Add Reusability for component refs

library/coreGeneric/src/main/scala/japgolly/scalajs/react/Reusability.scala

@@ -351,6 +351,14 @@ object Reusability extends ReusabilityMacros with ScalaVersionSpecificReusabilit
   implicit def refFullF[F[_], I, A, O]: Reusability[Ref.FullF[F, I, A, O]] =
     refRaw[A | Null].contramap(_.raw)
 
+  /** Updating a reference doesn't trigger a component re-rendering, nor is the current reference value considered for reusability.
+   *
+   * Any `map`/`contramap` functions installed in the ref are ignored for the sake of reusability. If this is undesirable, pass around
+   * a [[Reusable]] ref instead.
+   */
+  implicit def refToComponentF[F[_], I, R, O, C]: Reusability[Ref.ToComponentF[F, I, R, O, C]] =
+    refFullF[F, I, R, O].narrow
+
   /** Updating a reference doesn't trigger a component re-rendering, nor is the current reference value considered for reusability. */
   implicit def nonEmptyRefHandleF[F[_], A]: Reusability[NonEmptyRef.HandleF[F, A]] =
     refRaw[A].contramap(_.raw)

library/tests/src/test/scala/japgolly/scalajs/react/core/ReusabilityTest.scala

@@ -120,6 +120,13 @@ object ReusabilityTest extends TestSuite {
       assertEq(r.test(a, b), a == b)
   }
 
+  private def testByRef[A: Reusability](create: => A)(implicit l: Line): Unit = {
+    val a = create
+    val b = create
+    assertEq(a ~=~ a, true)
+    assertEq(a ~=~ b, false)
+  }
+
   override def tests = Tests {
 
     "macros" - {
@@ -477,5 +484,18 @@ object ReusabilityTest extends TestSuite {
       assert(BigInt("10") ~=~ BigInt("10"))
       assert(BigInt("10") ~/~ BigInt("11"))
     }
+
+    "ref" - {
+      "handle" - testByRef(Ref[Int]: Ref.Handle[Int])
+      "simple" - testByRef(Ref[Int])
+      "vdom"   - testByRef(Ref.toAnyVdom())
+      "scala"  - testByRef(Ref.toScalaComponent(SampleComponent1.component))
+      "js"     - testByRef(Ref.toJsComponent(JsComponentEs6PTest.Component))
+    }
+
+    "nonEmptyRef" - {
+      "handle" - testByRef(NonEmptyRef[Int](6): NonEmptyRef.Handle[Int])
+      "simple" - testByRef(NonEmptyRef[Int](6))
+    }
   }
 }