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Reflection Library for the Scala Programming Language
/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala
package reflect
package internal
package transform
trait Erasure {
val global: SymbolTable
import global._
import definitions._
/** An extractor object for generic arrays */
object GenericArray {
/** Is `tp` an unbounded generic type (i.e. which could be instantiated
* with primitive as well as class types)?.
*/
private def genericCore(tp: Type): Type = tp.dealiasWiden match {
/* A Java Array is erased to Array[Object] (T can only be a reference type), where as a Scala Array[T] is
* erased to Object. However, there is only symbol for the Array class. So to make the distinction between
* a Java and a Scala array, we check if the owner of T comes from a Java class.
* This however caused issue scala/bug#5654. The additional test for EXISTENTIAL fixes it, see the ticket comments.
* In short, members of an existential type (e.g. `T` in `forSome { type T }`) can have pretty arbitrary
* owners (e.g. when computing lubs, is used). All packageClass symbols have `isJavaDefined == true`.
*/
case TypeRef(_, sym, _) if sym.isAbstractType && (!sym.owner.isJavaDefined || sym.hasFlag(Flags.EXISTENTIAL)) =>
tp
case ExistentialType(tparams, restp) =>
genericCore(restp)
case _ =>
NoType
}
/** If `tp` is of the form Array[...Array[T]...] where `T` is an abstract type
* then Some((N, T)) where N is the number of Array constructors enclosing `T`,
* otherwise None. Existentials on any level are ignored.
*/
def unapply(tp: Type): Option[(Int, Type)] = tp.dealiasWiden match {
case TypeRef(_, ArrayClass, List(arg)) =>
genericCore(arg) match {
case NoType =>
unapply(arg) match {
case Some((level, core)) => Some((level + 1, core))
case None => None
}
case core =>
Some((1, core))
}
case ExistentialType(tparams, restp) =>
unapply(restp)
case _ =>
None
}
}
/** Arrays despite their finality may turn up as refined type parents,
* e.g. with "tagged types" like Array[Int] with T.
*/
protected def unboundedGenericArrayLevel(tp: Type): Int = tp match {
case GenericArray(level, core) if !(core <:< AnyRefTpe) => level
case RefinedType(ps, _) if ps.nonEmpty => logResult(s"Unbounded generic level for $tp is")((ps map unboundedGenericArrayLevel).max)
case _ => 0
}
// @M #2585 when generating a java generic signature that includes
// a selection of an inner class p.I, (p = `pre`, I = `cls`) must
// rewrite to p'.I, where p' refers to the class that directly defines
// the nested class I.
//
// See also #2585 marker in javaSig: there, type arguments must be
// included (use pre.baseType(cls.owner)).
//
// This requires that cls.isClass.
protected def rebindInnerClass(pre: Type, cls: Symbol): Type =
if (cls.isTopLevel || cls.isLocalToBlock) pre else cls.owner.tpe_*
/** The type of the argument of a value class reference after erasure
* This method needs to be called at a phase no later than erasurephase
*/
def erasedValueClassArg(tref: TypeRef): Type = {
assert(!phase.erasedTypes)
val clazz = tref.sym
if (valueClassIsParametric(clazz)) {
val underlying = tref.memberType(clazz.derivedValueClassUnbox).resultType
boxingErasure(underlying)
} else {
scalaErasure(underlyingOfValueClass(clazz))
}
}
/** Does this value class have an underlying type that's a type parameter of
* the class itself?
* This method needs to be called at a phase no later than erasurephase
*/
def valueClassIsParametric(clazz: Symbol): Boolean = {
assert(!phase.erasedTypes)
clazz.typeParams contains
clazz.derivedValueClassUnbox.tpe.resultType.typeSymbol
}
abstract class ErasureMap extends TypeMap {
def mergeParents(parents: List[Type]): Type
def eraseNormalClassRef(tref: TypeRef): Type = {
val TypeRef(pre, clazz, args) = tref
val pre1 = apply(rebindInnerClass(pre, clazz))
val args1 = Nil
if ((pre eq pre1) && (args eq args1)) tref // OPT
else typeRef(pre1, clazz, args1) // #2585
}
protected def eraseDerivedValueClassRef(tref: TypeRef): Type = erasedValueClassArg(tref)
def apply(tp: Type): Type = tp match {
case ConstantType(ct) =>
// erase classOf[List[_]] to classOf[List]. special case for classOf[Unit], avoid erasing to classOf[BoxedUnit].
if (ct.tag == ClazzTag && ct.typeValue.typeSymbol != UnitClass) ConstantType(Constant(apply(ct.typeValue)))
else tp
case st: ThisType if st.sym.isPackageClass =>
tp
case st: SubType =>
apply(st.supertype)
case tref @ TypeRef(pre, sym, args) =>
if (sym eq ArrayClass)
if (unboundedGenericArrayLevel(tp) == 1) ObjectTpe
else if (args.head.typeSymbol.isBottomClass) arrayType(ObjectTpe)
else typeRef(apply(pre), sym, args map applyInArray)
else if ((sym eq AnyClass) || (sym eq AnyValClass) || (sym eq SingletonClass)) ObjectTpe
else if (sym eq UnitClass) BoxedUnitTpe
else if (sym.isRefinementClass) apply(mergeParents(tp.parents))
else if (sym.isDerivedValueClass) eraseDerivedValueClassRef(tref)
else if (sym.isClass) eraseNormalClassRef(tref)
else apply(sym.info asSeenFrom (pre, sym.owner)) // alias type or abstract type
case PolyType(tparams, restpe) =>
apply(restpe)
case ExistentialType(tparams, restpe) =>
apply(restpe)
case mt @ MethodType(params, restpe) =>
MethodType(
cloneSymbolsAndModify(params, ErasureMap.this),
if (restpe.typeSymbol == UnitClass) UnitTpe
// this replaces each typeref that refers to an argument
// by the type `p.tpe` of the actual argument p (p in params)
else apply(mt.resultType(mt.paramTypes)))
case RefinedType(parents, decls) =>
apply(mergeParents(parents))
case AnnotatedType(_, atp) =>
apply(atp)
case ClassInfoType(parents, decls, clazz) =>
val newParents =
if (parents.isEmpty || (clazz eq ObjectClass) || isPrimitiveValueClass(clazz)) Nil
else if (clazz eq ArrayClass) ObjectTpe :: Nil
else {
val erasedParents = parents mapConserve this
// drop first parent for traits -- it has been normalized to a class by now,
// but we should drop that in bytecode
if (clazz.hasFlag(Flags.TRAIT) && !clazz.hasFlag(Flags.JAVA))
ObjectTpe :: erasedParents.tail.filter(_.typeSymbol ne ObjectClass)
else erasedParents
}
if (newParents eq parents) tp
else ClassInfoType(newParents, decls, clazz)
// can happen while this map is being used before erasure (e.g. when reasoning about sam types)
// the regular mapOver will cause a class cast exception because TypeBounds don't erase to TypeBounds
case _: BoundedWildcardType => tp // skip
case _ =>
mapOver(tp)
}
/* scala/bug#10551, scala/bug#10646:
*
* There are a few contexts in which it's important to erase types referencing
* derived value classes to the value class itself, not the underlying. As
* of right now, those are:
* - inside of `classOf`
* - the element type of an `ArrayValue`
* In those cases, the value class needs to be detected and erased using
* `javaErasure`, which treats refs to value classes the same as any other
* `TypeRef`. This used to be done by matching on `tr@TypeRef(_,sym,_)`, and
* checking whether `sym.isDerivedValueClass`, but there are more types with
* `typeSymbol.isDerivedValueClass` than just `TypeRef`s (`ExistentialType`
* is one of the easiest to bump into, e.g. `classOf[VC[_]]`).
*
* tl;dr if you're trying to erase a value class ref to the value class itself
* and not going through this method, you're inviting trouble into your life.
*/
def applyInArray(tp: Type): Type = {
if (tp.typeSymbol.isDerivedValueClass) javaErasure(tp)
else apply(tp)
}
}
protected def verifyJavaErasure = false
/** The erasure |T| of a type T. This is:
*
* - For a constant type classOf[T], classOf[|T|], unless T is Unit. For any other constant type, itself.
* - For a type-bounds structure, the erasure of its upper bound.
* - For every other singleton type, the erasure of its supertype.
* - For a typeref scala.Array+[T] where T is an abstract type, AnyRef.
* - For a typeref scala.Array+[T] where T is not an abstract type, scala.Array+[|T|].
* - For a typeref scala.Any or scala.AnyVal, java.lang.Object.
* - For a typeref scala.Unit, scala.runtime.BoxedUnit.
* - For a typeref P.C[Ts] where C refers to a class, |P|.C.
* (Where P is first rebound to the class that directly defines C.)
* - For a typeref P.C[Ts] where C refers to an alias type, the erasure of C's alias.
* - For a typeref P.C[Ts] where C refers to an abstract type, the
* erasure of C's upper bound.
* - For a non-empty type intersection (possibly with refinement)
* - in scala, the erasure of the intersection dominator
* - in java, the erasure of its first parent <--- @PP: not yet in spec.
* - For an empty type intersection, java.lang.Object.
* - For a method type (Fs)scala.Unit, (|Fs|)scala#Unit.
* - For any other method type (Fs)Y, (|Fs|)|T|.
* - For a polymorphic type, the erasure of its result type.
* - For the class info type of java.lang.Object, the same type without any parents.
* - For a class info type of a value class, the same type without any parents.
* - For any other class info type with parents Ps, the same type with
* parents |Ps|, but with duplicate references of Object removed.
* - for all other types, the type itself (with any sub-components erased)
*/
def erasure(sym: Symbol): ErasureMap =
if (sym == NoSymbol || !sym.enclClass.isJavaDefined) scalaErasure
else if (verifyJavaErasure && sym.isMethod) verifiedJavaErasure
else javaErasure
/** This is used as the Scala erasure during the erasure phase itself
* It differs from normal erasure in that value classes are erased to ErasedValueTypes which
* are then later converted to the underlying parameter type in phase posterasure.
*/
def specialErasure(sym: Symbol)(tp: Type): Type =
if (sym != NoSymbol && sym.enclClass.isJavaDefined)
erasure(sym)(tp)
else if (sym.isClassConstructor)
specialConstructorErasure(sym.owner, tp)
else
specialScalaErasure(tp)
def specialConstructorErasure(clazz: Symbol, tpe: Type): Type = {
tpe match {
case PolyType(tparams, restpe) =>
specialConstructorErasure(clazz, restpe)
case ExistentialType(tparams, restpe) =>
specialConstructorErasure(clazz, restpe)
case mt @ MethodType(params, restpe) =>
MethodType(
cloneSymbolsAndModify(params, specialScalaErasure),
specialConstructorErasure(clazz, restpe))
case TypeRef(pre, `clazz`, args) =>
typeRef(pre, clazz, List())
case tp =>
if (!(clazz == ArrayClass || tp.isError))
assert(clazz == ArrayClass || tp.isError, s"!!! unexpected constructor erasure $tp for $clazz")
specialScalaErasure(tp)
}
}
/** Scala's more precise erasure than java's is problematic as follows:
*
* - Symbols are read from classfiles and populated with types
* - The textual signature read from the bytecode is forgotten
* - Bytecode generation must know the precise signature of a method
* - the signature is derived from the erasure of the method type
* - If that derivation does not adhere to the rules by which the original
* signature was created, a NoSuchMethod error will result.
*
* For this reason and others (such as distinguishing constructors from other methods)
* erasure is now (Symbol, Type) => Type rather than Type => Type.
*/
class ScalaErasureMap extends ErasureMap {
/** In scala, calculate a useful parent.
* An intersection such as `Object with Trait` erases to Trait.
*/
def mergeParents(parents: List[Type]): Type =
intersectionDominator(parents)
}
class JavaErasureMap extends ErasureMap {
/** In java, always take the first parent.
* An intersection such as `Object with Trait` erases to Object.
*/
def mergeParents(parents: List[Type]): Type =
if (parents.isEmpty) ObjectTpe
else parents.head
override protected def eraseDerivedValueClassRef(tref: TypeRef): Type = eraseNormalClassRef(tref)
}
object scalaErasure extends ScalaErasureMap
/** This is used as the Scala erasure during the erasure phase itself
* It differs from normal erasure in that value classes are erased to ErasedValueTypes which
* are then later unwrapped to the underlying parameter type in phase posterasure.
*/
object specialScalaErasure extends ScalaErasureMap {
override def eraseDerivedValueClassRef(tref: TypeRef): Type =
ErasedValueType(tref.sym, erasedValueClassArg(tref))
}
object javaErasure extends JavaErasureMap
object verifiedJavaErasure extends JavaErasureMap {
override def apply(tp: Type): Type = {
val res = javaErasure(tp)
val old = scalaErasure(tp)
if (!(res =:= old))
log("Identified divergence between java/scala erasure:\n scala: " + old + "\n java: " + res)
res
}
}
object boxingErasure extends ScalaErasureMap {
private var boxPrimitives = true
override def applyInArray(tp: Type): Type = {
val saved = boxPrimitives
boxPrimitives = false
try super.applyInArray(tp)
finally boxPrimitives = saved
}
override def eraseNormalClassRef(tref: TypeRef) =
if (boxPrimitives && isPrimitiveValueClass(tref.sym)) boxedClass(tref.sym).tpe
else super.eraseNormalClassRef(tref)
override def eraseDerivedValueClassRef(tref: TypeRef) =
super.eraseNormalClassRef(tref)
}
/** The intersection dominator (SLS 3.7) of a list of types is computed as follows.
*
* - If the list contains one or more occurrences of scala.Array with
* type parameters El1, El2, ... then the dominator is scala.Array with
* type parameter of intersectionDominator(List(El1, El2, ...)). <--- @PP: not yet in spec.
* - Otherwise, the list is reduced to a subsequence containing only types
* which are not subtypes of other listed types (the span.)
* - If the span is empty, the dominator is Object.
* - If the span contains a class Tc which is not a trait and which is
* not Object, the dominator is Tc. <--- @PP: "which is not Object" not in spec.
* - Otherwise, the dominator is the first element of the span.
*/
def intersectionDominator(parents: List[Type]): Type = {
if (parents.isEmpty) ObjectTpe
else {
val psyms = parents map (_.typeSymbol)
if (psyms contains ArrayClass) {
// treat arrays specially
arrayType(
intersectionDominator(
parents filter (_.typeSymbol == ArrayClass) map (_.typeArgs.head)))
} else {
// implement new spec for erasure of refined types.
def isUnshadowed(psym: Symbol) =
!(psyms exists (qsym => (psym ne qsym) && (qsym isNonBottomSubClass psym)))
val cs = parents.iterator.filter { p => // isUnshadowed is a bit expensive, so try classes first
val psym = p.typeSymbol
psym.initialize
psym.isClass && !psym.isTrait && isUnshadowed(psym)
}
(if (cs.hasNext) cs else parents.iterator.filter(p => isUnshadowed(p.typeSymbol))).next()
}
}
}
/** The symbol's erased info. This is the type's erasure, except for the following primitive symbols:
*
* - $asInstanceOf --> [T]T
* - $isInstanceOf --> [T]scala#Boolean
* - synchronized --> [T](x: T)T
* - class Array --> [T]C where C is the erased classinfo of the Array class.
* - Array[T]. --> {scala#Int)Array[T]
*
* An abstract type's info erases to a TypeBounds type consisting of the erasures of the abstract type's bounds.
*/
def transformInfo(sym: Symbol, tp: Type): Type = {
// Do not erase the primitive `synchronized` method's info or the info of its parameter.
// We do erase the info of its type param so that subtyping can relate its bounds after erasure.
def synchronizedPrimitive(sym: Symbol) =
sym == Object_synchronized || (sym.owner == Object_synchronized && sym.isTerm)
if (sym == Object_asInstanceOf || synchronizedPrimitive(sym))
sym.info
else if (sym == Object_isInstanceOf || sym == ArrayClass)
PolyType(sym.info.typeParams, specialErasure(sym)(sym.info.resultType))
else if (sym.isAbstractType)
TypeBounds(WildcardType, WildcardType) // TODO why not use the erasure of the type's bounds, as stated in the doc?
else if (sym.isTerm && sym.owner == ArrayClass) {
if (sym.isClassConstructor) // TODO: switch on name for all branches -- this one is sym.name == nme.CONSTRUCTOR
tp match {
case MethodType(params, TypeRef(pre, sym1, args)) =>
MethodType(cloneSymbolsAndModify(params, specialErasure(sym)),
typeRef(specialErasure(sym)(pre), sym1, args))
}
else if (sym.name == nme.apply)
tp
else if (sym.name == nme.update)
(tp: @unchecked) match {
case MethodType(List(index, tvar), restpe) =>
MethodType(List(index.cloneSymbol.setInfo(specialErasure(sym)(index.tpe)), tvar), UnitTpe)
}
else specialErasure(sym)(tp)
} else if (
sym.owner != NoSymbol &&
sym.owner.owner == ArrayClass &&
sym == Array_update.paramss.head(1)) { // TODO: can we simplify the guard, perhaps cache the symbol to compare to?
// special case for Array.update: the non-erased type remains, i.e. (Int,A)Unit
// since the erasure type map gets applied to every symbol, we have to catch the
// symbol here
tp
} else {
// TODO OPT: altogether, there are 9 symbols that we special-case.
// Could we get to the common case more quickly by looking them up in a set?
specialErasure(sym)(tp)
}
}
}