readme.md

• https://issues.scala-lang.org/browse/SI-7288 ? or another issue?

build.sbt

scalaVersion := "2.11.8"

ClassFormatErrorBug.scala

package com.example

case class Foo[F[_], A](step: F[Foo.Step[A]])

object Foo {
  class Step[A]
  object Done {
    def unapply[A](a: Step[A]): Boolean = true
  }
}

object ClassFormatErrorBug {
  implicit class AnyOps[A](actual: A) {
    def mustMatch[B](f: PartialFunction[A, B]): Unit = {
    }
  }

  type Id[+A] = A

  def main(args: Array[String]): Unit = {
    val s = new Foo[Id, String](new Foo.Step[String])

    s.step mustMatch {
      case Foo.Done() => true
    }
  }
}

log

[info] Running com.example.ClassFormatErrorBug 
[error] (run-main-0) java.lang.ClassFormatError: Duplicate method name&signature in class file com/example/ClassFormatErrorBug$$anonfun$main$1
java.lang.ClassFormatError: Duplicate method name&signature in class file com/example/ClassFormatErrorBug$$anonfun$main$1
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        at com.example.ClassFormatErrorBug$.main(Main.scala:23)
        at com.example.ClassFormatErrorBug.main(Main.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
[trace] Stack trace suppressed: run last compile:run for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
        at scala.sys.package$.error(package.scala:27)