package dotty.tools.dotc
package transform
import TreeTransforms._
import core.DenotTransformers._
import core.Symbols._
import core.Contexts._
import core.Types._
import core.Flags._
import core.Decorators._
import core.StdNames.nme
import core.Names._
import core.NameOps._
import core.Phases._
import ast.Trees._
import SymUtils._
import ExplicitOuter.outer
import util.Attachment
import util.NameTransformer
import util.Positions._
import collection.{ mutable, immutable }
import collection.mutable.{ HashMap, HashSet, LinkedHashMap, LinkedHashSet, TreeSet }
object LambdaLift {
private val NJ = NameTransformer.NAME_JOIN_STRING
private class NoPath extends Exception
}
/** This phase performs the necessary rewritings to eliminate classes and methods
* nested in other methods. In detail:
* 1. It adds all free variables of local functions as additional parameters (proxies).
* 2. It rebinds references to free variables to the corresponding proxies,
* 3. It lifts all local functions and classes out as far as possible, but at least
* to the enclosing class.
* 4. It stores free variables of non-trait classes as additional fields of the class.
* The fields serve as proxies for methods in the class, which avoids the need
* of passing additional parameters to these methods.
*
* A particularly tricky case are local traits. These cannot store free variables
* as field proxies, because LambdaLift runs after Mixin, so the fields cannot be
* expanded anymore. Instead, methods of local traits get free variables of
* the trait as additional proxy parameters. The difference between local classes
* and local traits is illustrated by the two rewritings below.
*
* def f(x: Int) = { def f(x: Int) = new C(x).f2
* class C { ==> class C(x$1: Int) {
* def f2 = x def f2 = x$1
* } }
* new C().f2
* }
*
* def f(x: Int) = { def f(x: Int) = new C().f2(x)
* trait T { ==> trait T
* def f2 = x def f2(x$1: Int) = x$1
* } }
* class C extends T class C extends T
* new C().f2
* }
*/
class LambdaLift extends MiniPhase with IdentityDenotTransformer { thisTransform =>
import LambdaLift._
import ast.tpd._
/** the following two members override abstract members in Transform */
val phaseName: String = "lambdaLift"
val treeTransform = new LambdaLifter
override def relaxedTyping = true
override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[Constructors])
// Constructors has to happen before LambdaLift because the lambda lift logic
// becomes simpler if it can assume that parameter accessors have already been
// converted to parameters in super calls. Without this it is very hard to get
// lambda lift for super calls right. Witness the implementation restrictions to
// this effect in scalac.
class LambdaLifter extends TreeTransform {
override def phase = thisTransform
private type SymSet = TreeSet[Symbol]
/** A map storing free variables of functions and classes */
private val free = new LinkedHashMap[Symbol, SymSet]
/** A map storing the free variable proxies of functions and classes.
* For every function and class, this is a map from the free variables
* of that function or class to the proxy symbols accessing them.
*/
private val proxyMap = new LinkedHashMap[Symbol, Map[Symbol, Symbol]]
/** A hashtable storing calls between functions */
private val called = new LinkedHashMap[Symbol, SymSet]
/** Symbols that are called from an inner class. */
private val calledFromInner = new HashSet[Symbol]
/** A map from local methods and classes to the owners to which they will be lifted as members.
* For methods and classes that do not have any dependencies this will be the enclosing package.
* symbols with packages as lifted owners will subsequently represented as static
* members of their toplevel class, unless their enclosing class was already static.
* Note: During tree transform (which runs at phase LambdaLift + 1), liftedOwner
* is also used to decide whether a method had a term owner before.
*/
private val liftedOwner = new HashMap[Symbol, Symbol]
/** The outer parameter of a constructor */
private val outerParam = new HashMap[Symbol, Symbol]
/** Buffers for lifted out classes and methods, indexed by owner */
private val liftedDefs = new HashMap[Symbol, mutable.ListBuffer[Tree]]
/** A flag to indicate whether new free variables have been found */
private var changedFreeVars: Boolean = _
/** A flag to indicate whether lifted owners have changed */
private var changedLiftedOwner: Boolean = _
private val ord: Ordering[Symbol] = Ordering.by((_: Symbol).id) // Dotty deviation: Type annotation needed. TODO: figure out why
private def newSymSet = TreeSet.empty[Symbol](ord)
private def symSet(f: LinkedHashMap[Symbol, SymSet], sym: Symbol): SymSet =
f.getOrElseUpdate(sym, newSymSet)
def freeVars(sym: Symbol): List[Symbol] = free get sym match {
case Some(set) => set.toList
case None => Nil
}
def proxyOf(sym: Symbol, fv: Symbol) = proxyMap.getOrElse(sym, Map.empty)(fv)
def proxies(sym: Symbol): List[Symbol] = freeVars(sym).map(proxyOf(sym, _))
/** A symbol is local if it is owned by a term or a local trait,
* or if it is a constructor of a local symbol.
*/
def isLocal(sym: Symbol)(implicit ctx: Context): Boolean = {
val owner = sym.maybeOwner
owner.isTerm ||
owner.is(Trait) && isLocal(owner) ||
sym.isConstructor && isLocal(owner)
}
/** Set `liftedOwner(sym)` to `owner` if `owner` is more deeply nested
* than the previous value of `liftedowner(sym)`.
*/
def narrowLiftedOwner(sym: Symbol, owner: Symbol)(implicit ctx: Context) =
if (sym.maybeOwner.isTerm &&
owner.isProperlyContainedIn(liftedOwner(sym)) &&
owner != sym) {
ctx.log(i"narrow lifted $sym to $owner")
changedLiftedOwner = true
liftedOwner(sym) = owner
}
/** Mark symbol `sym` as being free in `enclosure`, unless `sym` is defined
* in `enclosure` or there is an intermediate class properly containing `enclosure`
* in which `sym` is also free. Also, update `liftedOwner` of `enclosure` so
* that `enclosure` can access `sym`, or its proxy in an intermediate class.
* This means:
*
* 1. If there is an intermediate class in which `sym` is free, `enclosure`
* must be contained in that class (in order to access the `sym proxy stored
* in the class).
*
* 2. If there is no intermediate class, `enclosure` must be contained
* in the class enclosing `sym`.
*
* @return If there is a non-trait class between `enclosure` and
* the owner of `sym`, the largest such class.
* Otherwise, if there is a trait between `enclosure` and
* the owner of `sym`, the largest such trait.
* Otherwise, NoSymbol.
*
* @pre sym.owner.isTerm, (enclosure.isMethod || enclosure.isClass)
*
* The idea of `markFree` is illustrated with an example:
*
* def f(x: int) = {
* class C {
* class D {
* val y = x
* }
* }
* }
*
* In this case `x` is free in the primary constructor of class `C`.
* but it is not free in `D`, because after lambda lift the code would be transformed
* as follows:
*
* def f(x$0: int) {
* class C(x$0: int) {
* val x$1 = x$0
* class D {
* val y = outer.x$1
* }
* }
* }
*/
private def markFree(sym: Symbol, enclosure: Symbol)(implicit ctx: Context): Symbol = try {
if (!enclosure.exists) throw new NoPath
if (enclosure == sym.enclosure) NoSymbol
else {
ctx.debuglog(i"mark free: ${sym.showLocated} with owner ${sym.maybeOwner} marked free in $enclosure")
val intermediate =
if (enclosure.is(PackageClass)) enclosure
else markFree(sym, enclosure.enclosure)
narrowLiftedOwner(enclosure, intermediate orElse sym.enclosingClass)
if (!intermediate.isRealClass || enclosure.isConstructor) {
// Constructors and methods nested inside traits get the free variables
// of the enclosing trait or class.
// Conversely, local traits do not get free variables.
if (!enclosure.is(Trait))
if (symSet(free, enclosure).add(sym)) {
changedFreeVars = true
ctx.log(i"$sym is free in $enclosure")
}
}
if (intermediate.isRealClass) intermediate
else if (enclosure.isRealClass) enclosure
else if (intermediate.isClass) intermediate
else if (enclosure.isClass) enclosure
else NoSymbol
}
} catch {
case ex: NoPath =>
println(i"error lambda lifting ${ctx.compilationUnit}: $sym is not visible from $enclosure")
throw ex
}
private def markCalled(callee: Symbol, caller: Symbol)(implicit ctx: Context): Unit = {
ctx.debuglog(i"mark called: $callee of ${callee.owner} is called by $caller in ${caller.owner}")
assert(isLocal(callee))
symSet(called, caller) += callee
if (callee.enclosingClass != caller.enclosingClass) calledFromInner += callee
}
private class CollectDependencies extends EnclosingMethodTraverser {
def traverse(enclosure: Symbol, tree: Tree)(implicit ctx: Context) = try { //debug
val sym = tree.symbol
def narrowTo(thisClass: ClassSymbol) = {
val enclClass = enclosure.enclosingClass
narrowLiftedOwner(enclosure,
if (enclClass.isContainedIn(thisClass)) thisClass
else enclClass) // unknown this reference, play it safe and assume the narrowest possible owner
}
tree match {
case tree: Ident =>
if (isLocal(sym)) {
if (sym is Label)
assert(enclosure == sym.enclosure,
i"attempt to refer to label $sym from nested $enclosure")
else if (sym is Method) markCalled(sym, enclosure)
else if (sym.isTerm) markFree(sym, enclosure)
}
def captureImplicitThis(x: Type): Unit = {
x match {
case tr@TermRef(x, _) if (!tr.termSymbol.isStatic) => captureImplicitThis(x)
case x: ThisType if (!x.tref.typeSymbol.isStaticOwner) => narrowTo(x.tref.typeSymbol.asClass)
case _ =>
}
}
captureImplicitThis(tree.tpe)
case tree: Select =>
if (sym.is(Method) && isLocal(sym)) markCalled(sym, enclosure)
case tree: This =>
narrowTo(tree.symbol.asClass)
case tree: DefDef =>
if (sym.owner.isTerm && !sym.is(Label))
liftedOwner(sym) = sym.enclosingPackageClass
// this will make methods in supercall constructors of top-level classes owned
// by the enclosing package, which means they will be static.
// On the other hand, all other methods will be indirectly owned by their
// top-level class. This avoids possible deadlocks when a static method
// has to access its enclosing object from the outside.
else if (sym.isConstructor) {
if (sym.isPrimaryConstructor && isLocal(sym.owner) && !sym.owner.is(Trait))
// add a call edge from the constructor of a local non-trait class to
// the class itself. This is done so that the constructor inherits
// the free variables of the class.
symSet(called, sym) += sym.owner
tree.vparamss.head.find(_.name == nme.OUTER) match {
case Some(vdef) => outerParam(sym) = vdef.symbol
case _ =>
}
}
case tree: TypeDef =>
if (sym.owner.isTerm) liftedOwner(sym) = sym.topLevelClass.owner
case tree: Template =>
liftedDefs(tree.symbol.owner) = new mutable.ListBuffer
case _ =>
}
foldOver(enclosure, tree)
} catch { //debug
case ex: Exception =>
println(i"$ex while traversing $tree")
throw ex
}
}
/** Compute final free variables map `fvs by closing over caller dependencies. */
private def computeFreeVars()(implicit ctx: Context): Unit =
do {
changedFreeVars = false
for {
caller <- called.keys
callee <- called(caller)
fvs <- free get callee
fv <- fvs
} markFree(fv, caller)
} while (changedFreeVars)
/** Compute final liftedOwner map by closing over caller dependencies */
private def computeLiftedOwners()(implicit ctx: Context): Unit =
do {
changedLiftedOwner = false
for {
caller <- called.keys
callee <- called(caller)
} {
val normalizedCallee = callee.skipConstructor
val calleeOwner = normalizedCallee.owner
if (calleeOwner.isTerm) narrowLiftedOwner(caller, liftedOwner(normalizedCallee))
else {
assert(calleeOwner.is(Trait))
// methods nested inside local trait methods cannot be lifted out
// beyond the trait. Note that we can also call a trait method through
// a qualifier; in that case no restriction to lifted owner arises.
if (caller.isContainedIn(calleeOwner))
narrowLiftedOwner(caller, calleeOwner)
}
}
} while (changedLiftedOwner)
private def newName(sym: Symbol)(implicit ctx: Context): Name =
if (sym.isAnonymousFunction && sym.owner.is(Method, butNot = Label))
(sym.name ++ NJ ++ sym.owner.name).freshened
else sym.name.freshened
private def generateProxies()(implicit ctx: Context): Unit =
for ((owner, freeValues) <- free.toIterator) {
val newFlags = Synthetic | (if (owner.isClass) ParamAccessor | Private else Param)
ctx.debuglog(i"free var proxy: ${owner.showLocated}, ${freeValues.toList}%, %")
proxyMap(owner) = {
for (fv <- freeValues.toList) yield {
val proxyName = newName(fv)
val proxy = ctx.newSymbol(owner, proxyName.asTermName, newFlags, fv.info, coord = fv.coord)
if (owner.isClass) proxy.enteredAfter(thisTransform)
(fv, proxy)
}
}.toMap
}
private def liftedInfo(local: Symbol)(implicit ctx: Context): Type = local.info match {
case MethodTpe(pnames, ptypes, restpe) =>
val ps = proxies(local)
MethodType(
ps.map(_.name.asTermName) ++ pnames,
ps.map(_.info) ++ ptypes,
restpe)
case info => info
}
private def liftLocals()(implicit ctx: Context): Unit = {
for ((local, lOwner) <- liftedOwner) {
val (newOwner, maybeStatic) =
if (lOwner is Package) {
val encClass = local.enclosingClass
val topClass = local.topLevelClass
val preferEncClass =
encClass.isStatic &&
// non-static classes can capture owners, so should be avoided
(encClass.isProperlyContainedIn(topClass) ||
// can be false for symbols which are defined in some weird combination of supercalls.
encClass.is(ModuleClass, butNot = Package)
// needed to not cause deadlocks in classloader. see t5375.scala
)
if (preferEncClass) (encClass, EmptyFlags)
else (topClass, JavaStatic)
}
else (lOwner, EmptyFlags)
local.copySymDenotation(
owner = newOwner,
name = newName(local),
initFlags = local.flags &~ (InSuperCall | Module) | Private | maybeStatic,
// drop Module because class is no longer a singleton in the lifted context.
info = liftedInfo(local)).installAfter(thisTransform)
}
for (local <- free.keys)
if (!liftedOwner.contains(local))
local.copySymDenotation(info = liftedInfo(local)).installAfter(thisTransform)
}
private def init(implicit ctx: Context) = {
(new CollectDependencies).traverse(NoSymbol, ctx.compilationUnit.tpdTree)
computeFreeVars()
computeLiftedOwners()
generateProxies()(ctx.withPhase(thisTransform.next))
liftLocals()(ctx.withPhase(thisTransform.next))
}
override def prepareForUnit(tree: Tree)(implicit ctx: Context) = {
val lifter = new LambdaLifter
lifter.init(ctx.withPhase(thisTransform))
lifter
}
private def currentEnclosure(implicit ctx: Context) =
ctx.owner.enclosingMethodOrClass
private def inCurrentOwner(sym: Symbol)(implicit ctx: Context) =
sym.enclosure == currentEnclosure
private def proxy(sym: Symbol)(implicit ctx: Context): Symbol = {
def liftedEnclosure(sym: Symbol) = liftedOwner.getOrElse(sym, sym.enclosure)
def searchIn(enclosure: Symbol): Symbol = {
if (!enclosure.exists) {
def enclosures(encl: Symbol): List[Symbol] =
if (encl.exists) encl :: enclosures(liftedEnclosure(encl)) else Nil
throw new IllegalArgumentException(i"Could not find proxy for ${sym.showDcl} in ${sym.ownersIterator.toList}, encl = $currentEnclosure, owners = ${currentEnclosure.ownersIterator.toList}%, %; enclosures = ${enclosures(currentEnclosure)}%, %")
}
ctx.debuglog(i"searching for $sym(${sym.owner}) in $enclosure")
proxyMap get enclosure match {
case Some(pmap) =>
pmap get sym match {
case Some(proxy) => return proxy
case none =>
}
case none =>
}
searchIn(liftedEnclosure(enclosure))
}
if (inCurrentOwner(sym)) sym else searchIn(currentEnclosure)
}
private def memberRef(sym: Symbol)(implicit ctx: Context, info: TransformerInfo): Tree = {
val clazz = sym.enclosingClass
val qual =
if (clazz.isStaticOwner || ctx.owner.enclosingClass == clazz)
singleton(clazz.thisType)
else if (ctx.owner.isConstructor)
outerParam.get(ctx.owner) match {
case Some(param) => outer.path(start = Ident(param.termRef), toCls = clazz)
case _ => outer.path(toCls = clazz)
}
else outer.path(toCls = clazz)
transformFollowingDeep(qual.select(sym))
}
private def proxyRef(sym: Symbol)(implicit ctx: Context, info: TransformerInfo): Tree = {
val psym = proxy(sym)(ctx.withPhase(thisTransform))
transformFollowingDeep(if (psym.owner.isTerm) ref(psym) else memberRef(psym))
}
private def addFreeArgs(sym: Symbol, args: List[Tree])(implicit ctx: Context, info: TransformerInfo) =
free get sym match {
case Some(fvs) => fvs.toList.map(proxyRef(_)) ++ args
case _ => args
}
private def addFreeParams(tree: Tree, proxies: List[Symbol])(implicit ctx: Context, info: TransformerInfo): Tree = proxies match {
case Nil => tree
case proxies =>
val sym = tree.symbol
val freeParamDefs = proxies.map(proxy =>
transformFollowingDeep(ValDef(proxy.asTerm).withPos(tree.pos)).asInstanceOf[ValDef])
def proxyInit(field: Symbol, param: Symbol) =
transformFollowingDeep(memberRef(field).becomes(ref(param)))
/** Initialize proxy fields from proxy parameters and map `rhs` from fields to parameters */
def copyParams(rhs: Tree) = {
val fvs = freeVars(sym.owner)
val classProxies = fvs.map(proxyOf(sym.owner, _))
val constrProxies = fvs.map(proxyOf(sym, _))
ctx.debuglog(i"copy params ${constrProxies.map(_.showLocated)}%, % to ${classProxies.map(_.showLocated)}%, %}")
seq((classProxies, constrProxies).zipped.map(proxyInit), rhs)
}
tree match {
case tree: DefDef =>
cpy.DefDef(tree)(
vparamss = tree.vparamss.map(freeParamDefs ++ _),
rhs =
if (sym.isPrimaryConstructor && !sym.owner.is(Trait)) copyParams(tree.rhs)
else tree.rhs)
case tree: Template =>
cpy.Template(tree)(body = freeParamDefs ++ tree.body)
}
}
private def liftDef(tree: MemberDef)(implicit ctx: Context, info: TransformerInfo): Tree = {
val buf = liftedDefs(tree.symbol.owner)
transformFollowing(rename(tree, tree.symbol.name)).foreachInThicket(buf += _)
EmptyTree
}
private def needsLifting(sym: Symbol) = liftedOwner contains sym
override def transformIdent(tree: Ident)(implicit ctx: Context, info: TransformerInfo) = {
val sym = tree.symbol
tree.tpe match {
case tpe @ TermRef(prefix, _) =>
if (prefix eq NoPrefix)
if (sym.enclosure != currentEnclosure && !sym.isStatic)
(if (sym is Method) memberRef(sym) else proxyRef(sym)).withPos(tree.pos)
else if (sym.owner.isClass) // sym was lifted out
ref(sym).withPos(tree.pos)
else
tree
else if (!prefixIsElidable(tpe)) ref(tpe)
else tree
case _ =>
tree
}
}
override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo) =
cpy.Apply(tree)(tree.fun, addFreeArgs(tree.symbol, tree.args)).withPos(tree.pos)
override def transformClosure(tree: Closure)(implicit ctx: Context, info: TransformerInfo) =
cpy.Closure(tree)(env = addFreeArgs(tree.meth.symbol, tree.env))
override def transformDefDef(tree: DefDef)(implicit ctx: Context, info: TransformerInfo) = {
val sym = tree.symbol
val paramsAdded =
if (free.contains(sym)) addFreeParams(tree, proxies(sym)).asInstanceOf[DefDef]
else tree
if (needsLifting(sym)) liftDef(paramsAdded)
else paramsAdded
}
override def transformReturn(tree: Return)(implicit ctx: Context, info: TransformerInfo) = tree.expr match {
case Block(stats, value) =>
Block(stats, Return(value, tree.from)).withPos(tree.pos)
case _ =>
tree
}
override def transformTemplate(tree: Template)(implicit ctx: Context, info: TransformerInfo) = {
val cls = ctx.owner
val impl = addFreeParams(tree, proxies(cls)).asInstanceOf[Template]
cpy.Template(impl)(body = impl.body ++ liftedDefs.remove(cls).get)
}
override def transformTypeDef(tree: TypeDef)(implicit ctx: Context, info: TransformerInfo) =
if (needsLifting(tree.symbol)) liftDef(tree) else tree
}
}
