scala.tools.nsc.transform.Delambdafy.scala Maven / Gradle / Ivy
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/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc. dba Akka
*
* 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.tools.nsc
package transform
import symtab._
import Flags._
import scala.annotation._
import scala.collection.mutable
/**
* This transformer is responsible for preparing Function nodes for runtime,
* by translating to a tree that will be converted to an invokedynamic by the backend.
*
* The main assumption it makes is that a Function {args => body} has been turned into
* {args => liftedBody()} where lifted body is a top level method that implements the body of the function.
* Currently Uncurry is responsible for that transformation.
*
* From this shape of Function, Delambdafy will create:
*
* An application of the captured arguments to a fictional symbol representing the lambda factory.
* This will be translated by the backed into an invokedynamic using a bootstrap method in JDK8's `LambdaMetaFactory`.
* The captured arguments include `this` if `liftedBody` is unable to be made STATIC.
*/
abstract class Delambdafy extends Transform with TypingTransformers with ast.TreeDSL with TypeAdaptingTransformer {
import global._
import definitions._
val analyzer: global.analyzer.type = global.analyzer
/** the following two members override abstract members in Transform */
val phaseName: String = "delambdafy"
final case class LambdaMetaFactoryCapable(lambdaTarget: Symbol, arity: Int, functionalInterface: Symbol, sam: Symbol, bridges: List[Symbol], isSerializable: Boolean)
/** Get the symbol of the target lifted lambda body method from a function. I.e. if
* the function is {args => anonfun(args)} then this method returns anonfun's symbol
*/
private def targetMethod(fun: Function): Symbol = fun match {
case Function(_, Apply(target, _)) => target.symbol
case _ =>
// any other shape of Function is unexpected at this point
abort(s"could not understand function with tree $fun")
}
override def newPhase(prev: scala.tools.nsc.Phase): StdPhase = {
if (settings.Ydelambdafy.value == "method") new Phase(prev)
else new SkipPhase(prev)
}
class SkipPhase(prev: scala.tools.nsc.Phase) extends StdPhase(prev) {
def apply(unit: global.CompilationUnit): Unit = ()
}
protected def newTransformer(unit: CompilationUnit): AstTransformer =
new DelambdafyTransformer(unit)
class DelambdafyTransformer(unit: CompilationUnit) extends TypingTransformer(unit) {
// we need to know which methods refer to the 'this' reference so that we can determine which lambdas need access to it
// TODO: this looks expensive, so I made it a lazy val. Can we make it more pay-as-you-go / optimize for common shapes?
private[this] lazy val methodReferencesThis: collection.Set[Symbol] =
(new ThisReferringMethodsTraverser).methodReferencesThisIn(unit.body)
private def mkLambdaMetaFactoryCall(fun: Function, target: Symbol, functionalInterface: Symbol, samUserDefined: Symbol, userSamCls: Symbol, isSpecialized: Boolean): Tree = {
/* user-defined SAM types should have gotten a class symbol made for them in `typer` */
assert(isFunctionType(fun.tpe) || (samUserDefined.exists && userSamCls.isClass), s"$fun / ${fun.symbol} / ${fun.tpe}")
val pos = fun.pos
def isSelfParam(p: Symbol) = p.isSynthetic && p.name == nme.SELF
val hasSelfParam = isSelfParam(target.firstParam)
val allCapturedArgRefs = {
// find which variables are free in the lambda because those are captures that need to be
// passed into the constructor of the anonymous function class
val captureArgs = FreeVarTraverser.freeVarsOf(fun).iterator.map(capture =>
gen.mkAttributedRef(capture) setPos pos
).toList
if (!hasSelfParam) captureArgs.filterNot(arg => isSelfParam(arg.symbol))
else if (currentMethod.hasFlag(Flags.STATIC)) captureArgs
else (gen.mkAttributedThis(fun.symbol.enclClass) setPos pos) :: captureArgs
}
// Create a symbol representing a fictional lambda factory method that accepts the captured
// arguments and returns the SAM type.
val msym = {
val meth = currentOwner.newMethod(nme.ANON_FUN_NAME, pos, ARTIFACT)
val capturedParams = meth.newSyntheticValueParams(allCapturedArgRefs.map(_.tpe))
meth.setInfo(MethodType(capturedParams, fun.tpe))
}
// We then apply this symbol to the captures.
val apply = localTyper.typedPos(pos)(Apply(Ident(msym), allCapturedArgRefs))
// TODO: this is a bit gross
val sam = samUserDefined orElse {
if (isSpecialized) functionalInterface.info.decls.find(_.isDeferred).get
else functionalInterface.info.member(nme.apply)
}
// no need for adaptation when the implemented sam is of a specialized built-in function type
val lambdaTarget = if (isSpecialized) target else createBoxingBridgeMethodIfNeeded(fun, target, functionalInterface, sam)
val isSerializable = samUserDefined == NoSymbol || functionalInterface.isNonBottomSubClass(definitions.SerializableClass)
val samBridges = logResultIf[List[Symbol]](s"will add SAM bridges for $fun", _.nonEmpty) {
userSamCls.fold[List[Symbol]](Nil) {
_.info.findMember(sam.name, excludedFlags = 0L, requiredFlags = BRIDGE, stableOnly = false) match {
case NoSymbol => Nil
case bridges if bridges.isOverloaded => bridges.alternatives
case bridge => bridge :: Nil
}
}
}
// The backend needs to know the target of the lambda and the functional interface in order
// to emit the invokedynamic instruction. We pass this information as tree attachment.
//
// see https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/LambdaMetafactory.html
// instantiatedMethodType is derived from lambdaTarget's signature
// samMethodType is derived from samOf(functionalInterface)'s signature
apply.updateAttachment(LambdaMetaFactoryCapable(lambdaTarget, fun.vparams.length, functionalInterface, sam, samBridges, isSerializable))
apply
}
private val boxingBridgeMethods = mutable.ArrayBuffer[Tree]()
private def reboxValueClass(tp: Type) = tp match {
case ErasedValueType(valueClazz, _) => TypeRef(NoPrefix, valueClazz, Nil)
case _ => tp
}
// exclude primitives and value classes, which need special boxing
private def isReferenceType(tp: Type) = !tp.isInstanceOf[ErasedValueType] && {
val sym = tp.typeSymbol
!(isPrimitiveValueClass(sym) || sym.isDerivedValueClass)
}
// determine which lambda target to use with java's LMF -- create a new one if scala-specific boxing is required
def createBoxingBridgeMethodIfNeeded(fun: Function, target: Symbol, @unused functionalInterface: Symbol, sam: Symbol): Symbol = {
val oldClass = fun.symbol.enclClass
val pos = fun.pos
// At erasure, there won't be any captured arguments (they are added in constructors)
val functionParamTypes = exitingErasure(target.info.paramTypes)
val functionResultType = exitingErasure(target.info.resultType)
val samParamTypes = exitingErasure(sam.info.paramTypes)
val samResultType = exitingErasure(sam.info.resultType)
/* How to satisfy the linking invariants of https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/LambdaMetafactory.html
*
* Given samMethodType: (U1..Un)Ru and function type T1,..., Tn => Rt (the target method created by uncurry)
*
* Do we need a bridge, or can we use the original lambda target for implMethod: ( A1..An)Ra
* (We can ignore capture here.)
*
* If, for i=1..N:
* Ai =:= Ui || (Ai <:< Ui <:< AnyRef)
* Ru =:= void || (Ra =:= Ru || (Ra <:< AnyRef, Ru <:< AnyRef))
*
* We can use the target method as-is -- if not, we create a bridging one that uses the types closest
* to the target method that still meet the above requirements.
*/
val resTpOk = (
samResultType =:= UnitTpe
|| functionResultType =:= samResultType
|| (isReferenceType(samResultType) && isReferenceType(functionResultType))) // per spec, no further correspondence required
def paramTpsOk = samParamTypes.corresponds(functionParamTypes)((samParamTp, funParamTp) =>
funParamTp =:= samParamTp ||
(isReferenceType(funParamTp) && isReferenceType(samParamTp) && funParamTp <:< samParamTp))
if (resTpOk && paramTpsOk) target
else {
// We have to construct a new lambda target that bridges to the one created by uncurry.
// The bridge must satisfy the above invariants, while also minimizing adaptation on our end.
// LMF will insert runtime casts according to the spec at the above link.
// we use the more precise type between samParamTp and funParamTp to minimize boxing in the bridge method
// we are constructing a method whose signature matches the sam's signature (because the original target did not)
// whenever a type in the sam's signature is (erases to) a primitive type, we must pick the sam's version,
// as we don't implement the logic regarding widening that's performed by LMF -- we require =:= for primitives
//
// We use the sam's type for the check whether we're dealing with a reference type, as it could be a generic type,
// which means the function's parameter -- even if it expects a value class -- will need to be
// boxed on the generic call to the sam method.
val bridgeParamTypes = map2(samParamTypes, functionParamTypes) { (samParamTp, funParamTp) =>
if (isReferenceType(samParamTp) && funParamTp <:< samParamTp) funParamTp
else postErasure.elimErasedValueType(samParamTp)
}
val bridgeResultType =
if (resTpOk && isReferenceType(samResultType) && functionResultType <:< samResultType) functionResultType
else postErasure.elimErasedValueType(samResultType)
val typeAdapter = new TypeAdapter { def typedPos(pos: Position)(tree: Tree): Tree = localTyper.typedPos(pos)(tree) }
import typeAdapter.{adaptToType, unboxValueClass}
val targetParams = target.paramss.head
val numCaptures = targetParams.length - functionParamTypes.length
val (targetCapturedParams, targetFunctionParams) = targetParams.splitAt(numCaptures)
val methSym = oldClass.newMethod(target.name.append("$adapted").toTermName, target.pos, target.flags | FINAL | ARTIFACT | STATIC)
val bridgeCapturedParams = targetCapturedParams.map(param => methSym.newSyntheticValueParam(param.tpe, param.name.toTermName))
val bridgeFunctionParams =
map2(targetFunctionParams, bridgeParamTypes)((param, tp) => methSym.newSyntheticValueParam(tp, param.name.toTermName))
val bridgeParams = bridgeCapturedParams ::: bridgeFunctionParams
methSym setInfo MethodType(bridgeParams, bridgeResultType)
oldClass.info.decls enter methSym
val forwarderCall = localTyper.typedPos(pos) {
val capturedArgRefs = bridgeCapturedParams map gen.mkAttributedRef
val functionArgRefs =
map3(bridgeFunctionParams, functionParamTypes, targetParams.drop(numCaptures)) { (bridgeParam, functionParamTp, targetParam) =>
val bridgeParamRef = gen.mkAttributedRef(bridgeParam)
val targetParamTp = targetParam.tpe
// TODO: can we simplify this to something like `adaptToType(adaptToType(bridgeParamRef, functionParamTp), targetParamTp)`?
val unboxed =
functionParamTp match {
case ErasedValueType(clazz, underlying) =>
// when the original function expected an argument of value class type,
// the original target will expect the unboxed underlying value,
// whereas the bridge will receive the boxed value (since the sam's argument type did not match and we had to adapt)
localTyper.typed(unboxValueClass(bridgeParamRef, clazz, underlying), targetParamTp)
case _ => bridgeParamRef
}
adaptToType(unboxed, targetParamTp)
}
gen.mkMethodCall(Select(gen.mkAttributedThis(oldClass), target), capturedArgRefs ::: functionArgRefs)
}
val forwarderResultType =
if (samResultType.isInstanceOf[ErasedValueType] && functionResultType.isInstanceOf[ErasedValueType]) bridgeResultType
else functionResultType
val bridge = postErasure.newTransformer(unit).transform(DefDef(methSym, List(bridgeParams.map(ValDef(_))),
adaptToType(forwarderCall.setType(forwarderResultType), bridgeResultType))).asInstanceOf[DefDef]
boxingBridgeMethods += bridge
bridge.symbol
}
}
private def transformFunction(originalFunction: Function): Tree = {
val target = targetMethod(originalFunction)
assert(target.hasFlag(Flags.STATIC), "static")
target.setFlag(notPRIVATE)
val funSym = originalFunction.tpe.typeSymbolDirect
// The functional interface that can be used to adapt the lambda target method `target` to the given function type.
val (functionalInterface, isSpecialized) =
if (!isFunctionSymbol(funSym)) (funSym, false)
else {
val specializedName =
specializeTypes.specializedFunctionName(funSym,
exitingErasure(target.info.paramTypes).map(reboxValueClass) :+ reboxValueClass(exitingErasure(target.info.resultType))).toTypeName
val isSpecialized = specializedName != funSym.name
val functionalInterface =
if (isSpecialized) {
// Unfortunately we still need to use custom functional interfaces for specialized functions so that the
// unboxed apply method is left abstract for us to implement.
currentRun.runDefinitions.Scala_Java8_CompatPackage.info.decl(specializedName.prepend("J"))
}
else FunctionClass(originalFunction.vparams.length)
(functionalInterface, isSpecialized)
}
val (sam, synthCls) = originalFunction.attachments.get[SAMFunction] match {
case Some(SAMFunction(_, sam, synthCls)) => (sam, synthCls)
case None => (NoSymbol, NoSymbol)
}
mkLambdaMetaFactoryCall(originalFunction, target, functionalInterface, sam, synthCls, isSpecialized)
}
// here's the main entry point of the transform
override def transform(tree: Tree): Tree = tree match {
// the main thing we care about is lambdas
case fun: Function =>
super.transform(transformFunction(fun))
case Template(_, _, _) =>
def pretransform(tree: Tree): Tree = tree match {
case dd: DefDef if dd.symbol.isDelambdafyTarget =>
if (!dd.symbol.hasFlag(STATIC) && methodReferencesThis(dd.symbol)) {
gen.mkStatic(dd, dd.symbol.name, sym => sym)
} else {
dd.symbol.setFlag(STATIC)
dd
}
case t => t
}
try {
// during this call boxingBridgeMethods will be populated from the Function case
val Template(parents, self, body) = super.transform(deriveTemplate(tree)(_.mapConserve(pretransform))): @unchecked
Template(parents, self, body ++ boxingBridgeMethods)
} finally boxingBridgeMethods.clear()
case dd: DefDef if dd.symbol.isLiftedMethod && !dd.symbol.isDelambdafyTarget =>
// scala/bug#9390 emit lifted methods that don't require a `this` reference as STATIC
// delambdafy targets are excluded as they are made static by `transformFunction`.
// a synchronized method cannot be static (`methodReferencesThis` will not see the implicit this reference due to `this.synchronized`)
if (!dd.symbol.hasFlag(STATIC) && !methodReferencesThis(dd.symbol)) {
dd.symbol.setFlag(STATIC)
dd.symbol.removeAttachment[mixer.NeedStaticImpl.type]
}
super.transform(tree)
case Apply(fun, outer :: rest) if shouldElideOuterArg(fun.symbol, outer) =>
val nullOuter = gen.mkZero(outer.tpe)
treeCopy.Apply(tree, transform(fun), nullOuter :: transformTrees(rest))
case _ => super.transform(tree)
}
} // DelambdafyTransformer
private def shouldElideOuterArg(fun: Symbol, outerArg: Tree): Boolean =
fun.isConstructor && treeInfo.isQualifierSafeToElide(outerArg) && fun.hasAttachment[OuterArgCanBeElided.type]
// A traverser that finds symbols used but not defined in the given Tree
// TODO freeVarTraverser in LambdaLift does a very similar task. With some
// analysis this could probably be unified with it
class FreeVarTraverser extends InternalTraverser {
val freeVars = mutable.LinkedHashSet[Symbol]()
val declared = mutable.LinkedHashSet[Symbol]()
override def traverse(tree: Tree) = {
tree match {
case Function(args, _) =>
args foreach {arg => declared += arg.symbol}
case ValDef(_, _, _, _) =>
declared += tree.symbol
case _: Bind =>
declared += tree.symbol
case Ident(_) =>
val sym = tree.symbol
if ((sym != NoSymbol) && sym.isLocalToBlock && sym.isTerm && !sym.isMethod && !declared.contains(sym)) freeVars += sym
case _ =>
}
tree.traverse(this)
}
}
object FreeVarTraverser {
def freeVarsOf(function: Function) = {
val freeVarsTraverser = new FreeVarTraverser
freeVarsTraverser.traverse(function)
freeVarsTraverser.freeVars
}
}
// finds all methods that reference 'this'
class ThisReferringMethodsTraverser extends InternalTraverser {
// the set of methods that refer to this
private val thisReferringMethods = mutable.Set.empty[Symbol]
// the set of lifted lambda body methods that each method refers to
private val liftedMethodReferences = mutable.Map.empty[Symbol, mutable.Set[Symbol]]
def methodReferencesThisIn(tree: Tree): collection.Set[Symbol] = {
traverse(tree)
liftedMethodReferences.keys foreach refersToThis
thisReferringMethods
}
// recursively find methods that refer to 'this' directly or indirectly via references to other methods
// for each method found add it to the referrers set
private def refersToThis(symbol: Symbol): Boolean = {
val seen = mutable.Set[Symbol]()
def loop(symbol: Symbol): Boolean = {
if (seen(symbol)) false
else {
seen += symbol
(thisReferringMethods contains symbol) ||
(liftedMethodReferences.contains(symbol) && liftedMethodReferences(symbol).exists(loop)) && {
// add it early to memoize
debuglog(s"$symbol indirectly refers to 'this'")
thisReferringMethods += symbol
true
}
}
}
loop(symbol)
}
private var currentMethod: Symbol = NoSymbol
override def traverse(tree: Tree) = tree match {
case _: DefDef if tree.symbol.hasFlag(SYNCHRONIZED) =>
thisReferringMethods add tree.symbol
case DefDef(_, _, _, _, _, _) if tree.symbol.isDelambdafyTarget || tree.symbol.isLiftedMethod =>
// we don't expect defs within defs. At this phase trees should be very flat
if (currentMethod.exists) devWarning("Found a def within a def at a phase where defs are expected to be flattened out.")
currentMethod = tree.symbol
tree.traverse(this)
currentMethod = NoSymbol
case fun@Function(_, _) =>
// we don't drill into functions because at the beginning of this phase they will always refer to 'this'.
// They'll be of the form {(args...) => this.anonfun(args...)}
// but we do need to make note of the lifted body method in case it refers to 'this'
if (currentMethod.exists) liftedMethodReferences.getOrElseUpdate(currentMethod, mutable.Set()) += targetMethod(fun)
case Apply(sel @ Select(This(_), _), args) if sel.symbol.isLiftedMethod =>
if (currentMethod.exists) liftedMethodReferences.getOrElseUpdate(currentMethod, mutable.Set()) += sel.symbol
super.traverseTrees(args)
case Apply(fun, outer :: rest) if shouldElideOuterArg(fun.symbol, outer) =>
fun.traverse(this)
super.traverseTrees(rest)
case This(_) =>
if (currentMethod.exists && tree.symbol == currentMethod.enclClass) {
debuglog(s"$currentMethod directly refers to 'this'")
thisReferringMethods add currentMethod
}
case _: ClassDef if !tree.symbol.isTopLevel =>
case _: DefDef =>
case _ =>
tree.traverse(this)
}
}
}
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