Definitions.scala

package dotty.tools
package dotc
package core

import scala.annotation.{threadUnsafe => tu}
import Types.*, Contexts.*, Symbols.*, SymDenotations.*, StdNames.*, Names.*, Phases.*
import Flags.*, Scopes.*, Decorators.*, NameOps.*, Periods.*, NullOpsDecorator.*
import unpickleScala2.Scala2Unpickler.ensureConstructor
import scala.collection.mutable
import collection.mutable
import Denotations.{SingleDenotation, staticRef}
import util.{SimpleIdentityMap, SourceFile, NoSource}
import typer.ImportInfo.RootRef
import Comments.{Comment, docCtx}
import util.Spans.NoSpan
import config.Feature
import Symbols.requiredModuleRef
import cc.{CapturingType, CaptureSet, EventuallyCapturingType}

import scala.annotation.tailrec

object Definitions {

  /** The maximum number of elements in a tuple or product.
   *  This should be removed once we go to hlists.
   */
  val MaxTupleArity: Int = 22

  /** The maximum arity N of a function type that's implemented
   *  as a trait `scala.FunctionN`. Functions of higher arity are possible,
   *  but are mapped in erasure to functions taking a single parameter of type
   *  Object[].
   *  The limit 22 is chosen for Scala2x interop. It could be something
   *  else without affecting the set of programs that can be compiled.
   */
  val MaxImplementedFunctionArity: Int = MaxTupleArity
}

/** A class defining symbols and types of standard definitions
 *
 */
class Definitions {
  import Definitions.*

  private var initCtx: Context = _
  private given currentContext[Dummy_so_its_a_def]: Context = initCtx

  private def newPermanentSymbol[N <: Name](owner: Symbol, name: N, flags: FlagSet, info: Type) =
    newSymbol(owner, name, flags | Permanent, info)

  private def newPermanentClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, infoFn: ClassSymbol => Type) =
    newClassSymbol(owner, name, flags | Permanent | NoInits | Open, infoFn)

  private def enterCompleteClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, parents: List[TypeRef]): ClassSymbol =
    enterCompleteClassSymbol(owner, name, flags, parents, newScope(owner.nestingLevel + 1))

  private def enterCompleteClassSymbol(owner: Symbol, name: TypeName, flags: FlagSet, parents: List[TypeRef], decls: Scope) =
    newCompleteClassSymbol(owner, name, flags | Permanent | NoInits | Open, parents, decls).entered

  private def enterTypeField(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
    scope.enter(newPermanentSymbol(cls, name, flags, TypeBounds.empty))

  private def enterTypeParam(cls: ClassSymbol, name: TypeName, flags: FlagSet, scope: MutableScope) =
    enterTypeField(cls, name, flags | ClassTypeParamCreationFlags, scope)

  private def enterSyntheticTypeParam(cls: ClassSymbol, paramFlags: FlagSet, scope: MutableScope, suffix: String = "T0") =
    enterTypeParam(cls, suffix.toTypeName, paramFlags, scope)

  // NOTE: Ideally we would write `parentConstrs: => Type*` but SIP-24 is only
  // implemented in Dotty and not in Scala 2.
  // See <http://docs.scala-lang.org/sips/pending/repeated-byname.html>.
  private def enterSpecialPolyClass(name: TypeName, paramFlags: FlagSet, parentConstrs: => Seq[Type]): ClassSymbol = {
    val completer = new LazyType {
      def complete(denot: SymDenotation)(using Context): Unit = {
        val cls = denot.asClass.classSymbol
        val paramDecls = newScope
        val typeParam = enterSyntheticTypeParam(cls, paramFlags, paramDecls)
        def instantiate(tpe: Type) =
          if (tpe.typeParams.nonEmpty) tpe.appliedTo(typeParam.typeRef)
          else tpe
        val parents = parentConstrs.toList map instantiate
        denot.info = ClassInfo(ScalaPackageClass.thisType, cls, parents, paramDecls)
      }
    }
    newPermanentClassSymbol(ScalaPackageClass, name, Artifact, completer).entered
  }

  /** The trait FunctionN and ContextFunctionN for some N
   *  @param  name   The name of the trait to be created
   *
   *  FunctionN traits follow this template:
   *
   *      trait FunctionN[-T0,...-T{N-1}, +R] extends Object {
   *        def apply($x0: T0, ..., $x{N_1}: T{N-1}): R
   *      }
   *
   *  That is, they follow the template given for Function2..Function22 in the
   *  standard library, but without `tupled` and `curried` methods and without
   *  a `toString`.
   *
   *  ContextFunctionN traits follow this template:
   *
   *      trait ContextFunctionN[-T0,...,-T{N-1}, +R] extends Object {
   *        def apply(using $x0: T0, ..., $x{N_1}: T{N-1}): R
   *      }
   *  ImpureXYZFunctionN follow this template:
   *
   *      type ImpureXYZFunctionN[-T0,...,-T{N-1}, +R] = {cap} XYZFunctionN[T0,...,T{N-1}, R]
   */
  private def newFunctionNType(name: TypeName): Symbol = {
    val impure = name.startsWith("Impure")
    val completer = new LazyType {
      def complete(denot: SymDenotation)(using Context): Unit = {
        val arity = name.functionArity
        if impure then
          val argParamNames = List.tabulate(arity)(tpnme.syntheticTypeParamName)
          val argVariances = List.fill(arity)(Contravariant)
          val underlyingName = name.asSimpleName.drop(6)
          val underlyingClass = ScalaPackageVal.requiredClass(underlyingName)
          denot.info = TypeAlias(
            HKTypeLambda(argParamNames :+ "R".toTypeName, argVariances :+ Covariant)(
              tl => List.fill(arity + 1)(TypeBounds.empty),
              tl => CapturingType(underlyingClass.typeRef.appliedTo(tl.paramRefs),
                CaptureSet.universal)
            ))
        else
          val cls = denot.asClass.classSymbol
          val decls = newScope
          val paramNamePrefix = tpnme.scala ++ str.NAME_JOIN ++ name ++ str.EXPAND_SEPARATOR
          val argParamRefs = List.tabulate(arity) { i =>
            enterTypeParam(cls, paramNamePrefix ++ "T" ++ (i + 1).toString, Contravariant, decls).typeRef
          }
          val resParamRef = enterTypeParam(cls, paramNamePrefix ++ "R", Covariant, decls).typeRef
          val methodType = MethodType.companion(
            isContextual = name.isContextFunction,
            isImplicit = false)
          decls.enter(newMethod(cls, nme.apply, methodType(argParamRefs, resParamRef), Deferred))
          denot.info =
            ClassInfo(ScalaPackageClass.thisType, cls, ObjectType :: Nil, decls)
      }
    }
    if impure then
      newPermanentSymbol(ScalaPackageClass, name, EmptyFlags, completer)
    else
      newPermanentClassSymbol(ScalaPackageClass, name, Trait | NoInits, completer)
  }

  private def newMethod(cls: ClassSymbol, name: TermName, info: Type, flags: FlagSet = EmptyFlags): TermSymbol =
    newPermanentSymbol(cls, name, flags | Method, info).asTerm

  private def enterMethod(cls: ClassSymbol, name: TermName, info: Type, flags: FlagSet = EmptyFlags): TermSymbol =
    newMethod(cls, name, info, flags).entered

  private def enterPermanentSymbol(name: Name, info: Type, flags: FlagSet = EmptyFlags): Symbol =
    val sym = newPermanentSymbol(ScalaPackageClass, name, flags, info)
    ScalaPackageClass.currentPackageDecls.enter(sym)
    sym

  private def enterAliasType(name: TypeName, tpe: Type, flags: FlagSet = EmptyFlags): TypeSymbol =
    enterPermanentSymbol(name, TypeAlias(tpe), flags).asType

  private def enterBinaryAlias(name: TypeName, op: (Type, Type) => Type): TypeSymbol =
    enterAliasType(name,
      HKTypeLambda(TypeBounds.empty :: TypeBounds.empty :: Nil)(
      tl => op(tl.paramRefs(0), tl.paramRefs(1))))

  private def enterPolyMethod(cls: ClassSymbol, name: TermName, typeParamCount: Int,
                    resultTypeFn: PolyType => Type,
                    flags: FlagSet = EmptyFlags,
                    bounds: TypeBounds = TypeBounds.empty,
                    useCompleter: Boolean = false) = {
    val tparamNames = PolyType.syntheticParamNames(typeParamCount)
    val tparamInfos = tparamNames map (_ => bounds)
    def ptype = PolyType(tparamNames)(_ => tparamInfos, resultTypeFn)
    val info =
      if (useCompleter)
        new LazyType {
          def complete(denot: SymDenotation)(using Context): Unit =
            denot.info = ptype
        }
      else ptype
    enterMethod(cls, name, info, flags)
  }

  private def enterT1ParameterlessMethod(cls: ClassSymbol, name: TermName, resultTypeFn: PolyType => Type, flags: FlagSet) =
    enterPolyMethod(cls, name, 1, resultTypeFn, flags)

  private def mkArityArray(name: String, arity: Int, countFrom: Int): Array[TypeRef | Null] = {
    val arr = new Array[TypeRef | Null](arity + 1)
    for (i <- countFrom to arity) arr(i) = requiredClassRef(name + i)
    arr
  }

  private def completeClass(cls: ClassSymbol, ensureCtor: Boolean = true): ClassSymbol = {
    if (ensureCtor) ensureConstructor(cls, cls.denot.asClass, EmptyScope)
    if (cls.linkedClass.exists) cls.linkedClass.markAbsent()
    cls
  }

  @tu lazy val RootClass: ClassSymbol = newPackageSymbol(
    NoSymbol, nme.ROOT, (root, rootcls) => ctx.base.rootLoader(root)).moduleClass.asClass
  @tu lazy val RootPackage: TermSymbol = newSymbol(
    NoSymbol, nme.ROOTPKG, PackageCreationFlags, TypeRef(NoPrefix, RootClass))

  @tu lazy val EmptyPackageVal: TermSymbol = newPackageSymbol(
    RootClass, nme.EMPTY_PACKAGE, (emptypkg, emptycls) => ctx.base.rootLoader(emptypkg)).entered
  @tu lazy val EmptyPackageClass: ClassSymbol = EmptyPackageVal.moduleClass.asClass

  /** A package in which we can place all methods and types that are interpreted specially by the compiler */
  @tu lazy val OpsPackageVal: TermSymbol = newCompletePackageSymbol(RootClass, nme.OPS_PACKAGE).entered
  @tu lazy val OpsPackageClass: ClassSymbol = OpsPackageVal.moduleClass.asClass

  @tu lazy val ScalaPackageVal: TermSymbol = requiredPackage(nme.scala)
  @tu lazy val ScalaMathPackageVal: TermSymbol = requiredPackage("scala.math")
  @tu lazy val ScalaPackageClass: ClassSymbol = {
    val cls = ScalaPackageVal.moduleClass.asClass
    cls.info.decls.openForMutations.useSynthesizer(
      name =>
        if (name.isTypeName && name.isSyntheticFunction) newFunctionNType(name.asTypeName)
        else NoSymbol)
    cls
  }
  @tu lazy val ScalaPackageObject: Symbol = requiredModule("scala.package")
  @tu lazy val ScalaRuntimePackageVal: TermSymbol = requiredPackage("scala.runtime")
  @tu lazy val ScalaRuntimePackageClass: ClassSymbol = ScalaRuntimePackageVal.moduleClass.asClass
  @tu lazy val JavaPackageVal: TermSymbol = requiredPackage(nme.java)
  @tu lazy val JavaPackageClass: ClassSymbol = JavaPackageVal.moduleClass.asClass
  @tu lazy val JavaLangPackageVal: TermSymbol = requiredPackage(jnme.JavaLang)
  @tu lazy val JavaLangPackageClass: ClassSymbol = JavaLangPackageVal.moduleClass.asClass

  // fundamental modules
  @tu lazy val SysPackage : Symbol = requiredModule("scala.sys.package")
    @tu lazy val Sys_error: Symbol = SysPackage.moduleClass.requiredMethod(nme.error)

  @tu lazy val ScalaXmlPackageClass: Symbol = getPackageClassIfDefined("scala.xml")

  @tu lazy val CompiletimePackageClass: Symbol = requiredPackage("scala.compiletime").moduleClass
    @tu lazy val Compiletime_codeOf: Symbol = CompiletimePackageClass.requiredMethod("codeOf")
    @tu lazy val Compiletime_erasedValue  : Symbol = CompiletimePackageClass.requiredMethod("erasedValue")
    @tu lazy val Compiletime_uninitialized: Symbol = CompiletimePackageClass.requiredMethod("uninitialized")
    @tu lazy val Compiletime_error        : Symbol = CompiletimePackageClass.requiredMethod(nme.error)
    @tu lazy val Compiletime_requireConst : Symbol = CompiletimePackageClass.requiredMethod("requireConst")
    @tu lazy val Compiletime_constValue   : Symbol = CompiletimePackageClass.requiredMethod("constValue")
    @tu lazy val Compiletime_constValueOpt: Symbol = CompiletimePackageClass.requiredMethod("constValueOpt")
    @tu lazy val Compiletime_summonFrom   : Symbol = CompiletimePackageClass.requiredMethod("summonFrom")
    @tu lazy val Compiletime_summonInline   : Symbol = CompiletimePackageClass.requiredMethod("summonInline")
  @tu lazy val CompiletimeTestingPackage: Symbol = requiredPackage("scala.compiletime.testing")
    @tu lazy val CompiletimeTesting_typeChecks: Symbol = CompiletimeTestingPackage.requiredMethod("typeChecks")
    @tu lazy val CompiletimeTesting_typeCheckErrors: Symbol = CompiletimeTestingPackage.requiredMethod("typeCheckErrors")
    @tu lazy val CompiletimeTesting_ErrorClass: ClassSymbol = requiredClass("scala.compiletime.testing.Error")
    @tu lazy val CompiletimeTesting_Error: Symbol = requiredModule("scala.compiletime.testing.Error")
      @tu lazy val CompiletimeTesting_Error_apply = CompiletimeTesting_Error.requiredMethod(nme.apply)
    @tu lazy val CompiletimeTesting_ErrorKind: Symbol = requiredModule("scala.compiletime.testing.ErrorKind")
      @tu lazy val CompiletimeTesting_ErrorKind_Parser: Symbol = CompiletimeTesting_ErrorKind.requiredMethod("Parser")
      @tu lazy val CompiletimeTesting_ErrorKind_Typer: Symbol = CompiletimeTesting_ErrorKind.requiredMethod("Typer")
  @tu lazy val CompiletimeOpsPackage: Symbol = requiredPackage("scala.compiletime.ops")
    @tu lazy val CompiletimeOpsAnyModuleClass: Symbol = requiredModule("scala.compiletime.ops.any").moduleClass
    @tu lazy val CompiletimeOpsIntModuleClass: Symbol = requiredModule("scala.compiletime.ops.int").moduleClass
    @tu lazy val CompiletimeOpsLongModuleClass: Symbol = requiredModule("scala.compiletime.ops.long").moduleClass
    @tu lazy val CompiletimeOpsFloatModuleClass: Symbol = requiredModule("scala.compiletime.ops.float").moduleClass
    @tu lazy val CompiletimeOpsDoubleModuleClass: Symbol = requiredModule("scala.compiletime.ops.double").moduleClass
    @tu lazy val CompiletimeOpsStringModuleClass: Symbol = requiredModule("scala.compiletime.ops.string").moduleClass
    @tu lazy val CompiletimeOpsBooleanModuleClass: Symbol = requiredModule("scala.compiletime.ops.boolean").moduleClass

  /** Note: We cannot have same named methods defined in Object and Any (and AnyVal, for that matter)
   *  because after erasure the Any and AnyVal references get remapped to the Object methods
   *  which would result in a double binding assertion failure.
   * Instead we do the following:
   *
   *  - Have some methods exist only in Any, and remap them with the Erasure denotation
   *    transformer to be owned by Object.
   *  - Have other methods exist only in Object.
   * To achieve this, we synthesize all Any and Object methods; Object methods no longer get
   * loaded from a classfile.
   */
  @tu lazy val AnyClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.Any, Abstract, Nil), ensureCtor = false)
  def AnyType: TypeRef = AnyClass.typeRef
  @tu lazy val MatchableClass: ClassSymbol = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.Matchable, Trait, AnyType :: Nil), ensureCtor = false)
  def MatchableType: TypeRef = MatchableClass.typeRef
  @tu lazy val AnyValClass: ClassSymbol =
    val res = completeClass(enterCompleteClassSymbol(ScalaPackageClass, tpnme.AnyVal, Abstract, List(AnyType, MatchableType)))
    // Mark companion as absent, so that class does not get re-completed
    val companion = ScalaPackageVal.info.decl(nme.AnyVal).symbol
    companion.moduleClass.markAbsent()
    companion.markAbsent()
    res

  def AnyValType: TypeRef = AnyValClass.typeRef

    @tu lazy val Any_== : TermSymbol          = enterMethod(AnyClass, nme.EQ, methOfAny(BooleanType), Final)
    @tu lazy val Any_!= : TermSymbol          = enterMethod(AnyClass, nme.NE, methOfAny(BooleanType), Final)
    @tu lazy val Any_equals: TermSymbol       = enterMethod(AnyClass, nme.equals_, methOfAny(BooleanType))
    @tu lazy val Any_hashCode: TermSymbol     = enterMethod(AnyClass, nme.hashCode_, MethodType(Nil, IntType))
    @tu lazy val Any_toString: TermSymbol     = enterMethod(AnyClass, nme.toString_, MethodType(Nil, StringType))
    @tu lazy val Any_## : TermSymbol          = enterMethod(AnyClass, nme.HASHHASH, ExprType(IntType), Final)
    @tu lazy val Any_isInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOf_, _ => BooleanType, Final)
    @tu lazy val Any_asInstanceOf: TermSymbol = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOf_, _.paramRefs(0), Final)
    @tu lazy val Any_typeTest: TermSymbol     = enterT1ParameterlessMethod(AnyClass, nme.isInstanceOfPM, _ => BooleanType, Final | SyntheticArtifact)
    @tu lazy val Any_typeCast: TermSymbol     = enterT1ParameterlessMethod(AnyClass, nme.asInstanceOfPM, _.paramRefs(0), Final | SyntheticArtifact | StableRealizable)
      // generated by pattern matcher and explicit nulls, eliminated by erasure

    /** def getClass[A >: this.type](): Class[? <: A] */
    @tu lazy val Any_getClass: TermSymbol =
        enterPolyMethod(
          AnyClass, nme.getClass_, 1,
          pt => MethodType(Nil, ClassClass.typeRef.appliedTo(TypeBounds.upper(pt.paramRefs(0)))),
          Final,
          bounds = TypeBounds.lower(AnyClass.thisType))

    def AnyMethods: List[TermSymbol] = List(Any_==, Any_!=, Any_equals, Any_hashCode,
      Any_toString, Any_##, Any_getClass, Any_isInstanceOf, Any_asInstanceOf, Any_typeTest, Any_typeCast)

  @tu lazy val ObjectClass: ClassSymbol = {
    val cls = requiredClass("java.lang.Object")
    assert(!cls.isCompleted, "race for completing java.lang.Object")
    cls.info = ClassInfo(cls.owner.thisType, cls, List(AnyType, MatchableType), newScope)
    cls.setFlag(NoInits | JavaDefined)

    ensureConstructor(cls, cls.denot.asClass, EmptyScope)
    val companion = JavaLangPackageVal.info.decl(nme.Object).symbol.asTerm
    NamerOps.makeConstructorCompanion(companion, cls)
    cls
  }
  def ObjectType: TypeRef = ObjectClass.typeRef

  /** A type alias of Object used to represent any reference to Object in a Java
   *  signature, the secret sauce is that subtype checking treats it specially:
   *
   *    tp <:< FromJavaObject
   *
   *  is equivalent to:
   *
   *    tp <:< Any
   *
   *  This is useful to avoid usability problems when interacting with Java
   *  code where Object is the top type. This is safe because this type will
   *  only appear in signatures of Java definitions in positions where `Object`
   *  might appear, let's enumerate all possible cases this gives us:
   *
   *  1. At the top level:
   *
   *       // A.java
   *       void meth1(Object arg) {}
   *       <T> void meth2(T arg) {} // T implicitly extends Object
   *
   *       // B.scala
   *       meth1(1) // OK
   *       meth2(1) // OK
   *
   *     This is safe even though Int is not a subtype of Object, because Erasure
   *     will detect the mismatch and box the value type.
   *
   *  2. In a class type parameter:
   *
   *       // A.java
   *       void meth3(scala.List<Object> arg) {}
   *       <T> void meth4(scala.List<T> arg) {}
   *
   *       // B.scala
   *       meth3(List[Int](1)) // OK
   *       meth4(List[Int](1)) // OK
   *
   *     At erasure, type parameters are removed and value types are boxed.
   *
   *  3. As the type parameter of an array:
   *
   *       // A.java
   *       void meth5(Object[] arg) {}
   *       <T> void meth6(T[] arg) {}
   *
   *       // B.scala
   *       meth5(Array[Int](1)) // error: Array[Int] is not a subtype of Array[Object]
   *       meth6(Array[Int](1)) // error: Array[Int] is not a subtype of Array[T & Object]
   *
   *
   *     This is a bit more subtle: at erasure, Arrays keep their type parameter,
   *     and primitive Arrays are not subtypes of reference Arrays on the JVM,
   *     so we can't pass an Array of Int where a reference Array is expected.
   *     Array is invariant in Scala, so `meth5` is safe even if we use `FromJavaObject`,
   *     but generic Arrays are treated specially: we always add `& Object` (and here
   *     we mean the normal java.lang.Object type) to these types when they come from
   *     Java signatures (see `translateJavaArrayElementType`), this ensure that `meth6`
   *     is safe to use.
   *
   *  4. As the repeated argument of a varargs method:
   *
   *       // A.java
   *       void meth7(Object... args) {}
   *       <T> void meth8(T... args) {}
   *
   *       // B.scala
   *       meth7(1) // OK (creates a reference array)
   *       meth8(1) // OK (creates a primitive array and copies it into a reference array at Erasure)
   *       val ai = Array[Int](1)
   *       meth7(ai: _*) // OK (will copy the array at Erasure)
   *       meth8(ai: _*) // OK (will copy the array at Erasure)
   *
   *     Java repeated arguments are erased to arrays, so it would be safe to treat
   *     them in the same way: add an `& Object` to the parameter type to disallow
   *     passing primitives, but that would be very inconvenient as it is common to
   *     want to pass a primitive to an Object repeated argument (e.g.
   *     `String.format("foo: %d", 1)`). So instead we type them _without_ adding the
   *     `& Object` and let `ElimRepeated` and `Erasure` take care of doing any necessary adaptation
   *     (note that adapting a primitive array to a reference array requires
   *     copying the whole array, so this transformation only preserves semantics
   *     if the callee does not try to mutate the varargs array which is a reasonable
   *     assumption to make).
   *
   *
   *  This mechanism is similar to `ObjectTpeJavaRef` in Scala 2, except that we
   *  create a new symbol with its own name, this is needed because this type
   *  can show up in inferred types and therefore needs to be preserved when
   *  pickling so that unpickled trees pass `-Ycheck`.
   *
   *  Note that by default we pretty-print `FromJavaObject` as `Object` or simply omit it
   *  if it's the sole upper-bound of a type parameter, use `-Yprint-debug` to explicitly
   *  display it.
   */
  @tu lazy val FromJavaObjectSymbol: TypeSymbol =
    newPermanentSymbol(OpsPackageClass, tpnme.FromJavaObject, JavaDefined, TypeAlias(ObjectType)).entered
  def FromJavaObjectType: TypeRef = FromJavaObjectSymbol.typeRef

  @tu lazy val AnyRefAlias: TypeSymbol = enterAliasType(tpnme.AnyRef, ObjectType)
  def AnyRefType: TypeRef = AnyRefAlias.typeRef

    @tu lazy val Object_eq: TermSymbol = enterMethod(ObjectClass, nme.eq, methOfAnyRef(BooleanType), Final)
    @tu lazy val Object_ne: TermSymbol = enterMethod(ObjectClass, nme.ne, methOfAnyRef(BooleanType), Final)
    @tu lazy val Object_synchronized: TermSymbol = enterPolyMethod(ObjectClass, nme.synchronized_, 1,
        pt => MethodType(List(pt.paramRefs(0)), pt.paramRefs(0)), Final)
    @tu lazy val Object_clone: TermSymbol = enterMethod(ObjectClass, nme.clone_, MethodType(Nil, ObjectType), Protected)
    @tu lazy val Object_finalize: TermSymbol = enterMethod(ObjectClass, nme.finalize_, MethodType(Nil, UnitType), Protected)
    @tu lazy val Object_notify: TermSymbol = enterMethod(ObjectClass, nme.notify_, MethodType(Nil, UnitType), Final)
    @tu lazy val Object_notifyAll: TermSymbol = enterMethod(ObjectClass, nme.notifyAll_, MethodType(Nil, UnitType), Final)
    @tu lazy val Object_wait: TermSymbol = enterMethod(ObjectClass, nme.wait_, MethodType(Nil, UnitType), Final)
    @tu lazy val Object_waitL: TermSymbol = enterMethod(ObjectClass, nme.wait_, MethodType(LongType :: Nil, UnitType), Final)
    @tu lazy val Object_waitLI: TermSymbol = enterMethod(ObjectClass, nme.wait_, MethodType(LongType :: IntType :: Nil, UnitType), Final)

    def ObjectMethods: List[TermSymbol] = List(Object_eq, Object_ne, Object_synchronized, Object_clone,
        Object_finalize, Object_notify, Object_notifyAll, Object_wait, Object_waitL, Object_waitLI)

  /** Methods in Object and Any that do not have a side effect */
  @tu lazy val pureMethods: List[TermSymbol] = List(Any_==, Any_!=, Any_equals, Any_hashCode,
    Any_toString, Any_##, Any_getClass, Any_isInstanceOf, Any_typeTest, Object_eq, Object_ne)

  @tu lazy val AnyKindClass: ClassSymbol = {
    val cls = newCompleteClassSymbol(ScalaPackageClass, tpnme.AnyKind, AbstractFinal | Permanent, Nil, newScope(0))
    if (!ctx.settings.YnoKindPolymorphism.value)
      // Enable kind-polymorphism by exposing scala.AnyKind
      cls.entered
    cls
  }
  def AnyKindType: TypeRef = AnyKindClass.typeRef

  @tu lazy val andType: TypeSymbol = enterBinaryAlias(tpnme.AND, AndType(_, _))
  @tu lazy val orType: TypeSymbol = enterBinaryAlias(tpnme.OR, OrType(_, _, soft = false))

  /** Method representing a throw */
  @tu lazy val throwMethod: TermSymbol = enterMethod(OpsPackageClass, nme.THROWkw,
      MethodType(List(ThrowableType), NothingType))

  @tu lazy val NothingClass: ClassSymbol = enterCompleteClassSymbol(
    ScalaPackageClass, tpnme.Nothing, AbstractFinal, List(AnyType))
  def NothingType: TypeRef = NothingClass.typeRef
  @tu lazy val NullClass: ClassSymbol = {
    // When explicit-nulls is enabled, Null becomes a direct subtype of Any and Matchable
    val parents = if ctx.explicitNulls then AnyType :: MatchableType :: Nil else ObjectType :: Nil
    enterCompleteClassSymbol(ScalaPackageClass, tpnme.Null, AbstractFinal, parents)
  }
  def NullType: TypeRef = NullClass.typeRef

  @tu lazy val InvokerModule = requiredModule("scala.runtime.coverage.Invoker")
  @tu lazy val InvokedMethodRef = InvokerModule.requiredMethodRef("invoked")

  @tu lazy val ImplicitScrutineeTypeSym =
    newPermanentSymbol(ScalaPackageClass, tpnme.IMPLICITkw, EmptyFlags, TypeBounds.empty).entered
  def ImplicitScrutineeTypeRef: TypeRef = ImplicitScrutineeTypeSym.typeRef

  @tu lazy val ScalaPredefModule: Symbol = requiredModule("scala.Predef")
    @tu lazy val Predef_conforms : Symbol = ScalaPredefModule.requiredMethod(nme.conforms_)
    @tu lazy val Predef_classOf  : Symbol = ScalaPredefModule.requiredMethod(nme.classOf)
    @tu lazy val Predef_identity : Symbol = ScalaPredefModule.requiredMethod(nme.identity)
    @tu lazy val Predef_undefined: Symbol = ScalaPredefModule.requiredMethod(nme.???)
  @tu lazy val ScalaPredefModuleClass: ClassSymbol = ScalaPredefModule.moduleClass.asClass

  @tu lazy val SubTypeClass: ClassSymbol = requiredClass("scala.<:<")
  @tu lazy val SubType_refl: Symbol = SubTypeClass.companionModule.requiredMethod(nme.refl)

  @tu lazy val DummyImplicitClass: ClassSymbol = requiredClass("scala.DummyImplicit")

  @tu lazy val ScalaRuntimeModule: Symbol = requiredModule("scala.runtime.ScalaRunTime")
    def runtimeMethodRef(name: PreName): TermRef = ScalaRuntimeModule.requiredMethodRef(name)
    def ScalaRuntime_drop: Symbol = runtimeMethodRef(nme.drop).symbol
    @tu lazy val ScalaRuntime__hashCode: Symbol = ScalaRuntimeModule.requiredMethod(nme._hashCode_)
    @tu lazy val ScalaRuntime_toArray: Symbol = ScalaRuntimeModule.requiredMethod(nme.toArray)
    @tu lazy val ScalaRuntime_toObjectArray: Symbol = ScalaRuntimeModule.requiredMethod(nme.toObjectArray)

  @tu lazy val BoxesRunTimeModule: Symbol = requiredModule("scala.runtime.BoxesRunTime")
    @tu lazy val BoxesRunTimeModule_externalEquals: Symbol = BoxesRunTimeModule.info.decl(nme.equals_).suchThat(toDenot(_).info.firstParamTypes.size == 2).symbol
  @tu lazy val ScalaStaticsModule: Symbol = requiredModule("scala.runtime.Statics")
    def staticsMethodRef(name: PreName): TermRef = ScalaStaticsModule.requiredMethodRef(name)
    def staticsMethod(name: PreName): TermSymbol = ScalaStaticsModule.requiredMethod(name)

  @tu lazy val DottyArraysModule: Symbol = requiredModule("scala.runtime.Arrays")
    @tu lazy val newGenericArrayMethod: TermSymbol = DottyArraysModule.requiredMethod("newGenericArray")
    @tu lazy val newArrayMethod: TermSymbol = DottyArraysModule.requiredMethod("newArray")

  def getWrapVarargsArrayModule: Symbol = ScalaRuntimeModule

  // The set of all wrap{X, Ref}Array methods, where X is a value type
  val WrapArrayMethods: PerRun[collection.Set[Symbol]] = new PerRun({
    val methodNames = ScalaValueTypes.map(ast.tpd.wrapArrayMethodName) `union` Set(nme.wrapRefArray)
    methodNames.map(getWrapVarargsArrayModule.requiredMethod(_))
  })

  @tu lazy val ListClass: Symbol        = requiredClass("scala.collection.immutable.List")
  def ListType: TypeRef                 = ListClass.typeRef
  @tu lazy val ListModule: Symbol       = requiredModule("scala.collection.immutable.List")
  @tu lazy val ListModule_apply: Symbol = ListModule.requiredMethod(nme.apply)
  def ListModuleAlias: Symbol           = ScalaPackageClass.requiredMethod(nme.List)
  @tu lazy val NilModule: Symbol        = requiredModule("scala.collection.immutable.Nil")
  def NilType: TermRef                  = NilModule.termRef
  @tu lazy val ConsClass: Symbol        = requiredClass("scala.collection.immutable.::")
  def ConsType: TypeRef                 = ConsClass.typeRef
  @tu lazy val SeqFactoryClass: Symbol  = requiredClass("scala.collection.SeqFactory")

  @tu lazy val SingletonClass: ClassSymbol =
    // needed as a synthetic class because Scala 2.x refers to it in classfiles
    // but does not define it as an explicit class.
    enterCompleteClassSymbol(
      ScalaPackageClass, tpnme.Singleton, PureInterfaceCreationFlags | Final,
      List(AnyType), EmptyScope)
  @tu lazy val SingletonType: TypeRef = SingletonClass.typeRef

  @tu lazy val CollectionSeqType: TypeRef  = requiredClassRef("scala.collection.Seq")
  @tu lazy val SeqType: TypeRef            = requiredClassRef("scala.collection.immutable.Seq")
  @tu lazy val SeqModule: Symbol           = requiredModule("scala.collection.immutable.Seq")
  @tu lazy val SeqModule_apply: Symbol     = SeqModule.requiredMethod(nme.apply)
  def SeqModuleAlias: Symbol               = ScalaPackageClass.requiredMethod(nme.Seq)
  def SeqClass(using Context): ClassSymbol = SeqType.symbol.asClass
    @tu lazy val Seq_apply        : Symbol = SeqClass.requiredMethod(nme.apply)
    @tu lazy val Seq_head         : Symbol = SeqClass.requiredMethod(nme.head)
    @tu lazy val Seq_drop         : Symbol = SeqClass.requiredMethod(nme.drop)
    @tu lazy val Seq_lengthCompare: Symbol = SeqClass.requiredMethod(nme.lengthCompare, List(IntType))
    @tu lazy val Seq_length       : Symbol = SeqClass.requiredMethod(nme.length)
    @tu lazy val Seq_toSeq        : Symbol = SeqClass.requiredMethod(nme.toSeq)


  @tu lazy val StringOps: Symbol = requiredClass("scala.collection.StringOps")
    @tu lazy val StringOps_format: Symbol  = StringOps.requiredMethod(nme.format)

  @tu lazy val ArrayType: TypeRef = requiredClassRef("scala.Array")
  def ArrayClass(using Context): ClassSymbol = ArrayType.symbol.asClass
    @tu lazy val Array_apply     : Symbol = ArrayClass.requiredMethod(nme.apply)
    @tu lazy val Array_update    : Symbol = ArrayClass.requiredMethod(nme.update)
    @tu lazy val Array_length    : Symbol = ArrayClass.requiredMethod(nme.length)
    @tu lazy val Array_clone     : Symbol = ArrayClass.requiredMethod(nme.clone_)
    @tu lazy val ArrayConstructor: Symbol = ArrayClass.requiredMethod(nme.CONSTRUCTOR)

  @tu lazy val ArrayModule: Symbol = requiredModule("scala.Array")
  def ArrayModuleClass: Symbol = ArrayModule.moduleClass

  @tu lazy val IArrayModule: Symbol = requiredModule("scala.IArray")
  def IArrayModuleClass: Symbol = IArrayModule.moduleClass

  @tu lazy val UnitType: TypeRef = valueTypeRef("scala.Unit", java.lang.Void.TYPE, UnitEnc, nme.specializedTypeNames.Void)
  def UnitClass(using Context): ClassSymbol = UnitType.symbol.asClass
  def UnitModuleClass(using Context): Symbol = UnitType.symbol.asClass.linkedClass
  @tu lazy val BooleanType: TypeRef = valueTypeRef("scala.Boolean", java.lang.Boolean.TYPE, BooleanEnc, nme.specializedTypeNames.Boolean)
  def BooleanClass(using Context): ClassSymbol = BooleanType.symbol.asClass
    @tu lazy val Boolean_!  : Symbol = BooleanClass.requiredMethod(nme.UNARY_!)
    @tu lazy val Boolean_&& : Symbol = BooleanClass.requiredMethod(nme.ZAND) // ### harmonize required... calls
    @tu lazy val Boolean_|| : Symbol = BooleanClass.requiredMethod(nme.ZOR)
    @tu lazy val Boolean_== : Symbol =
      BooleanClass.info.member(nme.EQ).suchThat(_.info.firstParamTypes match {
        case List(pt) => pt.isRef(BooleanClass)
        case _ => false
      }).symbol
    @tu lazy val Boolean_!= : Symbol =
      BooleanClass.info.member(nme.NE).suchThat(_.info.firstParamTypes match {
        case List(pt) => pt.isRef(BooleanClass)
        case _ => false
      }).symbol

  @tu lazy val ByteType: TypeRef = valueTypeRef("scala.Byte", java.lang.Byte.TYPE, ByteEnc, nme.specializedTypeNames.Byte)
  def ByteClass(using Context): ClassSymbol = ByteType.symbol.asClass
  @tu lazy val ShortType: TypeRef = valueTypeRef("scala.Short", java.lang.Short.TYPE, ShortEnc, nme.specializedTypeNames.Short)
  def ShortClass(using Context): ClassSymbol = ShortType.symbol.asClass
  @tu lazy val CharType: TypeRef = valueTypeRef("scala.Char", java.lang.Character.TYPE, CharEnc, nme.specializedTypeNames.Char)
  def CharClass(using Context): ClassSymbol = CharType.symbol.asClass
  @tu lazy val IntType: TypeRef = valueTypeRef("scala.Int", java.lang.Integer.TYPE, IntEnc, nme.specializedTypeNames.Int)
  def IntClass(using Context): ClassSymbol = IntType.symbol.asClass
    @tu lazy val Int_-  : Symbol = IntClass.requiredMethod(nme.MINUS, List(IntType))
    @tu lazy val Int_+  : Symbol = IntClass.requiredMethod(nme.PLUS, List(IntType))
    @tu lazy val Int_/  : Symbol = IntClass.requiredMethod(nme.DIV, List(IntType))
    @tu lazy val Int_*  : Symbol = IntClass.requiredMethod(nme.MUL, List(IntType))
    @tu lazy val Int_== : Symbol = IntClass.requiredMethod(nme.EQ, List(IntType))
    @tu lazy val Int_>= : Symbol = IntClass.requiredMethod(nme.GE, List(IntType))
    @tu lazy val Int_<= : Symbol = IntClass.requiredMethod(nme.LE, List(IntType))
  @tu lazy val LongType: TypeRef = valueTypeRef("scala.Long", java.lang.Long.TYPE, LongEnc, nme.specializedTypeNames.Long)
  def LongClass(using Context): ClassSymbol = LongType.symbol.asClass
    @tu lazy val Long_+ : Symbol = LongClass.requiredMethod(nme.PLUS, List(LongType))
    @tu lazy val Long_* : Symbol = LongClass.requiredMethod(nme.MUL, List(LongType))
    @tu lazy val Long_/ : Symbol = LongClass.requiredMethod(nme.DIV, List(LongType))

  @tu lazy val FloatType: TypeRef = valueTypeRef("scala.Float", java.lang.Float.TYPE, FloatEnc, nme.specializedTypeNames.Float)
  def FloatClass(using Context): ClassSymbol = FloatType.symbol.asClass
  @tu lazy val DoubleType: TypeRef = valueTypeRef("scala.Double", java.lang.Double.TYPE, DoubleEnc, nme.specializedTypeNames.Double)
  def DoubleClass(using Context): ClassSymbol = DoubleType.symbol.asClass

  @tu lazy val BoxedUnitClass: ClassSymbol = requiredClass("scala.runtime.BoxedUnit")
    def BoxedUnit_UNIT(using Context): TermSymbol = BoxedUnitClass.linkedClass.requiredValue("UNIT")
    def BoxedUnit_TYPE(using Context): TermSymbol = BoxedUnitClass.linkedClass.requiredValue("TYPE")

  @tu lazy val BoxedBooleanClass: ClassSymbol = requiredClass("java.lang.Boolean")
  @tu lazy val BoxedByteClass   : ClassSymbol = requiredClass("java.lang.Byte")
  @tu lazy val BoxedShortClass  : ClassSymbol = requiredClass("java.lang.Short")
  @tu lazy val BoxedCharClass   : ClassSymbol = requiredClass("java.lang.Character")
  @tu lazy val BoxedIntClass    : ClassSymbol = requiredClass("java.lang.Integer")
  @tu lazy val BoxedLongClass   : ClassSymbol = requiredClass("java.lang.Long")
  @tu lazy val BoxedFloatClass  : ClassSymbol = requiredClass("java.lang.Float")
  @tu lazy val BoxedDoubleClass : ClassSymbol = requiredClass("java.lang.Double")

  @tu lazy val BoxedBooleanModule: TermSymbol = requiredModule("java.lang.Boolean")
  @tu lazy val BoxedByteModule   : TermSymbol = requiredModule("java.lang.Byte")
  @tu lazy val BoxedShortModule  : TermSymbol = requiredModule("java.lang.Short")
  @tu lazy val BoxedCharModule   : TermSymbol = requiredModule("java.lang.Character")
  @tu lazy val BoxedIntModule    : TermSymbol = requiredModule("java.lang.Integer")
  @tu lazy val BoxedLongModule   : TermSymbol = requiredModule("java.lang.Long")
  @tu lazy val BoxedFloatModule  : TermSymbol = requiredModule("java.lang.Float")
  @tu lazy val BoxedDoubleModule : TermSymbol = requiredModule("java.lang.Double")
  @tu lazy val BoxedUnitModule   : TermSymbol = requiredModule("java.lang.Void")

  @tu lazy val ByNameParamClass2x: ClassSymbol = enterSpecialPolyClass(tpnme.BYNAME_PARAM_CLASS, Covariant, Seq(AnyType))

  @tu lazy val RepeatedParamClass: ClassSymbol = enterSpecialPolyClass(tpnme.REPEATED_PARAM_CLASS, Covariant, Seq(ObjectType, SeqType))

  @tu lazy val IntoType: TypeSymbol = enterAliasType(tpnme.INTO, HKTypeLambda(TypeBounds.empty :: Nil)(_.paramRefs(0)))

  // fundamental classes
  @tu lazy val StringClass: ClassSymbol = requiredClass("java.lang.String")
  def StringType: Type = StringClass.typeRef
  @tu lazy val StringModule: Symbol = StringClass.linkedClass
    @tu lazy val String_+ : TermSymbol = enterMethod(StringClass, nme.raw.PLUS, methOfAny(StringType), Final)
    @tu lazy val String_valueOf_Object: Symbol = StringModule.info.member(nme.valueOf).suchThat(_.info.firstParamTypes match {
      case List(pt) => pt.isAny || pt.stripNull.isAnyRef
      case _ => false
    }).symbol

  @tu lazy val JavaCloneableClass: ClassSymbol        = requiredClass("java.lang.Cloneable")
  @tu lazy val NullPointerExceptionClass: ClassSymbol = requiredClass("java.lang.NullPointerException")
  @tu lazy val IndexOutOfBoundsException: ClassSymbol = requiredClass("java.lang.IndexOutOfBoundsException")
  @tu lazy val ClassClass: ClassSymbol                = requiredClass("java.lang.Class")
  @tu lazy val BoxedNumberClass: ClassSymbol          = requiredClass("java.lang.Number")
  @tu lazy val ClassCastExceptionClass: ClassSymbol   = requiredClass("java.lang.ClassCastException")
    @tu lazy val ClassCastExceptionClass_stringConstructor: TermSymbol  = ClassCastExceptionClass.info.member(nme.CONSTRUCTOR).suchThat(_.info.firstParamTypes match {
      case List(pt) =>
        pt.stripNull.isRef(StringClass)
      case _ => false
    }).symbol.asTerm
  @tu lazy val ArithmeticExceptionClass: ClassSymbol  = requiredClass("java.lang.ArithmeticException")
    @tu lazy val ArithmeticExceptionClass_stringConstructor: TermSymbol  = ArithmeticExceptionClass.info.member(nme.CONSTRUCTOR).suchThat(_.info.firstParamTypes match {
      case List(pt) =>
        pt.stripNull.isRef(StringClass)
      case _ => false
    }).symbol.asTerm

  @tu lazy val JavaSerializableClass: ClassSymbol     = requiredClass("java.io.Serializable")

  @tu lazy val ComparableClass: ClassSymbol           = requiredClass("java.lang.Comparable")

  @tu lazy val SystemClass: ClassSymbol               = requiredClass("java.lang.System")
  @tu lazy val SystemModule: Symbol              = SystemClass.linkedClass

  @tu lazy val NoSuchElementExceptionClass = requiredClass("java.util.NoSuchElementException")
  def NoSuchElementExceptionType = NoSuchElementExceptionClass.typeRef
  @tu lazy val IllegalArgumentExceptionClass = requiredClass("java.lang.IllegalArgumentException")
  def IllegalArgumentExceptionType = IllegalArgumentExceptionClass.typeRef

  // in scalac modified to have Any as parent

  @tu lazy val ThrowableType: TypeRef             = requiredClassRef("java.lang.Throwable")
  def ThrowableClass(using Context): ClassSymbol  = ThrowableType.symbol.asClass
  @tu lazy val ExceptionClass: ClassSymbol        = requiredClass("java.lang.Exception")
  @tu lazy val RuntimeExceptionClass: ClassSymbol = requiredClass("java.lang.RuntimeException")

  @tu lazy val SerializableType: TypeRef       = JavaSerializableClass.typeRef
  def SerializableClass(using Context): ClassSymbol = SerializableType.symbol.asClass

  @tu lazy val JavaBigIntegerClass: ClassSymbol = requiredClass("java.math.BigInteger")
  @tu lazy val JavaBigDecimalClass: ClassSymbol = requiredClass("java.math.BigDecimal")
  @tu lazy val JavaCalendarClass: ClassSymbol = requiredClass("java.util.Calendar")
  @tu lazy val JavaDateClass: ClassSymbol = requiredClass("java.util.Date")
  @tu lazy val JavaFormattableClass: ClassSymbol = requiredClass("java.util.Formattable")
  @tu lazy val JavaRecordClass: Symbol = getClassIfDefined("java.lang.Record")

  @tu lazy val JavaEnumClass: ClassSymbol = {
    val cls = requiredClass("java.lang.Enum")
    // jl.Enum has a single constructor protected(name: String, ordinal: Int).
    // We remove the arguments from the primary constructor, and enter
    // a new constructor symbol with 2 arguments, so that both
    // `X extends jl.Enum[X]` and `X extends jl.Enum[X](name, ordinal)`
    // pass typer and go through jl.Enum-specific checks in RefChecks.
    cls.infoOrCompleter match {
      case completer: ClassfileLoader =>
        cls.info = new ClassfileLoader(completer.classfile) {
          override def complete(root: SymDenotation)(using Context): Unit = {
            super.complete(root)
            val constr = cls.primaryConstructor
            val noArgInfo = constr.info match {
              case info: PolyType =>
                info.resType match {
                  case meth: MethodType =>
                    info.derivedLambdaType(
                      resType = meth.derivedLambdaType(
                      paramNames = Nil, paramInfos = Nil))
                }
            }
            val argConstr = constr.copy().entered
            constr.info = noArgInfo
            constr.termRef.recomputeDenot()
          }
        }
        cls
    }
  }
  def JavaEnumType = JavaEnumClass.typeRef

  @tu lazy val MethodHandleClass: ClassSymbol        = requiredClass("java.lang.invoke.MethodHandle")
  @tu lazy val MethodHandlesLookupClass: ClassSymbol = requiredClass("java.lang.invoke.MethodHandles.Lookup")
  @tu lazy val VarHandleClass: ClassSymbol           = requiredClass("java.lang.invoke.VarHandle")

  @tu lazy val StringBuilderClass: ClassSymbol = requiredClass("scala.collection.mutable.StringBuilder")
  @tu lazy val MatchErrorClass   : ClassSymbol = requiredClass("scala.MatchError")
  @tu lazy val ConversionClass   : ClassSymbol = requiredClass("scala.Conversion").typeRef.symbol.asClass

  @tu lazy val StringAddClass    : ClassSymbol = requiredClass("scala.runtime.StringAdd")
    @tu lazy val StringAdd_+ : Symbol = StringAddClass.requiredMethod(nme.raw.PLUS)

  @tu lazy val StringContextClass: ClassSymbol = requiredClass("scala.StringContext")
    @tu lazy val StringContext_s  : Symbol = StringContextClass.requiredMethod(nme.s)
    @tu lazy val StringContext_raw: Symbol = StringContextClass.requiredMethod(nme.raw_)
    @tu lazy val StringContext_f  : Symbol = StringContextClass.requiredMethod(nme.f)
    @tu lazy val StringContext_parts: Symbol = StringContextClass.requiredMethod(nme.parts)
  @tu lazy val StringContextModule: Symbol = StringContextClass.companionModule
    @tu lazy val StringContextModule_apply: Symbol = StringContextModule.requiredMethod(nme.apply)
    @tu lazy val StringContextModule_standardInterpolator: Symbol = StringContextModule.requiredMethod(nme.standardInterpolator)
    @tu lazy val StringContextModule_processEscapes: Symbol = StringContextModule.requiredMethod(nme.processEscapes)

  @tu lazy val PartialFunctionClass: ClassSymbol = requiredClass("scala.PartialFunction")
    @tu lazy val PartialFunction_apply: Symbol = PartialFunctionClass.requiredMethod(nme.apply)
    @tu lazy val PartialFunction_isDefinedAt: Symbol = PartialFunctionClass.requiredMethod(nme.isDefinedAt)
    @tu lazy val PartialFunction_applyOrElse: Symbol = PartialFunctionClass.requiredMethod(nme.applyOrElse)

  @tu lazy val AbstractPartialFunctionClass: ClassSymbol = requiredClass("scala.runtime.AbstractPartialFunction")
  @tu lazy val FunctionXXLClass: ClassSymbol = requiredClass("scala.runtime.FunctionXXL")
  @tu lazy val ScalaSymbolClass: ClassSymbol = requiredClass("scala.Symbol")
  @tu lazy val DynamicClass: ClassSymbol = requiredClass("scala.Dynamic")
  @tu lazy val OptionClass: ClassSymbol = requiredClass("scala.Option")
  @tu lazy val SomeClass: ClassSymbol = requiredClass("scala.Some")
  @tu lazy val NoneModule: Symbol = requiredModule("scala.None")

  @tu lazy val EnumClass: ClassSymbol = requiredClass("scala.reflect.Enum")
    @tu lazy val Enum_ordinal: Symbol = EnumClass.requiredMethod(nme.ordinal)

  @tu lazy val EnumValueSerializationProxyClass: ClassSymbol = requiredClass("scala.runtime.EnumValueSerializationProxy")
    @tu lazy val EnumValueSerializationProxyConstructor: TermSymbol =
      EnumValueSerializationProxyClass.requiredMethod(nme.CONSTRUCTOR, List(ClassType(TypeBounds.empty), IntType))

  @tu lazy val ProductClass: ClassSymbol = requiredClass("scala.Product")
    @tu lazy val Product_canEqual          : Symbol = ProductClass.requiredMethod(nme.canEqual_)
    @tu lazy val Product_productArity      : Symbol = ProductClass.requiredMethod(nme.productArity)
    @tu lazy val Product_productElement    : Symbol = ProductClass.requiredMethod(nme.productElement)
    @tu lazy val Product_productElementName: Symbol = ProductClass.requiredMethod(nme.productElementName)
    @tu lazy val Product_productPrefix     : Symbol = ProductClass.requiredMethod(nme.productPrefix)

  @tu lazy val IteratorClass: ClassSymbol = requiredClass("scala.collection.Iterator")
  def IteratorModule(using Context): Symbol = IteratorClass.companionModule

  @tu lazy val ModuleSerializationProxyClass: ClassSymbol = requiredClass("scala.runtime.ModuleSerializationProxy")
    @tu lazy val ModuleSerializationProxyConstructor: TermSymbol =
      ModuleSerializationProxyClass.requiredMethod(nme.CONSTRUCTOR, List(ClassType(TypeBounds.empty)))

  @tu lazy val MirrorClass: ClassSymbol = requiredClass("scala.deriving.Mirror")
  @tu lazy val Mirror_ProductClass: ClassSymbol = requiredClass("scala.deriving.Mirror.Product")
    @tu lazy val Mirror_Product_fromProduct: Symbol = Mirror_ProductClass.requiredMethod(nme.fromProduct)
  @tu lazy val Mirror_SumClass: ClassSymbol = requiredClass("scala.deriving.Mirror.Sum")
  @tu lazy val Mirror_SingletonClass: ClassSymbol = requiredClass("scala.deriving.Mirror.Singleton")
  @tu lazy val Mirror_SingletonProxyClass: ClassSymbol = requiredClass("scala.deriving.Mirror.SingletonProxy")

  @tu lazy val LanguageModule: Symbol = requiredModule("scala.language")
  @tu lazy val LanguageModuleClass: Symbol = LanguageModule.moduleClass.asClass
  @tu lazy val LanguageExperimentalModule: Symbol = requiredModule("scala.language.experimental")
  @tu lazy val LanguageDeprecatedModule: Symbol = requiredModule("scala.language.deprecated")
  @tu lazy val NonLocalReturnControlClass: ClassSymbol = requiredClass("scala.runtime.NonLocalReturnControl")
  @tu lazy val SelectableClass: ClassSymbol = requiredClass("scala.Selectable")
  @tu lazy val WithoutPreciseParameterTypesClass: Symbol = requiredClass("scala.Selectable.WithoutPreciseParameterTypes")

  @tu lazy val ManifestClass: ClassSymbol = requiredClass("scala.reflect.Manifest")
  @tu lazy val ManifestFactoryModule: Symbol = requiredModule("scala.reflect.ManifestFactory")
  @tu lazy val ClassManifestFactoryModule: Symbol = requiredModule("scala.reflect.ClassManifestFactory")
  @tu lazy val OptManifestClass: ClassSymbol = requiredClass("scala.reflect.OptManifest")
  @tu lazy val NoManifestModule: Symbol = requiredModule("scala.reflect.NoManifest")

  @tu lazy val ReflectPackageClass: Symbol = requiredPackage("scala.reflect.package").moduleClass
  @tu lazy val ClassTagClass: ClassSymbol = requiredClass("scala.reflect.ClassTag")
    @tu lazy val ClassTagClass_unapply: Symbol = ClassTagClass.requiredMethod("unapply")
  @tu lazy val ClassTagModule: Symbol = ClassTagClass.companionModule
    @tu lazy val ClassTagModule_apply: Symbol = ClassTagModule.requiredMethod(nme.apply)

  @tu lazy val ReflectSelectableTypeRef: TypeRef = requiredClassRef("scala.reflect.Selectable")

  @tu lazy val TypeTestClass: ClassSymbol = requiredClass("scala.reflect.TypeTest")
    @tu lazy val TypeTest_unapply: Symbol = TypeTestClass.requiredMethod(nme.unapply)
  @tu lazy val TypeTestModule_identity: Symbol = TypeTestClass.companionModule.requiredMethod(nme.identity)

  @tu lazy val QuotedExprClass: ClassSymbol = requiredClass("scala.quoted.Expr")

  @tu lazy val QuotesClass: ClassSymbol = requiredClass("scala.quoted.Quotes")
    @tu lazy val Quotes_reflect: Symbol = QuotesClass.requiredValue("reflect")
      @tu lazy val Quotes_reflect_asTerm: Symbol = Quotes_reflect.requiredMethod("asTerm")
      @tu lazy val Quotes_reflect_Apply: Symbol = Quotes_reflect.requiredValue("Apply")
        @tu lazy val Quotes_reflect_Apply_apply: Symbol = Quotes_reflect_Apply.requiredMethod(nme.apply)
      @tu lazy val Quotes_reflect_TypeApply: Symbol = Quotes_reflect.requiredValue("TypeApply")
        @tu lazy val Quotes_reflect_TypeApply_apply: Symbol = Quotes_reflect_TypeApply.requiredMethod(nme.apply)
      @tu lazy val Quotes_reflect_Assign: Symbol = Quotes_reflect.requiredValue("Assign")
        @tu lazy val Quotes_reflect_Assign_apply: Symbol = Quotes_reflect_Assign.requiredMethod(nme.apply)
      @tu lazy val Quotes_reflect_Inferred: Symbol = Quotes_reflect.requiredValue("Inferred")
        @tu lazy val Quotes_reflect_Inferred_apply: Symbol = Quotes_reflect_Inferred.requiredMethod(nme.apply)
      @tu lazy val Quotes_reflect_Literal: Symbol = Quotes_reflect.requiredValue("Literal")
      @tu lazy val Quotes_reflect_Literal_apply: Symbol = Quotes_reflect_Literal.requiredMethod(nme.apply)
      @tu lazy val Quotes_reflect_TreeMethods: Symbol = Quotes_reflect.requiredMethod("TreeMethods")
        @tu lazy val Quotes_reflect_TreeMethods_asExpr: Symbol = Quotes_reflect_TreeMethods.requiredMethod("asExpr")
      @tu lazy val Quotes_reflect_TypeRepr: Symbol = Quotes_reflect.requiredValue("TypeRepr")
        @tu lazy val Quotes_reflect_TypeRepr_of: Symbol = Quotes_reflect_TypeRepr.requiredMethod("of")
        @tu lazy val Quotes_reflect_TypeRepr_typeConstructorOf: Symbol = Quotes_reflect_TypeRepr.requiredMethod("typeConstructorOf")
      @tu lazy val Quotes_reflect_TypeReprMethods: Symbol = Quotes_reflect.requiredValue("TypeReprMethods")
        @tu lazy val Quotes_reflect_TypeReprMethods_asType: Symbol = Quotes_reflect_TypeReprMethods.requiredMethod("asType")
      @tu lazy val Quotes_reflect_TypeTreeType: Symbol = Quotes_reflect.requiredType("TypeTree")
      @tu lazy val Quotes_reflect_TermType: Symbol = Quotes_reflect.requiredType("Term")
      @tu lazy val Quotes_reflect_BooleanConstant: Symbol = Quotes_reflect.requiredValue("BooleanConstant")
      @tu lazy val Quotes_reflect_ByteConstant: Symbol = Quotes_reflect.requiredValue("ByteConstant")
      @tu lazy val Quotes_reflect_ShortConstant: Symbol = Quotes_reflect.requiredValue("ShortConstant")
      @tu lazy val Quotes_reflect_IntConstant: Symbol = Quotes_reflect.requiredValue("IntConstant")
      @tu lazy val Quotes_reflect_LongConstant: Symbol = Quotes_reflect.requiredValue("LongConstant")
      @tu lazy val Quotes_reflect_FloatConstant: Symbol = Quotes_reflect.requiredValue("FloatConstant")
      @tu lazy val Quotes_reflect_DoubleConstant: Symbol = Quotes_reflect.requiredValue("DoubleConstant")
      @tu lazy val Quotes_reflect_CharConstant: Symbol = Quotes_reflect.requiredValue("CharConstant")
      @tu lazy val Quotes_reflect_StringConstant: Symbol = Quotes_reflect.requiredValue("StringConstant")
      @tu lazy val Quotes_reflect_UnitConstant: Symbol = Quotes_reflect.requiredValue("UnitConstant")
      @tu lazy val Quotes_reflect_NullConstant: Symbol = Quotes_reflect.requiredValue("NullConstant")
      @tu lazy val Quotes_reflect_ClassOfConstant: Symbol = Quotes_reflect.requiredValue("ClassOfConstant")


  @tu lazy val QuoteUnpicklerClass: ClassSymbol = requiredClass("scala.quoted.runtime.QuoteUnpickler")
    @tu lazy val QuoteUnpickler_unpickleExprV2: Symbol = QuoteUnpicklerClass.requiredMethod("unpickleExprV2")
    @tu lazy val QuoteUnpickler_unpickleTypeV2: Symbol = QuoteUnpicklerClass.requiredMethod("unpickleTypeV2")

  @tu lazy val QuoteMatchingClass: ClassSymbol = requiredClass("scala.quoted.runtime.QuoteMatching")
    @tu lazy val QuoteMatching_ExprMatch: Symbol = QuoteMatchingClass.requiredMethod("ExprMatch")
    @tu lazy val QuoteMatching_ExprMatchModule: Symbol = QuoteMatchingClass.requiredClass("ExprMatchModule")
    @tu lazy val QuoteMatching_TypeMatch: Symbol = QuoteMatchingClass.requiredMethod("TypeMatch")
    @tu lazy val QuoteMatching_TypeMatchModule: Symbol = QuoteMatchingClass.requiredClass("TypeMatchModule")
  @tu lazy val QuoteMatchingModule: Symbol = requiredModule("scala.quoted.runtime.QuoteMatching")
    @tu lazy val QuoteMatching_KNil: Symbol = QuoteMatchingModule.requiredType("KNil")
    @tu lazy val QuoteMatching_KCons: Symbol = QuoteMatchingModule.requiredType("KCons")

  @tu lazy val ToExprModule: Symbol = requiredModule("scala.quoted.ToExpr")
    @tu lazy val ToExprModule_BooleanToExpr: Symbol = ToExprModule.requiredMethod("BooleanToExpr")
    @tu lazy val ToExprModule_ByteToExpr: Symbol = ToExprModule.requiredMethod("ByteToExpr")
    @tu lazy val ToExprModule_ShortToExpr: Symbol = ToExprModule.requiredMethod("ShortToExpr")
    @tu lazy val ToExprModule_IntToExpr: Symbol = ToExprModule.requiredMethod("IntToExpr")
    @tu lazy val ToExprModule_LongToExpr: Symbol = ToExprModule.requiredMethod("LongToExpr")
    @tu lazy val ToExprModule_FloatToExpr: Symbol = ToExprModule.requiredMethod("FloatToExpr")
    @tu lazy val ToExprModule_DoubleToExpr: Symbol = ToExprModule.requiredMethod("DoubleToExpr")
    @tu lazy val ToExprModule_CharToExpr: Symbol = ToExprModule.requiredMethod("CharToExpr")
    @tu lazy val ToExprModule_StringToExpr: Symbol = ToExprModule.requiredMethod("StringToExpr")

  @tu lazy val QuotedRuntimeModule: Symbol = requiredModule("scala.quoted.runtime.Expr")
    @tu lazy val QuotedRuntime_exprQuote  : Symbol = QuotedRuntimeModule.requiredMethod("quote")
    @tu lazy val QuotedRuntime_exprSplice : Symbol = QuotedRuntimeModule.requiredMethod("splice")
    @tu lazy val QuotedRuntime_exprNestedSplice : Symbol = QuotedRuntimeModule.requiredMethod("nestedSplice")

  @tu lazy val QuotedRuntime_SplicedTypeAnnot: ClassSymbol = requiredClass("scala.quoted.runtime.SplicedType")

  @tu lazy val QuotedRuntimePatterns: Symbol = requiredModule("scala.quoted.runtime.Patterns")
    @tu lazy val QuotedRuntimePatterns_patternHole: Symbol = QuotedRuntimePatterns.requiredMethod("patternHole")
    @tu lazy val QuotedRuntimePatterns_patternHigherOrderHole: Symbol = QuotedRuntimePatterns.requiredMethod("patternHigherOrderHole")
    @tu lazy val QuotedRuntimePatterns_higherOrderHole: Symbol = QuotedRuntimePatterns.requiredMethod("higherOrderHole")
    @tu lazy val QuotedRuntimePatterns_patternTypeAnnot: ClassSymbol = QuotedRuntimePatterns.requiredClass("patternType")
    @tu lazy val QuotedRuntimePatterns_fromAboveAnnot: ClassSymbol = QuotedRuntimePatterns.requiredClass("fromAbove")

  @tu lazy val QuotedTypeClass: ClassSymbol = requiredClass("scala.quoted.Type")
    @tu lazy val QuotedType_splice: Symbol = QuotedTypeClass.requiredType(tpnme.Underlying)

  @tu lazy val QuotedTypeModule: Symbol = QuotedTypeClass.companionModule
    @tu lazy val QuotedTypeModule_of: Symbol = QuotedTypeModule.requiredMethod("of")

  @tu lazy val MacroAnnotationClass: ClassSymbol = requiredClass("scala.annotation.MacroAnnotation")

  @tu lazy val CanEqualClass: ClassSymbol = getClassIfDefined("scala.Eql").orElse(requiredClass("scala.CanEqual")).asClass
    def CanEqual_canEqualAny(using Context): TermSymbol =
      val methodName = if CanEqualClass.name == tpnme.Eql then nme.eqlAny else nme.canEqualAny
      CanEqualClass.companionModule.requiredMethod(methodName)

  @tu lazy val CanThrowClass: ClassSymbol = requiredClass("scala.CanThrow")
  @tu lazy val throwsAlias: Symbol = ScalaRuntimePackageVal.requiredType(tpnme.THROWS)

  @tu lazy val TypeBoxClass: ClassSymbol = requiredClass("scala.runtime.TypeBox")
    @tu lazy val TypeBox_CAP: TypeSymbol = TypeBoxClass.requiredType(tpnme.CAP)

  @tu lazy val MatchCaseClass: ClassSymbol = requiredClass("scala.runtime.MatchCase")
  @tu lazy val NotGivenClass: ClassSymbol = requiredClass("scala.util.NotGiven")
    @tu lazy val NotGiven_value: Symbol = NotGivenClass.companionModule.requiredMethod(nme.value)

  @tu lazy val ValueOfClass: ClassSymbol = requiredClass("scala.ValueOf")

  @tu lazy val FromDigitsClass: ClassSymbol           = requiredClass("scala.util.FromDigits")
  @tu lazy val FromDigits_WithRadixClass: ClassSymbol = requiredClass("scala.util.FromDigits.WithRadix")
  @tu lazy val FromDigits_DecimalClass: ClassSymbol   = requiredClass("scala.util.FromDigits.Decimal")
  @tu lazy val FromDigits_FloatingClass: ClassSymbol  = requiredClass("scala.util.FromDigits.Floating")

  @tu lazy val XMLTopScopeModule: Symbol = requiredModule("scala.xml.TopScope")

  @tu lazy val MainAnnotationClass: ClassSymbol = requiredClass("scala.annotation.MainAnnotation")
  @tu lazy val MainAnnotationInfo: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Info")
  @tu lazy val MainAnnotationParameter: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Parameter")
  @tu lazy val MainAnnotationParameterAnnotation: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.ParameterAnnotation")
  @tu lazy val MainAnnotationCommand: ClassSymbol = requiredClass("scala.annotation.MainAnnotation.Command")

  @tu lazy val CommandLineParserModule: Symbol = requiredModule("scala.util.CommandLineParser")
    @tu lazy val CLP_ParseError: ClassSymbol = CommandLineParserModule.requiredClass("ParseError").typeRef.symbol.asClass
    @tu lazy val CLP_parseArgument: Symbol = CommandLineParserModule.requiredMethod("parseArgument")
    @tu lazy val CLP_parseRemainingArguments: Symbol = CommandLineParserModule.requiredMethod("parseRemainingArguments")
    @tu lazy val CLP_showError: Symbol = CommandLineParserModule.requiredMethod("showError")

  @tu lazy val TupleTypeRef: TypeRef = requiredClassRef("scala.Tuple")
  def TupleClass(using Context): ClassSymbol = TupleTypeRef.symbol.asClass
    @tu lazy val Tuple_cons: Symbol = TupleClass.requiredMethod("*:")
  @tu lazy val EmptyTupleModule: Symbol = requiredModule("scala.EmptyTuple")
  @tu lazy val NonEmptyTupleTypeRef: TypeRef = requiredClassRef("scala.NonEmptyTuple")
  def NonEmptyTupleClass(using Context): ClassSymbol = NonEmptyTupleTypeRef.symbol.asClass
    lazy val NonEmptyTuple_tail: Symbol = NonEmptyTupleClass.requiredMethod("tail")
  @tu lazy val PairClass: ClassSymbol = requiredClass("scala.*:")

  @tu lazy val TupleXXLClass: ClassSymbol = requiredClass("scala.runtime.TupleXXL")
  def TupleXXLModule(using Context): Symbol = TupleXXLClass.companionModule

    def TupleXXL_fromIterator(using Context): Symbol = TupleXXLModule.requiredMethod("fromIterator")
    def TupleXXL_unapplySeq(using Context): Symbol = TupleXXLModule.requiredMethod(nme.unapplySeq)

  @tu lazy val RuntimeTupleMirrorTypeRef: TypeRef = requiredClassRef("scala.runtime.TupleMirror")

  @tu lazy val RuntimeTuplesModule: Symbol = requiredModule("scala.runtime.Tuples")
  @tu lazy val RuntimeTuplesModuleClass: Symbol = RuntimeTuplesModule.moduleClass
    @tu lazy val RuntimeTuples_consIterator: Symbol = RuntimeTuplesModule.requiredMethod("consIterator")
    @tu lazy val RuntimeTuples_concatIterator: Symbol = RuntimeTuplesModule.requiredMethod("concatIterator")
    @tu lazy val RuntimeTuples_apply: Symbol = RuntimeTuplesModule.requiredMethod("apply")
    @tu lazy val RuntimeTuples_cons: Symbol = RuntimeTuplesModule.requiredMethod("cons")
    @tu lazy val RuntimeTuples_size: Symbol = RuntimeTuplesModule.requiredMethod("size")
    @tu lazy val RuntimeTuples_tail: Symbol = RuntimeTuplesModule.requiredMethod("tail")
    @tu lazy val RuntimeTuples_concat: Symbol = RuntimeTuplesModule.requiredMethod("concat")
    @tu lazy val RuntimeTuples_toArray: Symbol = RuntimeTuplesModule.requiredMethod("toArray")
    @tu lazy val RuntimeTuples_productToArray: Symbol = RuntimeTuplesModule.requiredMethod("productToArray")
    @tu lazy val RuntimeTuples_isInstanceOfTuple: Symbol = RuntimeTuplesModule.requiredMethod("isInstanceOfTuple")
    @tu lazy val RuntimeTuples_isInstanceOfEmptyTuple: Symbol = RuntimeTuplesModule.requiredMethod("isInstanceOfEmptyTuple")
    @tu lazy val RuntimeTuples_isInstanceOfNonEmptyTuple: Symbol = RuntimeTuplesModule.requiredMethod("isInstanceOfNonEmptyTuple")

  @tu lazy val TupledFunctionTypeRef: TypeRef = requiredClassRef("scala.util.TupledFunction")
  def TupledFunctionClass(using Context): ClassSymbol = TupledFunctionTypeRef.symbol.asClass
  def RuntimeTupleFunctionsModule(using Context): Symbol = requiredModule("scala.runtime.TupledFunctions")

  @tu lazy val boundaryModule: Symbol = requiredModule("scala.util.boundary")
  @tu lazy val LabelClass: Symbol = requiredClass("scala.util.boundary.Label")
  @tu lazy val BreakClass: Symbol = requiredClass("scala.util.boundary.Break")

  @tu lazy val CapsModule: Symbol = requiredModule("scala.caps")
    @tu lazy val captureRoot: TermSymbol = CapsModule.requiredValue("cap")
    @tu lazy val CapsUnsafeModule: Symbol = requiredModule("scala.caps.unsafe")
    @tu lazy val Caps_unsafeBox: Symbol = CapsUnsafeModule.requiredMethod("unsafeBox")
    @tu lazy val Caps_unsafeUnbox: Symbol = CapsUnsafeModule.requiredMethod("unsafeUnbox")
    @tu lazy val Caps_unsafeBoxFunArg: Symbol = CapsUnsafeModule.requiredMethod("unsafeBoxFunArg")
    @tu lazy val Caps_SealedAnnot: ClassSymbol = requiredClass("scala.caps.Sealed")

  // Annotation base classes
  @tu lazy val AnnotationClass: ClassSymbol = requiredClass("scala.annotation.Annotation")
  @tu lazy val StaticAnnotationClass: ClassSymbol = requiredClass("scala.annotation.StaticAnnotation")
  @tu lazy val RefiningAnnotationClass: ClassSymbol = requiredClass("scala.annotation.RefiningAnnotation")

  // Annotation classes
  @tu lazy val AllowConversionsAnnot: ClassSymbol = requiredClass("scala.annotation.allowConversions")
  @tu lazy val AnnotationDefaultAnnot: ClassSymbol = requiredClass("scala.annotation.internal.AnnotationDefault")
  @tu lazy val BeanPropertyAnnot: ClassSymbol = requiredClass("scala.beans.BeanProperty")
  @tu lazy val BooleanBeanPropertyAnnot: ClassSymbol = requiredClass("scala.beans.BooleanBeanProperty")
  @tu lazy val BodyAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Body")
  @tu lazy val CapabilityAnnot: ClassSymbol = requiredClass("scala.annotation.capability")
  @tu lazy val ChildAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Child")
  @tu lazy val ContextResultCountAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ContextResultCount")
  @tu lazy val ProvisionalSuperClassAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ProvisionalSuperClass")
  @tu lazy val DeprecatedAnnot: ClassSymbol = requiredClass("scala.deprecated")
  @tu lazy val DeprecatedOverridingAnnot: ClassSymbol = requiredClass("scala.deprecatedOverriding")
  @tu lazy val DeprecatedInheritanceAnnot: ClassSymbol = requiredClass("scala.deprecatedInheritance")
  @tu lazy val ImplicitAmbiguousAnnot: ClassSymbol = requiredClass("scala.annotation.implicitAmbiguous")
  @tu lazy val ImplicitNotFoundAnnot: ClassSymbol = requiredClass("scala.annotation.implicitNotFound")
  @tu lazy val InlineParamAnnot: ClassSymbol = requiredClass("scala.annotation.internal.InlineParam")
  @tu lazy val ErasedParamAnnot: ClassSymbol = requiredClass("scala.annotation.internal.ErasedParam")
  @tu lazy val InvariantBetweenAnnot: ClassSymbol = requiredClass("scala.annotation.internal.InvariantBetween")
  @tu lazy val MainAnnot: ClassSymbol = requiredClass("scala.main")
  @tu lazy val MappedAlternativeAnnot: ClassSymbol = requiredClass("scala.annotation.internal.MappedAlternative")
  @tu lazy val MigrationAnnot: ClassSymbol = requiredClass("scala.annotation.migration")
  @tu lazy val NowarnAnnot: ClassSymbol = requiredClass("scala.annotation.nowarn")
  @tu lazy val UnusedAnnot: ClassSymbol = requiredClass("scala.annotation.unused")
  @tu lazy val TransparentTraitAnnot: ClassSymbol = requiredClass("scala.annotation.transparentTrait")
  @tu lazy val NativeAnnot: ClassSymbol = requiredClass("scala.native")
  @tu lazy val RepeatedAnnot: ClassSymbol = requiredClass("scala.annotation.internal.Repeated")
  @tu lazy val SourceFileAnnot: ClassSymbol = requiredClass("scala.annotation.internal.SourceFile")
  @tu lazy val ScalaSignatureAnnot: ClassSymbol = requiredClass("scala.reflect.ScalaSignature")
  @tu lazy val ScalaLongSignatureAnnot: ClassSymbol = requiredClass("scala.reflect.ScalaLongSignature")
  @tu lazy val ScalaStrictFPAnnot: ClassSymbol = requiredClass("scala.annotation.strictfp")
  @tu lazy val ScalaStaticAnnot: ClassSymbol = requiredClass("scala.annotation.static")
  @tu lazy val SerialVersionUIDAnnot: ClassSymbol = requiredClass("scala.SerialVersionUID")
  @tu lazy val TailrecAnnot: ClassSymbol = requiredClass("scala.annotation.tailrec")
  @tu lazy val ThreadUnsafeAnnot: ClassSymbol = requiredClass("scala.annotation.threadUnsafe")
  @tu lazy val ConstructorOnlyAnnot: ClassSymbol = requiredClass("scala.annotation.constructorOnly")
  @tu lazy val CompileTimeOnlyAnnot: ClassSymbol = requiredClass("scala.annotation.compileTimeOnly")
  @tu lazy val SwitchAnnot: ClassSymbol = requiredClass("scala.annotation.switch")
  @tu lazy val ExperimentalAnnot: ClassSymbol = requiredClass("scala.annotation.experimental")
  @tu lazy val ThrowsAnnot: ClassSymbol = requiredClass("scala.throws")
  @tu lazy val TransientAnnot: ClassSymbol = requiredClass("scala.transient")
  @tu lazy val UncheckedAnnot: ClassSymbol = requiredClass("scala.unchecked")
  @tu lazy val UncheckedStableAnnot: ClassSymbol = requiredClass("scala.annotation.unchecked.uncheckedStable")
  @tu lazy val UncheckedVarianceAnnot: ClassSymbol = requiredClass("scala.annotation.unchecked.uncheckedVariance")
  @tu lazy val UncheckedCapturesAnnot: ClassSymbol = requiredClass("scala.annotation.unchecked.uncheckedCaptures")
  @tu lazy val VolatileAnnot: ClassSymbol = requiredClass("scala.volatile")
  @tu lazy val WithPureFunsAnnot: ClassSymbol = requiredClass("scala.annotation.internal.WithPureFuns")
  @tu lazy val BeanGetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.beanGetter")
  @tu lazy val BeanSetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.beanSetter")
  @tu lazy val FieldMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.field")
  @tu lazy val GetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.getter")
  @tu lazy val ParamMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.param")
  @tu lazy val SetterMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.setter")
  @tu lazy val CompanionClassMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.companionClass")
  @tu lazy val CompanionMethodMetaAnnot: ClassSymbol = requiredClass("scala.annotation.meta.companionMethod")
  @tu lazy val ShowAsInfixAnnot: ClassSymbol = requiredClass("scala.annotation.showAsInfix")
  @tu lazy val FunctionalInterfaceAnnot: ClassSymbol = requiredClass("java.lang.FunctionalInterface")
  @tu lazy val TargetNameAnnot: ClassSymbol = requiredClass("scala.annotation.targetName")
  @tu lazy val VarargsAnnot: ClassSymbol = requiredClass("scala.annotation.varargs")
  @tu lazy val SinceAnnot: ClassSymbol = requiredClass("scala.annotation.since")
  @tu lazy val RequiresCapabilityAnnot: ClassSymbol = requiredClass("scala.annotation.internal.requiresCapability")
  @tu lazy val RetainsAnnot: ClassSymbol = requiredClass("scala.annotation.retains")
  @tu lazy val RetainsByNameAnnot: ClassSymbol = requiredClass("scala.annotation.retainsByName")

  @tu lazy val JavaRepeatableAnnot: ClassSymbol = requiredClass("java.lang.annotation.Repeatable")

  // A list of meta-annotations that are relevant for fields and accessors
  @tu lazy val NonBeanMetaAnnots: Set[Symbol] =
    Set(FieldMetaAnnot, GetterMetaAnnot, ParamMetaAnnot, SetterMetaAnnot, CompanionClassMetaAnnot, CompanionMethodMetaAnnot)
  @tu lazy val MetaAnnots: Set[Symbol] =
    NonBeanMetaAnnots + BeanGetterMetaAnnot + BeanSetterMetaAnnot

  // A list of annotations that are commonly used to indicate that a field/method argument or return
  // type is not null. These annotations are used by the nullification logic in JavaNullInterop to
  // improve the precision of type nullification.
  // We don't require that any of these annotations be present in the class path, but we want to
  // create Symbols for the ones that are present, so they can be checked during nullification.
  @tu lazy val NotNullAnnots: List[ClassSymbol] = getClassesIfDefined(
    "javax.annotation.Nonnull" ::
    "javax.validation.constraints.NotNull" ::
    "androidx.annotation.NonNull" ::
    "android.support.annotation.NonNull" ::
    "android.annotation.NonNull" ::
    "com.android.annotations.NonNull" ::
    "org.eclipse.jdt.annotation.NonNull" ::
    "edu.umd.cs.findbugs.annotations.NonNull" ::
    "org.checkerframework.checker.nullness.qual.NonNull" ::
    "org.checkerframework.checker.nullness.compatqual.NonNullDecl" ::
    "org.jetbrains.annotations.NotNull" ::
    "org.springframework.lang.NonNull" ::
    "org.springframework.lang.NonNullApi" ::
    "org.springframework.lang.NonNullFields" ::
    "lombok.NonNull" ::
    "reactor.util.annotation.NonNull" ::
    "reactor.util.annotation.NonNullApi" ::
    "io.reactivex.annotations.NonNull" :: Nil)

  // convenient one-parameter method types
  def methOfAny(tp: Type): MethodType = MethodType(List(AnyType), tp)
  def methOfAnyVal(tp: Type): MethodType = MethodType(List(AnyValType), tp)
  def methOfAnyRef(tp: Type): MethodType = MethodType(List(ObjectType), tp)

  // Derived types

  def RepeatedParamType: TypeRef = RepeatedParamClass.typeRef

  def ClassType(arg: Type)(using Context): Type = {
    val ctype = ClassClass.typeRef
    if (ctx.phase.erasedTypes) ctype else ctype.appliedTo(arg)
  }

  /** The enumeration type, goven a value of the enumeration */
  def EnumType(sym: Symbol)(using Context): TypeRef =
    // given (in java): "class A { enum E { VAL1 } }"
    //  - sym: the symbol of the actual enumeration value (VAL1)
    //  - .owner: the ModuleClassSymbol of the enumeration (object E)
    //  - .linkedClass: the ClassSymbol of the enumeration (class E)
    sym.owner.linkedClass.typeRef

  object FunctionOf {
    def apply(args: List[Type], resultType: Type, isContextual: Boolean = false)(using Context): Type =
      val mt = MethodType.companion(isContextual, false)(args, resultType)
      if mt.hasErasedParams then RefinedType(ErasedFunctionClass.typeRef, nme.apply, mt)
      else FunctionNOf(args, resultType, isContextual)
    def unapply(ft: Type)(using Context): Option[(List[Type], Type, Boolean)] = {
      ft.dealias match
        case ErasedFunctionOf(mt) =>
          Some(mt.paramInfos, mt.resType, mt.isContextualMethod)
        case dft =>
          val tsym = dft.typeSymbol
          if isFunctionSymbol(tsym) && ft.isRef(tsym) then
            val targs = dft.argInfos
            if (targs.isEmpty) None
            else Some(targs.init, targs.last, tsym.name.isContextFunction)
          else None
    }
  }

  object PolyOrErasedFunctionOf {
    /** Matches a refined `PolyFunction` or `ErasedFunction` type and extracts the apply info.
     *
     *  Pattern: `(PolyFunction | ErasedFunction) { def apply: $mt }`
     */
    def unapply(ft: Type)(using Context): Option[MethodicType] = ft.dealias match
      case RefinedType(parent, nme.apply, mt: MethodicType)
      if parent.derivesFrom(defn.PolyFunctionClass) || parent.derivesFrom(defn.ErasedFunctionClass) =>
        Some(mt)
      case _ => None
  }

   object FunctionNOf {
    /** Create a `FunctionN` or `ContextFunctionN` type applied to the arguments and result type */
    def apply(args: List[Type], resultType: Type, isContextual: Boolean = false)(using Context): Type =
      FunctionType(args.length, isContextual).appliedTo(args ::: resultType :: Nil)

    /** Matches a (possibly aliased) `FunctionN[...]` or `ContextFunctionN[...]`.
     *  Extracts the list of function argument types, the result type and whether function is contextual.
     */
    def unapply(tpe: AppliedType)(using Context): Option[(List[Type], Type, Boolean)] = {
      if !isFunctionNType(tpe) then None
      else Some(tpe.args.init, tpe.args.last, tpe.typeSymbol.name.isContextFunction)
    }
  }

  object RefinedFunctionOf {
    /** Matches a refined `PolyFunction`/`FunctionN[...]`/`ContextFunctionN[...]`.
     *  Extracts the method type type and apply info.
     */
    def unapply(tpe: RefinedType)(using Context): Option[MethodOrPoly] = {
      tpe.refinedInfo match
        case mt: MethodOrPoly
        if tpe.refinedName == nme.apply
        && (tpe.parent.derivesFrom(defn.PolyFunctionClass) || isFunctionNType(tpe.parent)) =>
          Some(mt)
        case _ => None
    }
  }

  object PolyFunctionOf {
    /** Matches a refined `PolyFunction` type and extracts the apply info.
     *
     *  Pattern: `PolyFunction { def apply: $pt }`
     */
    def unapply(tpe: RefinedType)(using Context): Option[MethodOrPoly] =
      tpe.refinedInfo match
        case mt: MethodOrPoly
        if tpe.refinedName == nme.apply && tpe.parent.derivesFrom(defn.PolyFunctionClass) =>
          Some(mt)
        case _ => None

    def isValidPolyFunctionInfo(info: Type)(using Context): Boolean =
      def isValidMethodType(info: Type) = info match
        case info: MethodType =>
          !info.resType.isInstanceOf[MethodOrPoly] && // Has only one parameter list
          !info.isVarArgsMethod &&
          !info.isMethodWithByNameArgs // No by-name parameters
        case _ => false
      info match
        case info: PolyType => isValidMethodType(info.resType)
        case _ => isValidMethodType(info)
  }

  object ErasedFunctionOf {
    /** Matches a refined `ErasedFunction` type and extracts the apply info.
     *
     *  Pattern: `ErasedFunction { def apply: $mt }`
     */
    def unapply(ft: Type)(using Context): Option[MethodType] = ft.dealias match
      case RefinedType(parent, nme.apply, mt: MethodType)
      if parent.derivesFrom(defn.ErasedFunctionClass) =>
        Some(mt)
      case _ => None
  }

  object PartialFunctionOf {
    def apply(arg: Type, result: Type)(using Context): Type =
      PartialFunctionClass.typeRef.appliedTo(arg :: result :: Nil)
    def unapply(pft: Type)(using Context): Option[(Type, List[Type])] =
      if (pft.isRef(PartialFunctionClass)) {
        val targs = pft.dealias.argInfos
        if (targs.length == 2) Some((targs.head, targs.tail)) else None
      }
      else None
  }

  object ArrayOf {
    def apply(elem: Type)(using Context): Type =
      if (ctx.erasedTypes) JavaArrayType(elem)
      else ArrayType.appliedTo(elem :: Nil)
    def unapply(tp: Type)(using Context): Option[Type] = tp.dealias match {
      case AppliedType(at, arg :: Nil) if at.isRef(ArrayType.symbol) => Some(arg)
      case JavaArrayType(tp) if ctx.erasedTypes => Some(tp)
      case _ => None
    }
  }

  object MatchCase {
    def apply(pat: Type, body: Type)(using Context): Type =
      MatchCaseClass.typeRef.appliedTo(pat, body)
    def unapply(tp: Type)(using Context): Option[(Type, Type)] = tp match {
      case AppliedType(tycon, pat :: body :: Nil) if tycon.isRef(MatchCaseClass) =>
        Some((pat, body))
      case _ =>
        None
    }
    def isInstance(tp: Type)(using Context): Boolean = tp match {
      case AppliedType(tycon: TypeRef, _) =>
        tycon.name == tpnme.MatchCase && // necessary pre-filter to avoid forcing symbols
        tycon.isRef(MatchCaseClass)
      case _ => false
    }
  }

  /** An extractor for multi-dimensional arrays.
   *  Note that this will also extract the high bound if an
   *  element type is a wildcard upper-bounded by an array. E.g.
   *
   *     Array[? <: Array[? <: Number]]
   *
   *  would match
   *
   *     MultiArrayOf(<? <: Number>, 2)
   */
  object MultiArrayOf {
    def apply(elem: Type, ndims: Int)(using Context): Type =
      if (ndims == 0) elem else ArrayOf(apply(elem, ndims - 1))
    def unapply(tp: Type)(using Context): Option[(Type, Int)] = tp match {
      case ArrayOf(elemtp) =>
        def recur(elemtp: Type): Option[(Type, Int)] = elemtp.dealias match {
          case tp @ TypeBounds(lo, hi @ MultiArrayOf(finalElemTp, n)) =>
            Some(finalElemTp, n)
          case MultiArrayOf(finalElemTp, n) => Some(finalElemTp, n + 1)
          case _ => Some(elemtp, 1)
        }
        recur(elemtp)
      case _ =>
        None
    }
  }

  /** Extractor for context function types representing by-name parameters, of the form
   *  `() ?=> T`.
   *  Under purefunctions, this becomes `() ?-> T` or `{r1, ..., rN} () ?-> T`.
   */
  object ByNameFunction:
    def apply(tp: Type)(using Context): Type = tp match
      case tp @ EventuallyCapturingType(tp1, refs) if tp.annot.symbol == RetainsByNameAnnot =>
        CapturingType(apply(tp1), refs)
      case _ =>
        defn.ContextFunction0.typeRef.appliedTo(tp :: Nil)
    def unapply(tp: Type)(using Context): Option[Type] = tp match
      case tp @ AppliedType(tycon, arg :: Nil) if defn.isByNameFunctionClass(tycon.typeSymbol) =>
        Some(arg)
      case tp @ AnnotatedType(parent, _) =>
        unapply(parent)
      case _ =>
        None

  final def isByNameFunctionClass(sym: Symbol): Boolean =
    sym eq ContextFunction0

  def isByNameFunction(tp: Type)(using Context): Boolean = tp match
    case ByNameFunction(_) => true
    case _ => false

  final def isCompiletime_S(sym: Symbol)(using Context): Boolean =
    sym.name == tpnme.S && sym.owner == CompiletimeOpsIntModuleClass

  private val compiletimePackageAnyTypes: Set[Name] = Set(
    tpnme.Equals, tpnme.NotEquals, tpnme.IsConst, tpnme.ToString
  )
  private val compiletimePackageNumericTypes: Set[Name] = Set(
    tpnme.Plus, tpnme.Minus, tpnme.Times, tpnme.Div, tpnme.Mod,
    tpnme.Lt, tpnme.Gt, tpnme.Ge, tpnme.Le,
    tpnme.Abs, tpnme.Negate, tpnme.Min, tpnme.Max
  )
  private val compiletimePackageIntTypes: Set[Name] = compiletimePackageNumericTypes ++ Set[Name](
    tpnme.ToString, // ToString is moved to ops.any and deprecated for ops.int
    tpnme.NumberOfLeadingZeros, tpnme.ToLong, tpnme.ToFloat, tpnme.ToDouble,
    tpnme.Xor, tpnme.BitwiseAnd, tpnme.BitwiseOr, tpnme.ASR, tpnme.LSL, tpnme.LSR
  )
  private val compiletimePackageLongTypes: Set[Name] = compiletimePackageNumericTypes ++ Set[Name](
    tpnme.NumberOfLeadingZeros, tpnme.ToInt, tpnme.ToFloat, tpnme.ToDouble,
    tpnme.Xor, tpnme.BitwiseAnd, tpnme.BitwiseOr, tpnme.ASR, tpnme.LSL, tpnme.LSR
  )
  private val compiletimePackageFloatTypes: Set[Name] = compiletimePackageNumericTypes ++ Set[Name](
    tpnme.ToInt, tpnme.ToLong, tpnme.ToDouble
  )
  private val compiletimePackageDoubleTypes: Set[Name] = compiletimePackageNumericTypes ++ Set[Name](
    tpnme.ToInt, tpnme.ToLong, tpnme.ToFloat
  )
  private val compiletimePackageBooleanTypes: Set[Name] = Set(tpnme.Not, tpnme.Xor, tpnme.And, tpnme.Or)
  private val compiletimePackageStringTypes: Set[Name] = Set(
    tpnme.Plus, tpnme.Length, tpnme.Substring, tpnme.Matches, tpnme.CharAt
  )
  private val compiletimePackageOpTypes: Set[Name] =
    Set(tpnme.S)
    ++ compiletimePackageAnyTypes
    ++ compiletimePackageIntTypes
    ++ compiletimePackageLongTypes
    ++ compiletimePackageFloatTypes
    ++ compiletimePackageDoubleTypes
    ++ compiletimePackageBooleanTypes
    ++ compiletimePackageStringTypes

  final def isCompiletimeAppliedType(sym: Symbol)(using Context): Boolean =
    compiletimePackageOpTypes.contains(sym.name)
    && (
         isCompiletime_S(sym)
      || sym.owner == CompiletimeOpsAnyModuleClass && compiletimePackageAnyTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsIntModuleClass && compiletimePackageIntTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsLongModuleClass && compiletimePackageLongTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsFloatModuleClass && compiletimePackageFloatTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsDoubleModuleClass && compiletimePackageDoubleTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsBooleanModuleClass && compiletimePackageBooleanTypes.contains(sym.name)
      || sym.owner == CompiletimeOpsStringModuleClass && compiletimePackageStringTypes.contains(sym.name)
    )

  // ----- Scala-2 library patches --------------------------------------

  /** The `scala.runtime.stdLibPacthes` package contains objects
   *  that contain defnitions that get added as members to standard library
   *  objects with the same name.
   */
  @tu lazy val StdLibPatchesPackage: TermSymbol = requiredPackage("scala.runtime.stdLibPatches")
  @tu private lazy val ScalaPredefModuleClassPatch: Symbol = getModuleIfDefined("scala.runtime.stdLibPatches.Predef").moduleClass
  @tu private lazy val LanguageModuleClassPatch: Symbol = getModuleIfDefined("scala.runtime.stdLibPatches.language").moduleClass

  /** If `sym` is a patched library class, the source file of its patch class,
   *  otherwise `NoSource`
   */
  def patchSource(sym: Symbol)(using Context): SourceFile =
    if sym == ScalaPredefModuleClass then ScalaPredefModuleClassPatch.source
    else if sym == LanguageModuleClass then LanguageModuleClassPatch.source
    else NoSource

  /** A finalizer that patches standard library classes.
   *  It copies all non-private, non-synthetic definitions from `patchCls`
   *  to `denot` while changing their owners to `denot`. Before that it deletes
   *  any definitions of `denot` that have the same name as one of the copied
   *  definitions.
   *
   *  If an object is present in both the original class and the patch class,
   *  it is not overwritten. Instead its members are copied recursively.
   *
   *  To avpid running into cycles on bootstrap, patching happens only if `patchCls`
   *  is read from a classfile.
   */
  def patchStdLibClass(denot: ClassDenotation)(using Context): Unit =
    def patch2(denot: ClassDenotation, patchCls: Symbol): Unit =
      val scope = denot.info.decls.openForMutations

      def recurse(patch: Symbol) = patch.is(Module) && scope.lookup(patch.name).exists

      def makeClassSymbol(patch: Symbol, parents: List[Type], selfInfo: TypeOrSymbol) =
        newClassSymbol(
          owner = denot.symbol,
          name = patch.name.asTypeName,
          flags = patch.flags,
          // need to rebuild a fresh ClassInfo
          infoFn = cls => ClassInfo(
            prefix = denot.symbol.thisType,
            cls = cls,
            declaredParents = parents, // assume parents in patch don't refer to symbols in the patch
            decls = newScope,
            selfInfo =
              if patch.is(Module)
              then TermRef(denot.symbol.thisType, patch.name.sourceModuleName)
              else selfInfo // assume patch self type annotation does not refer to symbols in the patch
          ),
          privateWithin = patch.privateWithin,
          coord = denot.symbol.coord,
          assocFile = denot.symbol.associatedFile
        )

      def makeNonClassSymbol(patch: Symbol) =
        if patch.is(Inline) then
          // Inline symbols contain trees in annotations, which is coupled
          // with the underlying symbol.
          // Changing owner for inline symbols is a simple workaround.
          patch.denot = patch.denot.copySymDenotation(owner = denot.symbol)
          patch
        else
          // change `info` which might contain reference to the patch
          patch.copy(
            owner = denot.symbol,
            info =
              if patch.is(Module)
              then TypeRef(denot.symbol.thisType, patch.name.moduleClassName)
              else patch.info // assume non-object info does not refer to symbols in the patch
          )

      if patchCls.exists then
        val patches = patchCls.info.decls.filter(patch =>
          !patch.isConstructor && !patch.isOneOf(PrivateOrSynthetic))
        for patch <- patches if !recurse(patch) do
          val e = scope.lookupEntry(patch.name)
          if e != null then scope.unlink(e)
        for patch <- patches do
          patch.ensureCompleted()
          if !recurse(patch) then
            val sym =
              patch.info match
              case ClassInfo(_, _, parents, _, selfInfo) =>
                makeClassSymbol(patch, parents, selfInfo)
              case _ =>
                makeNonClassSymbol(patch)
              end match
            sym.annotations = patch.annotations
            scope.enter(sym)
          if patch.isClass then
            patch2(scope.lookup(patch.name).asClass, patch)

    def patchWith(patchCls: Symbol) =
      denot.sourceModule.info = denot.typeRef // we run into a cyclic reference when patching if this line is omitted
      patch2(denot, patchCls)

    if denot.name == tpnme.Predef.moduleClassName && denot.symbol == ScalaPredefModuleClass then
      patchWith(ScalaPredefModuleClassPatch)
    else if denot.name == tpnme.language.moduleClassName && denot.symbol == LanguageModuleClass then
      patchWith(LanguageModuleClassPatch)
  end patchStdLibClass

  // ----- Symbol sets ---------------------------------------------------

  @tu lazy val topClasses: Set[Symbol] = Set(AnyClass, MatchableClass, ObjectClass, AnyValClass)

  @tu lazy val untestableClasses: Set[Symbol] = Set(NothingClass, NullClass, SingletonClass)

  /** Base classes that are assumed to be pure for the purposes of capture checking.
   *  Every class inheriting from a pure baseclass is pure.
   */
  @tu lazy val pureBaseClasses = Set(defn.AnyValClass, defn.ThrowableClass)

  /** Non-inheritable lasses that are assumed to be pure for the purposes of capture checking,
   */
  @tu lazy val pureSimpleClasses = Set(StringClass, NothingClass, NullClass)

  @tu lazy val AbstractFunctionType: Array[TypeRef] = mkArityArray("scala.runtime.AbstractFunction", MaxImplementedFunctionArity, 0).asInstanceOf[Array[TypeRef]]
  val AbstractFunctionClassPerRun: PerRun[Array[Symbol]] = new PerRun(AbstractFunctionType.map(_.symbol.asClass))
  def AbstractFunctionClass(n: Int)(using Context): Symbol = AbstractFunctionClassPerRun()(using ctx)(n)

  @tu lazy val caseClassSynthesized: List[Symbol] = List(
    Any_hashCode, Any_equals, Any_toString, Product_canEqual, Product_productArity,
    Product_productPrefix, Product_productElement, Product_productElementName)

  val LazyHolder: PerRun[Map[Symbol, Symbol]] = new PerRun({
    def holderImpl(holderType: String) = requiredClass("scala.runtime." + holderType)
    Map[Symbol, Symbol](
      IntClass     -> holderImpl("LazyInt"),
      LongClass    -> holderImpl("LazyLong"),
      BooleanClass -> holderImpl("LazyBoolean"),
      FloatClass   -> holderImpl("LazyFloat"),
      DoubleClass  -> holderImpl("LazyDouble"),
      ByteClass    -> holderImpl("LazyByte"),
      CharClass    -> holderImpl("LazyChar"),
      ShortClass   -> holderImpl("LazyShort")
    )
    .withDefaultValue(holderImpl("LazyRef"))
  })

  @tu lazy val TupleType: Array[TypeRef | Null] = mkArityArray("scala.Tuple", MaxTupleArity, 1)

  def isSpecializedTuple(cls: Symbol)(using Context): Boolean =
    cls.isClass && TupleSpecializedClasses.exists(tupleCls => cls.name.isSpecializedNameOf(tupleCls.name))

  def SpecializedTuple(base: Symbol, args: List[Type])(using Context): Symbol =
    base.owner.requiredClass(base.name.specializedName(args))

  /** Cached function types of arbitary arities.
   *  Function types are created on demand with newFunctionNTrait, which is
   *  called from a synthesizer installed in ScalaPackageClass.
   */
  private class FunType(prefix: String):
    private var classRefs: Array[TypeRef | Null] = new Array(22)
    def apply(n: Int): TypeRef =
      while n >= classRefs.length do
        val classRefs1 = new Array[TypeRef | Null](classRefs.length * 2)
        Array.copy(classRefs, 0, classRefs1, 0, classRefs.length)
        classRefs = classRefs1
      if classRefs(n) == null then
        val funName = s"scala.$prefix$n"
        classRefs(n) =
          if prefix.startsWith("Impure")
          then staticRef(funName.toTypeName).symbol.typeRef
          else requiredClassRef(funName)
      classRefs(n).nn
  end FunType

  private def funTypeIdx(isContextual: Boolean, isImpure: Boolean): Int =
      (if isContextual then 1 else 0)
    + (if isImpure     then 2 else 0)

  private val funTypeArray: IArray[FunType] =
    val arr = Array.ofDim[FunType](8)
    val choices = List(false, true)
    for contxt <- choices; impure <- choices do
      var str = "Function"
      if contxt then str = "Context" + str
      if impure then str = "Impure" + str
      arr(funTypeIdx(contxt, impure)) = FunType(str)
    IArray.unsafeFromArray(arr)

  def FunctionSymbol(n: Int, isContextual: Boolean = false, isImpure: Boolean = false)(using Context): Symbol =
    funTypeArray(funTypeIdx(isContextual, isImpure))(n).symbol

  @tu lazy val Function0_apply: Symbol = Function0.requiredMethod(nme.apply)
  @tu lazy val ContextFunction0_apply: Symbol = ContextFunction0.requiredMethod(nme.apply)

  @tu lazy val Function0: Symbol = FunctionSymbol(0)
  @tu lazy val Function1: Symbol = FunctionSymbol(1)
  @tu lazy val Function2: Symbol = FunctionSymbol(2)
  @tu lazy val ContextFunction0: Symbol = FunctionSymbol(0, isContextual = true)

  def FunctionType(n: Int, isContextual: Boolean = false, isImpure: Boolean = false)(using Context): TypeRef =
    FunctionSymbol(n, isContextual && !ctx.erasedTypes, isImpure).typeRef

  lazy val PolyFunctionClass = requiredClass("scala.PolyFunction")
  def PolyFunctionType = PolyFunctionClass.typeRef

  lazy val ErasedFunctionClass = requiredClass("scala.runtime.ErasedFunction")
  def ErasedFunctionType = ErasedFunctionClass.typeRef

  /** If `cls` is a class in the scala package, its name, otherwise EmptyTypeName */
  def scalaClassName(cls: Symbol)(using Context): TypeName = cls.denot match
    case clsd: ClassDenotation if clsd.owner eq ScalaPackageClass =>
      clsd.name.asInstanceOf[TypeName]
    case _ =>
      EmptyTypeName

  /** If type `ref` refers to a class in the scala package, its name, otherwise EmptyTypeName */
  def scalaClassName(ref: Type)(using Context): TypeName = scalaClassName(ref.classSymbol)

  private def isVarArityClass(cls: Symbol, prefix: String) =
    cls.isClass
    && cls.owner.eq(ScalaPackageClass)
    && cls.name.testSimple(name =>
      name.startsWith(prefix)
      && name.length > prefix.length
      && digitsOnlyAfter(name, prefix.length))

  private def digitsOnlyAfter(name: SimpleName, idx: Int): Boolean =
    idx == name.length || name(idx).isDigit && digitsOnlyAfter(name, idx + 1)

  def isBottomClass(cls: Symbol): Boolean =
    if ctx.mode.is(Mode.SafeNulls) && !ctx.phase.erasedTypes
    then cls == NothingClass
    else isBottomClassAfterErasure(cls)

  def isBottomClassAfterErasure(cls: Symbol): Boolean = cls == NothingClass || cls == NullClass

  /** Is any function class where
   *   - FunctionXXL
   *   - FunctionN for N >= 0
   *   - ContextFunctionN for N >= 0
   */
  def isFunctionClass(cls: Symbol): Boolean = scalaClassName(cls).isFunction

  /** Is a function class, or an impure function type alias */
  def isFunctionSymbol(sym: Symbol): Boolean =
    sym.isType && (sym.owner eq ScalaPackageClass) && sym.name.isFunction

  /** Is a function class where
   *    - FunctionN for N >= 0 and N != XXL
   */
  def isPlainFunctionClass(cls: Symbol) = isVarArityClass(cls, str.Function)

  /** Is an context function class.
   *   - ContextFunctionN for N >= 0
   */
  def isContextFunctionClass(cls: Symbol): Boolean = scalaClassName(cls).isContextFunction

  /** Is either FunctionXXL or  a class that will be erased to FunctionXXL
   *   - FunctionXXL
   *   - FunctionN for N >= 22
   *   - ContextFunctionN for N >= 22
   */
  def isXXLFunctionClass(cls: Symbol): Boolean = {
    val name = scalaClassName(cls)
    (name eq tpnme.FunctionXXL) || name.functionArity > MaxImplementedFunctionArity
  }

  /** Is a synthetic function class
   *    - FunctionN for N > 22
   *    - ContextFunctionN for N >= 0
   *    - ErasedFunctionN for N > 0
   *    - ErasedContextFunctionN for N > 0
   */
  def isSyntheticFunctionClass(cls: Symbol): Boolean = scalaClassName(cls).isSyntheticFunction

  def isAbstractFunctionClass(cls: Symbol): Boolean = isVarArityClass(cls, str.AbstractFunction)
  def isTupleClass(cls: Symbol): Boolean = isVarArityClass(cls, str.Tuple)
  def isProductClass(cls: Symbol): Boolean = isVarArityClass(cls, str.Product)

  def isBoxedUnitClass(cls: Symbol): Boolean =
    cls.isClass && (cls.owner eq ScalaRuntimePackageClass) && cls.name == tpnme.BoxedUnit

  /** Returns the erased type of the function class `cls`
   *    - FunctionN for N > 22 becomes FunctionXXL
   *    - FunctionN for 22 > N >= 0 remains as FunctionN
   *    - ContextFunctionN for N > 22 becomes FunctionXXL
   *    - ContextFunctionN for N <= 22 becomes FunctionN
   *    - ErasedFunctionN becomes Function0
   *    - ImplicitErasedFunctionN becomes Function0
   *    - anything else becomes a NoType
   */
  def functionTypeErasure(cls: Symbol): Type =
    val arity = scalaClassName(cls).functionArity
    if arity > 22 then FunctionXXLClass.typeRef
    else if arity >= 0 then FunctionType(arity)
    else NoType

  private val JavaImportFns: List[RootRef] = List(
    RootRef(() => JavaLangPackageVal.termRef)
  )

  private val ScalaImportFns: List[RootRef] =
    JavaImportFns :+
    RootRef(() => ScalaPackageVal.termRef)

  private val PredefImportFns: RootRef =
    RootRef(() => ScalaPredefModule.termRef, isPredef=true)

  @tu private lazy val YimportsImportFns: List[RootRef] = ctx.settings.Yimports.value.map { name =>
    val denot =
      getModuleIfDefined(name).suchThat(_.is(Module)) `orElse`
      getPackageClassIfDefined(name).suchThat(_.is(Package))
    if !denot.exists then
      report.error(s"error: bad preamble import $name")
    val termRef = denot.symbol.termRef
    RootRef(() => termRef)
  }

  @tu private lazy val JavaRootImportFns: List[RootRef] = JavaImportFns

  @tu private lazy val ScalaRootImportFns: List[RootRef] =
    if !ctx.settings.Yimports.isDefault then YimportsImportFns
    else if ctx.settings.YnoImports.value then Nil
    else if ctx.settings.YnoPredef.value then ScalaImportFns
    else ScalaImportFns :+ PredefImportFns

  @tu private lazy val JavaRootImportTypes: List[TermRef] = JavaRootImportFns.map(_.refFn())
  @tu private lazy val ScalaRootImportTypes: List[TermRef] = ScalaRootImportFns.map(_.refFn())
  @tu private lazy val JavaUnqualifiedOwnerTypes: Set[NamedType] = unqualifiedTypes(JavaRootImportTypes)
  @tu private lazy val ScalaUnqualifiedOwnerTypes: Set[NamedType] = unqualifiedTypes(ScalaRootImportTypes)

  /** Are we compiling a java source file? */
  private def isJavaContext(using Context): Boolean =
    ctx.compilationUnit.isJava

  private def unqualifiedTypes(refs: List[TermRef]) =
    val types = refs.toSet[NamedType]
    types ++ types.map(_.symbol.moduleClass.typeRef)

  /** Lazy references to the root imports */
  def rootImportFns(using Context): List[RootRef] =
    if isJavaContext then JavaRootImportFns
    else ScalaRootImportFns

  /** Root types imported by default */
  def rootImportTypes(using Context): List[TermRef] =
    if isJavaContext then JavaRootImportTypes
    else ScalaRootImportTypes

  /** Modules whose members are in the default namespace and their module classes */
  def unqualifiedOwnerTypes(using Context): Set[NamedType] =
    if isJavaContext then JavaUnqualifiedOwnerTypes
    else ScalaUnqualifiedOwnerTypes

  /** Names of the root import symbols that can be hidden by other imports */
  @tu lazy val ShadowableImportNames: Set[TermName] = Set("Predef".toTermName)

  /** Class symbols for which no class exist at runtime */
  @tu lazy val NotRuntimeClasses: Set[Symbol] = Set(AnyClass, MatchableClass, AnyValClass, NullClass, NothingClass)

  @tu lazy val SpecialClassTagClasses: Set[Symbol] = Set(UnitClass, AnyClass, AnyValClass)

  @tu lazy val SpecialManifestClasses: Set[Symbol] = Set(AnyClass, AnyValClass, ObjectClass, NullClass, NothingClass)

  /** Classes that are known not to have an initializer irrespective of
   *  whether NoInits is set. Note: FunctionXXLClass is in this set
   *  because if it is compiled by Scala2, it does not get a NoInit flag.
   *  But since it is introduced only at erasure, there's no chance
   *  for augmentScala2Traits to do anything on a class that inherits it. So
   *  it also misses an implementation class, which means that the usual scheme
   *  of calling a superclass init in the implementation class of a Scala2
   *  trait gets screwed up. Therefore, it is mandatory that FunctionXXL
   *  is treated as a NoInit trait.
   */
  @tu lazy val NoInitClasses: Set[Symbol] = NotRuntimeClasses + FunctionXXLClass

  def isPolymorphicAfterErasure(sym: Symbol): Boolean =
     (sym eq Any_isInstanceOf) || (sym eq Any_asInstanceOf) || (sym eq Object_synchronized)

  /** Is this type a `TupleN` type?
   *
   * @return true if the dealiased type of `tp` is `TupleN[T1, T2, ..., Tn]`
   */
  def isTupleNType(tp: Type)(using Context): Boolean = {
    val tp1 = tp.dealias
    val arity = tp1.argInfos.length
    arity <= MaxTupleArity && {
      val tupletp = TupleType(arity)
      tupletp != null && tp1.isRef(tupletp.symbol)
    }
  }

  def tupleType(elems: List[Type]): Type = {
    val arity = elems.length
    if 0 < arity && arity <= MaxTupleArity then
      val tupletp = TupleType(arity)
      if tupletp != null then tupletp.appliedTo(elems)
      else TypeOps.nestedPairs(elems)
    else TypeOps.nestedPairs(elems)
  }

  def isProductSubType(tp: Type)(using Context): Boolean = tp.derivesFrom(ProductClass)

  /** Is `tp` (an alias) of either a scala.FunctionN or a scala.ContextFunctionN
   *  instance?
   */
  def isNonRefinedFunction(tp: Type)(using Context): Boolean =
    val arity = functionArity(tp)
    val sym = tp.dealias.typeSymbol

    arity >= 0
    && isFunctionClass(sym)
    && tp.isRef(
        FunctionType(arity, sym.name.isContextFunction).typeSymbol,
        skipRefined = false)
  end isNonRefinedFunction

  /** Returns whether `tp` is an instance or a refined instance of:
   *  - scala.FunctionN
   *  - scala.ContextFunctionN
   */
  def isFunctionNType(tp: Type)(using Context): Boolean =
    isNonRefinedFunction(tp.dropDependentRefinement)

  /** Returns whether `tp` is an instance or a refined instance of:
   *  - scala.FunctionN
   *  - scala.ContextFunctionN
   *  - ErasedFunction
   *  - PolyFunction
   */
  def isFunctionType(tp: Type)(using Context): Boolean =
    isFunctionNType(tp)
    || tp.derivesFrom(defn.PolyFunctionClass)   // TODO check for refinement?
    || tp.derivesFrom(defn.ErasedFunctionClass) // TODO check for refinement?

  private def withSpecMethods(cls: ClassSymbol, bases: List[Name], paramTypes: Set[TypeRef]) =
    for base <- bases; tp <- paramTypes do
      cls.enter(newSymbol(cls, base.specializedName(List(tp)), Method, ExprType(tp)))
    cls

  @tu lazy val Tuple1: ClassSymbol = withSpecMethods(requiredClass("scala.Tuple1"), List(nme._1), Tuple1SpecializedParamTypes)
  @tu lazy val Tuple2: ClassSymbol = withSpecMethods(requiredClass("scala.Tuple2"), List(nme._1, nme._2), Tuple2SpecializedParamTypes)

  @tu lazy val TupleSpecializedClasses: Set[Symbol]               = Set(Tuple1, Tuple2)
  @tu lazy val Tuple1SpecializedParamTypes: Set[TypeRef]          = Set(IntType, LongType, DoubleType)
  @tu lazy val Tuple2SpecializedParamTypes: Set[TypeRef]          = Set(IntType, LongType, DoubleType, CharType, BooleanType)
  @tu lazy val Tuple1SpecializedParamClasses: PerRun[Set[Symbol]] = new PerRun(Tuple1SpecializedParamTypes.map(_.symbol))
  @tu lazy val Tuple2SpecializedParamClasses: PerRun[Set[Symbol]] = new PerRun(Tuple2SpecializedParamTypes.map(_.symbol))

  // Specialized type parameters defined for scala.Function{0,1,2}.
  @tu lazy val Function1SpecializedParamTypes: List[TypeRef] =
    List(IntType, LongType, FloatType, DoubleType)
  @tu lazy val Function2SpecializedParamTypes: List[TypeRef] =
    List(IntType, LongType, DoubleType)
  @tu lazy val Function0SpecializedReturnTypes: List[TypeRef] =
    ScalaNumericValueTypeList :+ UnitType :+ BooleanType
  @tu lazy val Function1SpecializedReturnTypes: List[TypeRef] =
    List(UnitType, BooleanType, IntType, FloatType, LongType, DoubleType)
  @tu lazy val Function2SpecializedReturnTypes: List[TypeRef] =
    Function1SpecializedReturnTypes

  @tu lazy val Function1SpecializedParamClasses: PerRun[collection.Set[Symbol]] =
    new PerRun(Function1SpecializedParamTypes.toSet.map(_.symbol))
  @tu lazy val Function2SpecializedParamClasses: PerRun[collection.Set[Symbol]] =
    new PerRun(Function2SpecializedParamTypes.toSet.map(_.symbol))
  @tu lazy val Function0SpecializedReturnClasses: PerRun[collection.Set[Symbol]] =
    new PerRun(Function0SpecializedReturnTypes.toSet.map(_.symbol))
  @tu lazy val Function1SpecializedReturnClasses: PerRun[collection.Set[Symbol]] =
    new PerRun(Function1SpecializedReturnTypes.toSet.map(_.symbol))
  @tu lazy val Function2SpecializedReturnClasses: PerRun[collection.Set[Symbol]] =
    new PerRun(Function2SpecializedReturnTypes.toSet.map(_.symbol))

  def isSpecializableTuple(base: Symbol, args: List[Type])(using Context): Boolean =
    args.length <= 2 && base.isClass && TupleSpecializedClasses.exists(base.asClass.derivesFrom) && args.match
      case List(x)    => Tuple1SpecializedParamClasses().contains(x.classSymbol)
      case List(x, y) => Tuple2SpecializedParamClasses().contains(x.classSymbol) && Tuple2SpecializedParamClasses().contains(y.classSymbol)
      case _          => false
    && base.owner.denot.info.member(base.name.specializedName(args)).exists // when dotc compiles the stdlib there are no specialised classes

  def isSpecializableFunction(cls: ClassSymbol, paramTypes: List[Type], retType: Type)(using Context): Boolean =
    paramTypes.length <= 2
    && (cls.derivesFrom(FunctionSymbol(paramTypes.length)) || isByNameFunctionClass(cls))
    && isSpecializableFunctionSAM(paramTypes, retType)

  /** If the Single Abstract Method of a Function class has this type, is it specializable? */
  def isSpecializableFunctionSAM(paramTypes: List[Type], retType: Type)(using Context): Boolean =
    paramTypes.length <= 2 && (paramTypes match {
      case Nil =>
        Function0SpecializedReturnClasses().contains(retType.typeSymbol)
      case List(paramType0) =>
        Function1SpecializedParamClasses().contains(paramType0.typeSymbol) &&
        Function1SpecializedReturnClasses().contains(retType.typeSymbol)
      case List(paramType0, paramType1) =>
        Function2SpecializedParamClasses().contains(paramType0.typeSymbol) &&
        Function2SpecializedParamClasses().contains(paramType1.typeSymbol) &&
        Function2SpecializedReturnClasses().contains(retType.typeSymbol)
      case _ =>
        false
    })

  @tu lazy val Function0SpecializedApplyNames: List[TermName] =
    for r <- Function0SpecializedReturnTypes
    yield nme.apply.specializedFunction(r, Nil).asTermName

  @tu lazy val Function1SpecializedApplyNames: List[TermName] =
    for
      r  <- Function1SpecializedReturnTypes
      t1 <- Function1SpecializedParamTypes
    yield
      nme.apply.specializedFunction(r, List(t1)).asTermName

  @tu lazy val Function2SpecializedApplyNames: List[TermName] =
    for
      r  <- Function2SpecializedReturnTypes
      t1 <- Function2SpecializedParamTypes
      t2 <- Function2SpecializedParamTypes
    yield
      nme.apply.specializedFunction(r, List(t1, t2)).asTermName

  @tu lazy val FunctionSpecializedApplyNames: collection.Set[Name] =
    Set.concat(Function0SpecializedApplyNames, Function1SpecializedApplyNames, Function2SpecializedApplyNames)

  def functionArity(tp: Type)(using Context): Int = tp.functionArgInfos.length - 1

  /** Return underlying context function type (i.e. instance of an ContextFunctionN class)
   *  or NoType if none exists. The following types are considered as underlying types:
   *   - the alias of an alias type
   *   - the instance or origin of a TypeVar (i.e. the result of a stripTypeVar)
   *   - the upper bound of a TypeParamRef in the current constraint
   */
  def asContextFunctionType(tp: Type)(using Context): Type =
    tp.stripTypeVar.dealias match
      case tp1: TypeParamRef if ctx.typerState.constraint.contains(tp1) =>
        asContextFunctionType(TypeComparer.bounds(tp1).hiBound)
      case tp1 @ ErasedFunctionOf(mt) if mt.isContextualMethod =>
        tp1
      case tp1 =>
        if tp1.typeSymbol.name.isContextFunction && isFunctionNType(tp1) then tp1
        else NoType

  /** Is `tp` an context function type? */
  def isContextFunctionType(tp: Type)(using Context): Boolean =
    asContextFunctionType(tp).exists

  /** An extractor for context function types `As ?=> B`, possibly with
   *  dependent refinements. Optionally returns a triple consisting of the argument
   *  types `As`, the result type `B` and a whether the type is an erased context function.
   */
  object ContextFunctionType:
    def unapply(tp: Type)(using Context): Option[(List[Type], Type)] =
      asContextFunctionType(tp) match
        case PolyFunctionOf(mt: MethodType) =>
          Some((mt.paramInfos, mt.resType))
        case tp1 if tp1.exists =>
          val args = tp1.functionArgInfos
          Some((args.init, args.last))
        case _ => None

  /* Returns a list of erased booleans marking whether parameters are erased, for a function type. */
  def erasedFunctionParameters(tp: Type)(using Context): List[Boolean] = tp.dealias match {
    case ErasedFunctionOf(mt) => mt.erasedParams
    case tp if isFunctionNType(tp) => List.fill(functionArity(tp)) { false }
    case _ => Nil
  }

  /** A whitelist of Scala-2 classes that are known to be pure */
  def isAssuredNoInits(sym: Symbol): Boolean =
    (sym `eq` SomeClass) || isTupleClass(sym)

  /** If `cls` is Tuple1..Tuple22, add the corresponding *: type as last parent to `parents` */
  def adjustForTuple(cls: ClassSymbol, tparams: List[TypeSymbol], parents: List[Type]): List[Type] = {
    if !isTupleClass(cls) then parents
    else if tparams.isEmpty then parents :+ TupleTypeRef
    else
      assert(parents.head.typeSymbol == ObjectClass)
      TypeOps.nestedPairs(tparams.map(_.typeRef)) :: parents.tail
  }

  /** If it is BoxedUnit, remove `java.io.Serializable` from `parents`. */
  def adjustForBoxedUnit(cls: ClassSymbol, parents: List[Type]): List[Type] =
    if (isBoxedUnitClass(cls)) parents.filter(_.typeSymbol != JavaSerializableClass)
    else parents

  private val HasProblematicGetClass: Set[Name] = Set(
    tpnme.AnyVal, tpnme.Byte, tpnme.Short, tpnme.Char, tpnme.Int, tpnme.Long, tpnme.Float, tpnme.Double,
    tpnme.Unit, tpnme.Boolean)

  /** When typing a primitive value class or AnyVal, we ignore the `getClass`
   *  member: it's supposed to be an override of the `getClass` defined on `Any`,
   *  but in dotty `Any#getClass` is polymorphic so it ends up being an overload.
   *  This is especially problematic because it means that when writing:
   *
   *    1.asInstanceOf[Int & AnyRef].getClass
   *
   *  the `getClass` that returns `Class[Int]` defined in Int can be selected,
   *  but this call is specified to return `classOf[Integer]`, see
   *  tests/run/t5568.scala.
   *
   *  FIXME: remove all the `getClass` methods defined in the standard library
   *  so we don't have to hot-patch it like this.
   */
  def hasProblematicGetClass(className: Name): Boolean =
    HasProblematicGetClass.contains(className)

  /** Is synthesized symbol with alphanumeric name allowed to be used as an infix operator? */
  def isInfix(sym: Symbol)(using Context): Boolean =
    (sym eq Object_eq) || (sym eq Object_ne)

  @tu lazy val assumedTransparentNames: Map[Name, Set[Symbol]] =
    // add these for now, until we had a chance to retrofit 2.13 stdlib
    // we should do a more through sweep through it then.
    val strs = Map(
      "Any" -> Set("scala"),
      "AnyVal" -> Set("scala"),
      "Matchable" -> Set("scala"),
      "Product" -> Set("scala"),
      "Object" -> Set("java.lang"),
      "Comparable" -> Set("java.lang"),
      "Serializable" -> Set("java.io"),
      "BitSetOps" -> Set("scala.collection"),
      "IndexedSeqOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "IterableOnceOps" -> Set("scala.collection"),
      "IterableOps" -> Set("scala.collection"),
      "LinearSeqOps" -> Set("scala.collection", "scala.collection.immutable"),
      "MapOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "SeqOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "SetOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "SortedMapOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "SortedOps" -> Set("scala.collection"),
      "SortedSetOps" -> Set("scala.collection", "scala.collection.mutable", "scala.collection.immutable"),
      "StrictOptimizedIterableOps" -> Set("scala.collection"),
      "StrictOptimizedLinearSeqOps" -> Set("scala.collection"),
      "StrictOptimizedMapOps" -> Set("scala.collection", "scala.collection.immutable"),
      "StrictOptimizedSeqOps" -> Set("scala.collection", "scala.collection.immutable"),
      "StrictOptimizedSetOps" -> Set("scala.collection", "scala.collection.immutable"),
      "StrictOptimizedSortedMapOps" -> Set("scala.collection", "scala.collection.immutable"),
      "StrictOptimizedSortedSetOps" -> Set("scala.collection", "scala.collection.immutable"),
      "ArrayDequeOps" -> Set("scala.collection.mutable"),
      "DefaultSerializable" -> Set("scala.collection.generic"),
      "IsIterable" -> Set("scala.collection.generic"),
      "IsIterableLowPriority" -> Set("scala.collection.generic"),
      "IsIterableOnce" -> Set("scala.collection.generic"),
      "IsIterableOnceLowPriority" -> Set("scala.collection.generic"),
      "IsMap" -> Set("scala.collection.generic"),
      "IsSeq" -> Set("scala.collection.generic"))
    strs.map { case (simple, pkgs) => (
        simple.toTypeName,
        pkgs.map(pkg => staticRef(pkg.toTermName, isPackage = true).symbol.moduleClass)
      )
    }

  def isAssumedTransparent(sym: Symbol): Boolean =
    assumedTransparentNames.get(sym.name) match
      case Some(pkgs) => pkgs.contains(sym.owner)
      case none => false

  // ----- primitive value class machinery ------------------------------------------

  class PerRun[T](generate: Context ?=> T) {
    private var current: RunId = NoRunId
    private var cached: T = _
    def apply()(using Context): T = {
      if (current != ctx.runId) {
        cached = generate
        current = ctx.runId
      }
      cached
    }
  }

  @tu lazy val ScalaNumericValueTypeList: List[TypeRef] = List(
    ByteType, ShortType, CharType, IntType, LongType, FloatType, DoubleType)

  @tu private lazy val ScalaNumericValueTypes: collection.Set[TypeRef] = ScalaNumericValueTypeList.toSet
  @tu private lazy val ScalaValueTypes: collection.Set[TypeRef] = ScalaNumericValueTypes `union` Set(UnitType, BooleanType)

  val ScalaNumericValueClasses: PerRun[collection.Set[Symbol]] = new PerRun(ScalaNumericValueTypes.map(_.symbol))
  val ScalaValueClasses: PerRun[collection.Set[Symbol]]        = new PerRun(ScalaValueTypes.map(_.symbol))

  val ScalaBoxedClasses: PerRun[collection.Set[Symbol]] = new PerRun(
    Set(BoxedByteClass, BoxedShortClass, BoxedCharClass, BoxedIntClass, BoxedLongClass, BoxedFloatClass, BoxedDoubleClass, BoxedUnitClass, BoxedBooleanClass)
  )

  private val valueTypeEnc = mutable.Map[TypeName, PrimitiveClassEnc]()
  private val typeTags = mutable.Map[TypeName, Name]().withDefaultValue(nme.specializedTypeNames.Object)

//  private val unboxedTypeRef = mutable.Map[TypeName, TypeRef]()
//  private val javaTypeToValueTypeRef = mutable.Map[Class[?], TypeRef]()
//  private val valueTypeNamesToJavaType = mutable.Map[TypeName, Class[?]]()

  private def valueTypeRef(name: String, jtype: Class[?], enc: Int, tag: Name): TypeRef = {
    val vcls = requiredClassRef(name)
    valueTypeEnc(vcls.name) = enc
    typeTags(vcls.name) = tag
//    unboxedTypeRef(boxed.name) = vcls
//    javaTypeToValueTypeRef(jtype) = vcls
//    valueTypeNamesToJavaType(vcls.name) = jtype
    vcls
  }

  /** The type of the boxed class corresponding to primitive value type `tp`. */
  def boxedType(tp: Type)(using Context): TypeRef = {
    val cls = tp.classSymbol
    if (cls eq ByteClass)         BoxedByteClass
    else if (cls eq ShortClass)   BoxedShortClass
    else if (cls eq CharClass)    BoxedCharClass
    else if (cls eq IntClass)     BoxedIntClass
    else if (cls eq LongClass)    BoxedLongClass
    else if (cls eq FloatClass)   BoxedFloatClass
    else if (cls eq DoubleClass)  BoxedDoubleClass
    else if (cls eq UnitClass)    BoxedUnitClass
    else if (cls eq BooleanClass) BoxedBooleanClass
    else sys.error(s"Not a primitive value type: $tp")
  }.typeRef

  def unboxedType(tp: Type)(using Context): TypeRef = {
    val cls = tp.classSymbol
    if (cls eq BoxedByteClass)         ByteType
    else if (cls eq BoxedShortClass)   ShortType
    else if (cls eq BoxedCharClass)    CharType
    else if (cls eq BoxedIntClass)     IntType
    else if (cls eq BoxedLongClass)    LongType
    else if (cls eq BoxedFloatClass)   FloatType
    else if (cls eq BoxedDoubleClass)  DoubleType
    else if (cls eq BoxedUnitClass)    UnitType
    else if (cls eq BoxedBooleanClass) BooleanType
    else sys.error(s"Not a boxed primitive value type: $tp")
  }

  /** The JVM tag for `tp` if it's a primitive, `java.lang.Object` otherwise. */
  def typeTag(tp: Type)(using Context): Name = typeTags(scalaClassName(tp))

//  /** The `Class[?]` of a primitive value type name */
//  def valueTypeNameToJavaType(name: TypeName)(using Context): Option[Class[?]] =
//    valueTypeNamesToJavaType.get(if (name.firstPart eq nme.scala) name.lastPart.toTypeName else name)

  type PrimitiveClassEnc = Int

  val ByteEnc: Int = 2
  val ShortEnc: Int = ByteEnc * 3
  val CharEnc: Int = 5
  val IntEnc: Int = ShortEnc * CharEnc
  val LongEnc: Int = IntEnc * 7
  val FloatEnc: Int = LongEnc * 11
  val DoubleEnc: Int = FloatEnc * 13
  val BooleanEnc: Int = 17
  val UnitEnc: Int = 19

  def isValueSubType(tref1: TypeRef, tref2: TypeRef)(using Context): Boolean =
    valueTypeEnc(tref2.name) % valueTypeEnc(tref1.name) == 0
  def isValueSubClass(sym1: Symbol, sym2: Symbol): Boolean =
    valueTypeEnc(sym2.asClass.name) % valueTypeEnc(sym1.asClass.name) == 0

  @tu lazy val specialErasure: SimpleIdentityMap[Symbol, ClassSymbol] =
    SimpleIdentityMap.empty[Symbol]
      .updated(AnyClass, ObjectClass)
      .updated(MatchableClass, ObjectClass)
      .updated(AnyValClass, ObjectClass)
      .updated(SingletonClass, ObjectClass)
      .updated(TupleClass, ProductClass)
      .updated(NonEmptyTupleClass, ProductClass)
      .updated(PairClass, ObjectClass)

  // ----- Initialization ---------------------------------------------------

  /** Lists core classes that don't have underlying bytecode, but are synthesized on-the-fly in every reflection universe */
  @tu lazy val syntheticScalaClasses: List[TypeSymbol] =
    List(
      AnyClass,
      MatchableClass,
      AnyRefAlias,
      AnyKindClass,
      andType,
      orType,
      RepeatedParamClass,
      ByNameParamClass2x,
      IntoType,
      AnyValClass,
      NullClass,
      NothingClass,
      SingletonClass)

  @tu lazy val syntheticCoreClasses: List[Symbol] = syntheticScalaClasses ++ List(
    EmptyPackageVal,
    OpsPackageClass)

  /** Lists core methods that don't have underlying bytecode, but are synthesized on-the-fly in every reflection universe */
  @tu lazy val syntheticCoreMethods: List[TermSymbol] =
    AnyMethods ++ ObjectMethods ++ List(String_+, throwMethod)

  @tu lazy val reservedScalaClassNames: Set[Name] = syntheticScalaClasses.map(_.name).toSet

  private var isInitialized = false

  def init()(using Context): Unit = {
    this.initCtx = ctx
    if (!isInitialized) {
      // force initialization of every symbol that is synthesized or hijacked by the compiler
      syntheticCoreClasses
      syntheticCoreMethods
      ScalaValueClasses()
      JavaEnumClass
      // end force initialization
      isInitialized = true
    }
    addSyntheticSymbolsComments
  }

  /** Definitions used in Lazy Vals implementation */
  val LazyValsModuleName = "scala.runtime.LazyVals"
  @tu lazy val LazyValsModule = requiredModule(LazyValsModuleName)
  @tu lazy val LazyValsWaitingState = requiredClass(s"$LazyValsModuleName.Waiting")
  @tu lazy val LazyValsControlState = requiredClass(s"$LazyValsModuleName.LazyValControlState")

  def addSyntheticSymbolsComments(using Context): Unit =
    def add(sym: Symbol, doc: String) = ctx.docCtx.foreach(_.addDocstring(sym, Some(Comment(NoSpan, doc))))

    add(AnyClass,
    """/** Class `Any` is the root of the Scala class hierarchy.  Every class in a Scala
      | *  execution environment inherits directly or indirectly from this class.
      | *
      | * Starting with Scala 2.10 it is possible to directly extend `Any` using ''universal traits''.
      | * A ''universal trait'' is a trait that extends `Any`, only has `def`s as members, and does no initialization.
      | *
      | * The main use case for universal traits is to allow basic inheritance of methods for [[scala.AnyVal value classes]].
      | * For example,
      | *
      | * {{{
      | *     trait Printable extends Any {
      | *       def print(): Unit = println(this)
      | *     }
      | *     class Wrapper(val underlying: Int) extends AnyVal with Printable
      | *
      | *     val w = new Wrapper(3)
      | *     w.print()
      | * }}}
      | *
      | * See the [[https://docs.scala-lang.org/overviews/core/value-classes.html Value Classes and Universal Traits]] for more
      | * details on the interplay of universal traits and value classes.
      | */
    """.stripMargin)

    add(Any_==,
    """/** Test two objects for equality.
      | *  The expression `x == that` is equivalent to `if (x eq null) that eq null else x.equals(that)`.
      | *
      | *  @param  that  the object to compare against this object for equality.
      | *  @return       `true` if the receiver object is equivalent to the argument; `false` otherwise.
      | */
    """.stripMargin)

    add(Any_!=,
    """/** Test two objects for inequality.
      | *
      | *  @param  that  the object to compare against this object for equality.
      | *  @return       `true` if !(this == that), `false` otherwise.
      | */
    """.stripMargin)

    add(Any_equals,
    """/** Compares the receiver object (`this`) with the argument object (`that`) for equivalence.
      | *
      | *  Any implementation of this method should be an [[https://en.wikipedia.org/wiki/Equivalence_relation equivalence relation]]:
      | *
      | *  - It is reflexive: for any instance `x` of type `Any`, `x.equals(x)` should return `true`.
      | *  - It is symmetric: for any instances `x` and `y` of type `Any`, `x.equals(y)` should return `true` if and
      | *    only if `y.equals(x)` returns `true`.
      | *  - It is transitive: for any instances `x`, `y`, and `z` of type `Any` if `x.equals(y)` returns `true` and
      | *    `y.equals(z)` returns `true`, then `x.equals(z)` should return `true`.
      | *
      | *  If you override this method, you should verify that your implementation remains an equivalence relation.
      | *  Additionally, when overriding this method it is usually necessary to override `hashCode` to ensure that
      | *  objects which are "equal" (`o1.equals(o2)` returns `true`) hash to the same [[scala.Int]].
      | *  (`o1.hashCode.equals(o2.hashCode)`).
      | *
      | *  @param  that    the object to compare against this object for equality.
      | *  @return         `true` if the receiver object is equivalent to the argument; `false` otherwise.
      | */
    """.stripMargin)

    add(Any_hashCode,
    """/** Calculates a hash code value for the object.
      | *
      | *  The default hashing algorithm is platform dependent.
      | *
      | *  Note that it is allowed for two objects to have identical hash codes (`o1.hashCode.equals(o2.hashCode)`) yet
      | *  not be equal (`o1.equals(o2)` returns `false`).  A degenerate implementation could always return `0`.
      | *  However, it is required that if two objects are equal (`o1.equals(o2)` returns `true`) that they have
      | *  identical hash codes (`o1.hashCode.equals(o2.hashCode)`).  Therefore, when overriding this method, be sure
      | *  to verify that the behavior is consistent with the `equals` method.
      | *
      | *  @return   the hash code value for this object.
      | */
    """.stripMargin)

    add(Any_toString,
    """/** Returns a string representation of the object.
      | *
      | *  The default representation is platform dependent.
      | *
      | *  @return a string representation of the object.
      | */
    """.stripMargin)

    add(Any_##,
    """/** Equivalent to `x.hashCode` except for boxed numeric types and `null`.
      | *  For numerics, it returns a hash value which is consistent
      | *  with value equality: if two value type instances compare
      | *  as true, then ## will produce the same hash value for each
      | *  of them.
      | *  For `null` returns a hashcode where `null.hashCode` throws a
      | *  `NullPointerException`.
      | *
      | *  @return   a hash value consistent with ==
      | */
    """.stripMargin)

    add(Any_isInstanceOf,
    """/** Test whether the dynamic type of the receiver object is `T0`.
      | *
      | *  Note that the result of the test is modulo Scala's erasure semantics.
      | *  Therefore the expression `1.isInstanceOf[String]` will return `false`, while the
      | *  expression `List(1).isInstanceOf[List[String]]` will return `true`.
      | *  In the latter example, because the type argument is erased as part of compilation it is
      | *  not possible to check whether the contents of the list are of the specified type.
      | *
      | *  @return `true` if the receiver object is an instance of erasure of type `T0`; `false` otherwise.
      | */
    """.stripMargin)

    add(Any_asInstanceOf,
    """/** Cast the receiver object to be of type `T0`.
      | *
      | *  Note that the success of a cast at runtime is modulo Scala's erasure semantics.
      | *  Therefore the expression `1.asInstanceOf[String]` will throw a `ClassCastException` at
      | *  runtime, while the expression `List(1).asInstanceOf[List[String]]` will not.
      | *  In the latter example, because the type argument is erased as part of compilation it is
      | *  not possible to check whether the contents of the list are of the requested type.
      | *
      | *  @throws ClassCastException if the receiver object is not an instance of the erasure of type `T0`.
      | *  @return the receiver object.
      | */
    """.stripMargin)

    add(Any_getClass,
    """/** Returns the runtime class representation of the object.
      | *
      | *  @return a class object corresponding to the runtime type of the receiver.
      | */
    """.stripMargin)

    add(MatchableClass,
    """/** The base trait of types that can be safely pattern matched against.
      | *
      | *   See [[https://docs.scala-lang.org/scala3/reference/other-new-features/matchable.html]].
      | */
    """.stripMargin)

    add(AnyRefAlias,
    """/** Class `AnyRef` is the root class of all ''reference types''.
      | *  All types except the value types descend from this class.
      | */
    """.stripMargin)

    add(Object_eq,
    """/** Tests whether the argument (`that`) is a reference to the receiver object (`this`).
      | *
      | *  The `eq` method implements an [[https://en.wikipedia.org/wiki/Equivalence_relation equivalence relation]] on
      | *  non-null instances of `AnyRef`, and has three additional properties:
      | *
      | *   - It is consistent: for any non-null instances `x` and `y` of type `AnyRef`, multiple invocations of
      | *     `x.eq(y)` consistently returns `true` or consistently returns `false`.
      | *   - For any non-null instance `x` of type `AnyRef`, `x.eq(null)` and `null.eq(x)` returns `false`.
      | *   - `null.eq(null)` returns `true`.
      | *
      | *  When overriding the `equals` or `hashCode` methods, it is important to ensure that their behavior is
      | *  consistent with reference equality.  Therefore, if two objects are references to each other (`o1 eq o2`), they
      | *  should be equal to each other (`o1 == o2`) and they should hash to the same value (`o1.hashCode == o2.hashCode`).
      | *
      | *  @param  that    the object to compare against this object for reference equality.
      | *  @return         `true` if the argument is a reference to the receiver object; `false` otherwise.
      | */
    """.stripMargin)

    add(Object_ne,
    """/** Equivalent to `!(this eq that)`.
      | *
      | *  @param  that    the object to compare against this object for reference equality.
      | *  @return         `true` if the argument is not a reference to the receiver object; `false` otherwise.
      | */
    """.stripMargin)

    add(Object_synchronized,
    """/** Executes the code in `body` with an exclusive lock on `this`.
      | *
      | *  @param    body    the code to execute
      | *  @return           the result of `body`
      | */
    """.stripMargin)

    add(Object_clone,
    """/** Create a copy of the receiver object.
      | *
      | *  The default implementation of the `clone` method is platform dependent.
      | *
      | *  @note   not specified by SLS as a member of AnyRef
      | *  @return a copy of the receiver object.
      | */
    """.stripMargin)

    add(Object_finalize,
    """/** Called by the garbage collector on the receiver object when there
      | *  are no more references to the object.
      | *
      | *  The details of when and if the `finalize` method is invoked, as
      | *  well as the interaction between `finalize` and non-local returns
      | *  and exceptions, are all platform dependent.
      | *
      | *  @note   not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(Object_notify,
    """/** Wakes up a single thread that is waiting on the receiver object's monitor.
      | *
      | *  @note   not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(Object_notifyAll,
    """/** Wakes up all threads that are waiting on the receiver object's monitor.
      | *
      | *  @note   not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(Object_wait,
    """/** See [[https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--]].
      | *
      | *  @note   not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(Object_waitL,
    """/** See [[https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-]].
      | *
      | * @param timeout the maximum time to wait in milliseconds.
      | * @note not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(Object_waitLI,
    """/** See [[https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-]]
      | *
      | * @param timeout the maximum time to wait in milliseconds.
      | * @param nanos   additional time, in nanoseconds range 0-999999.
      | * @note not specified by SLS as a member of AnyRef
      | */
    """.stripMargin)

    add(AnyKindClass,
    """/** The super-type of all types.
      | *
      | *   See [[https://docs.scala-lang.org/scala3/reference/other-new-features/kind-polymorphism.html]].
      | */
    """.stripMargin)

    add(andType,
    """/** The intersection of two types.
      | *
      | *   See [[https://docs.scala-lang.org/scala3/reference/new-types/intersection-types.html]].
      | */
    """.stripMargin)

    add(orType,
    """/** The union of two types.
      | *
      | *   See [[https://docs.scala-lang.org/scala3/reference/new-types/union-types.html]].
      | */
    """.stripMargin)

    add(AnyValClass,
    """/** `AnyVal` is the root class of all ''value types'', which describe values
      | *  not implemented as objects in the underlying host system. Value classes
      | *  are specified in Scala Language Specification, section 12.2.
      | *
      | *  The standard implementation includes nine `AnyVal` subtypes:
      | *
      | *  [[scala.Double]], [[scala.Float]], [[scala.Long]], [[scala.Int]], [[scala.Char]],
      | *  [[scala.Short]], and [[scala.Byte]] are the ''numeric value types''.
      | *
      | *  [[scala.Unit]] and [[scala.Boolean]] are the ''non-numeric value types''.
      | *
      | *  Other groupings:
      | *
      | *   - The ''subrange types'' are [[scala.Byte]], [[scala.Short]], and [[scala.Char]].
      | *   - The ''integer types'' include the subrange types as well as [[scala.Int]] and [[scala.Long]].
      | *   - The ''floating point types'' are [[scala.Float]] and [[scala.Double]].
      | *
      | * Prior to Scala 2.10, `AnyVal` was a sealed trait. Beginning with Scala 2.10,
      | * however, it is possible to define a subclass of `AnyVal` called a ''user-defined value class''
      | * which is treated specially by the compiler. Properly-defined user value classes provide a way
      | * to improve performance on user-defined types by avoiding object allocation at runtime, and by
      | * replacing virtual method invocations with static method invocations.
      | *
      | * User-defined value classes which avoid object allocation...
      | *
      | *   - must have a single `val` parameter that is the underlying runtime representation.
      | *   - can define `def`s, but no `val`s, `var`s, or nested `traits`s, `class`es or `object`s.
      | *   - typically extend no other trait apart from `AnyVal`.
      | *   - cannot be used in type tests or pattern matching.
      | *   - may not override `equals` or `hashCode` methods.
      | *
      | * A minimal example:
      | * {{{
      | *     class Wrapper(val underlying: Int) extends AnyVal {
      | *       def foo: Wrapper = new Wrapper(underlying * 19)
      | *     }
      | * }}}
      | *
      | * It's important to note that user-defined value classes are limited, and in some circumstances,
      | * still must allocate a value class instance at runtime. These limitations and circumstances are
      | * explained in greater detail in the [[https://docs.scala-lang.org/overviews/core/value-classes.html Value Classes and Universal Traits]].
      | */
    """.stripMargin)

    add(NullClass,
    """/** `Null` is - together with [[scala.Nothing]] - at the bottom of the Scala type hierarchy.
      | *
      | * `Null` is the type of the `null` literal. It is a subtype of every type
      | * except those of value classes. Value classes are subclasses of [[AnyVal]], which includes
      | * primitive types such as [[Int]], [[Boolean]], and user-defined value classes.
      | *
      | * Since `Null` is not a subtype of value types, `null` is not a member of any such type.
      | * For instance, it is not possible to assign `null` to a variable of type [[scala.Int]].
      | */
    """.stripMargin)

    add(NothingClass,
    """/** `Nothing` is - together with [[scala.Null]] - at the bottom of Scala's type hierarchy.
      | *
      | *  `Nothing` is a subtype of every other type (including [[scala.Null]]); there exist
      | *  ''no instances'' of this type.  Although type `Nothing` is uninhabited, it is
      | *  nevertheless useful in several ways.  For instance, the Scala library defines a value
      | *  [[scala.collection.immutable.Nil]] of type `List[Nothing]`. Because lists are covariant in Scala,
      | *  this makes [[scala.collection.immutable.Nil]] an instance of `List[T]`, for any element of type `T`.
      | *
      | *  Another usage for Nothing is the return type for methods which never return normally.
      | *  One example is method error in [[scala.sys]], which always throws an exception.
      | */
    """.stripMargin)

    add(SingletonClass,
    """/** `Singleton` is used by the compiler as a supertype for singleton types. This includes literal types,
      | * as they are also singleton types.
      | *
      | * {{{
      | * scala> object A { val x = 42 }
      | * defined object A
      | *
      | * scala> implicitly[A.type <:< Singleton]
      | * res12: A.type <:< Singleton = generalized constraint
      | *
      | * scala> implicitly[A.x.type <:< Singleton]
      | * res13: A.x.type <:< Singleton = generalized constraint
      | *
      | * scala> implicitly[42 <:< Singleton]
      | * res14: 42 <:< Singleton = generalized constraint
      | *
      | * scala> implicitly[Int <:< Singleton]
      | * ^
      | * error: Cannot prove that Int <:< Singleton.
      | * }}}
      | *
      | * `Singleton` has a special meaning when it appears as an upper bound on a formal type
      | * parameter. Normally, type inference in Scala widens singleton types to the underlying
      | * non-singleton type. When a type parameter has an explicit upper bound of `Singleton`,
      | * the compiler infers a singleton type.
      | *
      | * {{{
      | * scala> def check42[T](x: T)(implicit ev: T =:= 42): T = x
      | * check42: [T](x: T)(implicit ev: T =:= 42)T
      | *
      | * scala> val x1 = check42(42)
      | * ^
      | * error: Cannot prove that Int =:= 42.
      | *
      | * scala> def singleCheck42[T <: Singleton](x: T)(implicit ev: T =:= 42): T = x
      | * singleCheck42: [T <: Singleton](x: T)(implicit ev: T =:= 42)T
      | *
      | * scala> val x2 = singleCheck42(42)
      | * x2: Int = 42
      | * }}}
      | *
      | * See also [[https://docs.scala-lang.org/sips/42.type.html SIP-23 about Literal-based Singleton Types]].
      | */
    """.stripMargin)
}