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Diffstat (limited to 'src/compiler/scala/tools/nsc/transform/Fields.scala')
| -rw-r--r-- | src/compiler/scala/tools/nsc/transform/Fields.scala | 787 |
1 files changed, 787 insertions, 0 deletions
diff --git a/src/compiler/scala/tools/nsc/transform/Fields.scala b/src/compiler/scala/tools/nsc/transform/Fields.scala new file mode 100644 index 0000000000..b2bf9fad3f --- /dev/null +++ b/src/compiler/scala/tools/nsc/transform/Fields.scala @@ -0,0 +1,787 @@ +/* NSC -- new Scala compiler + * Copyright 2005-2013 LAMP/EPFL + * @author + */ + +package scala.tools.nsc +package transform + +import scala.annotation.tailrec +import symtab.Flags._ + + +/** Synthesize accessors, fields (and bitmaps) for (lazy) vals and modules. + * + * During Namers, a `ValDef` that is `lazy`, deferred and/or defined in a trait carries its getter's symbol. + * The underlying field symbol does not exist until this phase. + * + * For `val`s defined in classes, we still emit a field immediately. + * TODO: uniformly assign getter symbol to all `ValDef`s, stop using `accessed`. + * + * This phase synthesizes accessors, fields and bitmaps (for lazy or init-checked vals under -Xcheckinit) + * in the first (closest in the subclassing lattice) subclass (not a trait) of a trait. + * + * For lazy vals and modules, we emit accessors that using double-checked locking (DCL) to balance thread safety + * and performance. For both lazy vals and modules, the a compute method contains the DCL's slow path. + * + * Local lazy vals do not receive bitmaps, but use a Lazy*Holder that has the volatile init bit and the computed value. + * See `mkLazyLocalDef`. + * + * Constructors will move the rhs to an assignment in the template body. + * Those statements then move to the template into the constructor, + * which means it will initialize the fields defined in this template (and execute the corresponding side effects). + * We need to maintain the connection between getter and rhs until after specialization so that it can duplicate vals. + * + * A ModuleDef is desugared to a ClassDef, an accessor (which reuses the module's term symbol) + * and a module var (unless the module is static and does not implement a member of a supertype, or we're in a trait). + * + * For subclasses of traits that define modules, a module var is mixed in, as well as the required module accessors. + * + * Phase ordering: + * - Runs after uncurry to deal with classes that implement SAM traits with ValDefs. + * - Runs before erasure (to get bridges), and thus before lambdalift/flatten, so that nested functions/definitions must be considered. + * - Lambdalift introduces new paramaccessors for captured vals, but runs too late in the pipeline, so + * mixins still synthesizes implementations for these accessors when a local trait that captures is subclassed. + * + * + * In the future, would like to get closer to dotty, which lifts a val's RHS (a similar thing is done for template-level statements) + * to a method `$_initialize_$1$x` instead of a block, which is used in the constructor to initialize the val. + * This makes for a nice unification of strict and lazy vals, in that the RHS is lifted to a method for both, + * with the corresponding compute method called at the appropriate time.) + * + * This only reduces the required number of methods per field declaration in traits, + * if we encode the name (and place in initialisation order) of the field + * in the name of its initializing method, to allow separate compilation. + * (The name mangling must include ordering, and thus complicate incremental compilation: + * ideally, we'd avoid renumbering unchanged methods, but that would result in + * different bytecode between clean recompiles and incremental ones). + * + * In the even longer term (Scala 3?), I agree with @DarkDimius that it would make sense + * to hide the difference between strict and lazy vals. All vals are lazy, + * but the memoization overhead is removed when we statically know they are forced during initialization. + * We could still expose the low-level field semantics through `private[this] val`s. + * + * In any case, the current behavior of overriding vals is pretty surprising. + * An overridden val's side-effect is still performed. + * The only change due to overriding is that its value is never written to the field + * (the overridden val's value is, of course, stored in the field in addition to its side-effect being performed). + * + * TODO: Java 9 support for vals defined in traits. They are currently emitted as final, + * but the write (putfield) to the val does not occur syntactically within the <init> method + * (it's done by the trait setter, which is called from the trait's mixin constructor, + * which is called from the subclass's constructor...) + */ +abstract class Fields extends InfoTransform with ast.TreeDSL with TypingTransformers with AccessorSynthesis { + import global._ + import definitions._ + + /** the following two members override abstract members in Transform */ + val phaseName: String = "fields" + + protected def newTransformer(unit: CompilationUnit): Transformer = new FieldsTransformer(unit) + override def transformInfo(sym: Symbol, tp: Type): Type = + if (sym.isJavaDefined || sym.isPackageClass || !sym.isClass) tp + else synthFieldsAndAccessors(tp) + + // TODO: drop PRESUPER support when we implement trait parameters in 2.13 + private def excludedAccessorOrFieldByFlags(statSym: Symbol): Boolean = statSym hasFlag PRESUPER + + // used for internal communication between info and tree transform of this phase -- not pickled, not in initialflags + // TODO: reuse MIXEDIN for NEEDS_TREES? + override def phaseNewFlags: Long = NEEDS_TREES | OVERRIDDEN_TRAIT_SETTER + + // informs the tree traversal of the shape of the tree to emit + // (it's an *overridden* trait setter) + private final val OVERRIDDEN_TRAIT_SETTER = TRANS_FLAG + + final val TRAIT_SETTER_FLAGS = NEEDS_TREES | DEFERRED | ProtectedLocal + + private def accessorImplementedInSubclass(accessor: Symbol) = + (accessor hasFlag SYNTHESIZE_IMPL_IN_SUBCLASS) && (accessor hasFlag (ACCESSOR | MODULE)) + + @inline final def notDeferredOrSynthImpl(sym: Symbol): Boolean = !(sym hasFlag DEFERRED) || (sym hasFlag SYNTHESIZE_IMPL_IN_SUBCLASS) + + private def synthesizeImplInSubclasses(accessor: Symbol): Unit = + accessor setFlag SYNTHESIZE_IMPL_IN_SUBCLASS + + private def setClonedTraitSetterFlags(clazz: Symbol, correspondingGetter: Symbol, cloneInSubclass: Symbol): Unit = { + val overridden = isOverriddenAccessor(correspondingGetter, clazz) + if (overridden) cloneInSubclass setFlag OVERRIDDEN_TRAIT_SETTER + else if (correspondingGetter.isEffectivelyFinal) cloneInSubclass setFlag FINAL + } + + // TODO: add MIXEDIN (see e.g., `accessed` on `Symbol`) + private def setMixedinAccessorFlags(orig: Symbol, cloneInSubclass: Symbol): Unit = + cloneInSubclass setFlag OVERRIDE | NEEDS_TREES resetFlag DEFERRED | SYNTHESIZE_IMPL_IN_SUBCLASS + + private def setFieldFlags(accessor: Symbol, fieldInSubclass: TermSymbol): Unit = + fieldInSubclass setFlag (NEEDS_TREES | + PrivateLocal + | (accessor getFlag MUTABLE | LAZY) + | (if (accessor hasFlag STABLE) 0 else MUTABLE) + ) + + + def checkAndClearOverriddenTraitSetter(setter: Symbol) = checkAndClear(OVERRIDDEN_TRAIT_SETTER)(setter) + def checkAndClearNeedsTrees(setter: Symbol) = checkAndClear(NEEDS_TREES)(setter) + def checkAndClear(flag: Long)(sym: Symbol) = + sym.hasFlag(flag) match { + case overridden => + sym resetFlag flag + overridden + } + + + private def isOverriddenAccessor(member: Symbol, site: Symbol): Boolean = { + val pre = site.thisType + @tailrec def loop(bcs: List[Symbol]): Boolean = { + // println(s"checking ${bcs.head} for member overriding $member (of ${member.owner})") + bcs.nonEmpty && bcs.head != member.owner && (matchingAccessor(pre, member, bcs.head) != NoSymbol || loop(bcs.tail)) + } + + member.exists && loop(site.info.baseClasses) + } + + + def matchingAccessor(pre: Type, member: Symbol, clazz: Symbol) = { + val res = member.matchingSymbol(clazz, pre) filter (sym => (sym hasFlag ACCESSOR) && notDeferredOrSynthImpl(sym)) + // if (res != NoSymbol) println(s"matching accessor for $member in $clazz = $res (under $pre)") + // else println(s"no matching accessor for $member in $clazz (under $pre) among ${clazz.info.decls}") + res + } + + + class FieldMemoization(accessorOrField: Symbol, site: Symbol) { + val tp = fieldTypeOfAccessorIn(accessorOrField, site.thisType) + // We can only omit strict vals of ConstantType. Lazy vals do not receive constant types (anymore). + // (See note at widenIfNecessary -- for example, the REPL breaks when we omit constant lazy vals) + // Note that a strict unit-typed val does receive a field, because we cannot omit the write to the field + // (well, we could emit it for non-@volatile ones, if I understand the memory model correctly, + // but that seems pretty edge-casey) + val constantTyped = tp.isInstanceOf[ConstantType] + } + + private def fieldTypeForGetterIn(getter: Symbol, pre: Type): Type = getter.info.finalResultType.asSeenFrom(pre, getter.owner) + private def fieldTypeForSetterIn(setter: Symbol, pre: Type): Type = setter.info.paramTypes.head.asSeenFrom(pre, setter.owner) + + // TODO: is there a more elegant way? + def fieldTypeOfAccessorIn(accessor: Symbol, pre: Type) = + if (accessor.isSetter) fieldTypeForSetterIn(accessor, pre) + else fieldTypeForGetterIn(accessor, pre) + + + // Constant/unit typed vals are not memoized (their value is so cheap it doesn't make sense to store it in a field) + // for a unit-typed getter, we perform the effect at the appropriate time (constructor for eager ones, lzyCompute for lazy), + // and have the getter just return Unit (who does that!?) + // NOTE: this only considers type, filter on flags first! + def fieldMemoizationIn(accessorOrField: Symbol, site: Symbol) = new FieldMemoization(accessorOrField, site) + + // drop field-targeting annotations from getters (done during erasure because we first need to create the field symbol) + // (in traits, getters must also hold annotations that target the underlying field, + // because the latter won't be created until the trait is mixed into a class) + // TODO do bean getters need special treatment to suppress field-targeting annotations in traits? + def dropFieldAnnotationsFromGetter(sym: Symbol) = + sym setAnnotations (sym.annotations filter AnnotationInfo.mkFilter(GetterTargetClass, defaultRetention = false)) + + def symbolAnnotationsTargetFieldAndGetter(sym: Symbol): Boolean = sym.isGetter && (sym.isLazy || sym.owner.isTrait) + + // A trait val/var or a lazy val does not receive an underlying field symbol until this phase. + // Since annotations need a carrier symbol from the beginning, both field- and getter-targeting annotations + // are kept on the getter symbol for these until they are dropped by dropFieldAnnotationsFromGetter + def getterTreeAnnotationsTargetFieldAndGetter(owner: Symbol, mods: Modifiers) = mods.isLazy || owner.isTrait + + // Propagate field-targeting annotations from getter to field. + // By the way, we must keep them around long enough to see them here (now that we have created the field), + // which is why dropFieldAnnotationsFromGetter is not called until erasure. + private def propagateFieldAnnotations(getter: Symbol, field: TermSymbol): Unit = + field setAnnotations (getter.annotations filter AnnotationInfo.mkFilter(FieldTargetClass, defaultRetention = true)) + + + // can't use the referenced field since it already tracks the module's moduleClass + private[this] val moduleOrLazyVarOf = perRunCaches.newMap[Symbol, Symbol] + + // TODO: can we drop FINAL? In any case, since these variables are MUTABLE, they cannot and will + // not be emitted as ACC_FINAL. They are FINAL in the Scala sense, though: cannot be overridden. + private final val ModuleOrLazyFieldFlags = FINAL | PrivateLocal | SYNTHETIC | NEEDS_TREES + + private def moduleInit(module: Symbol, moduleVar: Symbol) = { +// println(s"moduleInit for $module in ${module.ownerChain} --> ${moduleVarOf.get(module)}") + def moduleVarRef = gen.mkAttributedRef(moduleVar) + + // for local modules, we synchronize on the owner of the method that owns the module + val monitorHolder = This(moduleVar.owner.enclClass) + def needsInit = Apply(Select(moduleVarRef, Object_eq), List(CODE.NULL)) + val init = Assign(moduleVarRef, gen.newModule(module, moduleVar.info)) + + /** double-checked locking following https://shipilev.net/blog/2014/safe-public-construction/#_safe_publication + * + * public class SafeDCLFactory { + * private volatile Singleton instance; + * + * public Singleton get() { + * if (instance == null) { // check 1 + * synchronized(this) { + * if (instance == null) { // check 2 + * instance = new Singleton(); + * } + * } + * } + * return instance; + * } + * } + * + * TODO: optimize using local variable? + */ + val computeName = nme.newLazyValSlowComputeName(module.name) + val computeMethod = DefDef(NoMods, computeName, Nil, ListOfNil, TypeTree(UnitTpe), gen.mkSynchronized(monitorHolder)(If(needsInit, init, EmptyTree))) + Block(computeMethod :: If(needsInit, Apply(Ident(computeName), Nil), EmptyTree) :: Nil, + gen.mkCast(moduleVarRef, module.info.resultType)) + } + + // NoSymbol for lazy accessor sym with unit result type + def lazyVarOf(sym: Symbol) = moduleOrLazyVarOf.getOrElse(sym, NoSymbol) + + private def newLazyVarMember(clazz: Symbol, member: Symbol, tp: Type): TermSymbol = { + val flags = LAZY | (member.flags & FieldFlags) | ModuleOrLazyFieldFlags + val name = member.name.toTermName.append(reflect.NameTransformer.LOCAL_SUFFIX_STRING) + + // Set the MUTABLE flag because the field cannot be ACC_FINAL since we write to it outside of a constructor. + val sym = clazz.newVariable(name, member.pos.focus, flags) setInfo tp + + moduleOrLazyVarOf(member) = sym + sym + } + + + private object synthFieldsAndAccessors extends TypeMap { + private def newTraitSetter(getter: Symbol, clazz: Symbol) = { + // Add setter for an immutable, memoizing getter + // (can't emit during namers because we don't yet know whether it's going to be memoized or not) + val setterFlags = (getter.flags & ~(STABLE | PrivateLocal | OVERRIDE | IMPLICIT | FINAL)) | MUTABLE | ACCESSOR | TRAIT_SETTER_FLAGS + val setterName = nme.expandedSetterName(getter.name.setterName, clazz) + val setter = clazz.newMethod(setterName, getter.pos.focus, setterFlags) + val fieldTp = fieldTypeForGetterIn(getter, clazz.thisType) + // println(s"newTraitSetter in $clazz for $getter = $setterName : $fieldTp") + + getter.asTerm.referenced = setter + + setter setInfo MethodType(List(setter.newSyntheticValueParam(fieldTp)), UnitTpe) + setter + } + + private def newModuleAccessor(module: Symbol, site: Symbol, moduleVar: Symbol) = { + val accessor = site.newMethod(module.name.toTermName, site.pos, STABLE | MODULE | NEEDS_TREES) + + moduleOrLazyVarOf(accessor) = moduleVar + + // we're in the same prefix as module, so no need for site.thisType.memberType(module) + accessor setInfo MethodType(Nil, moduleVar.info) + accessor.setModuleClass(module.moduleClass) + + if (module.isPrivate) accessor.expandName(module.owner) + + accessor + } + + // needed for the following scenario (T could be trait or class) + // trait T { def f: Object }; object O extends T { object f }. Need to generate method f in O. + // marking it as an ACCESSOR so that it will get to `getterBody` when synthesizing trees below + // it should not be considered a MODULE + def newMatchingModuleAccessor(clazz: Symbol, module: Symbol): MethodSymbol = { + val acc = clazz.newMethod(module.name.toTermName, module.pos, (module.flags & ~MODULE) | STABLE | NEEDS_TREES | ACCESSOR) + acc.referenced = module + acc setInfo MethodType(Nil, module.moduleClass.tpe) + } + + + private def newSuperLazy(lazyCallingSuper: Symbol, site: Type, lazyVar: Symbol) = { + lazyCallingSuper.asTerm.referenced = lazyVar + + val tp = site.memberInfo(lazyCallingSuper) + + lazyVar setInfo tp.resultType + lazyCallingSuper setInfo tp + } + + private def classNeedsInfoTransform(cls: Symbol): Boolean = { + !(cls.isPackageClass || cls.isJavaDefined) && (currentRun.compiles(cls) || refChecks.isSeparatelyCompiledScalaSuperclass(cls)) + } + + def apply(tp0: Type): Type = tp0 match { + // TODO: make less destructive (name changes, decl additions, flag setting -- + // none of this is actually undone when travelling back in time using atPhase) + case tp@ClassInfoType(parents, decls, clazz) if clazz.isTrait => + // setters for trait vars or module accessor + val newDecls = collection.mutable.ListBuffer[Symbol]() + val origDecls = decls.toList + + // strict, memoized accessors will receive an implementation in first real class to extend this trait + origDecls.foreach { member => + if (member hasFlag ACCESSOR) { + val fieldMemoization = fieldMemoizationIn(member, clazz) + // check flags before calling makeNotPrivate + val accessorUnderConsideration = !(member hasFlag DEFERRED) + + // destructively mangle accessor's name (which may cause rehashing of decls), also sets flags + // this accessor has to be implemented in a subclass -- can't be private + if ((member hasFlag PRIVATE) && !fieldMemoization.constantTyped) member makeNotPrivate clazz + // Since we need to refer to `member` using a super call in a subclass, we must ensure that access is allowed. + // If `member` has an access boundary, make sure the `PROTECTED` flag is set, + // to widen from `private[foo]` to `protected[foo]` + // (note that `member.hasAccessBoundary` implies `!member.hasFlag(PRIVATE)`, so we don't have to `resetFlag PRIVATE`) + else if (member.isLazy && member.hasAccessBoundary) member setFlag PROTECTED + + // This must remain in synch with publicizeTraitMethod in Mixins, so that the + // synthesized member in a subclass and the trait member remain in synch regarding access. + // Otherwise, the member will not be seen as overriding the trait member, and `addForwarders`'s call to + // `membersBasedOnFlags` would see the deferred member in the trait, instead of the concrete (desired) one in the class + // not doing: if (member hasFlag PROTECTED) member setFlag notPROTECTED + + // must not reset LOCAL, as we must maintain protected[this]ness to allow that variance hole + // (not sure why this only problem only arose when we started setting the notPROTECTED flag) + + // derive trait setter after calling makeNotPrivate (so that names are mangled consistently) + if (accessorUnderConsideration && !fieldMemoization.constantTyped) { + synthesizeImplInSubclasses(member) + + if ((member hasFlag STABLE) && !(member hasFlag LAZY)) + newDecls += newTraitSetter(member, clazz) + } + } else if (member hasFlag MODULE) { + nonStaticModuleToMethod(member) + + member setFlag NEEDS_TREES + synthesizeImplInSubclasses(member) + } + } + + if (newDecls nonEmpty) { + val allDecls = newScope + origDecls foreach allDecls.enter + newDecls foreach allDecls.enter + ClassInfoType(parents, allDecls, clazz) + } else tp + + + case tp@ClassInfoType(parents, oldDecls, clazz) if !classNeedsInfoTransform(clazz) => tp + + // mix in fields & accessors for all mixed in traits + case tp@ClassInfoType(parents, oldDecls, clazz) => + + val site = clazz.thisType + + // setter conflicts cannot arise independently from a getter conflict, since a setter without a getter does not a val definition make + def getterConflictsExistingVal(getter: Symbol): Boolean = + getter.isGetter && { + val existingGetter = oldDecls.lookup(getter.name) + (existingGetter ne NoSymbol) && + ((site memberInfo existingGetter) matches (site memberInfo getter)) + } + + def newModuleVarMember(module: Symbol): TermSymbol = { + val moduleVar = + (clazz.newVariable(nme.moduleVarName(module.name.toTermName), module.pos.focus, MODULEVAR | ModuleOrLazyFieldFlags) + setInfo site.memberType(module).resultType + addAnnotation VolatileAttr) + + moduleOrLazyVarOf(module) = moduleVar + + moduleVar + } + + def newLazyVarMember(member: Symbol): TermSymbol = + Fields.this.newLazyVarMember(clazz, member, site.memberType(member).resultType) + + // a module does not need treatment here if it's static, unless it has a matching member in a superclass + // a non-static method needs a module var + val modulesAndLazyValsNeedingExpansion = + oldDecls.toList.filter(m => (m.isModule && (!m.isStatic || m.isOverridingSymbol)) || m.isLazy) + + val accessorSymbolSynth = checkedAccessorSymbolSynth(tp.typeSymbol) + + // expand module def in class/object (if they need it -- see modulesNeedingExpansion above) + val expandedModulesAndLazyVals = + modulesAndLazyValsNeedingExpansion flatMap { member => + if (member.isLazy) { + val lazyVar = newLazyVarMember(member) + propagateFieldAnnotations(member, lazyVar) + List(lazyVar, accessorSymbolSynth.newSlowPathSymbol(member)) + } + // expanding module def (top-level or nested in static module) + else List(if (member.isStatic) { // implies m.isOverridingSymbol as per above filter + // Need a module accessor, to implement/override a matching member in a superclass. + // Never a need for a module var if the module is static. + newMatchingModuleAccessor(clazz, member) + } else { + nonStaticModuleToMethod(member) + // must reuse symbol instead of creating an accessor + member setFlag NEEDS_TREES + newModuleVarMember(member) + }) + } + +// println(s"expanded modules for $clazz: $expandedModules") + + // afterOwnPhase, so traits receive trait setters for vals (needs to be at finest grain to avoid looping) + val synthInSubclass = + clazz.mixinClasses.flatMap(mixin => afterOwnPhase{mixin.info}.decls.toList.filter(accessorImplementedInSubclass)) + + // mixin field accessors -- + // invariant: (accessorsMaybeNeedingImpl, mixedInAccessorAndFields).zipped.forall(case (acc, clone :: _) => `clone` is clone of `acc` case _ => true) + val mixedInAccessorAndFields = synthInSubclass.map{ member => + def cloneAccessor() = { + val clonedAccessor = (member cloneSymbol clazz) setPos clazz.pos + setMixedinAccessorFlags(member, clonedAccessor) + + // note: check original member when deciding how to triage annotations, then act on the cloned accessor + if (symbolAnnotationsTargetFieldAndGetter(member)) // this simplifies to member.isGetter, but the full formulation really ties the triage together + dropFieldAnnotationsFromGetter(clonedAccessor) + + // if we don't cloneInfo, method argument symbols are shared between trait and subclasses --> lambalift proxy crash + // TODO: use derive symbol variant? +// println(s"cloning accessor $member to $clazz") + // start at uncurry so that we preserve that part of the history where an accessor has a NullaryMethodType + enteringUncurry { clonedAccessor setInfo ((clazz.thisType memberType member) cloneInfo clonedAccessor) } + clonedAccessor + } + + // when considering whether to mix in the trait setter, forget about conflicts -- they are reported for the getter + // a trait setter for an overridden val will receive a unit body in the tree transform + if (nme.isTraitSetterName(member.name)) { + val getter = member.getterIn(member.owner) + val clone = cloneAccessor() + + setClonedTraitSetterFlags(clazz, getter, clone) + // println(s"mixed in trait setter ${clone.defString}") + + List(clone) + } + // don't cause conflicts, skip overridden accessors contributed by supertraits (only act on the last overriding one) + // see pos/trait_fields_dependent_conflict.scala and neg/t1960.scala + else if (getterConflictsExistingVal(member) || isOverriddenAccessor(member, clazz)) Nil + else if (member hasFlag MODULE) { + val moduleVar = newModuleVarMember(member) + List(moduleVar, newModuleAccessor(member, clazz, moduleVar)) + } + else if (member hasFlag LAZY) { + val mixedinLazy = cloneAccessor() + val lazyVar = newLazyVarMember(mixedinLazy) // link lazy var member to the mixedin lazy accessor + + // propagate from original member. since mixed in one has only retained the annotations targeting the getter + propagateFieldAnnotations(member, lazyVar) + + // println(s"mixing in lazy var: $lazyVar for $member") + List(lazyVar, accessorSymbolSynth.newSlowPathSymbol(mixedinLazy), newSuperLazy(mixedinLazy, site, lazyVar)) + } + else if (member.isGetter && !fieldMemoizationIn(member, clazz).constantTyped) { + // add field if needed + val field = clazz.newValue(member.localName, member.pos) setInfo fieldTypeForGetterIn(member, clazz.thisType) + + setFieldFlags(member, field) + + propagateFieldAnnotations(member, field) + + List(cloneAccessor(), field) + } else List(cloneAccessor()) // no field needed (constant-typed getter has constant as its RHS) + } + + // println(s"mixedInAccessorAndFields for $clazz: $mixedInAccessorAndFields") + + // omit fields that are not memoized, retain all other members + def omittableField(sym: Symbol) = sym.isValue && !sym.isMethod && fieldMemoizationIn(sym, clazz).constantTyped + + val newDecls = + // under -Xcheckinit we generate all kinds of bitmaps, even when there are no lazy vals + if (expandedModulesAndLazyVals.isEmpty && mixedInAccessorAndFields.isEmpty && !settings.checkInit) + oldDecls.filterNot(omittableField) + else { + // must not alter `decls` directly + val newDecls = newScope + val enter = newDecls enter (_: Symbol) + val enterAll = (_: List[Symbol]) foreach enter + + expandedModulesAndLazyVals foreach enter + oldDecls foreach { d => if (!omittableField(d)) enter(d) } + mixedInAccessorAndFields foreach enterAll + + // both oldDecls and mixedInAccessorAndFields (a list of lists) contribute + val bitmapSyms = accessorSymbolSynth.computeBitmapInfos(newDecls.toList) + + bitmapSyms foreach enter + + newDecls + } + + // println(s"new decls for $clazz: $expandedModules ++ $mixedInAccessorAndFields") + + if (newDecls eq oldDecls) tp + else ClassInfoType(parents, newDecls, clazz) + + case tp => mapOver(tp) + } + } + + + // done by uncurry's info transformer + // instead of forcing every member's info to run said transformer, duplicate the flag update logic... + def nonStaticModuleToMethod(module: Symbol): Unit = + if (!module.isStatic) module setFlag METHOD | STABLE + + // scala/scala-dev#219, scala/scala-dev#268 + // Cast to avoid spurious mismatch in paths containing trait vals that have + // not been rebound to accessors in the subclass we're in now. + // For example, for a lazy val mixed into a class, the lazy var's info + // will not refer to symbols created during our info transformer, + // so if its type depends on a val that is now implemented after the info transformer, + // we'll get a mismatch when assigning `rhs` to `lazyVarOf(getter)`. + // TODO: could we rebind more aggressively? consider overriding in type equality? + def castHack(tree: Tree, pt: Type) = gen.mkAsInstanceOf(tree, pt) + + class FieldsTransformer(unit: CompilationUnit) extends TypingTransformer(unit) with CheckedAccessorTreeSynthesis { + protected def typedPos(pos: Position)(tree: Tree): Tree = localTyper.typedPos(pos)(tree) + + def mkTypedUnit(pos: Position) = typedPos(pos)(CODE.UNIT) + // TODO: clean up. this method is not used + def deriveUnitDef(stat: Tree) = deriveDefDef(stat)(_ => mkTypedUnit(stat.pos)) + + def mkAccessor(accessor: Symbol)(body: Tree) = typedPos(accessor.pos)(DefDef(accessor, body)).asInstanceOf[DefDef] + + // this makes trees for mixed in fields, as well as for bitmap fields (their RHS will be EmptyTree because they are initialized implicitly) + // if we decide to explicitly initialize, use this RHS: if (symbol.info.typeSymbol.asClass == BooleanClass) FALSE else ZERO) + // could detect it's a bitmap field with something like `sym.name.startsWith(nme.BITMAP_PREFIX)` (or perhaps something more robust...) + def mkTypedValDef(sym: Symbol, rhs: Tree = EmptyTree) = typedPos(sym.pos)(ValDef(sym, rhs)).asInstanceOf[ValDef] + + /** + * Desugar a local `lazy val x: Int = rhs` + * or a local `object x { ...}` (the rhs will be instantiating the module's class) into: + * + * ``` + * val x$lzy = new scala.runtime.LazyInt() + * def x$lzycompute(): Int = + * x$lzy.synchronized { + * if (x$lzy.initialized()) x$lzy.value() + * else x$lzy.initialize(rhs) // for a Unit-typed lazy val, this becomes `{ rhs ; x$lzy.initialize() }` to avoid passing around BoxedUnit + * } + * def x(): Int = if (x$lzy.initialized()) x$lzy.value() else x$lzycompute() + * ``` + * + * The expansion is the same for local lazy vals and local objects, + * except for the suffix of the underlying val's name ($lzy or $module) + */ + private def mkLazyLocalDef(lazySym: Symbol, rhs: Tree): Tree = { + import CODE._ + import scala.reflect.{NameTransformer => nx} + val owner = lazySym.owner + + val lazyValType = lazySym.tpe.resultType + val refClass = lazyHolders.getOrElse(lazyValType.typeSymbol, LazyRefClass) + val isUnit = refClass == LazyUnitClass + val refTpe = if (refClass != LazyRefClass) refClass.tpe else appliedType(refClass.typeConstructor, List(lazyValType)) + + val lazyName = lazySym.name.toTermName + val pos = lazySym.pos.focus + + val localLazyName = lazyName append (if (lazySym.isModule) nx.MODULE_VAR_SUFFIX_STRING else nx.LAZY_LOCAL_SUFFIX_STRING) + + // The lazy holder val need not be mutable, as we write to its field. + // In fact, it MUST not be mutable to avoid capturing it as an ObjectRef in lambdalift + // Must be marked LAZY to allow forward references, as in `def test2 { println(s.length) ; lazy val s = "abc" } + val holderSym = owner.newValue(localLazyName, pos, LAZY | ARTIFACT) setInfo refTpe + + val initializedSym = refTpe.member(nme.initialized) + val initializeSym = refTpe.member(nme.initialize) + + // LazyUnit does not have a `value` member + val valueSym = if (isUnit) NoSymbol else refTpe.member(nme.value) + + def initialized = Select(Ident(holderSym), initializedSym) + def initialize = Select(Ident(holderSym), initializeSym) + def getValue = if (isUnit) UNIT else Apply(Select(Ident(holderSym), valueSym), Nil) + + val computerSym = + owner.newMethod(lazyName append nme.LAZY_SLOW_SUFFIX, pos, ARTIFACT | PRIVATE) setInfo MethodType(Nil, lazyValType) + + val rhsAtComputer = rhs.changeOwner(lazySym -> computerSym) + + val computer = mkAccessor(computerSym)(gen.mkSynchronized(Ident(holderSym))( + If(initialized, getValue, + if (isUnit) Block(rhsAtComputer :: Nil, Apply(initialize, Nil)) + else Apply(initialize, rhsAtComputer :: Nil)))) + + val accessor = mkAccessor(lazySym)( + If(initialized, getValue, + Apply(Ident(computerSym), Nil))) + + // do last! + // remove STABLE: prevent replacing accessor call of type Unit by BoxedUnit.UNIT in erasure + // remove ACCESSOR: prevent constructors from eliminating the method body if the lazy val is + // lifted into a trait (TODO: not sure about the details here) + lazySym.resetFlag(STABLE | ACCESSOR) + + Thicket(mkTypedValDef(holderSym, New(refTpe)) :: computer :: accessor :: Nil) + } + + // synth trees for accessors/fields and trait setters when they are mixed into a class + def fieldsAndAccessors(clazz: Symbol): List[Tree] = { + + // Could be NoSymbol, which denotes an error, but it's refchecks' job to report it (this fallback is for robustness). + // This is the result of overriding a val with a def, so that no field is found in the subclass. + def fieldAccess(accessor: Symbol): Symbol = + afterOwnPhase { clazz.info.decl(accessor.localName) } + + def getterBody(getter: Symbol): Tree = + // accessor created by newMatchingModuleAccessor for a static module that does need an accessor + // (because there's a matching member in a super class) + if (getter.asTerm.referenced.isModule) + mkAccessor(getter)(castHack(Select(This(clazz), getter.asTerm.referenced), getter.info.resultType)) + else { + val fieldMemoization = fieldMemoizationIn(getter, clazz) + // TODO: drop getter for constant? (when we no longer care about producing identical bytecode?) + if (fieldMemoization.constantTyped) mkAccessor(getter)(gen.mkAttributedQualifier(fieldMemoization.tp)) + else fieldAccess(getter) match { + case NoSymbol => EmptyTree + case fieldSel => mkAccessor(getter)(castHack(Select(This(clazz), fieldSel), getter.info.resultType)) + } + } + + // println(s"accessorsAndFieldsNeedingTrees for $templateSym: $accessorsAndFieldsNeedingTrees") + def setterBody(setter: Symbol): Tree = + // trait setter in trait + if (clazz.isTrait) mkAccessor(setter)(EmptyTree) + // trait setter for overridden val in class + else if (checkAndClearOverriddenTraitSetter(setter)) mkAccessor(setter)(mkTypedUnit(setter.pos)) + // trait val/var setter mixed into class + else fieldAccess(setter) match { + case NoSymbol => EmptyTree + case fieldSel => afterOwnPhase { // the assign only type checks after our phase (assignment to val) + mkAccessor(setter)(Assign(Select(This(clazz), fieldSel), castHack(Ident(setter.firstParam), fieldSel.info))) + } + } + + def moduleAccessorBody(module: Symbol): Tree = + // added during synthFieldsAndAccessors using newModuleAccessor + // a module defined in a trait by definition can't be static (it's a member of the trait and thus gets a new instance for every outer instance) + if (clazz.isTrait) mkAccessor(module)(EmptyTree) + // symbol created by newModuleAccessor for a (non-trait) class + else { + mkAccessor(module)(moduleInit(module, moduleOrLazyVarOf(module))) + } + + val synthAccessorInClass = new SynthLazyAccessorsIn(clazz) + def superLazy(getter: Symbol): Tree = { + assert(!clazz.isTrait) + // this contortion was the only way I can get the super select to be type checked correctly.. + // TODO: why does SelectSuper not work? + val selectSuper = Select(Super(This(clazz), tpnme.EMPTY), getter.name) + + val lazyVar = lazyVarOf(getter) + val rhs = castHack(Apply(selectSuper, Nil), lazyVar.info) + + synthAccessorInClass.expandLazyClassMember(lazyVar, getter, rhs) + } + + (afterOwnPhase { clazz.info.decls } toList) filter checkAndClearNeedsTrees map { + case module if module hasAllFlags (MODULE | METHOD) => moduleAccessorBody(module) + case getter if getter hasAllFlags (LAZY | METHOD) => superLazy(getter) + case setter if setter.isSetter => setterBody(setter) + case getter if getter.hasFlag(ACCESSOR) => getterBody(getter) + case field if !(field hasFlag METHOD) => mkTypedValDef(field) // vals/vars and module vars (cannot have flags PACKAGE | JAVA since those never receive NEEDS_TREES) + case _ => EmptyTree + } filterNot (_ == EmptyTree) // there will likely be many EmptyTrees, but perhaps no thicket blocks that need expanding + } + + def rhsAtOwner(stat: ValOrDefDef, newOwner: Symbol): Tree = + atOwner(newOwner)(super.transform(stat.rhs.changeOwner(stat.symbol -> newOwner))) + + override def transform(stat: Tree): Tree = { + val currOwner = currentOwner // often a class, but not necessarily + val statSym = stat.symbol + + /* + For traits, the getter has the val's RHS, which is already constant-folded. There is no valdef. + For classes, we still have the classic scheme of private[this] valdef + getter & setter that read/assign to the field. + + There are two axes: (1) is there a side-effect to the val (2) does the val need storage? + For a ConstantType, both answers are "no". (For a unit-typed field, there's a side-effect, but no storage needed.) + + All others (getter for trait field, valdef for class field) have their rhs moved to an initialization statement. + Trait accessors for stored fields are made abstract (there can be no field in a trait). + (In some future version, accessors for non-stored, but effectful fields, + would receive a constant rhs, as the effect is performed by the initialization statement. + We could do this for unit-typed fields, but have chosen not to for backwards compatibility.) + */ + stat match { + // TODO: consolidate with ValDef case + // TODO: defer replacing ConstantTyped tree by the corresponding constant until erasure + // (until then, trees should not be constant-folded -- only their type tracks the resulting constant) + // also remove ACCESSOR flag since there won't be an underlying field to access? + case DefDef(_, _, _, _, _, rhs) if (statSym hasFlag ACCESSOR) + && (rhs ne EmptyTree) && !excludedAccessorOrFieldByFlags(statSym) + && !currOwner.isTrait // we've already done this for traits.. the asymmetry will be solved by the above todo + && fieldMemoizationIn(statSym, currOwner).constantTyped => + deriveDefDef(stat)(_ => gen.mkAttributedQualifier(rhs.tpe)) + + // deferred val, trait val, lazy val (local or in class) + case vd@ValDef(mods, name, tpt, rhs) if vd.symbol.hasFlag(ACCESSOR) && treeInfo.noFieldFor(vd, currOwner) => + val transformedRhs = atOwner(statSym)(transform(rhs)) + + if (rhs == EmptyTree) mkAccessor(statSym)(EmptyTree) + else if (currOwner.isTrait) mkAccessor(statSym)(castHack(transformedRhs, statSym.info.resultType)) + else if (!currOwner.isClass) mkLazyLocalDef(vd.symbol, transformedRhs) + else { + // TODO: make `synthAccessorInClass` a field and update it in atOwner? + // note that `LazyAccessorTreeSynth` is pretty lightweight + // (it's just a bunch of methods that all take a `clazz` parameter, which is thus stored as a field) + val synthAccessorInClass = new SynthLazyAccessorsIn(currOwner) + synthAccessorInClass.expandLazyClassMember(lazyVarOf(statSym), statSym, transformedRhs) + } + + // drop the val for (a) constant (pure & not-stored) and (b) not-stored (but still effectful) fields + case ValDef(mods, _, _, rhs) if (rhs ne EmptyTree) && !excludedAccessorOrFieldByFlags(statSym) + && currOwner.isClass && fieldMemoizationIn(statSym, currOwner).constantTyped => + EmptyThicket + + case ModuleDef(_, _, impl) => + // ??? The typer doesn't take kindly to seeing this ClassDef; we have to set NoType so it will be ignored. + val cd = super.transform(ClassDef(statSym.moduleClass, impl) setType NoType) + if (currOwner.isClass) cd + else { // local module -- symbols cannot be generated by info transformer, so do it all here + val Block(stats, _) = mkLazyLocalDef(statSym, gen.newModule(statSym, statSym.info.resultType)) + + Thicket(cd :: stats) + } + + case tree => + super.transform(tree) + + } + } + + + def transformTermsAtExprOwner(exprOwner: Symbol)(stat: Tree) = + if (stat.isTerm) atOwner(exprOwner)(transform(stat)) + else transform(stat) + + override def transformStats(stats: List[Tree], exprOwner: Symbol): List[Tree] = { + val addedStats = + if (!currentOwner.isClass || currentOwner.isPackageClass) Nil + else { + val thickets = fieldsAndAccessors(currentOwner) + if (thickets exists mustExplodeThicket) + thickets flatMap explodeThicket + else thickets + } + + val newStats = + stats mapConserve (if (exprOwner != currentOwner) transformTermsAtExprOwner(exprOwner) else transform) + + addedStats ::: (if (newStats eq stats) stats else { + // check whether we need to flatten thickets and drop empty ones + if (newStats exists mustExplodeThicket) + newStats flatMap explodeThicket + else newStats + }) + } + + } +} |