/* NSC -- new Scala compiler
* Copyright 2005-2010 LAMP/EPFL
* @author
*/
// $Id$
package scala.tools.nsc
package transform
import scala.collection.mutable.ListBuffer
import symtab.Flags._
import util.TreeSet
/** This phase converts classes with parameters into Java-like classes with
* fields, which are assigned to from constructors.
*/
abstract class Constructors extends Transform with ast.TreeDSL {
import global._
import definitions._
/** the following two members override abstract members in Transform */
val phaseName: String = "constructors"
protected def newTransformer(unit: CompilationUnit): Transformer =
new ConstructorTransformer(unit)
class ConstructorTransformer(unit: CompilationUnit) extends Transformer {
def transformClassTemplate(impl: Template): Template = {
val clazz = impl.symbol.owner // the transformed class
val stats = impl.body // the transformed template body
val localTyper = typer.atOwner(impl, clazz)
var constr: DefDef = null // The primary constructor
var constrParams: List[Symbol] = null // ... and its parameters
var constrBody: Block = null // ... and its body
// decompose primary constructor into the three entities above.
for (stat <- stats) {
stat match {
case ddef @ DefDef(_, _, _, List(vparams), _, rhs @ Block(_, Literal(_))) =>
if (ddef.symbol.isPrimaryConstructor) {
constr = ddef
constrParams = vparams map (_.symbol)
constrBody = rhs
}
case _ =>
}
}
assert((constr ne null) && (constrBody ne null), impl)
// The parameter accessor fields which are members of the class
val paramAccessors = clazz.constrParamAccessors
// The constructor parameter corresponding to an accessor
def parameter(acc: Symbol): Symbol =
parameterNamed(nme.getterName(acc.originalName))
// The constructor parameter with given name. This means the parameter
// has given name, or starts with given name, and continues with a `$' afterwards.
def parameterNamed(name: Name): Symbol = {
def matchesName(param: Symbol) =
param.name == name ||
param.name.startsWith(name) && param.name(name.length) == '$'
val ps = constrParams filter matchesName
if (ps.isEmpty) assert(false, "" + name + " not in " + constrParams)
ps.head
}
var thisRefSeen: Boolean = false
// A transformer for expressions that go into the constructor
val intoConstructorTransformer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case Apply(Select(This(_), _), List()) =>
// references to parameter accessor methods of own class become references to parameters
// outer accessors become references to $outer parameter
if ((tree.symbol hasFlag PARAMACCESSOR) && tree.symbol.owner == clazz)
gen.mkAttributedIdent(parameter(tree.symbol.accessed)) setPos tree.pos
else if (tree.symbol.outerSource == clazz && !clazz.isImplClass)
gen.mkAttributedIdent(parameterNamed(nme.OUTER)) setPos tree.pos
else
super.transform(tree)
case Select(This(_), _)
if ((tree.symbol hasFlag PARAMACCESSOR) && !tree.symbol.isSetter && tree.symbol.owner == clazz) =>
// references to parameter accessor field of own class become references to parameters
gen.mkAttributedIdent(parameter(tree.symbol)) setPos tree.pos
case Select(_, _) =>
thisRefSeen = true
super.transform(tree)
case This(_) =>
thisRefSeen = true
super.transform(tree)
case Super(_, _) =>
thisRefSeen = true
super.transform(tree)
case _ =>
super.transform(tree)
}
}
// Move tree into constructor, take care of changing owner from `oldowner' to constructor symbol
def intoConstructor(oldowner: Symbol, tree: Tree) =
intoConstructorTransformer.transform(
new ChangeOwnerTraverser(oldowner, constr.symbol)(tree))
// Should tree be moved in front of super constructor call?
def canBeMoved(tree: Tree) = tree match {
//todo: eliminate thisRefSeen
case ValDef(mods, _, _, _) =>
if (settings.Xwarninit.value)
if (!(mods hasFlag PRESUPER | PARAMACCESSOR) && !thisRefSeen &&
{ val g = tree.symbol.getter(tree.symbol.owner);
g != NoSymbol && !g.allOverriddenSymbols.isEmpty
})
unit.warning(tree.pos, "the semantics of this definition has changed;\nthe initialization is no longer be executed before the superclass is called")
(mods hasFlag PRESUPER | PARAMACCESSOR)// || !thisRefSeen && (!settings.future.value && !settings.checkInit.value)
case _ => false
}
// Create an assignment to class field `to' with rhs `from'
def mkAssign(to: Symbol, from: Tree): Tree =
localTyper.typed {
//util.trace("compiling "+unit+" ") {
atPos(to.pos) {
Assign(Select(This(clazz), to), from)
}
//}
}
// Create code to copy parameter to parameter accessor field.
// If parameter is $outer, check that it is not null.
def copyParam(to: Symbol, from: Symbol): Tree = {
import CODE._
var result = mkAssign(to, Ident(from))
if (from.name == nme.OUTER)
result =
atPos(to.pos) {
localTyper.typed {
IF (from ANY_EQ NULL) THEN THROW(NullPointerExceptionClass) ELSE result
}
}
result
}
// The list of definitions that go into class
val defBuf = new ListBuffer[Tree]
// The list of statements that go into constructor after superclass constructor call
val constrStatBuf = new ListBuffer[Tree]
// The list of statements that go into constructor before superclass constructor call
val constrPrefixBuf = new ListBuffer[Tree]
// The early initialized field definitions of the class (these are the class members)
val presupers = treeInfo.preSuperFields(stats)
// generate code to copy pre-initialized fields
for (stat <- constrBody.stats) {
constrStatBuf += stat
stat match {
case ValDef(mods, name, _, _) if (mods hasFlag PRESUPER) =>
// stat is the constructor-local definition of the field value
val fields = presupers filter (
vdef => nme.localToGetter(vdef.name) == name)
assert(fields.length == 1)
constrStatBuf += mkAssign(fields.head.symbol, Ident(stat.symbol))
case _ =>
}
}
// Triage all template definitions to go into defBuf, constrStatBuf, or constrPrefixBuf.
for (stat <- stats) stat match {
case DefDef(mods, name, tparams, vparamss, tpt, rhs) =>
// methods with constant result type get literals as their body
// all methods except the primary constructor go into template
stat.symbol.tpe match {
case MethodType(List(), tp @ ConstantType(c)) =>
defBuf += treeCopy.DefDef(
stat, mods, name, tparams, vparamss, tpt,
Literal(c) setPos rhs.pos setType tp)
case _ =>
if (!stat.symbol.isPrimaryConstructor) defBuf += stat
}
case ValDef(mods, name, tpt, rhs) =>
// val defs with constant right-hand sides are eliminated.
// for all other val defs, an empty valdef goes into the template and
// the initializer goes as an assignment into the constructor
// if the val def is an early initialized or a parameter accessor, it goes
// before the superclass constructor call, otherwise it goes after.
// Lazy vals don't get the assignment in the constructor.
if (!stat.symbol.tpe.isInstanceOf[ConstantType]) {
if (rhs != EmptyTree && !stat.symbol.hasFlag(LAZY)) {
val rhs1 = intoConstructor(stat.symbol, rhs);
(if (canBeMoved(stat)) constrPrefixBuf else constrStatBuf) += mkAssign(
stat.symbol, rhs1)
}
defBuf += treeCopy.ValDef(stat, mods, name, tpt, EmptyTree)
}
case ClassDef(_, _, _, _) =>
// classes are treated recursively, and left in the template
defBuf += new ConstructorTransformer(unit).transform(stat)
case _ =>
// all other statements go into the constructor
constrStatBuf += intoConstructor(impl.symbol, stat)
}
// ----------- avoid making fields for symbols that are not accessed --------------
// A sorted set of symbols that are known to be accessed outside the primary constructor.
val accessedSyms = new TreeSet[Symbol]((x, y) => x isLess y)
// a list of outer accessor symbols and their bodies
var outerAccessors: List[(Symbol, Tree)] = List()
// Could symbol's definition be omitted, provided it is not accessed?
// This is the case if the symbol is defined in the current class, and
// ( the symbol is an object private parameter accessor field, or
// the symbol is an outer accessor of a final class which does not override another outer accesser. )
def maybeOmittable(sym: Symbol) =
(sym.owner == clazz &&
((sym hasFlag PARAMACCESSOR) && sym.isPrivateLocal ||
sym.isOuterAccessor && sym.owner.isFinal && sym.allOverriddenSymbols.isEmpty))
// Is symbol known to be accessed outside of the primary constructor,
// or is it a symbol whose definition cannot be omitted anyway?
def mustbeKept(sym: Symbol) =
!maybeOmittable(sym) || (accessedSyms contains sym)
// A traverser to set accessedSyms and outerAccessors
val accessTraverser = new Traverser {
override def traverse(tree: Tree) = {
tree match {
case DefDef(_, _, _, _, _, body)
if (tree.symbol.isOuterAccessor && tree.symbol.owner == clazz && clazz.isFinal) =>
outerAccessors ::= (tree.symbol, body)
case Select(_, _) =>
if (!mustbeKept(tree.symbol)) accessedSyms addEntry tree.symbol
super.traverse(tree)
case _ =>
super.traverse(tree)
}
}
}
// first traverse all definitions except outeraccesors
// (outeraccessors are avoided in accessTraverser)
for (stat <- defBuf.iterator) accessTraverser.traverse(stat)
// then traverse all bodies of outeraccessors which are accessed themselves
// note: this relies on the fact that an outer accessor never calls another
// outer accessor in the same class.
for ((accSym, accBody) <- outerAccessors)
if (mustbeKept(accSym)) accessTraverser.traverse(accBody)
// Conflicting symbol list from parents: see bug #1960.
// It would be better to mangle the constructor parameter name since
// it can only be used internally, but I think we need more robust name
// mangling before we introduce more of it.
val parentSymbols = Map((for {
p <- impl.parents
if p.symbol.isTrait
sym <- p.symbol.info.nonPrivateMembers
if sym.isGetter && !sym.isOuterField
} yield sym.name -> p): _*)
// Initialize all parameters fields that must be kept.
val paramInits =
for (acc <- paramAccessors if mustbeKept(acc)) yield {
if (parentSymbols contains acc.name)
unit.error(acc.pos, "parameter '%s' requires field but conflicts with %s in '%s'".format(
acc.name, acc.name, parentSymbols(acc.name)))
copyParam(acc, parameter(acc))
}
// Assemble final constructor
defBuf += treeCopy.DefDef(
constr, constr.mods, constr.name, constr.tparams, constr.vparamss, constr.tpt,
treeCopy.Block(
constrBody,
paramInits ::: constrPrefixBuf.toList ::: constrStatBuf.toList,
constrBody.expr));
// Unlink all fields that can be dropped from class scope
for (sym <- clazz.info.decls.toList)
if (!mustbeKept(sym)) clazz.info.decls unlink sym
// Eliminate all field definitions that can be dropped from template
treeCopy.Template(impl, impl.parents, impl.self,
defBuf.toList filter (stat => mustbeKept(stat.symbol)))
} // transformClassTemplate
override def transform(tree: Tree): Tree =
tree match {
case ClassDef(mods, name, tparams, impl) if !tree.symbol.hasFlag(INTERFACE) =>
treeCopy.ClassDef(tree, mods, name, tparams, transformClassTemplate(impl))
case _ =>
super.transform(tree)
}
} // ConstructorTransformer
}