazy val Caps_unsafeBox: Symbol = CapsUnsafeModule.requiredMethod("unsafeBox")
+    @tu lazy val Caps_unsafeUnbox: Symbol = CapsUnsafeModule.requiredMethod("unsafeUnbox")
+    @tu lazy val Caps_unsafeBoxFunArg: Symbol = CapsUnsafeModule.requiredMethod("unsafeBoxFunArg")
 
   // Annotation base classes
   @tu lazy val AnnotationClass: ClassSymbol = requiredClass("scala.annotation.Annotation")

library/src/scala/caps.scala

@@ -7,20 +7,23 @@ import annotation.experimental
   /** The universal capture reference */
   val `*`: Any = ()
 
-  /** If argument is of type `cs T`, converts to type `box cs T`. This
-   *  avoids the error that would be raised when boxing `*`.
-   */
-  extension [T](x: T) def unsafeBox: T = x
+  object unsafe:
 
-  /** If argument is of type `box cs T`, converts to type `cs T`. This
-   *  avoids the error that would be raised when unboxing `*`.
-   */
-  extension [T](x: T) def unsafeUnbox: T = x
+    /** If argument is of type `cs T`, converts to type `box cs T`. This
+     *  avoids the error that would be raised when boxing `*`.
+     */
+    extension [T](x: T) def unsafeBox: T = x
 
-  /** If argument is of type `box cs T`, converts to type `cs T`. This
-   *  avoids the error that would be raised when unboxing `*`.
-   */
-  extension [T, U](f: T => U) def unsafeBoxFunArg: T => U = f
+    /** If argument is of type `box cs T`, converts to type `cs T`. This
+     *  avoids the error that would be raised when unboxing `*`.
+     */
+    extension [T](x: T) def unsafeUnbox: T = x
+
+    /** If argument is of type `box cs T`, converts to type `cs T`. This
+     *  avoids the error that would be raised when unboxing `*`.
+     */
+    extension [T, U](f: T => U) def unsafeBoxFunArg: T => U = f
+  end unsafe
 
   /** Mixing in this trait forces a trait or class to be pure, i.e.
    *  have no capabilities retained in its self type.

project/MiMaFilters.scala

@@ -20,5 +20,6 @@ object MiMaFilters {
     ProblemFilters.exclude[MissingClassProblem]("scala.runtime.stdLibPatches.language$experimental$captureChecking$"),
     ProblemFilters.exclude[MissingClassProblem]("scala.caps"),
     ProblemFilters.exclude[MissingClassProblem]("scala.caps$Pure"),
+    ProblemFilters.exclude[MissingClassProblem]("scala.caps$unsafe$"),
   )
 }

tests/pos-custom-args/captures/foreach.scala

@@ -1,4 +1,4 @@
-import caps.*
+import caps.unsafe.*
 def test =
   val tasks = new collection.mutable.ArrayBuffer[() => Unit]
   val _: Unit = tasks.foreach(((task: () => Unit) => task()).unsafeBoxFunArg)

tests/pos-custom-args/captures/unsafe-unbox.scala

@@ -1,4 +1,4 @@
-import caps.*
+import caps.unsafe.*
 def test =
   var finalizeActions = collection.mutable.ListBuffer[() => Unit]()
   val action = finalizeActions.remove(0).unsafeUnbox

tests/pos-custom-args/captures/vars1.scala

@@ -1,4 +1,4 @@
-import caps.*
+import caps.unsafe.*
 
 object Test:
   type ErrorHandler = (Int, String) => Unit

tests/pos-custom-args/no-experimental/dotty-experimental.scala

@@ -1,6 +1,6 @@
 package dotty.tools
 object test {
 
-  val x = caps.unsafeBox
+  val x = caps.unsafe.unsafeBox
 
 }