Scala REPL 在开始使用 scala.tools.nsc.interpreter 时崩溃

Question

我正在尝试使用scala.tools.nsc.interpreter 来启用交互式调试（如 Python 的 pdb/ipdb）：

val foo = 123

import scala.tools.nsc.Settings
import scala.tools.nsc.interpreter.{ ILoop, SimpleReader }

val repl = new ILoop
repl.settings = new Settings
repl.settings.usejavacp.value = true
repl.in = SimpleReader()
repl.createInterpreter()

repl.intp.bind("foo", "Int", foo)

repl.loop()
repl.closeInterpreter()

运行时，这是我得到的：

$ scala repl.scala
foo: Int = 123

scala> "hello"   
java.lang.NullPointerException
    at scala.concurrent.Await$$anonfun$ready$1.apply(package.scala:95)
    at scala.concurrent.Await$$anonfun$ready$1.apply(package.scala:95)
    at scala.concurrent.BlockContext$DefaultBlockContext$.blockOn(BlockContext.scala:53)
    at scala.concurrent.Await$.ready(package.scala:95)
    at scala.tools.nsc.interpreter.ILoop.processLine(ILoop.scala:402)
    at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:430)
    at Main$$anon$1.<init>(repl.scala:14)
    at Main$.main(repl.scala:1)
    at Main.main(repl.scala)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
    at scala.reflect.internal.util.ScalaClassLoader$class.asContext(ScalaClassLoader.scala:31)
    at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.asContext(ScalaClassLoader.scala:101)
    at scala.reflect.internal.util.ScalaClassLoader$class.run(ScalaClassLoader.scala:70)
    at scala.reflect.internal.util.ScalaClassLoader$URLClassLoader.run(ScalaClassLoader.scala:101)
    at scala.tools.nsc.CommonRunner$class.run(ObjectRunner.scala:22)
    at scala.tools.nsc.ObjectRunner$.run(ObjectRunner.scala:39)
    at scala.tools.nsc.CommonRunner$class.runAndCatch(ObjectRunner.scala:29)
    at scala.tools.nsc.ObjectRunner$.runAndCatch(ObjectRunner.scala:39)
    at scala.tools.nsc.ScriptRunner.scala$tools$nsc$ScriptRunner$$runCompiled(ScriptRunner.scala:175)
    at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
    at scala.tools.nsc.ScriptRunner$$anonfun$runScript$1.apply(ScriptRunner.scala:192)
    at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1$$anonfun$apply$mcZ$sp$1.apply(ScriptRunner.scala:161)
    at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply$mcZ$sp(ScriptRunner.scala:161)
    at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
    at scala.tools.nsc.ScriptRunner$$anonfun$withCompiledScript$1.apply(ScriptRunner.scala:129)
    at scala.tools.nsc.util.package$.trackingThreads(package.scala:43)
    at scala.tools.nsc.util.package$.waitingForThreads(package.scala:27)
    at scala.tools.nsc.ScriptRunner.withCompiledScript(ScriptRunner.scala:128)
    at scala.tools.nsc.ScriptRunner.runScript(ScriptRunner.scala:192)
    at scala.tools.nsc.ScriptRunner.runScriptAndCatch(ScriptRunner.scala:205)
    at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:67)
    at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:87)
    at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:98)
    at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:103)
    at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)


Abandoning crashed session.

scala> 

如果我删除 repl.intp.bind("foo", "Int", foo) 部分，这就是我得到的：

$ scala repl.scala 

scala> 123
null

Abandoning crashed session.

scala> 

我做错了什么？出于调试目的，在程序运行期间是否有更简单的方法进入交互式 REPL？断点、单步执行和检查本地人有时是行不通的。

我使用的是 Scala 2.11.5。

Answer 1

我不知道为什么这条评论没有神奇的星号：

  // start an interpreter with the given settings
  def process(settings: Settings): Boolean

所以你可以：

scala> repl process s
Welcome to Scala version 2.11.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_25).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :quit
res0: Boolean = true

或者你可以：

package myrepl

import scala.tools.nsc.Settings
import scala.tools.nsc.interpreter.{ ILoop, SimpleReader }

object Test extends App {
  val foo = 42
  val repl = new ILoop {
    override def printWelcome() = {
      intp.bind("foo", foo)
      super.printWelcome()
      echo("Customized...")
    }
  }
  val s = new Settings
  s.usejavacp.value = true
  repl.in = SimpleReader()
  repl process s
  /*
  repl.createInterpreter()

  repl.intp.bind("foo", "Int", foo)

  repl.loop()
  repl.closeInterpreter()
  */
}

和

$ scalac myrepl.scala && scala myrepl.Test
foo: Int = 42
Welcome to Scala version 2.11.5 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_20).
Type in expressions to have them evaluated.
Type :help for more information.
Customized...

scala> foo
res0: Int = 42

scala> :quit

还有，

  s.Xnojline.value  = true
  //repl.in = SimpleReader()

由于 repl 崩溃的错误，我将降级到 2.11.4...

Sbt 是通过 overriding createInterpreter and calling bind there 完成的。

编辑：

  val repl = new ILoop {
    override def printWelcome() = {
      //import scala.concurrent.duration._
      //Await.ready(globalFuture, 10.minutes) // sorry, it's private!
      super.printWelcome()
      echo("Customizing...")
      processLine("") // block for init to finish
      intp.bind("foo", foo)
    }
  }

私人globalFuture 是爆炸创业的障碍：

object Solid extends App {
  val foo = 42
  val repl = new ILoop {
    override def printWelcome() = {
      super.printWelcome()
      echo("Customized...")
    }
  }
  val s = new Settings
  s.Xnojline.value = true
  s.usejavacp.value = true
  repl.settings = s
  repl.createInterpreter()
  repl.in = SimpleReader()
  repl.intp.initializeSynchronous()
  repl.loopPostInit()
  repl.globalFuture = concurrent.Future.successful(true)

  repl.intp.bind("foo", "Int", foo)

  try repl.loop()
  finally repl.closeInterpreter()
}

-Yrepl-sync 选项在 2.11 中不再支持。