Backend triggers assertion in assertClassNotArray

[smarter]

The following code:

package foo
object Foo {
}                                                                                                                                   

Results in an assertion error:

java.lang.AssertionError: assertion failed: val <none>
        at scala.Predef$.assert(Predef.scala:165)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.assertClassNotArray(BCodeHelpers.scala:214)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.assertClassNotArrayNotPrimitive(BCodeHelpers.scala:219)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.getClassBTypeAndRegisterInnerClass(BCodeHelpers.scala:238)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$JCommonBuilder.getClassBTypeAndRegisterInnerClass(BCodeHelpers.scala:469)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.internalName(BCodeHelpers.scala:210)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$JCommonBuilder.internalName(BCodeHelpers.scala:469)
        at scala.tools.nsc.backend.jvm.BCodeHelpers$JMirrorBuilder.genMirrorClass(BCodeHelpers.scala:494)
        at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.visit(GenBCode.scala:164)
        at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.run(GenBCode.scala:126)
        at dotty.tools.backend.jvm.GenBCodePipeline.buildAndSendToDisk(GenBCode.scala:320)
        at dotty.tools.backend.jvm.GenBCodePipeline.run(GenBCode.scala:289)
        at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:40)
        at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:266)
        at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:264)
        at scala.collection.immutable.List.map(List.scala:273)
        at dotty.tools.dotc.core.Phases$Phase$class.runOn(Phases.scala:264)
        at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:33)
        at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:50)
        at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:47)
        at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
        at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
        at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply$mcV$sp(Run.scala:47)
        at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
        at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
        at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:68)
        at dotty.tools.dotc.Run.compileSources(Run.scala:41)
        at dotty.tools.dotc.Run.compile(Run.scala:32)
        at dotty.tools.dotc.Driver.doCompile(Driver.scala:20)
        at dotty.tools.dotc.Main$.doCompile(Main.scala:26)
        at dotty.tools.dotc.Driver.process(Driver.scala:31)
        at dotty.tools.dotc.Driver.main(Driver.scala:40)
        at dotty.tools.dotc.Main.main(Main.scala)
error: Error while emitting packobj.scala
assertion failed: val <none>
one error found

A quick bisection search shows that this started happening when #436 was merged.
Assigned to @DarkDimius .

[DarkDimius]

@smarter, I cannot reproduce.
at current master(6c6177c) works for me.

[smarter]

@DarkDimius : Can you try compiling the same fie twice?

[DarkDimius]

dark@reco ~/workspace/dotty ((6c6177c...)) $ cat tests/pos/empty-foo.scala
package foo
object Bar {
}

> runMain dotty.tools.dotc.Bench #runs 2 ./tests/pos/empty-foo.scala
[info] Running dotty.tools.dotc.Bench #runs 2 ./tests/pos/empty-foo.scala
[info] time elapsed: 687ms
[info] time elapsed: 38ms

Though It doesn't actually pass Ycheck:

> runMain dotty.tools.dotc.Bench #runs 2 ./tests/pos/empty-foo.scala -Ycheck:all
[info] Running dotty.tools.dotc.Bench #runs 2 ./tests/pos/empty-foo.scala -Ycheck:all
[info] checking ./tests/pos/empty-foo.scala after phase frontend
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{firstTransform, synthetics}
[info] checking ./tests/pos/empty-foo.scala after phase superaccessors
[info] checking ./tests/pos/empty-foo.scala after phase pickler
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{refchecks, elimRepeated, normalizeFlags, extmethods, tailrec}
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{patternMatcher, explicitOuter, splitter}
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{LazyVals, seqLiterals, intercepted, literalize, getters, elimByName, resolveSuper}
[info] checking ./tests/pos/empty-foo.scala after phase erasure
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{mixin, memoize, capturedVars, constructors}
[info] checking ./tests/pos/empty-foo.scala after phase TreeTransform:{lambdaLift, flatten, restoreScopes}
[info] exception while typing new foo.Bar$() of class class dotty.tools.dotc.ast.Trees$Apply # 91
[info] exception while typing final lazy module val Bar: foo.Bar$ = new foo.Bar$() of class class dotty.tools.dotc.ast.Trees$ValDef # 92
[info] exception while typing package foo {
[info]   final lazy module val Bar: foo.Bar$ = new foo.Bar$()
[info]   final module class Bar$ extends Object { this: <notype> =>
[info]     def <init>(): foo.Bar$ = {
[info]       Bar$.super()
[info]       ()
[info]     }
[info]   }
[info] } of class class dotty.tools.dotc.ast.Trees$PackageDef # 117
[info] *** error while checking after phase restoreScopes ***
[error] Exception in thread "main" java.lang.AssertionError: assertion failed: non member selection of constructor Bar$ in object Bar$ from foo.Bar$
[error]     at scala.Predef$.assert(Predef.scala:165)
[error]     at dotty.tools.dotc.transform.FirstTransform.checkPostCondition(FirstTransform.scala:43)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker$$anonfun$typedUnadapted$1.apply(TreeChecker.scala:183)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker$$anonfun$typedUnadapted$1.apply(TreeChecker.scala:183)
[error]     at scala.collection.immutable.List.foreach(List.scala:381)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted(TreeChecker.scala:183)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1088)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1086)
[error]     at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:147)
[error]     at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:51)
[error]     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1086)
[error]     at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1125)
[error]     at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1.apply(Applications.scala:516)
[error]     at dotty.tools.dotc.typer.Applications$$anonfun$realApply$1$1.apply(Applications.scala:512)
[error]     at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
[error]     at dotty.tools.dotc.typer.Applications$class.realApply$1(Applications.scala:512)
[error]     at dotty.tools.dotc.typer.Applications$class.typedApply(Applications.scala:578)
[error]     at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:58)
[error]     at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1038)
[error]     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1078)
[error]     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:93)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted(TreeChecker.scala:166)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1088)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1086)
[error]     at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:147)
[error]     at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:51)
[error]     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1086)
[error]     at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1125)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typedValDef$1.apply(Typer.scala:880)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typedValDef$1.apply(Typer.scala:874)
[error]     at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
[error]     at dotty.tools.dotc.typer.Typer.typedValDef(Typer.scala:874)
[error]     at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1023)
[error]     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1076)
[error]     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:93)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted(TreeChecker.scala:166)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1088)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1086)
[error]     at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:147)
[error]     at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:51)
[error]     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1086)
[error]     at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:1110)
[error]     at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:1121)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker.typedStats(TreeChecker.scala:275)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:969)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typedPackageDef$1.apply(Typer.scala:960)
[error]     at dotty.tools.dotc.util.Stats$.track(Stats.scala:35)
[error]     at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:960)
[error]     at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1066)
[error]     at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1078)
[error]     at dotty.tools.dotc.typer.ReTyper.typedUnadapted(ReTyper.scala:93)
[error]     at dotty.tools.dotc.transform.TreeChecker$Checker.typedUnadapted(TreeChecker.scala:166)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1088)
[error]     at dotty.tools.dotc.typer.Typer$$anonfun$typed$2.apply(Typer.scala:1086)
[error]     at dotty.tools.dotc.reporting.Reporting$class.traceIndented(Reporter.scala:147)
[error]     at dotty.tools.dotc.core.Contexts$Context.traceIndented(Contexts.scala:51)
[error]     at dotty.tools.dotc.typer.Typer.typed(Typer.scala:1086)
[error]     at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:1125)
[error]     at dotty.tools.dotc.transform.TreeChecker.check(TreeChecker.scala:100)
[error]     at dotty.tools.dotc.transform.TreeChecker.run(TreeChecker.scala:78)
[error]     at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:266)
[error]     at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:264)
[error]     at scala.collection.immutable.List.map(List.scala:273)
[error]     at dotty.tools.dotc.core.Phases$Phase$class.runOn(Phases.scala:264)
[error]     at dotty.tools.dotc.transform.TreeChecker.runOn(TreeChecker.scala:38)
[error]     at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:50)
[error]     at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:47)
[error]     at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
[error]     at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
[error]     at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply$mcV$sp(Run.scala:47)
[error]     at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
[error]     at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
[error]     at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:68)
[error]     at dotty.tools.dotc.Run.compileSources(Run.scala:41)
[error]     at dotty.tools.dotc.Run.compile(Run.scala:32)
[error]     at dotty.tools.dotc.Driver.doCompile(Driver.scala:20)
[error]     at dotty.tools.dotc.Bench$.dotty$tools$dotc$Bench$$super$doCompile(Bench.scala:38)
[error]     at dotty.tools.dotc.Bench$$anonfun$doCompile$1.apply(Bench.scala:38)
[error]     at dotty.tools.dotc.Bench$$anonfun$doCompile$1.apply(Bench.scala:36)
[error]     at dotty.tools.dotc.Bench$$anonfun$ntimes$1.apply(Bench.scala:30)
[error]     at dotty.tools.dotc.Bench$$anonfun$ntimes$1.apply(Bench.scala:30)
[error]     at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:142)
[error]     at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:142)
[error]     at scala.collection.immutable.Range.foreach(Range.scala:166)
[error]     at scala.collection.TraversableOnce$class.foldLeft(TraversableOnce.scala:142)
[error]     at scala.collection.AbstractTraversable.foldLeft(Traversable.scala:104)
[error]     at scala.collection.TraversableOnce$class.$div$colon(TraversableOnce.scala:136)
[error]     at scala.collection.AbstractTraversable.$div$colon(Traversable.scala:104)
[error]     at dotty.tools.dotc.Bench$.ntimes(Bench.scala:30)
[error]     at dotty.tools.dotc.Bench$.doCompile(Bench.scala:36)
[error]     at dotty.tools.dotc.Driver.process(Driver.scala:31)
[error]     at dotty.tools.dotc.Bench$.dotty$tools$dotc$Bench$$super$process(Bench.scala:53)
[error]     at dotty.tools.dotc.Bench$$anonfun$process$1.apply(Bench.scala:53)
[error]     at dotty.tools.dotc.Bench$$anonfun$process$1.apply(Bench.scala:53)
[error]     at dotty.tools.dotc.Bench$$anonfun$ntimes$1.apply(Bench.scala:30)
[error]     at dotty.tools.dotc.Bench$$anonfun$ntimes$1.apply(Bench.scala:30)
[error]     at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:142)
[error]     at scala.collection.TraversableOnce$$anonfun$foldLeft$1.apply(TraversableOnce.scala:142)
[error]     at scala.collection.immutable.Range.foreach(Range.scala:166)
[error]     at scala.collection.TraversableOnce$class.foldLeft(TraversableOnce.scala:142)
[error]     at scala.collection.AbstractTraversable.foldLeft(Traversable.scala:104)
[error]     at scala.collection.TraversableOnce$class.$div$colon(TraversableOnce.scala:136)
[error]     at scala.collection.AbstractTraversable.$div$colon(Traversable.scala:104)
[error]     at dotty.tools.dotc.Bench$.ntimes(Bench.scala:30)
[error]     at dotty.tools.dotc.Bench$.process(Bench.scala:53)
[error]     at dotty.tools.dotc.Driver.main(Driver.scala:40)
[error]     at dotty.tools.dotc.Bench.main(Bench.scala)
java.lang.RuntimeException: Nonzero exit code returned from runner: 1
    at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last dotty/compile:runMain for the full output.
[error] (dotty/compile:runMain) Nonzero exit code returned from runner: 1
[error] Total time: 1 s, completed Apr 4, 2015 2:02:27 AM

[DarkDimius]

I guess I know the issue.
Wait for PR.

[smarter]

OK, this appears to be very tricky to reproduce, here's a script that should help:

#!/bin/sh

set -x
mv ff ff.bak
mkdir newDir
cd newDir
echo "package ff\nobject Foo {}" > po.scala
cd ..
sbt "run ./newDir/po.scala"
sbt "run ./newDir/po.scala"

Put this in a file called bug.sh, then:

% sh bug.sh
+ mv ff ff.bak
+ mkdir newDir
mkdir: cannot create directory ‘newDir’: File exists
+ cd newDir
+ echo package ff\nobject Foo {}
+ cd ..
+ sbt run ./newDir/po.scala
[info] Loading global plugins from /home/smarter/.sbt/0.13/plugins
[info] Loading project definition from /home/smarter/opt/dotty/project
[info] Set current project to dotty (in build file:/home/smarter/opt/dotty/)
[info] Running dotty.tools.dotc.Main ./newDir/po.scala
[success] Total time: 3 s, completed Apr 4, 2015 2:25:20 AM
+ sbt run ./newDir/po.scala
[info] Loading global plugins from /home/smarter/.sbt/0.13/plugins
[info] Loading project definition from /home/smarter/opt/dotty/project
[info] Set current project to dotty (in build file:/home/smarter/opt/dotty/)
[info] Running dotty.tools.dotc.Main ./newDir/po.scala
[error] java.lang.AssertionError: assertion failed: val <none>
[error]         at scala.Predef$.assert(Predef.scala:165)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.assertClassNotArray(BCodeHelpers.scala:214)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.assertClassNotArrayNotPrimitive(BCodeHelpers.scala:219)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.getClassBTypeAndRegisterInnerClass(BCodeHelpers.scala:238)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$JCommonBuilder.getClassBTypeAndRegisterInnerClass(BCodeHelpers.scala:469)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$BCInnerClassGen$class.internalName(BCodeHelpers.scala:210)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$JCommonBuilder.internalName(BCodeHelpers.scala:469)
[error]         at scala.tools.nsc.backend.jvm.BCodeHelpers$JMirrorBuilder.genMirrorClass(BCodeHelpers.scala:494)
[error]         at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.visit(GenBCode.scala:164)
[error]         at dotty.tools.backend.jvm.GenBCodePipeline$Worker1.run(GenBCode.scala:126)
[error]         at dotty.tools.backend.jvm.GenBCodePipeline.buildAndSendToDisk(GenBCode.scala:320)
[error]         at dotty.tools.backend.jvm.GenBCodePipeline.run(GenBCode.scala:289)
[error]         at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:40)
[error]         at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:266)
[error]         at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:264)
[error]         at scala.collection.immutable.List.map(List.scala:273)
[error]         at dotty.tools.dotc.core.Phases$Phase$class.runOn(Phases.scala:264)
[error]         at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:33)
[error]         at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:50)
[error]         at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:47)
[error]         at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
[error]         at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
[error]         at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply$mcV$sp(Run.scala:47)
[error]         at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
[error]         at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:42)
[error]         at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:68)
[error]         at dotty.tools.dotc.Run.compileSources(Run.scala:41)
[error]         at dotty.tools.dotc.Run.compile(Run.scala:32)
[error]         at dotty.tools.dotc.Driver.doCompile(Driver.scala:20)
[error]         at dotty.tools.dotc.Main$.doCompile(Main.scala:26)
[error]         at dotty.tools.dotc.Driver.process(Driver.scala:31)
[error]         at dotty.tools.dotc.Driver.main(Driver.scala:40)
[error]         at dotty.tools.dotc.Main.main(Main.scala)
[error] error: Error while emitting po.scala
[error] assertion failed: val <none>
[error] one error found
java.lang.RuntimeException: Nonzero exit code returned from runner: 1
        at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last dotty/compile:run for the full output.
[error] (dotty/compile:run) Nonzero exit code returned from runner: 1
[error] Total time: 2 s, completed Apr 4, 2015 2:25:27 AM

[DarkDimius]

Was able to reproduce, after running the script in loop for around 20 times.

The problem that causes backend to go wild:
in case compiled jars are there, in some cases, module class Foo$ that is currently being compiled from tree, gets a JavaDefined flag. This should never happen.

[smarter]

Yes, I'm not crazy then :).

[DarkDimius]

That's some kind of bug in RestoreScopes. It:

1. in invalidateUndefinedCompanions artificially forges name of class Foo(not Foo$)
2. pkg.info.decl("Foo").asSymDenotation forces loading of Foo.class from classpath(that was generated just to emit static forwarders).
3. reading Foo.class from classpath defines pair of java-defined(as they do not have scalaSig annotation) classes Foo and Foo$
4. ignores that those classes are currently being compiled, treats them as being currently valid. I guess there's some side effect that actually makes classes that are read from bytecode override the ones that are currently being compiled somewhere. By the time of backend, tree has already wrong symbol.

It could have to do with #462.

@odersky, AFAIK you have made some fixes to RestoreScopes. Could you have a look?