Compiler crash when context bound is used inside type lambda

[t9dupuy]

Compiler version

3.6.3

Minimized code

trait Foo:
  type TC[T]
  type A[X: TC]                 // error (expected)
  type C = [X: TC] =>> List[X]  // crash

Output (click arrow to expand)

[info] compiling 1 Scala source to D:\scala\canopy\target\scala-3.6.3\classes ...
[info] 
[info]   exception occurred while typechecking D:\scala\canopy\src\main\scala\Main.scala
[info] root / Compile / compileIncremental 0s
[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: D:\scala\canopy\src\main\scala\Main.scala
[info]         during phase: typer
[info]                 mode: Mode(ImplicitsEnabled,ReadPositions)
[info]      library version: version 2.13.15
[info]     compiler version: version 3.6.3
[info]             settings: -Xsemanticdb true -classpath D:\scala\canopy\target\scala-3.6.3\classes;D:\packages\coursier\https\repo1.maven.org\maven2\org\scala-lang\scala3-library_3\3.6.3\scala3-library_3-3.6.3.jar;D:\packages\coursier\https\repo1.maven.org\maven2\com\sourcegraph\semanticdb-javac\0.10.3\semanticdb-javac-0.10.3.jar;D:\packages\coursier\https\repo1.maven.org\maven2\org\scala-lang\scala-library\2.13.15\scala-library-2.13.15.jar -d D:\scala\canopy\target\scala-3.6.3\classes -semanticdb-target D:\scala\canopy\target\scala-3.6.3\meta
[error] ## Exception when compiling 2 sources to D:\scala\canopy\target\scala-3.6.3\classes
[error] java.lang.IllegalArgumentException: Thicket {
[error]   X
[error]   lazy given val given_TC_X: X : TC
[error]  } does not have a symbol
[error] dotty.tools.dotc.typer.Namer.symbolOfTree(Namer.scala:105)
[error] dotty.tools.dotc.typer.Namer$TypeDefCompleter.completerTypeParams$$anonfun$1(Namer.scala:1037)
[error] scala.collection.immutable.List.map(List.scala:247)
[error] dotty.tools.dotc.typer.Namer$TypeDefCompleter.completerTypeParams(Namer.scala:1037)
[error] dotty.tools.dotc.typer.Namer$TypeDefCompleter.typeSig(Namer.scala:1044)
[error] dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:990)
[error] dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:859)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:175)
[error] dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:190)
[error] dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:192)
[error] dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:393)
[error] dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:3447)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3472)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3584)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3662)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3666)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3688)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3734)
[error] dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:3164)
[error] dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3488)
[error] dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3492)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3584)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3662)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3666)
[error] dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3688)
[error] dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3734)
[error] dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:3297)
[error] dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3534)
[error] dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3585)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3662)
[error] dotty.tools.dotc.typer.Typer.typed(Typer.scala:3666)
[error] dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3777)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:47)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:507)
[error] dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:53)
[error] dotty.tools.dotc.typer.TyperPhase.$anonfun$4(TyperPhase.scala:99)
[error] scala.collection.Iterator$$anon$6.hasNext(Iterator.scala:479)
[error] scala.collection.Iterator$$anon$9.hasNext(Iterator.scala:583)
[error] scala.collection.immutable.List.prependedAll(List.scala:152)
[error] scala.collection.immutable.List$.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:98)
[error] dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:343)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
[error] scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
[error] scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
[error] dotty.tools.dotc.Run.runPhases$1(Run.scala:336)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:383)
[error] dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:395)
[error] dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69)
[error] dotty.tools.dotc.Run.compileUnits(Run.scala:395)
[error] dotty.tools.dotc.Run.compileSources(Run.scala:282)
[error] dotty.tools.dotc.Run.compile(Run.scala:267)
[error] dotty.tools.dotc.Driver.doCompile(Driver.scala:37)
[error] dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141)
[error] dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22)
[error] sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:196)
[error] scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23)
[error] sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:252)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:186)
[error] sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:166)
[error] sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:241)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:166)
[error] sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:214)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:542)
[error] sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:542)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3(Incremental.scala:182)
[error] sbt.internal.inc.Incremental$.$anonfun$apply$3$adapted(Incremental.scala:180)
[error] sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:458)
[error] sbt.internal.inc.IncrementalCommon$CycleState.next(IncrementalCommon.scala:117)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:56)
[error] sbt.internal.inc.IncrementalCommon$$anon$1.next(IncrementalCommon.scala:52)
[error] sbt.internal.inc.IncrementalCommon.cycle(IncrementalCommon.scala:263)
[error] sbt.internal.inc.Incremental$.$anonfun$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:2443)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2393)
[error] sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:41)
[error] sbt.internal.io.Retry$.apply(Retry.scala:47)
[error] sbt.internal.io.Retry$.apply(Retry.scala:29)
[error] sbt.internal.io.Retry$.apply(Retry.scala:24)
[error] sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:41)
[error] sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2391)
[error] scala.Function1.$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:515)
[error] java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[error] java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[error] java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[error] java.base/java.lang.Thread.run(Thread.java:829)
[error]
[error] stack trace is suppressed; run 'last Compile / compileIncremental' for the full output
[error] (Compile / compileIncremental) java.lang.IllegalArgumentException: Thicket {
[error]   X
[error]   lazy given val given_TC_X: X : TC
[error]  } does not have a symbol

Expected behavior

This should fail to compile (result in an error) but not crash.

[mbovel]

This issue was picked for the Scala Issue Spree of tomorrow, Monday, February 24th. @natsukagami and @jan-pieter will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here.