step 27: not again! a crash in RefChecks!

java.lang.AssertionError: assertion failed:
  transformCaseApply: name = temp$macro$1 tree = temp$macro$1 / class scala.reflect.internal.Trees$Ident
     while compiling: /Users/xeno_by/Projects/macrology201/core/src/main/scala/Test.scala
        during phase: globalPhase=refchecks, enteringPhase=uncurry
     library version: version 2.11.0
    compiler version: version 2.11.0
  reconstructed args: -Ydead-code -bootclasspath /Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/lib/JObjC.jar:/Library/Java/JavaVirtualMachines/jdk1.7.0_40.jdk/Contents/Home/jre/classes:/Users/xeno_by/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.11.0.jar -optimise -Yinline -Yclosure-elim -Yinline-handlers -Yconst-opt -classpath /Users/xeno_by/Projects/macrology201/core/target/scala-2.11/classes:/Users/xeno_by/Projects/macrology201/macros/target/scala-2.11/classes:/Users/xeno_by/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.11.0.jar

  last tree to typer: type Test
       tree position: line 3 of /Users/xeno_by/Projects/macrology201/core/src/main/scala/Test.scala
            tree tpe: <notype>
              symbol: object Test
   symbol definition: class Test extends AnyRef (a ModuleClassSymbol)
      symbol package: <empty>
       symbol owners: object Test
           call site: object Test in package <empty>

== Source file context for tree position ==

     0 class C { override def toString = "C" }
     1
     2 object Test {
     3   def main(args: Array[String]): Unit = {
     4     val x1 = new Optional(new C)
     5     val x2 = x1.map(_.toString)
     6     println(x2)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer$$anonfun$2.apply$mcV$sp(RefChecks.scala:1709)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transformCaseApply(RefChecks.scala:1517)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:1707)
	at scala.tools.nsc.typechecker.RefChecks$RefCheckTransformer.transform(RefChecks.scala:111)

Unfortunately, a simple transformer doesn't cut it, crashing the compiler
during the refchecks phase. This is the little brother of the owner chain
corruption issue, again caused by the internal details of how scalac's
typechecker handles abstract syntax trees.

The problem at hand is caused by the fact that the typechecker doesn't
go into trees that are already typed, which means that it effectively
ignores untyped trees inserted under typed trees, and that's exactly
what our macro expands into. Later phases have an implicit assumption
that all the ASTs are typed, and that's what crashes refchecks.

If we inspect the expansion with -Xprint:typer, also enabling -Xprint-types,
we can identify the culprit:

    def main(args: Array[String]): Unit = {
      val x1: Optional[C] = new Optional[C]{Optional[C]}{(value: C)Optional[C]}(new C{C}{()C}(){C}){Optional[C]};
      val x2: Optional[String] = ({
        val temp$macro$1: Optional[C] = (x1{x1.type}: Optional[C]){Optional[C]};
        if (temp$macro$1.isEmpty{Boolean})
          new Optional[Null]{Optional[Null]}{(value: Null)Optional[Null]}(null{Null(null)}){Optional[Null]}
        else
          new Optional[String]{Optional[String]}{(value: String)Optional[String]}(temp$macro$1.toString{()String}(){String}){Optional[String]}{Optional[String]}
      }{Optional[String]}: Optional[String]){Optional[String]};
      scala.this{scala.type}.Predef.println{(x: Any)Unit}(x2{Optional[String]}){Unit}

Here we see the tree "temp$macro$1.toString{()String}(){String}",
which appears typed (has type information assigned to it), but one of its parts
(a reference to `temp$macro$1`) is untyped. That's our guy.

Author: xeno-by

project/Build.scala

@@ -35,7 +35,9 @@ object MyBuild extends Build {
     "core",
     file("core"),
     settings = buildSettings ++ Seq(
-      scalacOptions += "-optimize"
+      scalacOptions += "-optimize",
+      scalacOptions += "-Xprint:typer",
+      scalacOptions += "-Xprint-types"
     )
   ) dependsOn(macros)
 }