classcast error within the compiler

[bbeyl-it]

Compiler version

3.3.7
If you're not sure what version you're using, run print scalaVersion from sbt
(if you're running scalac manually, use scalac -version instead).

Minimized code

Can't provide due to client and time constraints

Output (click arrow to expand)

---

relevant part from build.sbt

   scalacOptions ++= Seq(
      // "-classpath", "foo:bar:...",         // Add to the classpath.
      "-encoding", "utf-8",                // Specify character encoding used by source files.
      "-deprecation",                      // Emit warning and location for usages of deprecated APIs.
      "-unchecked",                        // Enable additional warnings where generated code depends on assumptions.
      "-feature",                          // Emit warning and location for usages of features that should be imported explicitly.
      "-explain",                          // Explain errors in more detail.
      // "-explain-types",                    // Explain type errors in more detail.
      // "-indent",                           // Together with -rewrite, remove {...} syntax when possible due to significant indentation.
      // "-no-indent",                        // Require classical {...} syntax, indentation is not significant.
      "-new-syntax",                       // Require `then` and `do` in control expressions.
      // "-old-syntax",                       // Require `(...)` around conditions.
      // "-language:Scala2",                  // Compile Scala 2 code, highlight what needs updating
      // "-language:strictEquality",          // Require +derives Eql+ for using == or != comparisons
      // "-rewrite",                          // Attempt to fix code automatically. Use with -indent and ...-migration.
      // "-scalajs",                          // Compile in Scala.js mode (requires scalajs-library.jar on the classpath).
//      "-source:future",                       // Choices: future and future-migration. I use this to force future deprecation warnings, etc.
//      "-source:3.3-migration",                       // Choices: future and future-migration. I use this to force future deprecation warnings, etc.
//      "-Xfatal-warnings",                  // Fail on warnings, not just errors
      // "-Xmigration",                       // Warn about constructs whose behavior may have changed since version.
      // "-Ysafe-init",                       // Warn on field access before initialization
      // "-Yexplicit-nulls",                  // For explicit nulls behavior.
      // "-coverage-out", "coverage"          // Output "scoverage" metrics (new for Scala 3.2.0)
    ),
    javaOptions ++= Seq(
      "-Duser.language=en_US"
    ),
    javacOptions ++= Seq(
      "-Xlint:unchecked", "-Xlint:deprecation", // Java 8: "-Xdiags:verbose"),
      "-source", "21", "target", "21",
    ),

---

[info]   exception occurred while typechecking /home/.../scala/.../src/test/scala/eet/core/collection/interval/IntervalSpec.scala
[info] 
[info]   An unhandled exception was thrown in the compiler.
[info]   Please file a crash report here:
[info]   https://github.com/scala/scala3/issues/new/choose
[info]   For non-enriched exceptions, compile with -Xno-enrich-error-messages.
[info] 
[info] 
[info]      while compiling: /home/bbeyl/customer/uniper/projects/scala/eet-core/1.4/src/test/scala/eet/core/collection/interval/IntervalSpec.scala
[info]         during phase: typer
[info]                 mode: Mode(ImplicitsEnabled)
[info]      library version: version 2.13.16
[info]     compiler version: version 3.3.7
[info]             settings: -classpath /home/bbeyl/customer/uniper/projects/scala/eet-core/1.4/target/scala-3.3.7/test-classes:/home/bbeyl/customer/uniper/projects/scala/eet-core/1.4/target/scala-3.3.7/classes:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scala-lang/scala3-library_3/3.3.7/scala3-library_3-3.3.7.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/joda-time/joda-time/2.14.0/joda-time-2.14.0.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/joda/joda-convert/3.0.1/joda-convert-3.0.1.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/log4j/log4j/1.2.17/log4j-1.2.17.jar:/home/bbeyl/.m2/repository/org/slf4j/slf4j-api/1.7.22/slf4j-api-1.7.22.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/apache/commons/commons-math3/3.6.1/commons-math3-3.6.1.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalactic/scalactic_3/3.2.9/scalactic_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scala-lang/modules/scala-xml_3/2.0.1/scala-xml_3-2.0.1.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest_3/3.2.9/scalatest_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scala-lang/scala-library/2.13.16/scala-library-2.13.16.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-core_3/3.2.9/scalatest-core_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-featurespec_3/3.2.9/scalatest-featurespec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-flatspec_3/3.2.9/scalatest-flatspec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-freespec_3/3.2.9/scalatest-freespec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-funsuite_3/3.2.9/scalatest-funsuite_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-funspec_3/3.2.9/scalatest-funspec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-propspec_3/3.2.9/scalatest-propspec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-refspec_3/3.2.9/scalatest-refspec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-wordspec_3/3.2.9/scalatest-wordspec_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-diagrams_3/3.2.9/scalatest-diagrams_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-matchers-core_3/3.2.9/scalatest-matchers-core_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-shouldmatchers_3/3.2.9/scalatest-shouldmatchers_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-mustmatchers_3/3.2.9/scalatest-mustmatchers_3-3.2.9.jar:/home/bbeyl/customer/uniper/coursier/v1/https/uitartifactory.jfrog.io/uitartifactory/libs-release/org/scalatest/scalatest-compatible/3.2.9/scalatest-compatible-3.2.9.jar -d /home/bbeyl/customer/uniper/projects/scala/eet-core/1.4/target/scala-3.3.7/test-classes -deprecation true -encoding utf-8 -explain true -feature true -new-syntax true
[error] ## Exception when compiling 21 sources to /home/bbeyl/customer/uniper/projects/scala/eet-core/1.4/target/scala-3.3.7/test-classes
[error] java.lang.ClassCastException: class dotty.tools.dotc.core.Types$NoType$ cannot be cast to class dotty.tools.dotc.typer.Implicits$SearchFailureType (dotty.tools.dotc.core.Types$NoType$ and dotty.tools.dotc.typer.Implicits$SearchFailureType are in unnamed module of loader sbt.internal.classpath.ClassLoaderCache$Key$CachedClassLoader @6abc0a67)
[error] dotty.tools.dotc.typer.Implicits$SearchFailure.reason(Implicits.scala:417)
[error] dotty.tools.dotc.typer.ErrorReporting$Errors.selectErrorAddendum$$anonfun$1$$anonfun$1(ErrorReporting.scala:228)
[error] scala.collection.immutable.List.foreach(List.scala:334)
[error] dotty.tools.dotc.typer.ErrorReporting$Errors.selectErrorAddendum$$anonfun$1(ErrorReporting.scala:226)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.Option.foreach(Option.scala:437)
[error] dotty.tools.dotc.typer.ErrorReporting$Errors.selectErrorAddendum(ErrorReporting.scala:225)
[error] dotty.tools.dotc.typer.TypeAssigner.addendum$1(TypeAssigner.scala:176)
[error] dotty.tools.dotc.typer.TypeAssigner.$anonfun$1(TypeAssigner.scala:179)
[error] dotty.tools.dotc.reporting.NotAMember.msg(messages.scala:382)
[error] dotty.tools.dotc.reporting.Message.message$$anonfun$1(Message.scala:341)
[error] dotty.tools.dotc.reporting.Message.inMessageContext(Message.scala:337)
[error] dotty.tools.dotc.reporting.Message.message(Message.scala:341)
[error] dotty.tools.dotc.reporting.Message.isNonSensical(Message.scala:318)
[error] dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden(HideNonSensicalMessages.scala:17)
[error] dotty.tools.dotc.reporting.HideNonSensicalMessages.isHidden$(HideNonSensicalMessages.scala:10)
[error] dotty.tools.dotc.reporting.AbstractReporter.isHidden(AbstractReporter.scala:8)
[error] dotty.tools.dotc.reporting.Reporter.issueUnconfigured(Reporter.scala:164)
[error] dotty.tools.dotc.reporting.Reporter.go$1(Reporter.scala:204)
[error] dotty.tools.dotc.reporting.Reporter.issueIfNotSuppressed(Reporter.scala:223)
[error] dotty.tools.dotc.reporting.Reporter.report(Reporter.scala:226)
[error] dotty.tools.dotc.reporting.Reporter.flush$$anonfun$1(Reporter.scala:287)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.immutable.List.foreach(List.scala:334)
[error] dotty.tools.dotc.reporting.Reporter.flush(Reporter.scala:287)
[error] dotty.tools.dotc.core.TyperState.commit(TyperState.scala:176)
[error] dotty.tools.dotc.typer.Applications.fail$1(Applications.scala:1145)
[error] dotty.tools.dotc.typer.Applications.$anonfun$13$$anonfun$1(Applications.scala:1153)
[error] scala.Option.getOrElse(Option.scala:201)
[error] dotty.tools.dotc.typer.Applications.$anonfun$13(Applications.scala:1154)
[error] dotty.tools.dotc.typer.Typer.tryEither(Typer.scala:3441)
[error] dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:1155)
[error] dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:1198)
[error] dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:403)
[error] dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:122)
[error] dotty.tools.dotc.typer.Typer.typedInfixOp(Typer.scala:3032)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3187)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3229)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3299)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3303)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3352)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3371)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2768)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3136)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3140)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3228)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3299)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3303)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3325)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3371)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2911)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3181)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3229)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3299)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3303)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3414)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:45)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:467)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:51)
[error] dotty.tools.dotc.typer.TyperPhase.$anonfun$4(TyperPhase.scala:97)
[error] scala.collection.Iterator$$anon$6.hasNext(Iterator.scala:479)
[error] scala.collection.Iterator$$anon$9.hasNext(Iterator.scala:583)
[error] scala.collection.immutable.List.prependedAll(List.scala:155)
[error] scala.collection.immutable.List$.from(List.scala:685)
[error] scala.collection.immutable.List$.from(List.scala:682)
[error] scala.collection.IterableOps$WithFilter.map(Iterable.scala:900)
[error] dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:96)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:351)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1324)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:344)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:384)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:393)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:393)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:297)
[error] dotty.tools.dotc.Run.compile(Run.scala:282)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:196)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:252)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:186)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:166)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:241)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:166)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:214)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:542)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:542)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3(Incremental.scala:182)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3$adapted(Incremental.scala:180)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:458)
[error] sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:116)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:264)
[error] sbt.internal.inc.Incremental$.$anonfun$incrementalCompile$8(Incremental.scala:413)
[error] sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:500)
[error] sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:400)
[error] sbt.internal.inc.Incremental$.apply(Incremental.scala:208)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:542)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:496)
[error] sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332)
[error] sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:433)
[error] sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137)
[error] sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2471)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2421)
[error] sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:41)
[error] sbt.internal.io.Retry$.sbt$internal$io$Retry$$impl(Retry.scala:114)
[error] sbt.internal.io.Retry$.io(Retry.scala:102)
[error] sbt.internal.io.Retry$.io(Retry.scala:78)
[error] sbt.internal.io.Retry$.io(Retry.scala:67)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:41)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2419)
[error] scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63)
[error] sbt.std.Transform$$anon$4.work(Transform.scala:69)
[error] sbt.Execute.$anonfun$submit$2(Execute.scala:283)
[error] sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24)
[error] sbt.Execute.work(Execute.scala:292)
[error] sbt.Execute.$anonfun$submit$1(Execute.scala:283)
[error] sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] sbt.CompletionService$$anon$2.call(CompletionService.scala:65)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
[error] java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
[error] java.base/java.lang.Thread.run(Thread.java:833)
[error]            
[error] stack trace is suppressed; run last Test / compileIncremental for the full output
[error] (Test / compileIncremental) java.lang.ClassCastException: class dotty.tools.dotc.core.Types$NoType$ cannot be cast to class dotty.tools.dotc.typer.Implicits$SearchFailureType (dotty.tools.dotc.core.Types$NoType$ and dotty.tools.dotc.typer.Implicits$SearchFailureType are in unnamed module of loader sbt.internal.classpath.ClassLoaderCache$Key$CachedClassLoader @6abc0a67)
[error] Total time: 13 s, completed Nov 3, 2025, 9:44:47 AM
[IJ]

---

code compiles with scalac 3.3.5, 3.3.6

[tgodzik]

Thanks for reporting! @bracevac I see that you modified that part last:

  case class SearchFailure(tree: Tree) extends SearchResult {
    final def isAmbiguous: Boolean = tree.tpe.isInstanceOf[AmbiguousImplicits | TooUnspecific]
    final def reason: SearchFailureType = tree.tpe.asInstanceOf[SearchFailureType]
  }

should we just a match statement there, do you know cases where this would fail?

@bbeyl-it are you able to reproduce it on 3.7.3 version as well?

[bracevac]

Thanks for reporting! @bracevac I see that you modified that part last:

Wrong Oliv(i)er.

[tgodzik]

Ach right, I just read "Oliver" and my brain refused to read the surname 😅 So if anyone knows what could be the cause here or whether we can just add a match statement to fix it that would be useful.

@bbeyl-it it might also be useful if you are able to create a small reproduction.

[noti0na1]

Could be fixed by #18830 which is not backported to LTS?

[tgodzik]

looks like it, thanks! Will backport it.

[Gedochao]

(edited the original post for improved readability with snippets)

[Gedochao]

@bbeyl-it any chance you could confirm if this occurs with a recent Scala version, or just LTS? (preferably 3.7.3, 3.7.4-RC3 or a nightly of 3.8, like 3.8.0-RC1-bin-20251104-b83b3d9-NIGHTLY)

[bbeyl-it]

Crash occurs using scalac 3.3.7; with 3.3.5 it doesn't crash; unfortunately I can't check with other versions of the compiler because of client (== system owner) constraints.