/* NSC -- new Scala compiler * Copyright 2005-2013 LAMP/EPFL * @author Martin Odersky */ package scala.tools.nsc package transform import symtab._ import Flags._ import scala.annotation.tailrec import scala.collection.mutable // TODO: move lazy vals bitmap creation to lazy vals phase now that lazy vals are mixed in during fields abstract class Mixin extends InfoTransform with ast.TreeDSL { import global._ import definitions._ import CODE._ /** The name of the phase: */ val phaseName: String = "mixin" /** Some trait methods need to be implemented in subclasses, so they cannot be private. * * We used to publicize during explicitouter (for some reason), so the condition is a bit more involved now it's done here * (need to exclude lambdaLIFTED methods, as they do no exist during explicitouter and thus did not need to be excluded...) * * They may be protected, now that traits are compiled 1:1 to interfaces. * The same disclaimers about mapping Scala's notion of visibility to Java's apply: * we cannot emit PROTECTED methods in interfaces on the JVM, * but knowing that these trait methods are protected means we won't emit static forwarders. * * JVMLS: "Methods of interfaces may have any of the flags in Table 4.6-A set * except ACC_PROTECTED, ACC_FINAL, ACC_SYNCHRONIZED, and ACC_NATIVE (JLS ยง9.4)." * * TODO: can we just set the right flags from the start?? * could we use the final flag to indicate a private method is really-really-private? */ def publicizeTraitMethod(sym: Symbol): Unit = { if ((sym hasFlag PRIVATE) && !(sym hasFlag LIFTED) && ( // lambdalifted methods can remain private // super accessors by definition must be implemented in a subclass, so can't be private // TODO: why are they ever private in a trait to begin with!?!? (could just name mangle them to begin with) // TODO: can we add the SYNTHESIZE_IMPL_IN_SUBCLASS flag to super accessors symbols? (sym hasFlag SUPERACCESSOR) // an accessor / module *may* need to be implemented in a subclass, and thus cannot be private // TODO: document how we get here (lambdalift? fields has already made accessors not-private) || (sym hasFlag ACCESSOR | MODULE) && (sym hasFlag SYNTHESIZE_IMPL_IN_SUBCLASS))) sym.makeNotPrivate(sym.owner) // no need to make trait methods not-protected // (we used to have to move them to another class when interfaces could not have concrete methods) // see note in `synthFieldsAndAccessors` in Fields.scala // if (sym hasFlag PROTECTED) sym setFlag notPROTECTED } /** This map contains a binding (class -> info) if * the class with this info at phase mixinPhase has been treated for mixin composition */ private val treatedClassInfos = perRunCaches.newMap[Symbol, Type]() withDefaultValue NoType // --------- helper functions ----------------------------------------------- /** A member of a trait is implemented statically if its implementation after the * mixin transform is RHS of the method body (destined to be in a interface default method) * * To be statically implemented, a member must be a method that belonged to the trait's implementation class * before (i.e. it is not abstract). Not statically implemented are * - non-private modules: these are implemented directly in the mixin composition class * (private modules, on the other hand, are implemented statically, but their * module variable is not. all such private modules are lifted, because * non-lifted private modules have been eliminated in ExplicitOuter) * - field accessors and superaccessors, except for lazy value accessors which become initializer * methods in the impl class (because they can have arbitrary initializers) */ private def isImplementedStatically(sym: Symbol) = ( (sym.isMethod || ((sym hasFlag MODULE) && !sym.isStatic)) && notDeferred(sym) && sym.owner.isTrait && (!sym.isModule || sym.hasFlag(PRIVATE | LIFTED)) && (!(sym hasFlag (ACCESSOR | SUPERACCESSOR)) || sym.isLazy) && !sym.isPrivate && !sym.hasAllFlags(LIFTED | MODULE | METHOD) && !sym.isConstructor && (!sym.hasFlag(notPRIVATE | LIFTED) || sym.hasFlag(ACCESSOR | SUPERACCESSOR | MODULE)) ) private def isFieldWithBitmap(field: Symbol) = { field.info // ensure that nested objects are transformed // For checkinit consider normal value getters // but for lazy values only take into account lazy getters field.isLazy && field.isMethod && !field.isDeferred } def isTransientField(field: Symbol) = field.accessedOrSelf hasAnnotation TransientAttr /** Does this field require an initialized bit? * Note: fields of classes inheriting DelayedInit are not checked. * This is because they are neither initialized in the constructor * nor do they have a setter (not if they are vals anyway). The usual * logic for setting bitmaps does therefore not work for such fields. * That's why they are excluded. * Note: The `checkinit` option does not check if transient fields are initialized. */ private def needsInitFlag(sym: Symbol) = ( sym.isGetter && !sym.isInitializedToDefault && !isConstantType(sym.info.finalResultType) // SI-4742 && !sym.hasFlag(PARAMACCESSOR | SPECIALIZED | LAZY) && !sym.accessed.hasFlag(PRESUPER) && !sym.isOuterAccessor && !(sym.owner isSubClass DelayedInitClass) && !(sym.accessed hasAnnotation TransientAttr) ) /** Returns the symbol that is accessed by a super-accessor in a mixin composition. * * @param base The class in which everything is mixed together * @param member The symbol statically referred to by the superaccessor in the trait * @param mixinClass The mixin class that produced the superaccessor */ private def rebindSuper(base: Symbol, member: Symbol, mixinClass: Symbol): Symbol = exitingSpecialize { var bcs = base.info.baseClasses.dropWhile(mixinClass != _).tail var sym: Symbol = NoSymbol debuglog("starting rebindsuper " + base + " " + member + ":" + member.tpe + " " + mixinClass + " " + base.info.baseClasses + "/" + bcs) while (!bcs.isEmpty && sym == NoSymbol) { if (settings.debug) { val other = bcs.head.info.nonPrivateDecl(member.name) debuglog("rebindsuper " + bcs.head + " " + other + " " + other.tpe + " " + other.isDeferred) } sym = member.matchingSymbol(bcs.head, base.thisType).suchThat(sym => !sym.hasFlag(DEFERRED | BRIDGE)) bcs = bcs.tail } sym } // --------- type transformation ----------------------------------------------- @inline final def notDeferred(sym: Symbol) = fields.notDeferredOrSynthImpl(sym) /** Is member overridden (either directly or via a bridge) in base class sequence `bcs`? */ def isOverriddenAccessor(member: Symbol, bcs: List[Symbol]): Boolean = beforeOwnPhase { def hasOverridingAccessor(clazz: Symbol) = { clazz.info.nonPrivateDecl(member.name).alternatives.exists( sym => sym.hasFlag(ACCESSOR) && !sym.hasFlag(MIXEDIN) && notDeferred(sym) && matchesType(sym.tpe, member.tpe, alwaysMatchSimple = true)) } ( bcs.head != member.owner && (hasOverridingAccessor(bcs.head) || isOverriddenAccessor(member, bcs.tail)) ) } private def isUnitGetter(sym: Symbol) = sym.tpe.resultType.typeSymbol == UnitClass /** Add given member to given class, and mark member as mixed-in. */ def addMember(clazz: Symbol, member: Symbol): Symbol = { debuglog(s"mixing into $clazz: ${member.defString}") // This attachment is used to instruct the backend about which methids in traits require // a static trait impl method. We remove this from the new symbol created for the method // mixed into the subclass. member.removeAttachment[NeedStaticImpl.type] clazz.info.decls enter member setFlag MIXEDIN resetFlag JAVA_DEFAULTMETHOD } def cloneAndAddMember(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol = addMember(clazz, cloneBeforeErasure(mixinClass, mixinMember, clazz)) def cloneBeforeErasure(mixinClass: Symbol, mixinMember: Symbol, clazz: Symbol): Symbol = { val newSym = enteringErasure { // since we used `mixinMember` from the interface that represents the trait that's // being mixed in, have to instantiate the interface type params (that may occur in mixinMember's // info) as they are seen from the class. We can't use the member that we get from the // implementation class, as it's a clone that was made after erasure, and thus it does not // know its info at the beginning of erasure anymore. val sym = mixinMember cloneSymbol clazz val erasureMap = erasure.erasure(mixinMember) val erasedInterfaceInfo: Type = erasureMap(mixinMember.info) val specificForwardInfo = (clazz.thisType baseType mixinClass) memberInfo mixinMember val forwarderInfo = if (erasureMap(specificForwardInfo) =:= erasedInterfaceInfo) specificForwardInfo else { erasedInterfaceInfo } // Optimize: no need if mixinClass has no typeparams. // !!! JZ Really? What about the effect of abstract types, prefix? if (mixinClass.typeParams.isEmpty) sym else sym modifyInfo (_ => forwarderInfo) } newSym } def publicizeTraitMethods(clazz: Symbol) { if (treatedClassInfos(clazz) != clazz.info) { treatedClassInfos(clazz) = clazz.info assert(phase == currentRun.mixinPhase, phase) for (member <- clazz.info.decls) { if (member.isMethod) publicizeTraitMethod(member) else { assert(member.isTerm && !member.isDeferred, member) // disable assert to support compiling against code compiled by an older compiler (until we re-starr) // assert(member hasFlag LAZY | PRESUPER, s"unexpected $member in $clazz ${member.debugFlagString}") // lazy vals still leave field symbols lying around in traits -- TODO: never emit them to begin with // ditto for early init vals clazz.info.decls.unlink(member) } } debuglog("new defs of " + clazz + " = " + clazz.info.decls) } } /** Add all members to be mixed in into a (non-trait-) class * These are: * for every mixin trait T that is not also inherited by the superclass: * add late interface members to T and then: * - if a member M of T is forwarded to the implementation class, add * a forwarder for M unless one exists already. * The alias of the forwarder is the static member it forwards to. * - for every abstract accessor in T, add a field and an implementation for that accessor * - for every super accessor in T, add an implementation of that accessor * - for every module in T, add a module */ def addMixedinMembers(clazz: Symbol, unit: CompilationUnit) { def cloneAndAddMixinMember(mixinClass: Symbol, mixinMember: Symbol): Symbol = ( cloneAndAddMember(mixinClass, mixinMember, clazz) setPos clazz.pos resetFlag DEFERRED ) /* Mix in members of implementation class mixinClass into class clazz */ def mixinTraitForwarders(mixinClass: Symbol) { for (member <- mixinClass.info.decls ; if isImplementedStatically(member)) { member overridingSymbol clazz match { case NoSymbol => val isMemberOfClazz = clazz.info.findMember(member.name, 0, 0L, stableOnly = false).alternatives.contains(member) if (isMemberOfClazz) { def genForwarder(): Unit = { cloneAndAddMixinMember(mixinClass, member).asInstanceOf[TermSymbol] setAlias member } if (settings.XgenMixinForwarders) genForwarder() else { // `member` is a concrete method defined in `mixinClass`, which is a base class of // `clazz`, and the method is not overridden in `clazz`. A forwarder is needed if: // // - A non-trait base class of `clazz` defines a matching method. Example: // class C {def f: Int}; trait T extends C {def f = 1}; class D extends T // Even if C.f is abstract, the forwarder in D is needed, otherwise the JVM would // resolve `D.f` to `C.f`, see jvms-6.5.invokevirtual. // // - There exists another concrete, matching method in a parent interface `p` of // `clazz`, and the `mixinClass` does not itself extend `p`. In this case the // forwarder is needed to disambiguate. Example: // trait T1 {def f = 1}; trait T2 extends T1 {override def f = 2}; class C extends T2 // In C we don't need a forwarder for f because T2 extends T1, so the JVM resolves // C.f to T2.f non-ambiguously. See jvms-5.4.3.3, "maximally-specific method". // trait U1 {def f = 1}; trait U2 {self:U1 => override def f = 2}; class D extends U2 // In D the forwarder is needed, the interfaces U1 and U2 are unrelated at the JVM // level. @tailrec def existsCompetingMethod(baseClasses: List[Symbol]): Boolean = baseClasses match { case baseClass :: rest => if (baseClass ne mixinClass) { val m = member.overriddenSymbol(baseClass) val isCompeting = m.exists && { !m.owner.isTraitOrInterface || (!m.isDeferred && !mixinClass.isNonBottomSubClass(m.owner)) } isCompeting || existsCompetingMethod(rest) } else existsCompetingMethod(rest) case _ => false } if (existsCompetingMethod(clazz.baseClasses)) genForwarder() else if (!settings.nowarnDefaultJunitMethods && JUnitTestClass.exists && member.hasAnnotation(JUnitTestClass)) warning(member.pos, "JUnit tests in traits that are compiled as default methods are not executed by JUnit 4. JUnit 5 will fix this issue.") } } case _ => } } } /* Mix in members of trait mixinClass into class clazz. */ def mixinTraitMembers(mixinClass: Symbol) { // For all members of a trait's interface do: for (mixinMember <- mixinClass.info.decls) { if (mixinMember.hasFlag(SUPERACCESSOR)) { // mixin super accessors val superAccessor = addMember(clazz, mixinMember.cloneSymbol(clazz)) setPos clazz.pos assert(superAccessor.alias != NoSymbol, superAccessor) rebindSuper(clazz, mixinMember.alias, mixinClass) match { case NoSymbol => reporter.error(clazz.pos, "Member %s of mixin %s is missing a concrete super implementation.".format( mixinMember.alias, mixinClass)) case alias1 => if (alias1.owner.isJavaDefined && alias1.owner.isInterface && !clazz.parentSymbols.contains(alias1.owner)) { val suggestedParent = exitingTyper(clazz.info.baseType(alias1.owner)) reporter.error(clazz.pos, s"Unable to implement a super accessor required by trait ${mixinClass.name} unless $suggestedParent is directly extended by $clazz.") } superAccessor.asInstanceOf[TermSymbol] setAlias alias1 } } else if (mixinMember.hasFlag(ACCESSOR) && notDeferred(mixinMember) && (mixinMember hasFlag PARAMACCESSOR) && !isOverriddenAccessor(mixinMember, clazz.info.baseClasses)) { // mixin accessor for constructor parameter // (note that a paramaccessor cannot have a constant type as it must have a user-defined type) val mixedInAccessor = cloneAndAddMixinMember(mixinClass, mixinMember) val name = mixinMember.name if (!nme.isSetterName(name)) { // enteringPhase: the private field is moved to the implementation class by erasure, // so it can no longer be found in the mixinMember's owner (the trait) val accessed = enteringPickler(mixinMember.accessed) // #3857, need to retain info before erasure when cloning (since cloning only // carries over the current entry in the type history) val sym = enteringErasure { // so we have a type history entry before erasure clazz.newValue(mixinMember.localName, mixinMember.pos).setInfo(mixinMember.tpe.resultType) } sym updateInfo mixinMember.tpe.resultType // info at current phase val newFlags = ( (PrivateLocal) | (mixinMember getFlag MUTABLE) | (if (mixinMember.hasStableFlag) 0 else MUTABLE) ) addMember(clazz, sym setFlag newFlags setAnnotations accessed.annotations) } } } } if (clazz.isJavaDefined || treatedClassInfos(clazz) == clazz.info) return treatedClassInfos(clazz) = clazz.info assert(!clazz.isTrait && clazz.info.parents.nonEmpty, clazz) // first complete the superclass with mixed in members addMixedinMembers(clazz.superClass, unit) for (mc <- clazz.mixinClasses ; if mc.isTrait) { // @SEAN: adding trait tracking so we don't have to recompile transitive closures unit.depends += mc publicizeTraitMethods(mc) mixinTraitMembers(mc) mixinTraitForwarders(mc) } } override def transformInfo(sym: Symbol, tp: Type): Type = tp /** Return a map of single-use fields to the lazy value that uses them during initialization. * Each field has to be private and defined in the enclosing class, and there must * be exactly one lazy value using it. * * Such fields will be nulled after the initializer has memoized the lazy value. */ def singleUseFields(templ: Template): scala.collection.Map[Symbol, List[Symbol]] = { val usedIn = mutable.HashMap[Symbol, List[Symbol]]() withDefaultValue Nil object SingleUseTraverser extends Traverser { override def traverse(tree: Tree) { tree match { case Assign(lhs, rhs) => traverse(rhs) // assignments don't count case _ => if (tree.hasSymbolField && tree.symbol != NoSymbol) { val sym = tree.symbol if ((sym.hasAccessorFlag || (sym.isTerm && !sym.isMethod)) && sym.isPrivate && !(currentOwner.isGetter && currentOwner.accessed == sym) // getter && !definitions.isPrimitiveValueClass(sym.tpe.resultType.typeSymbol) && sym.owner == templ.symbol.owner && !sym.isLazy && !tree.isDef) { debuglog("added use in: " + currentOwner + " -- " + tree) usedIn(sym) ::= currentOwner } } super.traverse(tree) } } } SingleUseTraverser(templ) debuglog("usedIn: " + usedIn) usedIn filter { case (_, member :: Nil) => member.isValue && member.isLazy case _ => false } } // --------- term transformation ----------------------------------------------- protected def newTransformer(unit: CompilationUnit): Transformer = new MixinTransformer(unit) class MixinTransformer(unit : CompilationUnit) extends Transformer { /** The rootContext used for typing */ private val rootContext = erasure.NoContext.make(EmptyTree, rootMirror.RootClass, newScope) /** The typer */ private var localTyper: erasure.Typer = _ private def typedPos(pos: Position)(tree: Tree): Tree = localTyper.typedPos(pos)(tree) /** Map lazy values to the fields they should null after initialization. */ private var lazyValNullables: Map[Symbol, Set[Symbol]] = _ /** Map a field symbol to a unique integer denoting its position in the class layout. * For each class, fields defined by the class come after inherited fields. Mixed-in * fields count as fields defined by the class itself. */ private val fieldOffset = perRunCaches.newMap[Symbol, Int]() private val bitmapKindForCategory = perRunCaches.newMap[Name, ClassSymbol]() // ByteClass, IntClass, LongClass private def bitmapKind(field: Symbol): ClassSymbol = bitmapKindForCategory(bitmapCategory(field)) private def flagsPerBitmap(field: Symbol): Int = bitmapKind(field) match { case BooleanClass => 1 case ByteClass => 8 case IntClass => 32 case LongClass => 64 } /** The first transform; called in a pre-order traversal at phase mixin * (that is, every node is processed before its children). * What transform does: * - For every non-trait class, add all mixed in members to the class info. */ private def preTransform(tree: Tree): Tree = { val sym = tree.symbol tree match { case Template(parents, self, body) => localTyper = erasure.newTyper(rootContext.make(tree, currentOwner)) exitingMixin(currentOwner.owner.info)//todo: needed? if (!currentOwner.isTrait && !isPrimitiveValueClass(currentOwner)) addMixedinMembers(currentOwner, unit) else if (currentOwner.isTrait) publicizeTraitMethods(currentOwner) tree case _ => tree } } /** Examines the symbol and returns a name indicating what brand of * bitmap it requires. The possibilities are the BITMAP_* vals * defined in StdNames. If it needs no bitmap, nme.NO_NAME. * * bitmaps for checkinit fields are not inherited */ def bitmapCategory(field: Symbol): Name = { import nme._ if (isFieldWithBitmap(field)) if (isTransientField(field)) BITMAP_TRANSIENT else BITMAP_NORMAL else if (!field.isDeferred && settings.checkInit && needsInitFlag(field)) if (isTransientField(field)) BITMAP_CHECKINIT_TRANSIENT else BITMAP_CHECKINIT else NO_NAME } /** Add all new definitions to a non-trait class * These fall into the following categories: * - for a trait interface: * - abstract accessors for all fields in the implementation class * - for a non-trait class: * - A field for every in a mixin class * - Setters and getters for such fields * - getters for mixed in lazy fields are completed * - module variables and module creators for every module in a mixin class * (except if module is lifted -- in this case the module variable * is local to some function, and the creator method is static.) * - A super accessor for every super accessor in a mixin class * - Forwarders for all methods that are implemented statically * All superaccessors are completed with right-hand sides (@see completeSuperAccessor) * * @param clazz The class to which definitions are added */ private def addNewDefs(clazz: Symbol, stats: List[Tree]): List[Tree] = { val newDefs = mutable.ListBuffer[Tree]() /* Attribute given tree and anchor at given position */ def attributedDef(pos: Position, tree: Tree): Tree = { debuglog("add new def to " + clazz + ": " + tree) typedPos(pos)(tree) } /* The position of given symbol, or, if this is undefined, * the position of the current class. */ def position(sym: Symbol) = if (sym.pos == NoPosition) clazz.pos else sym.pos /* Add tree at given position as new definition */ def addDef(pos: Position, tree: Tree) { newDefs += attributedDef(pos, tree) } /* Add new method definition. * * @param sym The method symbol. * @param rhs The method body. */ def addDefDef(sym: Symbol, rhs: Tree = EmptyTree) = addDef(position(sym), DefDef(sym, rhs)) def addValDef(sym: Symbol, rhs: Tree = EmptyTree) = addDef(position(sym), ValDef(sym, rhs)) /* Add `newdefs` to `stats`, removing any abstract method definitions * in `stats` that are matched by some symbol defined in * `newDefs`. */ def add(stats: List[Tree], newDefs: List[Tree]) = { val newSyms = newDefs map (_.symbol) def isNotDuplicate(tree: Tree) = tree match { case DefDef(_, _, _, _, _, _) => val sym = tree.symbol !(sym.isDeferred && (newSyms exists (nsym => nsym.name == sym.name && (nsym.tpe matches sym.tpe)))) case _ => true } if (newDefs.isEmpty) stats else newDefs ::: (stats filter isNotDuplicate) } /* If `stat` is a superaccessor, complete it by adding a right-hand side. * Note: superaccessors are always abstract until this point. * The method to call in a superaccessor is stored in the accessor symbol's alias field. * The rhs is: * super.A(xs) where A is the super accessor's alias and xs are its formal parameters. * This rhs is typed and then mixin transformed. */ def completeSuperAccessor(stat: Tree) = stat match { case DefDef(_, _, _, vparams :: Nil, _, EmptyTree) if stat.symbol.isSuperAccessor => val body = atPos(stat.pos)(Apply(SuperSelect(clazz, stat.symbol.alias), vparams map (v => Ident(v.symbol)))) val pt = stat.symbol.tpe.resultType copyDefDef(stat)(rhs = enteringMixin(transform(localTyper.typed(body, pt)))) case _ => stat } /* * Return the bitmap field for 'offset'. Depending on the hierarchy it is possible to reuse * the bitmap of its parents. If that does not exist yet we create one. */ def bitmapFor(clazz0: Symbol, offset: Int, field: Symbol): Symbol = { val category = bitmapCategory(field) val bitmapName = nme.newBitmapName(category, offset / flagsPerBitmap(field)).toTermName val sym = clazz0.info.decl(bitmapName) assert(!sym.isOverloaded, sym) def createBitmap: Symbol = { val bitmapKind = bitmapKindForCategory(category) val sym = clazz0.newVariable(bitmapName, clazz0.pos) setInfo bitmapKind.tpe enteringTyper(sym addAnnotation VolatileAttr) category match { case nme.BITMAP_TRANSIENT | nme.BITMAP_CHECKINIT_TRANSIENT => sym addAnnotation TransientAttr case _ => } val init = bitmapKind match { case BooleanClass => ValDef(sym, FALSE) case _ => ValDef(sym, ZERO) } sym setFlag PrivateLocal clazz0.info.decls.enter(sym) addDef(clazz0.pos, init) sym } sym orElse createBitmap } def maskForOffset(offset: Int, sym: Symbol, kind: ClassSymbol): Tree = { def realOffset = offset % flagsPerBitmap(sym) if (kind == LongClass ) LIT(1L << realOffset) else LIT(1 << realOffset) } /* Return an (untyped) tree of the form 'Clazz.this.bmp = Clazz.this.bmp | mask'. */ def mkSetFlag(clazz: Symbol, offset: Int, valSym: Symbol, kind: ClassSymbol): Tree = { val bmp = bitmapFor(clazz, offset, valSym) def mask = maskForOffset(offset, valSym, kind) def x = This(clazz) DOT bmp def newValue = if (kind == BooleanClass) TRUE else (x GEN_| (mask, kind)) x === newValue } /* Return an (untyped) tree of the form 'clazz.this.bitmapSym & mask (==|!=) 0', the * precise comparison operator depending on the value of 'equalToZero'. */ def mkTest(clazz: Symbol, mask: Tree, bitmapSym: Symbol, equalToZero: Boolean, kind: ClassSymbol): Tree = { val bitmapTree = (This(clazz) DOT bitmapSym) def lhs = bitmapTree GEN_& (mask, kind) kind match { case BooleanClass => if (equalToZero) NOT(bitmapTree) else bitmapTree case _ => if (equalToZero) lhs GEN_== (ZERO, kind) else lhs GEN_!= (ZERO, kind) } } /* return a 'lazified' version of rhs. It uses double-checked locking to ensure * initialization is performed at most once. For performance reasons the double-checked * locking is split into two parts, the first (fast) path checks the bitmap without * synchronizing, and if that fails it initializes the lazy val within the * synchronization block (slow path). This way the inliner should optimize * the fast path because the method body is small enough. * Private fields used only in this initializer are subsequently set to null. * * @param clazz The class symbol * @param lzyVal The symbol of this lazy field * @param init The tree which initializes the field ( f = ) * @param offset The offset of this field in the flags bitmap * * The result will be a tree of the form * { if ((bitmap&n & MASK) == 0) this.l$compute() * else l$ * * ... * def l$compute() = { synchronized(this) { * if ((bitmap$n & MASK) == 0) { * init // l$ = * bitmap$n = bimap$n | MASK * }} * l$ * } * * ... * this.f1 = null * ... this.fn = null * } * where bitmap$n is a byte, int or long value acting as a bitmap of initialized values. * The kind of the bitmap determines how many bit indicators for lazy vals are stored in it. * For Int bitmap it is 32 and then 'n' in the above code is: (offset / 32), * the MASK is (1 << (offset % 32)). * If the class contains only a single lazy val then the bitmap is represented * as a Boolean and the condition checking is a simple bool test. */ def mkLazyMemberDef(clazz: Symbol, lzyVal: Symbol, init: List[Tree], retVal: Tree, offset: Int): Tree = { def nullify(sym: Symbol) = Select(This(clazz), sym.accessedOrSelf) === LIT(null) val bitmapSym = bitmapFor(clazz, offset, lzyVal) val kind = bitmapKind(lzyVal) val mask = maskForOffset(offset, lzyVal, kind) val nulls = lazyValNullables(lzyVal).toList sortBy (_.id) map nullify if (nulls.nonEmpty) log("nulling fields inside " + lzyVal + ": " + nulls) val pos = if (lzyVal.pos != NoPosition) lzyVal.pos else clazz.pos // TODO: is the else branch ever taken? val slowPathSym = clazz.newMethod(nme.newLazyValSlowComputeName(lzyVal.name.toTermName), pos, PRIVATE) setInfoAndEnter MethodType(Nil, lzyVal.tpe.resultType) def thisRef = gen.mkAttributedThis(clazz) def cond = mkTest(clazz, mask, bitmapSym, equalToZero = true, kind) val statsToSynch = init ::: List(mkSetFlag(clazz, offset, lzyVal, kind), UNIT) val synchedRhs = gen.mkSynchronizedCheck(thisRef, cond, statsToSynch, nulls) addDef(pos, DefDef(slowPathSym, Block(List(synchedRhs.changeOwner(currentOwner -> slowPathSym)), retVal))) typedPos(init.head.pos)(If(cond, Apply(Select(thisRef, slowPathSym), Nil), retVal)) } def mkCheckedAccessor(clazz: Symbol, retVal: Tree, offset: Int, pos: Position, fieldSym: Symbol): Tree = { val sym = fieldSym.getterIn(fieldSym.owner) val bitmapSym = bitmapFor(clazz, offset, sym) val kind = bitmapKind(sym) val mask = maskForOffset(offset, sym, kind) val msg = s"Uninitialized field: ${unit.source}: ${pos.line}" val result = IF (mkTest(clazz, mask, bitmapSym, equalToZero = false, kind)) . THEN (retVal) . ELSE (Throw(NewFromConstructor(UninitializedFieldConstructor, LIT(msg)))) typedPos(pos)(BLOCK(result, retVal)) } /* Complete lazy field accessors. Applies only to classes, * for its own (non inherited) lazy fields. If 'checkinit' * is enabled, getters that check for the initialized bit are * generated, and the class constructor is changed to set the * initialized bits. */ def addInitCheck(clazz: Symbol)(stat: DefDef): DefDef = { val sym = stat.symbol if (!clazz.isTrait && sym.isLazy && stat.rhs != EmptyTree) { assert(fieldOffset contains sym, sym) deriveDefDef(stat) { case t if isUnitGetter(sym) => mkLazyMemberDef(clazz, sym, List(t), UNIT, fieldOffset(sym)) case Block(stats, res) => mkLazyMemberDef(clazz, sym, stats, Select(This(clazz), res.symbol), fieldOffset(sym)) case t => t // pass specialized lazy vals through } } else if (!settings.checkInit) stat else if (needsInitFlag(sym) && stat.rhs != EmptyTree && !clazz.hasFlag(TRAIT)) { assert(fieldOffset contains sym, sym) deriveDefDef(stat)(rhs => (mkCheckedAccessor(clazz, _: Tree, fieldOffset(sym), stat.pos, sym)) ( if (isUnitGetter(sym)) UNIT else rhs ) ) } else if (sym.isConstructor) { deriveDefDef(stat)(addInitBits(clazz, _)) } else if (!clazz.isTrait && sym.isSetter) { val getter = sym.getterIn(clazz) if (needsInitFlag(getter) && fieldOffset.isDefinedAt(getter)) deriveDefDef(stat)(rhs => Block(List(rhs, localTyper.typed(mkSetFlag(clazz, fieldOffset(getter), getter, bitmapKind(getter)))), UNIT)) else stat } else stat } // @pre settings.checkInit class AddInitBitsTransformer(clazz: Symbol) extends Transformer { private def checkedGetter(lhs: Tree) = { val sym = clazz.info decl lhs.symbol.getterName suchThat (_.isGetter) if (needsInitFlag(sym) && (fieldOffset contains sym)) { debuglog("adding checked getter for: " + sym + " " + lhs.symbol.flagString) List(localTyper typed mkSetFlag(clazz, fieldOffset(sym), sym, bitmapKind(sym))) } else Nil } override def transformStats(stats: List[Tree], exprOwner: Symbol) = { // !!! Ident(self) is never referenced, is it supposed to be confirming // that self is anything in particular? super.transformStats( stats flatMap { case stat @ Assign(lhs @ Select(This(_), _), rhs) => stat :: checkedGetter(lhs) // remove initialization for default values -- TODO is this case ever hit? constructors does not generate Assigns with EmptyTree for the rhs AFAICT case Apply(lhs @ Select(Ident(self), _), EmptyTree.asList) if lhs.symbol.isSetter => Nil case stat => List(stat) }, exprOwner ) } } /* Adds statements to set the 'init' bit for each field initialized * in the body of a constructor. * @pre settings.checkInit */ def addInitBits(clazz: Symbol, rhs: Tree): Tree = new AddInitBitsTransformer(clazz) transform rhs // begin addNewDefs /* Fill the map from fields to offset numbers. * Instead of field symbols, the map keeps their getter symbols. This makes * code generation easier later. */ def buildBitmapOffsets() { def fold(fields: List[Symbol], category: Name) = { var idx = 0 fields foreach { f => fieldOffset(f) = idx idx += 1 } if (idx == 0) () else if (idx == 1) bitmapKindForCategory(category) = BooleanClass else if (idx < 9) bitmapKindForCategory(category) = ByteClass else if (idx < 33) bitmapKindForCategory(category) = IntClass else bitmapKindForCategory(category) = LongClass } clazz.info.decls.toList groupBy bitmapCategory foreach { case (nme.NO_NAME, _) => () case (category, fields) => fold(fields, category) } } buildBitmapOffsets() var stats1 = stats mapConserve { case dd: DefDef => addInitCheck(clazz)(dd) case stat => stat } def getterBody(getter: Symbol) = { assert(getter.isGetter) val readValue = { assert(getter.hasFlag(PARAMACCESSOR)) fieldAccess(getter) } if (!(settings.checkInit && needsInitFlag(getter))) readValue else mkCheckedAccessor(clazz, readValue, fieldOffset(getter), getter.pos, getter) } def setterBody(setter: Symbol) = { val getter = setter.getterIn(clazz) assert(getter.hasFlag(PARAMACCESSOR), s"missing implementation for non-paramaccessor $setter in $clazz") val setInitFlag = if (!(settings.checkInit && needsInitFlag(getter))) Nil else List(mkSetFlag(clazz, fieldOffset(getter), getter, bitmapKind(getter))) Block(Assign(fieldAccess(setter), Ident(setter.firstParam)) :: setInitFlag : _*) } def fieldAccess(accessor: Symbol) = Select(This(clazz), accessor.accessed) // for all symbols `sym` in the class definition, which are mixed in by mixinTraitMembers for (sym <- clazz.info.decls ; if sym hasFlag MIXEDIN) { // if current class is a trait, add an abstract method for accessor `sym` // ditto for a super accessor (will get an RHS in completeSuperAccessor) if (clazz.isTrait || sym.isSuperAccessor) addDefDef(sym) // implement methods mixed in from a supertrait (the symbols were created by mixinTraitMembers) else if (sym.hasFlag(ACCESSOR) && !sym.hasFlag(DEFERRED)) { assert(sym hasFlag (PARAMACCESSOR), s"mixed in $sym from $clazz is not lazy/param?!?") // add accessor definitions addDefDef(sym, if (sym.isSetter) setterBody(sym) else getterBody(sym)) } else if (!sym.isMethod) addValDef(sym) // field else if (!sym.isMacro) { // forwarder assert(sym.alias != NoSymbol, (sym, sym.debugFlagString, clazz)) // debuglog("New forwarder: " + sym.defString + " => " + sym.alias.defString) addDefDef(sym, Apply(SuperSelect(clazz, sym.alias), sym.paramss.head.map(Ident(_)))) } } stats1 = add(stats1, newDefs.toList) if (clazz.isTrait) stats1 = stats1.filter { case vd: ValDef => assert(vd.symbol.hasFlag(PRESUPER | PARAMACCESSOR), s"unexpected valdef $vd in trait $clazz") false case _ => true } if (!clazz.isTrait) stats1 = stats1 map completeSuperAccessor stats1 } private def nullableFields(templ: Template): Map[Symbol, Set[Symbol]] = { val scope = templ.symbol.owner.info.decls // if there are no lazy fields, take the fast path and save a traversal of the whole AST if (scope exists (_.isLazy)) { val map = mutable.Map[Symbol, Set[Symbol]]() withDefaultValue Set() // check what fields can be nulled for for ((field, users) <- singleUseFields(templ); lazyFld <- users if !lazyFld.accessed.hasAnnotation(TransientAttr)) map(lazyFld) += field map.toMap } else Map() } /** The transform that gets applied to a tree after it has been completely * traversed and possible modified by a preTransform. * This step will * - change parents of templates to conform to parents in the symbol info * - add all new definitions to a class or interface * - remove widening casts * - change calls to methods which are defined only in implementation classes * to static calls of methods in implementation modules (@see staticCall) * - change super calls to methods in implementation classes to static calls * (@see staticCall) */ private def postTransform(tree: Tree): Tree = { val sym = tree.symbol tree match { case templ @ Template(parents, self, body) => // change parents of templates to conform to parents in the symbol info val parents1 = currentOwner.info.parents map (t => TypeTree(t) setPos tree.pos) // mark fields which can be nulled afterward lazyValNullables = nullableFields(templ) withDefaultValue Set() // add all new definitions to current class or interface val statsWithNewDefs = addNewDefs(currentOwner, body) statsWithNewDefs foreach { case dd: DefDef if isTraitMethodRequiringStaticImpl(dd) => dd.symbol.updateAttachment(NeedStaticImpl) case _ => } treeCopy.Template(tree, parents1, self, statsWithNewDefs) case Select(qual, name) if sym.owner.isTrait && !sym.isMethod => assert(sym.hasFlag(PARAMACCESSOR | PRESUPER), s"!!! Unexpected reference to field $sym in trait $currentOwner") // refer to fields in some trait an abstract getter in the interface. val ifaceGetter = sym getterIn sym.owner if (ifaceGetter == NoSymbol) abort("No getter for " + sym + " in " + sym.owner) else typedPos(tree.pos)((qual DOT ifaceGetter)()) case Assign(Apply(lhs @ Select(qual, _), List()), rhs) => // assign to fields in some trait via an abstract setter in the interface. // Note that the case above has added the empty application. val setter = lhs.symbol.setterIn(lhs.symbol.owner.tpe.typeSymbol) setPos lhs.pos typedPos(tree.pos)((qual DOT setter)(rhs)) case _ => tree } } /** The main transform method. * This performs pre-order traversal preTransform at mixin phase; * when coming back, it performs a postTransform at phase after. */ override def transform(tree: Tree): Tree = { val saved = localTyper val tree1 = super.transform(preTransform(tree)) // localTyper needed when not flattening inner classes. parts after an // inner class will otherwise be typechecked with a wrong scope try exitingMixin(postTransform(tree1)) finally localTyper = saved } } private def isTraitMethodRequiringStaticImpl(dd: DefDef): Boolean = { val sym = dd.symbol dd.rhs.nonEmpty && sym.owner.isTrait && !sym.isPrivate && // no need to put implementations of private methods into a static method !sym.hasFlag(Flags.STATIC) } case object NeedStaticImpl extends PlainAttachment }