Case class with unusual field name kills the compiler

[dszakallas]

Welcome to Scala 2.12.4 (OpenJDK 64-Bit Server VM, Java 1.8.0_152).
Type in expressions for evaluation. Or try :help.

scala> case class A(`^$#`: Any)
ReplGlobal.abort: hash not in List(value hash)
error:
  hash not in List(value hash)
     while compiling: <console>
        during phase: constructors
     library version: version 2.12.4
    compiler version: version 2.12.4
  reconstructed args: -deprecation -feature

  last tree to typer: TypeTree(class Some)
       tree position: line 11 of <console>
            tree tpe: Some
              symbol: (final case) class Some in package scala
   symbol definition: final case class Some extends Option with Product with Serializable (a ClassSymbol)
      symbol package: scala
       symbol owners: class Some
           call site: class A in package $line3

<Cannot read source file>
scala.reflect.internal.FatalError:
  hash not in List(value hash)
     while compiling: <console>
        during phase: constructors
     library version: version 2.12.4
    compiler version: version 2.12.4
  reconstructed args: -deprecation -feature

  last tree to typer: TypeTree(class Some)
       tree position: line 11 of <console>
            tree tpe: Some
              symbol: (final case) class Some in package scala
   symbol definition: final case class Some extends Option with Product with Serializable (a ClassSymbol)
      symbol package: scala
       symbol owners: class Some
           call site: class A in package $line3

<Cannot read source file>
	at scala.reflect.internal.Reporting.abort(Reporting.scala:61)
	at scala.reflect.internal.Reporting.abort$(Reporting.scala:57)
	at scala.tools.nsc.interpreter.IMain$$anon$1.scala$tools$nsc$interpreter$ReplGlobal$$super$abort(IMain.scala:240)
	at scala.tools.nsc.interpreter.ReplGlobal.abort(ReplGlobal.scala:23)
	at scala.tools.nsc.interpreter.ReplGlobal.abort$(ReplGlobal.scala:21)
	at scala.tools.nsc.interpreter.IMain$$anon$1.abort(IMain.scala:240)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.parameterNamed(Constructors.scala:483)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.parameter(Constructors.scala:475)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.$anonfun$transformed$3(Constructors.scala:731)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.transformed(Constructors.scala:712)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.$anonfun$transform$1(Constructors.scala:85)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:85)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.$anonfun$triage$4(Constructors.scala:651)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.triage(Constructors.scala:623)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.<init>(Constructors.scala:591)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.transformed(Constructors.scala:694)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.$anonfun$transform$1(Constructors.scala:85)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:85)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.$anonfun$triage$4(Constructors.scala:651)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.triage(Constructors.scala:623)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.<init>(Constructors.scala:591)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.transformed(Constructors.scala:694)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.$anonfun$transform$1(Constructors.scala:85)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:85)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.$anonfun$triage$4(Constructors.scala:651)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.triage(Constructors.scala:623)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer$Triage.<init>(Constructors.scala:591)
	at scala.tools.nsc.transform.Constructors$TemplateTransformer.transformed(Constructors.scala:694)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.$anonfun$transform$1(Constructors.scala:85)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:85)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:29)
	at scala.reflect.api.Trees$Transformer.$anonfun$transformStats$1(Trees.scala:2589)
	at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2587)
	at scala.reflect.internal.Trees.$anonfun$itransform$7(Trees.scala:1438)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:25)
	at scala.reflect.internal.Trees.itransform(Trees.scala:1438)
	at scala.reflect.internal.Trees.itransform$(Trees.scala:1348)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:16)
	at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2555)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.super$transform(TypingTransformers.scala:40)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.$anonfun$transform$2(TypingTransformers.scala:42)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:30)
	at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:25)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:89)
	at scala.tools.nsc.transform.Constructors$ConstructorTransformer.transform(Constructors.scala:29)
	at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:140)
	at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:30)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$applyPhase$1(Global.scala:436)
	at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:429)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1(Global.scala:400)
	at scala.tools.nsc.Global$GlobalPhase.$anonfun$run$1$adapted(Global.scala:400)
	at scala.collection.Iterator.foreach(Iterator.scala:929)
	at scala.collection.Iterator.foreach$(Iterator.scala:929)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1417)
	at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:400)
	at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1452)
	at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1436)
	at scala.tools.nsc.Global$Run.compileSources(Global.scala:1429)
	at scala.tools.nsc.interpreter.IMain.compileSourcesKeepingRun(IMain.scala:431)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compileAndSaveRun(IMain.scala:800)
	at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:758)
	at scala.tools.nsc.interpreter.IMain$Request.compile$lzycompute(IMain.scala:947)
	at scala.tools.nsc.interpreter.IMain$Request.compile(IMain.scala:942)
	at scala.tools.nsc.interpreter.IMain.compile(IMain.scala:600)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:589)
	at scala.tools.nsc.interpreter.IMain.interpret(IMain.scala:561)
	at scala.tools.nsc.interpreter.ILoop.interpretStartingWith(ILoop.scala:869)
	at scala.tools.nsc.interpreter.ILoop.command(ILoop.scala:737)
	at scala.tools.nsc.interpreter.ILoop.processLine(ILoop.scala:455)
	at scala.tools.nsc.interpreter.ILoop.loop(ILoop.scala:476)
	at scala.tools.nsc.interpreter.ILoop.process(ILoop.scala:1052)
	at scala.tools.nsc.MainGenericRunner.runTarget$1(MainGenericRunner.scala:82)
	at scala.tools.nsc.MainGenericRunner.run$1(MainGenericRunner.scala:85)
	at scala.tools.nsc.MainGenericRunner.process(MainGenericRunner.scala:96)
	at scala.tools.nsc.MainGenericRunner$.main(MainGenericRunner.scala:101)
	at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

That entry seems to have slain the compiler.  Shall I replay
your session? I can re-run each line except the last one.
[y/n]

[hrhino]

But... why?

[dszakallas]

Why did I use such a name? Well I just wanted to try out whether Jackson's data binding for CSV works as I expect, and adheres to the alphabetic ordering of the mangled names, and I came up with such a name by accident. The original example had multiple fields of course.

[som-snytt]

The spec disallows embedded $, and says "host systems" may restrict back-quoted idents, but I wonder if it would be feasible and friendly to encode back-quoted a$# as a$dollar$hash. Our natural inclination is to enclose stuff in back-quotes and assume we're OK.

[SethTisue]

if we had a better selective-warning-suppression story, maybe there could be a warning when you use $ in an identifier, like "you're going out of spec here, I hope you know what you're doing" type of thing.

I have an urge to simply close the bug with a "well don't do that", but it's really not ideal for the compiler to crash on this, there is certainly room for improvement here.

[som-snytt]

Closing in favor of #8831 which may not be exact duplicate but serves as umbrella for dollar-inducements.

[SethTisue]

We are about to merge a PR (scala/scala#9008) that fixes #8831 without fixing this.

Regardless, I'm leaving this one closed since as @som-snytt indicates, this is actually within spec. Regardless, a PR that added a warning would be welcome, especially now that we have convenient warning suppression.