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scalascala.jsscala.rxscalatags

Scala.Rx with ScalaTags example compilation error

I tried the scala.js example https://github.com/lihaoyi/hands-on-scala-js and its scala.rx with scalatags part in advanced section. Example compiles are runs fine but when I try to use the latest scala.rx v 0.3.1 I get following compile errors:

[info] Compiling 19 Scala sources to /home/code/workspace/hands-on-scala-js-master/examples/demos/target/scala-2.11/classes...
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:14: 
[error] This Rx might leak! Either explicitly mark it unsafe (Rx.unsafe) or make an implicit RxCtx available
[error] in the enclosing scope, for example, by adding (implicit ctx: Ctx.Owner) to line 12: method main
[error]     val numChars = Rx{txt().length}
[error]                      ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:15: 
[error] This Rx might leak! Either explicitly mark it unsafe (Rx.unsafe) or make an implicit RxCtx available
[error] in the enclosing scope, for example, by adding (implicit ctx: Ctx.Owner) to line 12: method main
[error]     val numWords = Rx{
[error]                      ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:55: 
[error] This Rx might leak! Either explicitly mark it unsafe (Rx.unsafe) or make an implicit RxCtx available
[error] in the enclosing scope, for example, by adding (implicit ctx: Ctx.Owner) to line 42: method main2
[error]       for(fruit <- fruits) yield Rx {
[error]                                     ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:65: diverging implicit expansion for type Nothing => scalatags.JsDom.Frag
[error] starting with method rxFrag in object BasicRx
[error]         ul(fragments)
[error]            ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:72: not found: value Obs
[error]     Obs(r, skipInitial = true){
[error]     ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:72: not found: value skipInitial
[error]     Obs(r, skipInitial = true){
[error]            ^
[warn] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/webpage/WeatherSearch.scala:53: non-variable type argument scala.scalajs.js.Dynamic in type pattern scala.scalajs.js.Array[scala.scalajs.js.Dynamic] is unchecked since it is eliminated by erasure
[warn]         case jsonlist: js.Array[js.Dynamic] =>
[warn]                           ^
[warn] one warning found
[error] 6 errors found
[error] (demos/compile:compile) Compilation failed

It seems that ownership concept has somehow changed and also there is no Obs companion object.

I tried to fix these erros in BasicRx.scala: Old code:

@JSExport
def main(container: html.Div) = {

New code (Leakage fix):

@JSExport
def main(container: html.Div) = {
  implicit val ctx: Ctx.Owner = Ctx.Owner.safe()

Old code:

  implicit def rxFrag[T <% Frag](r: Rx[T]): Frag = {
    def rSafe: dom.Node = span(r()).render
    var last = rSafe

    Obs(r, skipInitial = true){
      val newLast = rSafe
      js.Dynamic.global.last = last
      last.parentNode.replaceChild(newLast, last)
      last = newLast
    }
    last
  }

New code (conversion fix):

  implicit def rxFrag[T <% Frag](r: Rx[T]): Frag = {
    def rSafe: dom.Node = span(r()).render
    var last = rSafe

    val thunk = () => {
      val newLast = rSafe
      js.Dynamic.global.last = last
      last.parentNode.replaceChild(newLast, last)
      last = newLast
    }
    new Obs(thunk, r)
    last
  }

But still get following error:

[info] Compiling 19 Scala sources to /home/code/workspace/hands-on-scala-js-master/examples/demos/target/scala-2.11/classes...
[warn] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/webpage/WeatherSearch.scala:53: non-variable type argument   scala.scalajs.js.Dynamic in type pattern scala.scalajs.js.Array[scala.scalajs.js.Dynamic] is unchecked since it is eliminated by erasure
[warn]         case jsonlist: js.Array[js.Dynamic] =>
[warn]                           ^
[error] /home/code/workspace/hands-on-scala-js-master/examples/demos/src/main/scala/advanced/BasicRx.scala:74: No implicit Ctx.Data is available here!
[error]     def rSafe: dom.Node = span(r()).render
[error]                                 ^

How to fix this one? And is the leakage fix correctly done?

Updating scalatags to 0.5.4. did not have any affect.

Solution

  • I helped contribute to the 0.3.x branch of scala.rx - and yep, the api is largely changed from 0.2.x. However, I also maintain a more recent version of the "framework" code you are looking at here:

    https://github.com/Voltir/framework.rx/blob/master/src/main/scala/framework/Framework.scala

    Also, it turns out that in the case of using js.App and its def main(), the correct way to get a Ctx.Owner is to use import rx.Ctx.Owner.Unsafe._. So long as that main function is evaluated a finite number of times (ie once) per page load, it is safe to allow a "leak". Your usage of Ctx.Owner.safe() wont work because the compiler can't prove that main is only called a finite number of times.

    One complete example of all of this can be found in the demo project of this library: https://github.com/Voltir/route.rx