Reject scala.runtime's mutable refs in safe mode

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

@@ -96,6 +96,35 @@ object SafeRefs {
     rejectSafe("scala.annotation.unchecked.uncheckedStable")
     rejectSafe("scala.annotation.unchecked.uncheckedVariance")
     rejectSafe("scala.annotation.unchecked.uncheckedCaptures")
+    // Reject mutable classes in scala.runtime
+    rejectSafe("scala.runtime.BooleanRef")
+    rejectSafe("scala.runtime.ByteRef")
+    rejectSafe("scala.runtime.CharRef")
+    rejectSafe("scala.runtime.DoubleRef")
+    rejectSafe("scala.runtime.FloatRef")
+    rejectSafe("scala.runtime.IntRef")
+    rejectSafe("scala.runtime.LongRef")
+    rejectSafe("scala.runtime.ShortRef")
+    rejectSafe("scala.runtime.ObjectRef")
+    rejectSafe("scala.runtime.VolatileBooleanRef")
+    rejectSafe("scala.runtime.VolatileByteRef")
+    rejectSafe("scala.runtime.VolatileCharRef")
+    rejectSafe("scala.runtime.VolatileDoubleRef")
+    rejectSafe("scala.runtime.VolatileFloatRef")
+    rejectSafe("scala.runtime.VolatileIntRef")
+    rejectSafe("scala.runtime.VolatileLongRef")
+    rejectSafe("scala.runtime.VolatileShortRef")
+    rejectSafe("scala.runtime.VolatileObjectRef")
+    rejectSafe("scala.runtime.LazyRef")
+    rejectSafe("scala.runtime.LazyBoolean")
+    rejectSafe("scala.runtime.LazyByte")
+    rejectSafe("scala.runtime.LazyChar")
+    rejectSafe("scala.runtime.LazyShort")
+    rejectSafe("scala.runtime.LazyInt")
+    rejectSafe("scala.runtime.LazyLong")
+    rejectSafe("scala.runtime.LazyFloat")
+    rejectSafe("scala.runtime.LazyDouble")
+    rejectSafe("scala.runtime.LazyUnit")
 
   private def fail(sym: Symbol, reason: String, pos: SrcPos)(using Context) =
     report.error(em"Cannot refer to ${sym.sanitizedDescription}${sym.showExtendedLocation} from safe code since $reason", pos)

tests/neg-custom-args/captures/safemode-refs.check

@@ -0,0 +1,48 @@
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:4:16 ------------------------------------------------------
+4 |  val ref = new scala.runtime.LongRef(0L)  // error
+  |                ^^^^^^^^^^^^^^^^^^^^^
+  |              Cannot refer to class LongRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:6:8 -------------------------------------------------------
+6 |    ref.elem = 42  // error
+  |    ^^^^^^^^
+  |    Cannot refer to class LongRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:8:16 ------------------------------------------------------
+8 |  val ref = new scala.runtime.ObjectRef("")  // error
+  |                ^^^^^^^^^^^^^^^^^^^^^^^
+  |            Cannot refer to class ObjectRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:10:8 ------------------------------------------------------
+10 |    ref.elem = "sk-123456"  // error
+   |    ^^^^^^^^
+   |    Cannot refer to class ObjectRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:12:16 -----------------------------------------------------
+12 |  val ref = new scala.runtime.VolatileIntRef(0)  // error
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     Cannot refer to class VolatileIntRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:14:8 ------------------------------------------------------
+14 |    ref.elem = 42  // error
+   |    ^^^^^^^^
+   |    Cannot refer to class VolatileIntRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:16:16 -----------------------------------------------------
+16 |  val ref = new scala.runtime.VolatileObjectRef[String]("")  // error
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |  Cannot refer to class VolatileObjectRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:18:8 ------------------------------------------------------
+18 |    ref.elem = "secret"  // error
+   |    ^^^^^^^^
+   |  Cannot refer to class VolatileObjectRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:20:16 -----------------------------------------------------
+20 |  val ref = new scala.runtime.LazyInt  // error
+   |                ^^^^^^^^^^^^^^^^^^^^^
+   |            Cannot refer to class LazyInt in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:22:8 ------------------------------------------------------
+22 |    ref.initialize(42)  // error
+   |    ^^^^^^^^^^^^^^
+   |    Cannot refer to class LazyInt in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:24:16 -----------------------------------------------------
+24 |  val ref = new scala.runtime.LazyRef[String]  // error
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            Cannot refer to class LazyRef in package scala.runtime from safe code since it is tagged @rejectSafe
+-- Error: tests/neg-custom-args/captures/safemode-refs.scala:26:8 ------------------------------------------------------
+26 |    ref.initialize("hello")  // error
+   |    ^^^^^^^^^^^^^^
+   |    Cannot refer to class LazyRef in package scala.runtime from safe code since it is tagged @rejectSafe

tests/neg-custom-args/captures/safemode-refs.scala

@@ -0,0 +1,26 @@
+import language.experimental.safe
+def assertPure(op: () -> Unit): Unit = ()
+def test1(): Unit =
+  val ref = new scala.runtime.LongRef(0L)  // error
+  assertPure: () =>
+    ref.elem = 42  // error
+def test2(): Unit =
+  val ref = new scala.runtime.ObjectRef("")  // error
+  assertPure: () =>
+    ref.elem = "sk-123456"  // error
+def test3(): Unit =
+  val ref = new scala.runtime.VolatileIntRef(0)  // error
+  assertPure: () =>
+    ref.elem = 42  // error
+def test4(): Unit =
+  val ref = new scala.runtime.VolatileObjectRef[String]("")  // error
+  assertPure: () =>
+    ref.elem = "secret"  // error
+def test5(): Unit =
+  val ref = new scala.runtime.LazyInt  // error
+  assertPure: () =>
+    ref.initialize(42)  // error
+def test6(): Unit =
+  val ref = new scala.runtime.LazyRef[String]  // error
+  assertPure: () =>
+    ref.initialize("hello")  // error