Type mismatch with Binding.scala involving scala.xml.Elem

Question

I'm failing to compile a simple example of Binding.scala, and being a newbie, I have no intuition how to fix it. Maybe the README is slightly outdated? The example at https://github.com/ThoughtWorksInc/Binding.scala-sample is even older and causes deprecation warnings.

My code, which I basically stuck together from the README, and even simplified a bit:

import com.thoughtworks.binding.dom
import org.scalajs.dom.document
import scala.scalajs.js.annotation.JSExport

@JSExport
object SampleMain {

  @dom
  def table = {
    <table border="1" cellPadding="5">
      <thead>
        <tr>
          <th>Name</th>
          <th>E-mail</th>
        </tr>
      </thead>
      <tbody>
      </tbody>
    </table>
  }

  @JSExport
  def main(): Unit = {
    dom.render(document.body, table)
  }

}

fastOptJS causes a compile error:

SampleMain.scala:25:9: overloaded method value render with alternatives:
[error]   (parent: org.scalajs.dom.raw.Node,children: com.thoughtworks.binding.Binding[com.thoughtworks.binding.Binding.BindingSeq[org.scalajs.dom.raw.Node]],dummy: Unit)Unit <and>
[error]   (parent: org.scalajs.dom.raw.Node,children: com.thoughtworks.binding.Binding.BindingSeq[org.scalajs.dom.raw.Node])Unit <and>
[error]   (parent: org.scalajs.dom.raw.Node,child: com.thoughtworks.binding.Binding[org.scalajs.dom.raw.Node])Unit
[error]  cannot be applied to (org.scalajs.dom.raw.HTMLElement, scala.xml.Elem)
[error]     dom.render(document.body, table)
[error]         ^

I suspected a problem with type inference and tried this type annotation: def table: com.thoughtworks.binding.Binding[org.scalajs.dom.html.Table] but this caused another error:

SampleMain.scala:11:6: type mismatch;
[error]  found   : scala.xml.Elem
[error]  required: com.thoughtworks.binding.Binding[org.scalajs.dom.html.Table]
[error]     (which expands to)  com.thoughtworks.binding.Binding[org.scalajs.dom.raw.HTMLTableElement]
[error]     <table border="1" cellPadding="5">
[error]      ^

I'd appreciate an explanation what is going wrong here.

---

Solution: https://stackoverflow.com/a/55137909/1862339

Answer 1

Turns out the problem was that the paradise compiler plugin was not picked up in my case. I'm building an SBT multi-project with Binding.scala in a sub-project only, and addCompilerPlugin does not propagate to sub-projects. To make it work, it needs to be added to the sub-project's settings like this:

lazy val client = (project in file("client"))
  .settings(
    libraryDependencies ++= Seq(
      "com.thoughtworks.binding" %%% "dom" % "11.6.0"
    ),
    addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)
  )
  .enablePlugins(ScalaJSPlugin)

Before I had addCompilerPlugin at the top-level of build.sbt, which did not work and caused the compile error.