🚓 testing library to use the Scala Presentation Compiler
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PC Plod is a testing library for macro and compiler plugin authors to make assertions of their libraries in the Presentation Compiler, i.e. ENSIME and Scala IDE.


Published as a regular artefact, the sbt installation is easy, but require a few more steps than just adding a regular library:

libraryDependencies += "org.ensime" %% "pcplod" % "1.2.1" % "test",

// WORKAROUND https://github.com/ensime/pcplod/issues/12
fork in Test := true,

javaOptions in Test ++= Seq(
  s"""-Dpcplod.settings=${(scalacOptions in Test).value.filterNot(_.contains(",")).mkString(",")}""",
  s"""-Dpcplod.classpath=${(fullClasspath in Test).value.map(_.data).mkString(",")}"""

The dependencyOverrides feature of SBT is recommended to ensure that the correct version of the scala compiler is used

dependencyOverrides += "org.scala-lang" % "scala-compiler" % scalaVersion.value

If you are testing a compiler plugin you may already be aware that you must add something like the following to your test configuration

scalacOptions in Test ++= {
  val jar = (packageBin in Compile).value
  Seq(s"-Xplugin:${jar.getAbsolutePath}", s"-Jdummy=${jar.lastModified}") // ensures recompile

How to use it

PC Plod uses the loan pattern to let you write tests in whatever testing framework you want.

Loading Scala Sources

Since you're simulating a scala developer who is using your macro / plugin to write scala code, you put the code that you want to test into the test/resources folder of your project (not test/scala). Add source resources as needed

import org.ensime.pcplod._
withPcPlod { pc =>
  // your tests here
  // more tests here

there is also a simplified variant (Mr Plod) which only supports one source (a simpler assertion API)

withMrPlod("path/to/package/foo.scala") { mr =>
  // your tests here

Making Assertions

The PcPlod instance has the following main assertions:

  • symbolAtPoint(res: String, p: Point): Option[String] - the name of the symbol at point.
  • typeAtPoint(res: String, p: Point): Option[String] - the return type of the symbol at the point.
  • messages: List[PcMessage]

Typically if symbolAtPoint or typeAtPoint do not work (or there are any errors) then your code is not expected to work in the presentation compiler.

A variant of typeAtPoint and symbolAtPoint without the res is provided for withMrPlod.

An implicit conversion for Point means that any of the following can be provided in its place:

  • Int the number of characters
  • (Int, Int) the line and column
  • Symbol corresponding to noddy syntax

with all counting from zero.

Noddy Syntax

Instead of having to manually count the location in the source, you can augment your test sources with a @noddy_syntax@ that will be stripped and treated as meta data when loaded:

object F@foo@oo {
  def bar(a@input_a@: String): Int = ???

in this case, the symbol 'foo will refer to the letter F of Foo and the symbol 'input_a will refer to the parameter a of bar (i.e. the character immediately before the marker). Noddy names can only be alphanumeric or underscore.