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The Scala 3 compiler, also known as Dotty.
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Throwing `RecursionOverflow` in `TreePickler` can lead to infinite loop #16447

Open WojciechMazur opened 1 year ago

WojciechMazur commented 1 year ago

When migrating one of Scala2 projects into Scala I ended up in infinite compilation loop. I was not yet able to minimize it, but I'm providing a thread dump of a compiler.

Compiler version

3.2.1

Minimized code

No minimization yet

Subsequent thread dump pointed to the same last method, so probably it's impossible to leave dotty.tools.dotc.core.Types$ThisType.underlying(Types.scala:2938) function call

Thread dump (click arrow to expand)

```scala "pool-11-thread-13" #356 prio=5 os_prio=0 cpu=6580194,19ms elapsed=6618,22s tid=0x00007f081cfc4800 nid=0x77889 runnable [0x00007f07e19c6000] java.lang.Thread.State: RUNNABLE at dotty.tools.dotc.core.Types$ThisType.underlying(Types.scala:2938) at dotty.tools.dotc.core.Types$TypeProxy.superType(Types.scala:1987) at dotty.tools.dotc.core.Types$Type.showPrefixSafely$1(Types.scala:887) at dotty.tools.dotc.core.Types$Type.findMember$$anonfun$1(Types.scala:891) at dotty.tools.dotc.core.Types$Type$$Lambda$8774/0x0000000102213c40.apply(Unknown Source) at dotty.tools.dotc.core.RecursionOverflow.explanation(TypeErrors.scala:47) at dotty.tools.dotc.core.RecursionOverflow.opsString$$anonfun$1(TypeErrors.scala:69) at dotty.tools.dotc.core.RecursionOverflow$$Lambda$8779/0x0000000102241840.apply(Unknown Source) at scala.collection.immutable.List.map(List.scala:246) at dotty.tools.dotc.core.RecursionOverflow.opsString(TypeErrors.scala:69) at dotty.tools.dotc.core.RecursionOverflow.produceMessage$$anonfun$4(TypeErrors.scala:79) at dotty.tools.dotc.core.RecursionOverflow$$Lambda$8775/0x0000000102210c40.apply(Unknown Source) at dotty.tools.dotc.reporting.NoExplanation.msg(Message.scala:154) at dotty.tools.dotc.reporting.Message.message(Message.scala:102) at dotty.tools.dotc.reporting.Message.isNonSensical(Message.scala:114) at dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden(HideNonSensicalMessages.scala:16) at dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden$(HideNonSensicalMessages.scala:10) at dotty.tools.dotc.reporting.AbstractReporter.isHidden(AbstractReporter.scala:8) at dotty.tools.dotc.reporting.Reporter.issueUnconfigured(Reporter.scala:155) at dotty.tools.dotc.reporting.Reporter.go$1(Reporter.scala:180) at dotty.tools.dotc.reporting.Reporter.issueIfNotSuppressed(Reporter.scala:199) at dotty.tools.dotc.reporting.Reporter.report(Reporter.scala:202) at dotty.tools.dotc.report$.error(report.scala:63) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:662) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$3(TreePickler.scala:432) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$3(TreePickler.scala:434) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6751/0x0000000101beb040.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:434) at dotty.tools.dotc.core.tasty.TreePickler.pickleTreeUnlessEmpty(TreePickler.scala:321) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:338) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$adapted$1(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6749/0x0000000101bea840.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:550) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$9$$anonfun$1(TreePickler.scala:474) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6779/0x0000000101bf9840.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.immutable.List.foreach(List.scala:333) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$9(TreePickler.scala:474) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$8(TreePickler.scala:474) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6778/0x0000000101bf8440.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:474) at dotty.tools.dotc.core.tasty.TreePickler.pickleTreeUnlessEmpty(TreePickler.scala:321) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:338) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$adapted$1(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6749/0x0000000101bea840.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:565) at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:365) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6745/0x0000000101be9040.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.immutable.List.foreach(List.scala:333) at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:365) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$26(TreePickler.scala:591) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$24(TreePickler.scala:592) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6761/0x0000000101bf1040.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:592) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$1(TreePickler.scala:335) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef$$anonfun$adapted$1(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6749/0x0000000101bea840.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleDef(TreePickler.scala:340) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:567) at dotty.tools.dotc.core.tasty.TreePickler.pickleStats$$anonfun$2(TreePickler.scala:365) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6745/0x0000000101be9040.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.immutable.List.foreach(List.scala:333) at dotty.tools.dotc.core.tasty.TreePickler.pickleStats(TreePickler.scala:365) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$29(TreePickler.scala:607) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree$$anonfun$adapted$27(TreePickler.scala:607) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6743/0x0000000101be7840.apply(Unknown Source) at scala.Function0.apply$mcV$sp(Function0.scala:42) at dotty.tools.dotc.core.tasty.TreePickler.withLength(TreePickler.scala:58) at dotty.tools.dotc.core.tasty.TreePickler.pickleTree(TreePickler.scala:607) at dotty.tools.dotc.core.tasty.TreePickler.pickle$$anonfun$1(TreePickler.scala:779) at dotty.tools.dotc.core.tasty.TreePickler$$Lambda$6742/0x0000000101be7040.applyVoid(Unknown Source) 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.dotc.core.tasty.TreePickler.pickle(TreePickler.scala:779) at dotty.tools.dotc.transform.Pickler.run$$anonfun$1$$anonfun$1(Pickler.scala:72) at dotty.tools.dotc.transform.Pickler$$Lambda$6741/0x0000000101be6840.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.immutable.List.foreach(List.scala:333) at dotty.tools.dotc.transform.Pickler.run$$anonfun$1(Pickler.scala:110) at dotty.tools.dotc.transform.Pickler$$Lambda$6738/0x0000000101be4040.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.immutable.List.foreach(List.scala:333) at dotty.tools.dotc.transform.Pickler.run(Pickler.scala:110) at dotty.tools.dotc.core.Phases$Phase.runOn$$anonfun$1(Phases.scala:316) at dotty.tools.dotc.core.Phases$Phase$$Lambda$6574/0x0000000100ff4040.apply(Unknown Source) at scala.collection.immutable.List.map(List.scala:250) at dotty.tools.dotc.core.Phases$Phase.runOn(Phases.scala:320) at dotty.tools.dotc.transform.Pickler.runOn(Pickler.scala:115) at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:233) at dotty.tools.dotc.Run$$Lambda$5632/0x00000001018f1840.applyVoid(Unknown Source) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1321) at dotty.tools.dotc.Run.runPhases$1(Run.scala:244) at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:252) at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:261) at dotty.tools.dotc.Run$$Lambda$5594/0x00000001018c3440.apply(Unknown Source) at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:68) at dotty.tools.dotc.Run.compileUnits(Run.scala:261) at dotty.tools.dotc.Run.compileSources(Run.scala:185) at dotty.tools.dotc.Run.compile(Run.scala:169) at dotty.tools.dotc.Driver.doCompile(Driver.scala:35) at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:88) - locked <0x00000000e036d438> (a dotty.tools.xsbt.CompilerBridgeDriver) at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22) at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:193) at sbt.internal.inc.MixedAnalyzingCompiler$$Lambda$5325/0x00000001015f0c40.apply$mcV$sp(Unknown Source) at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23) at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:248) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:183) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163) at sbt.internal.inc.MixedAnalyzingCompiler$$Lambda$5321/0x00000001015ed040.apply(Unknown Source) at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239) at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163) at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:211) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.IncrementalCompilerImpl$$Lambda$3110/0x0000000100ee7c40.apply(Unknown Source) at sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:179) at sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:177) at sbt.internal.inc.Incremental$$$Lambda$3117/0x0000000100ef7040.apply(Unknown Source) at sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:463) at sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116) at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56) at sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52) at sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263) at sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:418) at sbt.internal.inc.Incremental$$$Lambda$3153/0x0000000100f1a840.apply(Unknown Source) at sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:506) at sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:405) at sbt.internal.inc.Incremental$.apply(Incremental.scala:171) at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:488) at sbt.internal.inc.IncrementalCompilerImpl$$Lambda$3039/0x0000000100e84840.apply(Unknown Source) at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332) at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:425) at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137) at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2363) at sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2313) at sbt.Defaults$$$Lambda$3032/0x0000000100e83040.apply(Unknown Source) at sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:30) at sbt.internal.server.BspCompileTask$$$Lambda$3034/0x0000000100e87040.apply(Unknown Source) at sbt.internal.io.Retry$.apply(Retry.scala:46) at sbt.internal.io.Retry$.apply(Retry.scala:28) at sbt.internal.io.Retry$.apply(Retry.scala:23) at sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:30) at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2311) at sbt.Defaults$$$Lambda$892/0x00000001006d8040.apply(Unknown Source) at scala.Function1.$anonfun$compose$1(Function1.scala:49) at scala.Function1$$Lambda$291/0x0000000100461840.apply(Unknown Source) at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:62) at sbt.internal.util.$tilde$greater$$Lambda$2610/0x0000000100d29840.apply(Unknown Source) at sbt.std.Transform$$anon$4.work(Transform.scala:68) at sbt.Execute.$anonfun$submit$2(Execute.scala:282) at sbt.Execute$$Lambda$2640/0x0000000100d36c40.apply(Unknown Source) at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:23) at sbt.Execute.work(Execute.scala:291) at sbt.Execute.$anonfun$submit$1(Execute.scala:282) at sbt.Execute$$Lambda$2620/0x0000000100d2f440.apply(Unknown Source) at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265) at sbt.ConcurrentRestrictions$$anon$4$$Lambda$2627/0x0000000100d32040.apply(Unknown Source) at sbt.CompletionService$$anon$2.call(CompletionService.scala:64) at java.util.concurrent.FutureTask.run(java.base@11.0.9.1/FutureTask.java:264) at java.util.concurrent.Executors$RunnableAdapter.call(java.base@11.0.9.1/Executors.java:515) at java.util.concurrent.FutureTask.run(java.base@11.0.9.1/FutureTask.java:264) at java.util.concurrent.ThreadPoolExecutor.runWorker(java.base@11.0.9.1/ThreadPoolExecutor.java:1128) at java.util.concurrent.ThreadPoolExecutor$Worker.run(java.base@11.0.9.1/ThreadPoolExecutor.java:628) at java.lang.Thread.run(java.base@11.0.9.1/Thread.java:834)```
WojciechMazur commented 1 year ago

The error leading to an infinite loop was caused by the issue described in https://github.com/lampepfl/dotty/issues/16437 Even though this case leading to the infinite loop is already fixed, there seems to be a more general issue related to reporting errors.

odersky commented 1 year ago

I would not say this is about reporting errors but about preventing the compiler to get into illegal states. An underlying that points to itself is illegal. We cannot check for cycles (too expensive) so the scheme is to prevent that in the first place. If the illegal state is caused by an erroneous program it's not enough to report the error we also have to prevent the illegal state internally.