Pickler crashes when pickling a program compiled with Scala 2 library CC

[Linyxus]

Compiler version

main

Minimized code

First set the library to the capture checked one and then compile the following snippet:

object Test {
  def indentLines(level: Int, lines: Iterable[String]) =
    lines.map(line => line.split("\n").map("  " + _).mkString("\n"))

  def indentErrorMessages(messages: IndexedSeq[String]) =
    indentLines(1, messages)
}

Output

error when pickling type lines.type
error when pickling tree this
error when pickling tree [this,f : Any]
error when pickling tree [this,f : Any]*
error when pickling tree new _root_.scala.annotation.retains([this,f : Any]*)
error when pickling type Iterable[String]^{this, String => String}
error when pickling tree Iterable[String]^{this, String => String}
error when pickling tree def indentErrorMessages(messages: IndexedSeq[String]): Iterable[String]^{this, String => String} = Test.indentLines(1, messages)
...

[Linyxus]

I minimised the issue into the following which is independent of the capture checked library:

import language.experimental.captureChecking

trait Iterable[T] { self: Iterable[T]^ =>
  def map[U](f: T => U): Iterable[U]^{this, f}
}

object Test {
  def indentLines(level: Int, lines: Iterable[String]) =
    lines.map(line => line.split("\n").map("  " + _).mkString("\n"))

  def indentErrorMessages(messages: Iterable[String]) =
    indentLines(1, messages)
}

[Linyxus]

After typer, the function indentErrorMessages is typed as:

    def indentErrorMessages(messages: Iterable[String]): Iterable[String]^{this, String -> String} = Test.indentLines(1, messages)

The type of this in the capture set of the result type is TermParamRef(lines) (which is the term parameter from the indentLines function). It is invalid and crashes the pickler.

The cause is that when typing the application indentLines(1, messages), the dependency of the result type of the indentLines function is ignored by isResultDependent, which uses the refersToParamOf method to check whether an annotation has possible dependencies on the term parameters. That function, in turn, does not correctly handle the case when it contains a This reference whose type contains references to term parameters.