REPL crashing on standalone `_root_` reference

[prolativ]

Compiler version

3.3.2-RC1-bin-20230601-8814760-NIGHTLY - prints compiler stack trace, keeps REPL alive
3.3.1-RC1 - prints compiler stack trace, keeps REPL alive
3.3.0 - crashes REPL

Minimized code

scala> _root_

Output (click arrow to expand)

Warning: mocking up superclass for module class <root>
java.lang.AssertionError: assertion failed: Cannot create ClassBType from NoSymbol
	at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
	at dotty.tools.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:51)
	at dotty.tools.backend.jvm.BTypesFromSymbols.buildNestedInfo(BTypesFromSymbols.scala:218)
	at dotty.tools.backend.jvm.BTypesFromSymbols.setClassInfo(BTypesFromSymbols.scala:176)
	at dotty.tools.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol$$anonfun$1(BTypesFromSymbols.scala:64)
	at scala.collection.mutable.HashMap.getOrElse(HashMap.scala:436)
	at dotty.tools.backend.jvm.BTypesFromSymbols.classBTypeFromSymbol(BTypesFromSymbols.scala:65)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.getClassBType(BCodeHelpers.scala:177)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.getClassBType$(BCodeHelpers.scala:129)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.getClassBType(BCodeSkelBuilder.scala:74)
	at dotty.tools.backend.jvm.BCodeHelpers.primitiveOrClassToBType$1$$anonfun$1(BCodeHelpers.scala:714)
	at scala.collection.immutable.HashMap.getOrElse(HashMap.scala:683)
	at dotty.tools.backend.jvm.BCodeHelpers.primitiveOrClassToBType$1(BCodeHelpers.scala:714)
	at dotty.tools.backend.jvm.BCodeHelpers.dotty$tools$backend$jvm$BCodeHelpers$$typeToTypeKind(BCodeHelpers.scala:733)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.toTypeKind(BCodeHelpers.scala:201)
	at dotty.tools.backend.jvm.BCodeHelpers$BCInnerClassGen.toTypeKind$(BCodeHelpers.scala:129)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.toTypeKind(BCodeSkelBuilder.scala:74)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.symInfoTK(BCodeSkelBuilder.scala:103)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.addClassFields$$anonfun$2(BCodeSkelBuilder.scala:352)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.addClassFields(BCodeSkelBuilder.scala:358)
	at dotty.tools.backend.jvm.BCodeSkelBuilder$PlainSkelBuilder.genPlainClass(BCodeSkelBuilder.scala:232)
	at dotty.tools.backend.jvm.CodeGen.genClass(CodeGen.scala:138)
	at dotty.tools.backend.jvm.CodeGen.genClassDef$1(CodeGen.scala:55)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:101)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1$$anonfun$1(CodeGen.scala:99)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.backend.jvm.CodeGen.genClassDefs$1(CodeGen.scala:99)
	at dotty.tools.backend.jvm.CodeGen.genUnit(CodeGen.scala:104)
	at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:76)
	at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:327)
	at scala.collection.immutable.List.map(List.scala:246)
	at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:331)
	at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:87)
	at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:246)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321)
	at dotty.tools.dotc.Run.runPhases$1(Run.scala:262)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:270)
	at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:279)
	at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:67)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:279)
	at dotty.tools.dotc.Run.compileUnits(Run.scala:200)
	at dotty.tools.repl.ReplCompiler.compile(ReplCompiler.scala:87)
	at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:307)
	at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:269)
	at dotty.tools.repl.ReplDriver.loop$1(ReplDriver.scala:169)
	at dotty.tools.repl.ReplDriver.runUntilQuit$$anonfun$1(ReplDriver.scala:172)
	at dotty.tools.repl.ReplDriver.withRedirectedOutput(ReplDriver.scala:211)
	at dotty.tools.repl.ReplDriver.runBody$$anonfun$1(ReplDriver.scala:185)
	at dotty.tools.runner.ScalaClassLoader$.asContext(ScalaClassLoader.scala:80)
	at dotty.tools.repl.ReplDriver.runBody(ReplDriver.scala:185)
	at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:172)
	at dotty.tools.repl.ReplDriver.tryRunning(ReplDriver.scala:134)
	at dotty.tools.repl.Main$.main(Main.scala:7)
	at dotty.tools.repl.Main.main(Main.scala)
Error while emitting rs$line$1
assertion failed: Cannot create ClassBType from NoSymbol
1 error foun

Also code completions on _root_.<TAB> in REPL don't work

[scala-center-bot]

This issue was picked for the Issue Spree No. 32 of 20 June 2023 which takes place in 7 days. @Linyxus, @nmcb, @jan-pieter, @TheElectronWill will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here.

[som-snytt]

Did someone laugh because the message says, "mocking"?

Also compare

Welcome to Scala 3.3.0 (20.0.1, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> val _root_ = ""
val _root_: String = ""

scala> _root_.length
-- [E008] Not Found Error: ---------------------------------------------------------------------------------------------
1 |_root_.length
  |^^^^^^^^^^^^^
  |value length is not a member of <root>
1 error found

and

Welcome to Scala 2.13.11 (OpenJDK 64-Bit Server VM, Java 20.0.1).
Type in expressions for evaluation. Or try :help.

scala> val _root_ = ""
val _root_: String = ""

scala> _root_.length
              ^
       error: object length is not a member of package <root>
       ^
       warning: _root_ in root position of qualifier refers to the root package, not value _root_, which is in scope

scala> _root_
       ^
       error: reference to _root_ is ambiguous;
       it is both defined in <none> and imported subsequently by
       import _root_