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The Scala 3 compiler, also known as Dotty.
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Crash regarding F-bounded identity alias #20317

Open s5bug opened 2 months ago

s5bug commented 2 months ago

Compiler version

3.4.1, 3.4.2-RC1

Minimized code

type Foo[A] = A

def foo[A <: Foo[A]]: Unit = ()

Output (click arrow to expand)

3.4.2-RC1:

```scala java.lang.AssertionError: assertion failed: NoType at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8) at dotty.tools.dotc.core.Types$TypeBounds.<init>(Types.scala:5493) at dotty.tools.dotc.core.Types$AliasingBounds.<init>(Types.scala:5572) at dotty.tools.dotc.core.Types$TypeAlias.<init>(Types.scala:5596) at dotty.tools.dotc.core.Types$TypeAlias$.apply(Types.scala:5633) at dotty.tools.dotc.core.Types$Type.bounds(Types.scala:1813) at dotty.tools.dotc.core.GadtState.$anonfun$4$$anonfun$1(GadtConstraint.scala:197) at scala.collection.immutable.List.map(List.scala:246) at dotty.tools.dotc.core.GadtState.$anonfun$4(GadtConstraint.scala:201) at dotty.tools.dotc.core.Types$PolyType.<init>(Types.scala:4333) at dotty.tools.dotc.core.Types$PolyType$.apply(Types.scala:4439) at dotty.tools.dotc.core.GadtState.addToConstraint(GadtConstraint.scala:204) at dotty.tools.dotc.core.GadtState.addToConstraint$(GadtConstraint.scala:156) at dotty.tools.dotc.core.ProperGadtState.addToConstraint(GadtConstraint.scala:289) at dotty.tools.dotc.typer.Typer.typedDefDef(Typer.scala:2619) at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3119) at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3220) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3298) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3302) at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3324) at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3370) at dotty.tools.dotc.typer.Typer.typedClassDef(Typer.scala:2814) at dotty.tools.dotc.typer.Typer.typedTypeOrClassDef$1(Typer.scala:3125) at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:3129) at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3220) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3298) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3302) at dotty.tools.dotc.typer.Typer.traverse$1(Typer.scala:3324) at dotty.tools.dotc.typer.Typer.typedStats(Typer.scala:3370) at dotty.tools.dotc.typer.Typer.typedPackageDef(Typer.scala:2947) at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:3171) at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:3221) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3298) at dotty.tools.dotc.typer.Typer.typed(Typer.scala:3302) at dotty.tools.dotc.typer.Typer.typedExpr(Typer.scala:3413) at dotty.tools.dotc.typer.TyperPhase.typeCheck$$anonfun$1(TyperPhase.scala:47) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at dotty.tools.dotc.core.Phases$Phase.monitor(Phases.scala:477) at dotty.tools.dotc.typer.TyperPhase.typeCheck(TyperPhase.scala:53) at dotty.tools.dotc.typer.TyperPhase.$anonfun$4(TyperPhase.scala:99) at scala.collection.Iterator$$anon$6.hasNext(Iterator.scala:479) at scala.collection.Iterator$$anon$9.hasNext(Iterator.scala:583) at scala.collection.immutable.List.prependedAll(List.scala:152) at scala.collection.immutable.List$.from(List.scala:684) at scala.collection.immutable.List$.from(List.scala:681) at scala.collection.IterableOps$WithFilter.map(Iterable.scala:898) at dotty.tools.dotc.typer.TyperPhase.runOn(TyperPhase.scala:100) at dotty.tools.dotc.Run.runPhases$1$$anonfun$1(Run.scala:315) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15) at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10) at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323) at dotty.tools.dotc.Run.runPhases$1(Run.scala:337) at dotty.tools.dotc.Run.compileUnits$$anonfun$1(Run.scala:350) at dotty.tools.dotc.Run.compileUnits$$anonfun$adapted$1(Run.scala:360) at dotty.tools.dotc.util.Stats$.maybeMonitored(Stats.scala:69) at dotty.tools.dotc.Run.compileUnits(Run.scala:360) at dotty.tools.dotc.Run.compileSources(Run.scala:261) at dotty.tools.dotc.Run.compile(Run.scala:246) at dotty.tools.dotc.Driver.doCompile(Driver.scala:37) at dotty.tools.xsbt.CompilerBridgeDriver.run(CompilerBridgeDriver.java:141) at dotty.tools.xsbt.CompilerBridge.run(CompilerBridge.java:22) at sbt.internal.inc.AnalyzingCompiler.compile(AnalyzingCompiler.scala:91) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$7(MixedAnalyzingCompiler.scala:193) at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:23) at sbt.internal.inc.MixedAnalyzingCompiler.timed(MixedAnalyzingCompiler.scala:248) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4(MixedAnalyzingCompiler.scala:183) at sbt.internal.inc.MixedAnalyzingCompiler.$anonfun$compile$4$adapted(MixedAnalyzingCompiler.scala:163) at sbt.internal.inc.JarUtils$.withPreviousJar(JarUtils.scala:239) at sbt.internal.inc.MixedAnalyzingCompiler.compileScala$1(MixedAnalyzingCompiler.scala:163) at sbt.internal.inc.MixedAnalyzingCompiler.compile(MixedAnalyzingCompiler.scala:211) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileInternal$1$adapted(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.Incremental$.$anonfun$apply$5(Incremental.scala:180) at sbt.internal.inc.Incremental$.$anonfun$apply$5$adapted(Incremental.scala:178) at sbt.internal.inc.Incremental$$anon$2.run(Incremental.scala:464) at sbt.internal.inc.IncrementalCommon$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$8(Incremental.scala:419) at sbt.internal.inc.Incremental$.withClassfileManager(Incremental.scala:506) at sbt.internal.inc.Incremental$.incrementalCompile(Incremental.scala:406) at sbt.internal.inc.Incremental$.apply(Incremental.scala:172) at sbt.internal.inc.IncrementalCompilerImpl.compileInternal(IncrementalCompilerImpl.scala:534) at sbt.internal.inc.IncrementalCompilerImpl.$anonfun$compileIncrementally$1(IncrementalCompilerImpl.scala:488) at sbt.internal.inc.IncrementalCompilerImpl.handleCompilationError(IncrementalCompilerImpl.scala:332) at sbt.internal.inc.IncrementalCompilerImpl.compileIncrementally(IncrementalCompilerImpl.scala:425) at sbt.internal.inc.IncrementalCompilerImpl.compile(IncrementalCompilerImpl.scala:137) at sbt.Defaults$.compileIncrementalTaskImpl(Defaults.scala:2371) at sbt.Defaults$.$anonfun$compileIncrementalTask$2(Defaults.scala:2321) at sbt.internal.server.BspCompileTask$.$anonfun$compute$1(BspCompileTask.scala:31) at sbt.internal.io.Retry$.apply(Retry.scala:47) at sbt.internal.io.Retry$.apply(Retry.scala:29) at sbt.internal.io.Retry$.apply(Retry.scala:24) at sbt.internal.server.BspCompileTask$.compute(BspCompileTask.scala:31) at sbt.Defaults$.$anonfun$compileIncrementalTask$1(Defaults.scala:2319) at scala.Function1.$anonfun$compose$1(Function1.scala:49) at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63) at sbt.std.Transform$$anon$4.work(Transform.scala:69) at sbt.Execute.$anonfun$submit$2(Execute.scala:283) at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24) at sbt.Execute.work(Execute.scala:292) at sbt.Execute.$anonfun$submit$1(Execute.scala:283) at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265) at sbt.CompletionService$$anon$2.call(CompletionService.scala:65) at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539) at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) at java.base/java.lang.Thread.run(Thread.java:840) ```

etc

I minimized this from

type SemigroupStructural[A] =
  A & { def combine(a: A): A }
def combineAll[A <: SemigroupStructural[A]](
  i: A, l: List[A]
): A = l.foldLeft(i)(_.combine(_))

which also crashes (but differently, due to a stack overflow) rather than producing a compile error.

Unfortunately I lack scalac on this current computer and I can't figure out how to get Scastie to give me a real stacktrace:

Recursion limit exceeded.
Maybe there is an illegal cyclic reference?
If that's not the case, you could also try to increase the stacksize using the -Xss JVM option.
For the unprocessed stack trace, compile with -Yno-decode-stacktraces.
A recurring operation is (inner to outer):

  subtype (i : A) <:< B
  subtype (i : A) <:< B
Gedochao commented 2 months ago

On the latest nightly the output changes to:

-- Error: /Users/pchabelski/IdeaProjects/scala-cli-tests/compiler-repro/repro.scala:3:10 
3 |def foo[A <: Foo[A]]: Unit = ()
  |          ^
  |Recursion limit exceeded.
  |Maybe there is an illegal cyclic reference?
  |If that's not the case, you could also try to increase the stacksize using the -Xss JVM option.
  |For the unprocessed stack trace, compile with -Xno-decode-stacktraces.
  |A recurring operation is (inner to outer):
  |
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
  |  type parameters of A
  |  type parameters of A
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
  |  type parameters of A
  |  type parameters of A
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
  |  ...
  |
  |  type parameters of A
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
  |  type parameters of A
  |  type parameters of A
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
  |  type parameters of A
  |  type parameters of Foo[A]
  |  type parameters of  <: Foo[A]
1 error found