scala-reflect: SymbolTable assertion failed when there are multiple overloads with the same name as the type name

[neko-kai]

The following code:

package object example {
  def Self[A](a: A): Self[A] = ???
  def Self[A](unit: Unit): Self[A] = ???
}

package example {

  trait Self[A] {
    def self: A
  }

  object App extends App {
    println(scala.reflect.runtime.universe.typeOf[Self[Any]].toString)
  }

}

Actual:
Fails with the following exception:

Exception in thread "main" java.lang.AssertionError: assertion failed: Self
	at scala.reflect.internal.SymbolTable.throwAssertionError(SymbolTable.scala:170)
	at scala.reflect.internal.Symbols$Symbol.completeInfo(Symbols.scala:1528)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1517)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol$$anon$7.scala$reflect$runtime$SynchronizedSymbols$SynchronizedSymbol$$super$info(SynchronizedSymbols.scala:203)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.info(SynchronizedSymbols.scala:158)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.info$(SynchronizedSymbols.scala:158)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol$$anon$7.info(SynchronizedSymbols.scala:203)
	at scala.reflect.internal.Symbols$Symbol.initialize(Symbols.scala:1691)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.getFlag(SynchronizedSymbols.scala:153)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.getFlag$(SynchronizedSymbols.scala:152)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol$$anon$7.getFlag(SynchronizedSymbols.scala:203)
	at scala.reflect.internal.Symbols$Symbol.hasFlag(Symbols.scala:744)
	at scala.reflect.internal.HasFlags.hasJavaAnnotationFlag(HasFlags.scala:98)
	at scala.reflect.internal.HasFlags.hasJavaAnnotationFlag$(HasFlags.scala:98)
	at scala.reflect.internal.Symbols$Symbol.hasJavaAnnotationFlag(Symbols.scala:221)
	at scala.reflect.internal.Symbols$SymbolContextApiImpl.isJavaAnnotation(Symbols.scala:125)
	at scala.reflect.internal.Symbols$Symbol.symbolKind(Symbols.scala:2646)
	at scala.reflect.internal.Symbols$Symbol.sanitizedKindString(Symbols.scala:2677)
	at scala.reflect.internal.Symbols$Symbol.kindString(Symbols.scala:2685)
	at scala.reflect.internal.Symbols$Symbol.toString(Symbols.scala:2738)
	at scala.reflect.internal.Symbols$ClassSymbol.toString(Symbols.scala:3449)
	at java.base/java.lang.String.valueOf(String.java:3042)
	at java.base/java.lang.StringBuilder.append(StringBuilder.java:168)
	at scala.reflect.runtime.SymbolLoaders$PackageScope.$anonfun$enter$1(SymbolLoaders.scala:120)
	at scala.reflect.runtime.SymbolLoaders$PackageScope.enter(SymbolLoaders.scala:120)
	at scala.reflect.runtime.SymbolLoaders.initAndEnterClassAndModule(SymbolLoaders.scala:58)
	at scala.reflect.runtime.SymbolLoaders.initAndEnterClassAndModule$(SymbolLoaders.scala:51)
	at scala.reflect.runtime.JavaUniverse.initAndEnterClassAndModule(JavaUniverse.scala:30)
	at scala.reflect.runtime.SymbolLoaders$PackageScope.$anonfun$lookupEntry$1(SymbolLoaders.scala:151)
	at scala.reflect.runtime.SymbolLoaders$PackageScope.syncLockSynchronized(SymbolLoaders.scala:133)
	at scala.reflect.runtime.SymbolLoaders$PackageScope.lookupEntry(SymbolLoaders.scala:135)
	at scala.reflect.internal.Types$Type.findDecl(Types.scala:989)
	at scala.reflect.internal.Types$Type.decl(Types.scala:591)
	at scala.reflect.internal.SymbolTable.$anonfun$openPackageModule$1(SymbolTable.scala:346)
	at scala.reflect.internal.SymbolTable.$anonfun$openPackageModule$1$adapted(SymbolTable.scala:342)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:553)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:551)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1274)
	at scala.reflect.internal.SymbolTable.openPackageModule(SymbolTable.scala:342)
	at scala.reflect.internal.SymbolTable.openPackageModule(SymbolTable.scala:397)
	at scala.reflect.runtime.SymbolLoaders$LazyPackageType.$anonfun$complete$5(SymbolLoaders.scala:83)
	at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.scala:18)
	at scala.reflect.internal.SymbolTable.slowButSafeEnteringPhaseNotLaterThan(SymbolTable.scala:318)
	at scala.reflect.runtime.SymbolLoaders$LazyPackageType.complete(SymbolLoaders.scala:80)
	at scala.reflect.internal.Symbols$Symbol.completeInfo(Symbols.scala:1544)
	at scala.reflect.internal.Symbols$Symbol.info(Symbols.scala:1517)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol$$anon$9.scala$reflect$runtime$SynchronizedSymbols$SynchronizedSymbol$$super$info(SynchronizedSymbols.scala:209)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.info(SynchronizedSymbols.scala:158)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol.info$(SynchronizedSymbols.scala:158)
	at scala.reflect.runtime.SynchronizedSymbols$SynchronizedSymbol$$anon$9.info(SynchronizedSymbols.scala:209)
	at scala.reflect.internal.Types$TypeRef.baseClasses(Types.scala:2593)
	at scala.reflect.internal.tpe.FindMembers$FindMemberBase.init(FindMembers.scala:37)
	at scala.reflect.internal.tpe.FindMembers$FindMember.init(FindMembers.scala:256)
	at scala.reflect.internal.Types$Type.$anonfun$findMember$1(Types.scala:1033)
	at scala.reflect.internal.Types$Type.findMemberInternal$1(Types.scala:1032)
	at scala.reflect.internal.Types$Type.findMember(Types.scala:1037)
	at scala.reflect.internal.Types$Type.memberBasedOnName(Types.scala:666)
	at scala.reflect.internal.Types$Type.member(Types.scala:630)
	at scala.reflect.internal.Mirrors$RootsBase.staticClass(Mirrors.scala:60)
	at scala.reflect.internal.Mirrors$RootsBase.staticClass(Mirrors.scala:29)
	at example.App$$typecreator1$1.apply(package.scala:14)
	at scala.reflect.api.TypeTags$WeakTypeTagImpl.tpe$lzycompute(TypeTags.scala:237)
	at scala.reflect.api.TypeTags$WeakTypeTagImpl.tpe(TypeTags.scala:237)
	at scala.reflect.api.TypeTags.typeOf(TypeTags.scala:357)
	at scala.reflect.api.TypeTags.typeOf$(TypeTags.scala:357)
	at scala.reflect.api.Universe.typeOf(Universe.scala:73)
	at example.App$.delayedEndpoint$example$App$1(package.scala:14)
	at example.App$delayedInit$body.apply(package.scala:13)
	at scala.Function0.apply$mcV$sp(Function0.scala:39)
	at scala.Function0.apply$mcV$sp$(Function0.scala:39)
	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:17)
	at scala.App.$anonfun$main$1(App.scala:73)
	at scala.App.$anonfun$main$1$adapted(App.scala:73)
	at scala.collection.IterableOnceOps.foreach(IterableOnce.scala:553)
	at scala.collection.IterableOnceOps.foreach$(IterableOnce.scala:551)
	at scala.collection.AbstractIterable.foreach(Iterable.scala:921)
	at scala.App.main(App.scala:73)
	at scala.App.main$(App.scala:71)
	at example.App$.main(package.scala:13)
	at example.App.main(package.scala)

Process finished with exit code 1

Note that either removing one of the overloads or moving the Self trait from package example into the package object example makes it work:

// ok
package object example {
  def Self[A](a: A): Self[A] = ???
}

// ok
package object example {
  trait Self[A] {
    def self: A
  }
  def Self[A](a: A): Self[A] = ???
  def Self[A](unit: Unit): Self[A] = ???
}

Motivation for defining methods with the same name is to "package" implicit syntax together with the type in Scala 2, in absence of dotty's import-less extension methods. Example: https://scastie.scala-lang.org/EAdQeqJxTxCdmSlOvBmcag

[neko-kai]

Hmm, this is unlike a typical performance problem or a corner case in scala-reflect, this bug actually means that a class of types is simply unrepresentable in runtime universe currently.

/cc @retronym