Scala 2 compat: enable reflectiveSelectable for language.reflectiveCalls.

library/src/scala/Selectable.scala

@@ -1,5 +1,4 @@
 package scala
-import scala.reflect.ClassTag
 
 /** A marker trait for objects that support structural selection via
  *  `selectDynamic` and `applyDynamic`
@@ -22,3 +21,15 @@ import scala.reflect.ClassTag
  *  types of the method in the structural type.
  */
 trait Selectable extends Any
+
+object Selectable:
+  /* Scala 2 compat + allowing for cross-compilation:
+   * enable scala.reflect.Selectable.reflectiveSelectable when there is an
+   * import scala.language.reflectiveCalls in scope.
+   */
+  @deprecated(
+    "import scala.reflect.Selectable.reflectiveSelectable instead of scala.language.reflectiveCalls",
+    since = "3.0")
+  implicit def reflectiveSelectableFromLangReflectiveCalls(x: Any)(
+      using scala.languageFeature.reflectiveCalls): scala.reflect.Selectable =
+    scala.reflect.Selectable.reflectiveSelectable(x)

tests/run/structural-compat.scala

@@ -0,0 +1,133 @@
+// the old reflectiveCalls still works and is equivalent to
+// import scala.reflect.Selectable.reflectiveSelectable
+import scala.language.reflectiveCalls
+
+object Test {
+  class C { type S = String; type I }
+  class D extends C { type I = Int }
+
+  type Foo = {
+    def sel0: Int
+    def sel1: Int => Int
+    def fun0(x: Int): Int
+
+    def fun1(x: Int)(y: Int): Int
+    def fun2(x: Int): Int => Int
+    def fun3(a1: Int, a2: Int, a3: Int)
+            (a4: Int, a5: Int, a6: Int)
+            (a7: Int, a8: Int, a9: Int): Int
+
+    def fun4(implicit x: Int): Int
+    def fun5(x: Int)(implicit y: Int): Int
+
+    def fun6(x: C, y: x.S): Int
+    def fun7(x: C, y: x.I): Int
+    def fun8(y: C): y.S
+    def fun9(y: C): y.I
+  }
+
+  class Foo1 {
+    def sel0: Int = 1
+    def sel1: Int => Int = x => x
+    def fun0(x: Int): Int = x
+
+    def fun1(x: Int)(y: Int): Int = x + y
+    def fun2(x: Int): Int => Int = y => x * y
+    def fun3(a1: Int, a2: Int, a3: Int)
+            (a4: Int, a5: Int, a6: Int)
+            (a7: Int, a8: Int, a9: Int): Int = -1
+
+    def fun4(implicit x: Int): Int = x
+    def fun5(x: Int)(implicit y: Int): Int = x + y
+
+    def fun6(x: C, y: x.S): Int = 1
+    def fun7(x: C, y: x.I): Int = 2
+    def fun8(y: C): y.S = "Hello"
+    def fun9(y: C): y.I = 1.asInstanceOf[y.I]
+  }
+
+  class Foo2 extends scala.Selectable {
+    def sel0: Int = 1
+    def sel1: Int => Int = x => x
+    def fun0(x: Int): Int = x
+
+    def fun1(x: Int)(y: Int): Int = x + y
+    def fun2(x: Int): Int => Int = y => x * y
+    def fun3(a1: Int, a2: Int, a3: Int)
+            (a4: Int, a5: Int, a6: Int)
+            (a7: Int, a8: Int, a9: Int): Int = -1
+
+    def fun4(implicit x: Int): Int = x
+    def fun5(x: Int)(implicit y: Int): Int = x + y
+
+    def fun6(x: C, y: x.S): Int = 1
+    def fun7(x: C, y: x.I): Int = 2
+    def fun8(y: C): y.S = "Hello"
+    def fun9(y: C): y.I = 1.asInstanceOf[y.I]
+  }
+
+  def basic(x: Foo): Unit ={
+    assert(x.sel0 == 1)
+    assert(x.sel1(2) == 2)
+    assert(x.fun0(3) == 3)
+
+    val f = x.sel1
+    assert(f(3) == 3)
+  }
+
+  def currying(x: Foo): Unit = {
+    assert(x.fun1(1)(2) == 3)
+    assert(x.fun2(1)(2) == 2)
+    assert(x.fun3(1, 2, 3)(4, 5, 6)(7, 8, 9) == -1)
+  }
+
+  def etaExpansion(x: Foo): Unit = {
+    val f0 = x.fun0(_)
+    assert(f0(2) == 2)
+
+    val f1 = x.fun0 _
+    assert(f1(2) == 2)
+
+    val f2 = x.fun1(1)(_)
+    assert(f2(2) == 3)
+
+    val f3 = x.fun1(1) _
+    assert(f3(2) == 3)
+
+    val f4 = x.fun1(1)
+    assert(f4(2) == 3)
+  }
+
+  def implicits(x: Foo) = {
+    implicit val y = 2
+    assert(x.fun4 == 2)
+    assert(x.fun5(1) == 3)
+  }
+
+  // Limited support for dependant methods
+  def dependent(x: Foo) = {
+    val y = new D
+
+    assert(x.fun6(y, "Hello") == 1)
+    // assert(x.fun7(y, 1) == 2) // error: No ClassTag available for x.I
+
+    val s = x.fun8(y)
+    assert((s: String) == "Hello")
+
+    // val i = x.fun9(y) // error: rejected (blows up in pickler if not rejected)
+    // assert((i: String) == "Hello") // error: Type mismatch: found: y.S(i); required: String
+  }
+
+  def main(args: Array[String]): Unit = {
+    basic(new Foo1)
+    currying(new Foo1)
+    etaExpansion(new Foo1)
+    implicits(new Foo1)
+    dependent(new Foo1)
+    basic(new Foo2)
+    currying(new Foo2)
+    etaExpansion(new Foo2)
+    implicits(new Foo2)
+    dependent(new Foo2)
+  }
+}