It seems like the REPL will crash when TAB is pressed repeatedly. Immediately after REPL start, press TAB three to five times. This will result in a long error message, pasted below. The next command issued, for instance print(), will crash the REPL with an exception.

This error exists in 2.10 RC5, but not in 2.9.2.

Error message after tab presses:

scala> error:
while compiling:
during phase: global=erasure, atPhase=explicitouter
library version: version 2.10.0-RC5
compiler version: version 2.10.0-RC5
reconstructed args:

last tree to typer: TypeTree(class Unit)
symbol: class Unit in package scala (flags: final abstract)
symbol definition: final abstract class Unit extends AnyVal
tpe: Unit
symbol owners: class Unit -> package scala
context owners: object $eval -> package $line1

== Enclosing template or block ==

ClassDef( // class $eval extends Object in package $line1

"$eval"
[]
Template( // val <local $eval>: in object $eval, tree.tpe=type
"java.lang.Object" // parents
ValDef(
private
""


)
// 5 statements
DefDef( // def (): type in object $eval

""
[]
List(Nil)
// tree.tpe=type
Block( // tree.tpe=Unit
Apply( // def (): Object in class Object, tree.tpe=Object
$eval.super."" // def (): Object in class Object, tree.tpe=()Object
Nil
)
()
)
)
ValDef( // private[this] var value: scala.tools.nsc.interpreter.IMain in object $eval
private
"value "
// tree.tpe=scala.tools.nsc.interpreter.IMain

)
DefDef( // def value: scala.tools.nsc.interpreter.IMain in object $eval

"value"
[]
List(Nil)
// tree.tpe=scala.tools.nsc.interpreter.IMain
$eval.this."value " // private[this] var value: scala.tools.nsc.interpreter.IMain in object $eval, tree.tpe=scala.tools.nsc.interpreter.IMain
)
DefDef( // def value=(x$1: scala.tools.nsc.interpreter.IMain): Unit in object $eval

"value_$eq"
[]
// 1 parameter list
ValDef( // x$1: scala.tools.nsc.interpreter.IMain

"x$1"
// tree.tpe=scala.tools.nsc.interpreter.IMain

)
// tree.tpe=Unit
Assign( // tree.tpe=Unit
$eval.this."value " // private[this] var value: scala.tools.nsc.interpreter.IMain in object $eval, tree.tpe=scala.tools.nsc.interpreter.IMain
"x$1" // x$1: scala.tools.nsc.interpreter.IMain, tree.tpe=scala.tools.nsc.interpreter.IMain
)
)
DefDef( // def set(x: Any): Unit in object $eval

"set"
[]
// 1 parameter list
ValDef( // x: Any

"x"
// tree.tpe=Any

)
// tree.tpe=Unit
Apply( // def value_=(x$1: scala.tools.nsc.interpreter.IMain): Unit in object $eval, tree.tpe=Unit
$eval.this."value_$eq" // def value_=(x$1: scala.tools.nsc.interpreter.IMain): Unit in object $eval, tree.tpe=(x$1: scala.tools.nsc.interpreter.IMain)Unit
Apply( // final def asInstanceOfT0: T0 in class Any, tree.tpe=scala.tools.nsc.interpreter.IMain
TypeApply( // final def asInstanceOf[T0]: T0 in class Any, tree.tpe=()scala.tools.nsc.interpreter.IMain
"x"."asInstanceOf" // final def asInstanceOf[T0]: T0 in class Any, tree.tpe=T0T0
// tree.tpe=scala.tools.nsc.interpreter.IMain
)
Nil
)
)
)
)
)

== Expanded type of tree ==

TypeRef(TypeSymbol(final abstract class Unit extends AnyVal))

uncaught exception during compilation: java.lang.AssertionError

Exception after subsequent command:

scala> print()

Failed to initialize the REPL due to an unexpected error.
This is a bug, please, report it along with the error diagnostics printed below.
java.lang.AssertionError: assertion failed: TypeHistory(repl:2,Object,TypeHistory(erasure:2,Object,null))
at scala.reflect.internal.Symbols$TypeHistory.(Symbols.scala:3293)
at scala.reflect.internal.Symbols$Symbol.rawInfo(Symbols.scala:1301)
at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1227)
at scala.reflect.internal.Types$TypeMap$$anonfun$noChangeToSymbols$1.apply(Types.scala:4222)
at scala.reflect.internal.Types$TypeMap$$anonfun$noChangeToSymbols$1.apply(Types.scala:4222)
at scala.collection.LinearSeqOptimized$class.forall(LinearSeqOptimized.scala:69)
at scala.collection.immutable.List.forall(List.scala:78)
at scala.reflect.internal.Types$TypeMap.noChangeToSymbols(Types.scala:4222)
at scala.reflect.internal.Types$TypeMap.mapOver(Types.scala:4235)
at scala.reflect.internal.Types$TypeMap.mapOver(Types.scala:4138)
at scala.tools.nsc.transform.PostErasure$elimErasedValueType$.apply(PostErasure.scala:28)
at scala.tools.nsc.transform.PostErasure$class.transformInfo(PostErasure.scala:32)
at scala.tools.nsc.Global$postErasure$.transformInfo(Global.scala:567)
at scala.tools.nsc.transform.InfoTransform$Phase$$anon$1.transform(InfoTransform.scala:38)
at scala.reflect.internal.Symbols$Symbol.rawInfo(Symbols.scala:1299)
at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1227)
at scala.reflect.internal.Symbols$Symbol.tpe(Symbols.scala:1189)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$5$$anonfun$matches$1.apply(Erasure.scala:925)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$5$$anonfun$matches$1.apply(Erasure.scala:925)
at scala.reflect.internal.SymbolTable.atPhase(SymbolTable.scala:201)
at scala.reflect.internal.SymbolTable.afterPhase(SymbolTable.scala:210)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$5.matches(Erasure.scala:925)
at scala.tools.nsc.transform.OverridingPairs$Cursor.next(OverridingPairs.scala:204)
at scala.tools.nsc.transform.OverridingPairs$Cursor.(OverridingPairs.scala:224)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$5.(Erasure.scala:918)
at scala.tools.nsc.transform.Erasure$ErasureTransformer.scala$tools$nsc$transform$Erasure$ErasureTransformer$$checkNoDoubleDefs(Erasure.scala:918)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.preErase(Erasure.scala:1207)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1242)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1001)
at scala.reflect.api.Trees$Transformer.transformTemplate(Trees.scala:2840)
at scala.reflect.internal.Trees$$anonfun$itransform$4.apply(Trees.scala:1251)
at scala.reflect.internal.Trees$$anonfun$itransform$4.apply(Trees.scala:1250)
at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2872)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:34)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:28)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:19)
at scala.reflect.internal.Trees$class.itransform(Trees.scala:1249)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:12)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:12)
at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2833)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:48)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1254)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1001)
at scala.reflect.api.Trees$Transformer$$anonfun$transformStats$1.apply(Trees.scala:2863)
at scala.reflect.api.Trees$Transformer$$anonfun$transformStats$1.apply(Trees.scala:2861)
at scala.collection.immutable.List.loop$1(List.scala:164)
at scala.collection.immutable.List.mapConserve(List.scala:180)
at scala.reflect.api.Trees$Transformer.transformStats(Trees.scala:2861)
at scala.reflect.internal.Trees$$anonfun$itransform$7.apply(Trees.scala:1269)
at scala.reflect.internal.Trees$$anonfun$itransform$7.apply(Trees.scala:1269)
at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2872)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:34)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:28)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:19)
at scala.reflect.internal.Trees$class.itransform(Trees.scala:1268)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:12)
at scala.reflect.internal.SymbolTable.itransform(SymbolTable.scala:12)
at scala.reflect.api.Trees$Transformer.transform(Trees.scala:2833)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.scala$tools$nsc$transform$TypingTransformers$TypingTransformer$$super$transform(TypingTransformers.scala:44)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer$$anonfun$transform$2.apply(TypingTransformers.scala:46)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer$$anonfun$transform$2.apply(TypingTransformers.scala:46)
at scala.reflect.api.Trees$Transformer.atOwner(Trees.scala:2872)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.atOwner(TypingTransformers.scala:34)
at scala.tools.nsc.transform.TypingTransformers$TypingTransformer.transform(TypingTransformers.scala:46)
at scala.tools.nsc.transform.Erasure$ErasureTransformer$$anon$1.transform(Erasure.scala:1254)
at scala.tools.nsc.transform.Erasure$ErasureTransformer.transform(Erasure.scala:1264)
at scala.tools.nsc.transform.Erasure$ErasureTransformer.transform(Erasure.scala:876)
at scala.tools.nsc.ast.Trees$Transformer.transformUnit(Trees.scala:227)
at scala.tools.nsc.transform.Transform$Phase.apply(Transform.scala:30)
at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:461)
at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:428)
at scala.tools.nsc.Global$GlobalPhase$$anonfun$run$1.apply(Global.scala:428)
at scala.collection.Iterator$class.foreach(Iterator.scala:727)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1156)
at scala.tools.nsc.Global$GlobalPhase.run(Global.scala:428)
at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1574)
at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1548)
at scala.tools.nsc.Global$Run.compileSources(Global.scala:1544)
at scala.tools.nsc.interpreter.IMain.compileSourcesKeepingRun(IMain.scala:425)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compileAndSaveRun(IMain.scala:798)
at scala.tools.nsc.interpreter.IMain$ReadEvalPrint.compile(IMain.scala:758)
at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:615)
at scala.tools.nsc.interpreter.IMain.bind(IMain.scala:658)
at scala.tools.nsc.interpreter.IMain$$anonfun$quietBind$1.apply(IMain.scala:657)
at scala.tools.nsc.interpreter.IMain$$anonfun$quietBind$1.apply(IMain.scala:657)
at scala.tools.nsc.interpreter.IMain.beQuietDuring(IMain.scala:232)
at scala.tools.nsc.interpreter.IMain.quietBind(IMain.scala:657)
at scala.tools.nsc.interpreter.ILoop$$anonfun$process$1$$anonfun$apply$mcZ$sp$2.apply$mcV$sp(ILoop.scala:838)
at scala.tools.nsc.interpreter.ILoopInit$class.runThunks(ILoopInit.scala:122)
at scala.tools.nsc.interpreter.ILoop.runThunks(ILoop.scala:42)
at scala.tools.nsc.interpreter.ILoopInit$class.postInitialization(ILoopInit.scala:95)
at scala.tools.nsc.interpreter.ILoop.postInitialization(ILoop.scala:42)
at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply$mcV$sp(ILoopInit.scala:63)
at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply(ILoopInit.scala:60)
at scala.tools.nsc.interpreter.ILoopInit$$anonfun$createAsyncListener$1.apply(ILoopInit.scala:60)
at scala.tools.nsc.io.package$$anon$3.call(package.scala:40)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)