/* NSC -- new scala compiler
* Copyright 2005 LAMP/EPFL
* @author Martin Odersky
*/
// $Id$
package scala.tools.nsc.typechecker;
import symtab.Flags._;
import collection.mutable.HashMap;
import transform.InfoTransform;
/** Post-attribution checking and transformation.
* //todo: check whether we always check type parameter bounds.
*
* This phase performs the following checks.
*
* - All overrides conform to rules.
* - All type arguments conform to bounds.
* - All type variable uses conform to variance annotations.
* - No forward reference to a term symbol extends beyond a value definition.
*
* It performs the following transformations.
*
* - Local modules are replaced by variables and classes
* - Calls to case factory methods are replaced by new's.
* - References to parameter accessors with aliases are replaced by super references to
* these aliases.
*/
abstract class RefChecks extends InfoTransform {
import global._;
import definitions._;
import typer.{typed, typedOperator, atOwner};
import posAssigner.atPos;
/** the following two members override abstract members in Transform */
val phaseName: String = "refchecks";
override def phaseNewFlags: long = lateMETHOD;
def newTransformer(unit: CompilationUnit): RefCheckTransformer = new RefCheckTransformer(unit);
override def changesBaseClasses = false;
def transformInfo(sym: Symbol, tp: Type): Type = {
if (sym.isModule && !sym.isStatic) {
sym setFlag (lateMETHOD | STABLE);
PolyType(List(), tp)
} else tp
}
// var m$: T = null; or, if class member: local var m$: T = _;
def newModuleVarDef(accessor: Symbol) = {
val mvar = accessor.owner.newVariable(accessor.pos, nme.moduleVarName(accessor.name))
.setInfo(accessor.tpe.finalResultType);
if (mvar.owner.isClass) {
mvar setFlag (PRIVATE | LOCAL | SYNTHETIC);
mvar.owner.info.decls.enter(mvar);
}
ValDef(mvar, if (mvar.owner.isClass) EmptyTree else Literal(Constant(null)))
}
// def m: T = { if (m$ == null) m$ = new m$class; m$ }
def newModuleAccessDef(accessor: Symbol, mvar: Symbol) = {
var mvarRef = if (mvar.owner.isClass) Select(This(mvar.owner), mvar) else Ident(mvar);
DefDef(accessor, vparamss =>
Block(
List(
If(
Apply(Select(mvarRef, nme.eq), List(Literal(Constant(null)))),
Assign(mvarRef,
New(TypeTree(mvar.tpe),
List(for (val pt <- mvar.tpe.symbol.primaryConstructor.info.paramTypes)
yield This(accessor.owner.enclClass)))),//???
EmptyTree)),
mvarRef))
}
// def m: T;
def newModuleAccessDcl(accessor: Symbol) =
DefDef(accessor setFlag lateDEFERRED, vparamss => EmptyTree);
class RefCheckTransformer(unit: CompilationUnit) extends Transformer {
var localTyper: analyzer.Typer = typer;
// Override checking ------------------------------------------------------------
/** 1. Check all members of class `clazz' for overriding conditions.
* That is for overriding member M and overridden member O:
*
* 1.1. M must have the same or stronger access privileges as O.
* 1.2. O must not be final.
* 1.3. O is deferred, or M has `override' modifier.
* 1.4. If O is an immutable value, then so is M.
* 1.5. Neither M nor O are a parameterized type alias
* 1.6. If O is a type alias, then M is an alias of O.
* 1.7. If O is an abstract type then
* either M is an abstract type, and M's bounds are sharper than O's bounds.
* or M is an unparameterized type alias or class which conforms to O's bounds.
* 1.8. If O and M are values, then M's type is a subtype of O's type.
* 2. Check that only abstract classes have deferred members
* 3. Check that every member with an `override' modifier
* overrides some other member.
*/
private def checkAllOverrides(clazz: Symbol): unit = {
val self = clazz.thisType;
def infoString(sym: Symbol) = (
sym.toString() +
(if (sym.owner == clazz) ""
else (sym.locationString +
(if (sym.isAliasType) ", which equals " + self.memberInfo(sym)
else if (sym.isAbstractType) " with bounds " + self.memberInfo(sym)
else if (sym.isTerm) " of type " + self.memberInfo(sym)
else "")))
);
/* Check that all conditions for overriding `other' by `member' are met. */
def checkOverride(clazz: Symbol, member: Symbol, other: Symbol): unit = {
val pos = if (member.owner == clazz) member.pos else clazz.pos;
def overrideError(msg: String): unit =
if (other.tpe != ErrorType && member.tpe != ErrorType)
unit.error(pos, "error overriding " + infoString(other) +
";\n " + infoString(member) + " " + msg);
def overrideTypeError(): unit = {
if (other.tpe != ErrorType && member.tpe != ErrorType) {
overrideError("has incompatible type");
explainTypes(member.tpe, other.tpe);
}
}
//System.out.println(infoString(member) + " overrides " + infoString(other) + " in " + clazz);//DEBUG
// return if we already checked this combination elsewhere
if (member.owner != clazz) {
if ((member.owner isSubClass other.owner) &&
((member hasFlag DEFERRED) || !(other hasFlag DEFERRED))) {
//System.out.println(infoString(member) + " shadows1 " + infoString(other) " in " + clazz);//DEBUG
return;
}
if (clazz.info.parents exists (parent =>
(parent.symbol isSubClass other.owner) && (parent.symbol isSubClass member.owner) &&
((member hasFlag DEFERRED) || !(other hasFlag DEFERRED)))) {
//System.out.println(infoString(member) + " shadows2 " + infoString(other) + " in " + clazz);//DEBUG
return;
}
if (clazz.info.parents forall (parent =>
(parent.symbol isSubClass other.owner) == (parent.symbol isSubClass member.owner))) {
//System.out.println(infoString(member) + " shadows " + infoString(other) + " in " + clazz);//DEBUG
return;
}
}
if (member hasFlag PRIVATE) { // (1.1)
overrideError("has weaker access privileges; it should not be private");
} else if ((member hasFlag PROTECTED) && !(other hasFlag PROTECTED)) { // 1
overrideError("has weaker access privileges; it should not be protected");
} else if (other hasFlag FINAL) { // (1.2)
overrideError("cannot override final member");
} else if (!(other hasFlag DEFERRED) && !(member hasFlag (OVERRIDE | ABSOVERRIDE))) { // (1.3)
overrideError("needs `override' modifier");
} else if ((other hasFlag ABSOVERRIDE) && other.isIncompleteIn(clazz) && !(member hasFlag ABSOVERRIDE)) {
overrideError("needs `abstract override' modifiers");
} else if (other.isStable && !member.isStable) { // (1.4)
overrideError("needs to be an immutable value");
} else {
if (other.isAliasType) {
if (!member.typeParams.isEmpty) // (1.5)
overrideError("may not be parameterized");
if (!other.typeParams.isEmpty) // (1.5)
overrideError("may not override parameterized type");
if (!(self.memberType(member) =:= self.memberType(other))) // (1.6)
overrideTypeError();
} else if (other.isAbstractType) {
if (!member.typeParams.isEmpty) // (1.7)
overrideError("may not be parameterized");
if (!(self.memberInfo(other).bounds containsType self.memberType(member))) // (1.7)
overrideTypeError();
} else if (other.isTerm) {
if (!(self.memberInfo(member) <:< (self.memberInfo(other)))) // 8
overrideTypeError();
}
}
}
val opc = new overridingPairs.Cursor(clazz);
while (opc.hasNext) {
//System.out.println("overrides " + opc.overriding/* + ":" + opc.overriding.tpe*/ + opc.overriding.locationString + " " + opc.overridden/* + ":" + opc.overridden.tpe*/ + opc.overridden.locationString + opc.overridden.hasFlag(DEFERRED));//DEBUG
if (!opc.overridden.isClass) checkOverride(clazz, opc.overriding, opc.overridden);
opc.next
}
/*
// 1. Check all members for overriding conditions.
for (val bc <- clazz.info.baseClasses.tail; val other <- bc.info.decls.toList)
if (!other.isClass && !(other hasFlag PRIVATE) && !other.isConstructor) {
val member = clazz.tpe.member(other.name) filter
(sym => sym.owner != other.owner &&
(sym.isType || (self.memberType(sym) matches self.memberType(other))));
if (member hasFlag OVERLOADED) {
val alt1 = member.alternatives.head;
val alt2 = member.alternatives.tail.head;
val pos = if (alt1.owner == clazz) alt1.pos
else if (alt2.owner == clazz) alt2.pos
else clazz.pos;
unit.error(pos,
"ambiguous override: both " + infoString(alt1) +
"\n and " + infoString(alt2) +
"\n override " + infoString(other));
} else if (member != NoSymbol && !(member hasFlag LOCAL)) {
System.out.println("OVERRIDES " + member + member.locationString + " " + other + other.locationString);//debug
checkOverride(clazz, member, other);
}
}
*/
// 2. Check that only abstract classes have deferred members
if (clazz.isClass && !clazz.isTrait) {
def abstractClassError(mustBeTrait: boolean, msg: String): unit = {
unit.error(clazz.pos,
(if (clazz.isAnonymousClass || clazz.isModuleClass) "object creation impossible"
else if (mustBeTrait) clazz.toString() + " needs to be a trait"
else clazz.toString() + " needs to be abstract") + ", since " + msg);
clazz.setFlag(ABSTRACT);
}
for (val member <- clazz.tpe.members)
if ((member hasFlag DEFERRED) && !(clazz hasFlag ABSTRACT)) {
abstractClassError(false,
infoString(member) + " is not defined" +
(if (member.isVariable)
"\n(Note that variables need to be initialized to be defined)" else ""))
} else if ((member hasFlag ABSOVERRIDE) && member.isIncompleteIn(clazz)) {
val other = member.superSymbol(clazz);
abstractClassError(true,
infoString(member) + " is marked `abstract' and `override'" +
(if (other != NoSymbol)
" and overrides incomplete superclass member " + infoString(other)
else ""))
}
}
// 3. Check that every defined member with an `override' modifier overrides some other member.
for (val member <- clazz.info.decls.toList)
if ((member hasFlag (OVERRIDE | ABSOVERRIDE)) &&
(clazz.info.baseClasses.tail forall {
bc => member.matchingSymbol(bc, clazz.thisType) == NoSymbol
})) {
// for (val bc <- clazz.info.baseClasses.tail) System.out.println("" + bc + " has " + bc.info.decl(member.name) + ":" + bc.info.decl(member.name).tpe);//DEBUG
unit.error(member.pos, member.toString() + " overrides nothing");
member resetFlag OVERRIDE
}
}
// Basetype Checking --------------------------------------------------------
/** 1. Check that later type instances in the base-type sequence
* are subtypes of earlier type instances of the same trait.
* 2. Check that case classes do not inherit from case classes.
* 3. Check that at most one base type is a case-class.
*/
private def validateBaseTypes(clazz: Symbol): unit = {
val seenTypes = new Array[Type](clazz.info.closure.length);
var seenCaseClass = if (clazz hasFlag CASE) clazz else NoSymbol;
def validateTypes(tps: List[Type], includeSuper: boolean): unit = {
if (!tps.isEmpty) {
for (val tp <- tps.tail.reverse) validateType(tp, false);
if (includeSuper) validateType(tps.head, true);
}
}
def validateType(tp: Type, includeSuper: boolean): unit = {
val baseClass = tp.symbol;
if (baseClass.isClass) {
val index = clazz.info.closurePos(baseClass);
if (index >= 0) {
if (seenTypes(index) != null && !(seenTypes(index) <:< tp))
unit.error(clazz.pos, "illegal inheritance;\n " + clazz +
" inherits different type instances of " + baseClass +
":\n" + tp + " and " + seenTypes(index));
seenTypes(index) = tp;
// check that case classes do not inherit from case classes
if (baseClass hasFlag CASE) {
if (seenCaseClass != NoSymbol && seenCaseClass != baseClass)
unit.error(clazz.pos, "illegal combination of case " +
seenCaseClass + " and case " + baseClass + " in one object");
seenCaseClass = baseClass
}
}
validateTypes(tp.parents, includeSuper);
}
}
validateTypes(clazz.info.parents, true);
}
// Variance Checking --------------------------------------------------------
private val ContraVariance = -1;
private val NoVariance = 0;
private val CoVariance = 1;
private val AnyVariance = 2;
/** Check variance of type variables in this type
*/
private def validateVariance(base: Symbol, all: Type, variance: int): unit = {
def varianceString(variance: int): String =
if (variance == 1) "covariant"
else if (variance == -1) "contravariant"
else "invariant";
def relativeVariance(tvar: Symbol): int = {
val clazz = tvar.owner;
var sym = base;
var state = CoVariance;
while (sym != clazz && state != AnyVariance) {
//System.out.println("flip: " + sym + " " + sym.isParameter());//DEBUG
if ((sym hasFlag PARAM) && !sym.owner.isConstructor) state = -state;
else if (!sym.owner.isClass) state = AnyVariance;
else if (sym.isAliasType) state = NoVariance;
sym = sym.owner;
}
state
}
def validateVariance(tp: Type, variance: int): unit = tp match {
case ErrorType => ;
case WildcardType => ;
case NoType => ;
case NoPrefix => ;
case ThisType(_) => ;
case ConstantType(_) => ;
case SingleType(pre, sym) =>
validateVariance(pre, variance)
case TypeRef(pre, sym, args) =>
if (sym.variance != NoVariance) {
val v = relativeVariance(sym);
if (v != AnyVariance && sym.variance != v * variance) {
//System.out.println("relativeVariance(" + base + "," + sym + ") = " + v);//DEBUG
unit.error(base.pos,
varianceString(sym.variance) + " " + sym +
" occurs in " + varianceString(v * variance) +
" position in type " + all + " of " + base);
}
}
validateVariance(pre, variance);
validateVarianceArgs(args, variance, sym.typeParams);
case ClassInfoType(parents, decls, symbol) =>
validateVariances(parents, variance);
case RefinedType(parents, decls) =>
validateVariances(parents, variance);
case TypeBounds(lo, hi) =>
validateVariance(lo, -variance);
validateVariance(hi, variance);
case MethodType(formals, result) =>
validateVariance(result, variance);
case PolyType(tparams, result) =>
validateVariance(result, variance);
}
def validateVariances(tps: List[Type], variance: int): unit =
tps foreach (tp => validateVariance(tp, variance));
def validateVarianceArgs(tps: List[Type], variance: int, tparams: List[Symbol]): unit =
(tps zip tparams) foreach {
case Pair(tp, tparam) => validateVariance(tp, variance * tparam.variance)
}
validateVariance(all, variance)
}
// Forward reference checking ---------------------------------------------------
class LevelInfo(val outer: LevelInfo) {
val scope: Scope = if (outer == null) new Scope() else new Scope(outer.scope);
var maxindex: int = Integer.MIN_VALUE;
var refpos: int = _;
var refsym: Symbol = _;
}
private var currentLevel: LevelInfo = null;
private val symIndex = new HashMap[Symbol, int];
private def pushLevel(): unit =
currentLevel = new LevelInfo(currentLevel);
private def popLevel(): unit =
currentLevel = currentLevel.outer;
private def enterSyms(stats: List[Tree]): unit = {
var index = -1;
for (val stat <- stats) {
index = index + 1;
stat match {
case ClassDef(_, _, _, _, _) | DefDef(_, _, _, _, _, _) | ModuleDef(_, _, _) | ValDef(_, _, _, _) =>
assert(stat.symbol != NoSymbol, stat);//debug
if (stat.symbol.isLocal) {
currentLevel.scope.enter(newScopeEntry(stat.symbol, currentLevel.scope));
symIndex(stat.symbol) = index;
}
case _ =>
}
}
}
private def enterReference(pos: int, sym: Symbol): unit =
if (sym.isLocal) {
val e = currentLevel.scope.lookupEntry(sym.name);
if (e != null && sym == e.sym) {
var l = currentLevel;
while (l.scope != e.owner) l = l.outer;
val symindex = symIndex(sym);
if (l.maxindex < symindex) {
l.refpos = pos;
l.refsym = sym;
l.maxindex = symindex;
}
}
}
// Transformation ------------------------------------------------------------
override def transformStats(stats: List[Tree], exprOwner: Symbol): List[Tree] = {
pushLevel();
enterSyms(stats);
var index = -1;
val stats1 = stats flatMap { stat => index = index + 1; transformStat(stat, index) }
popLevel();
stats1
}
def transformStat(tree: Tree, index: int): List[Tree] = tree match {
case ModuleDef(mods, name, impl) =>
val sym = tree.symbol;
val cdef = ClassDef(mods | MODULE, name, List(), EmptyTree, impl)
.setPos(tree.pos)
.setSymbol(sym.moduleClass)
.setType(NoType);
if (sym.isStatic) List(transform(cdef))
else {
val vdef =
localTyper.typed {
atPos(tree.pos) {
newModuleVarDef(sym)
}
}
val ddef =
atPhase(phase.next) {
localTyper.typed {
if (sym.owner.isTrait) newModuleAccessDcl(sym)
else newModuleAccessDef(sym, vdef.symbol)
}
}
if (sym.owner.isTrait) transformTrees(List(cdef, ddef))
else transformTrees(List(cdef, vdef, ddef))
}
case ValDef(_, _, _, _) =>
val tree1 = transform(tree); // important to do before forward reference check
if (tree.symbol.isLocal && index <= currentLevel.maxindex) {
if (settings.debug.value) System.out.println(currentLevel.refsym);
unit.error(currentLevel.refpos, "forward reference extends over definition of " + tree.symbol);
}
List(tree1)
case Import(_, _) =>
List()
case _ =>
List(transform(tree))
}
override def transform(tree: Tree): Tree = try {
/* Convert a reference of a case factory to a new of the class it produces. */
def toConstructor: Tree = {
var tpe = tree.tpe;
while (!tpe.symbol.isClass) tpe = tpe.resultType;
assert(tpe.symbol hasFlag CASE);
typedOperator(atPos(tree.pos)(Select(New(TypeTree(tpe)), tpe.symbol.primaryConstructor)));
}
/* Check whether argument types conform to bounds of type parameters */
def checkBounds(tparams: List[Symbol], argtps: List[Type]): unit = try {
typer.infer.checkBounds(tree.pos, tparams, argtps, "");
} catch {
case ex: TypeError => unit.error(tree.pos, ex.getMessage());
}
val savedLocalTyper = localTyper;
val sym = tree.symbol;
var result = tree;
tree match {
case ClassDef(mods, name, tparams, tpe, impl) =>
validateVariance(sym, sym.info, CoVariance);
validateVariance(sym, sym.typeOfThis, CoVariance);
case DefDef(_, _, _, _, _, _) =>
validateVariance(sym, sym.tpe, CoVariance);
case ValDef(_, _, _, _) =>
validateVariance(sym, sym.tpe, if (sym.isVariable) NoVariance else CoVariance);
case AbsTypeDef(_, _, _, _) =>
validateVariance(sym, sym.info, CoVariance);
case AliasTypeDef(_, _, _, _) =>
validateVariance(sym, sym.info, CoVariance);
case Template(_, _) =>
localTyper = localTyper.atOwner(tree, currentOwner);
validateBaseTypes(currentOwner);
checkAllOverrides(currentOwner);
case TypeTree() =>
new TypeTraverser {
def traverse(tp: Type) = tp match {
case TypeRef(pre, sym, args) => checkBounds(sym.typeParams, args); this
case _ => this
}
} traverse tree.tpe
case TypeApply(fn, args) =>
checkBounds(fn.tpe.typeParams, args map (.tpe));
if (sym.isSourceMethod && sym.hasFlag(CASE)) result = toConstructor;
case New(tpt) =>
enterReference(tree.pos, tpt.tpe.symbol);
case Ident(name) =>
if (sym.isSourceMethod && sym.hasFlag(CASE))
result = toConstructor
else if (name != nme.WILDCARD && name != nme.WILDCARD_STAR.toTypeName) {
assert(sym != NoSymbol, tree);//debug
enterReference(tree.pos, sym);
}
case Select(qual, name) =>
if (sym.isSourceMethod && sym.hasFlag(CASE))
result = toConstructor
else qual match {
case Super(qualifier, mixin) =>
val base = currentOwner.enclClass;
if (sym hasFlag DEFERRED) {
val member = sym.overridingSymbol(base);//???
if (mixin != nme.EMPTY.toTypeName || member == NoSymbol ||
!((member hasFlag ABSOVERRIDE) && member.isIncompleteIn(base)))
unit.error(tree.pos, "symbol accessed from super may not be abstract");
}
//System.out.println("super: " + tree + " in " + base);//DEBUG
if (base.isTrait && sym.isTerm && mixin == nme.EMPTY.toTypeName) {
val superAccName = nme.superName(sym.name);
val superAcc = base.info.decl(superAccName) suchThat (.alias.==(sym));
assert(superAcc != NoSymbol, "" + sym + " " + base + " " + superAccName);//debug
val tree1 = Select(This(base), superAcc);
if (settings.debug.value) log("super-replacement: " + tree + "=>" + tree1);
result = atPos(tree.pos) {
Select(gen.This(base), superAcc) setType superAcc.tpe
}
}
case This(_) =>
if ((sym hasFlag PARAMACCESSOR) && (sym.alias != NoSymbol)) {
result = typed {
Select(
Super(qual.symbol, qual.symbol.info.parents.head.symbol.name) setPos qual.pos,
sym.alias) setPos tree.pos
}
if (settings.debug.value)
System.out.println("alias replacement: " + tree + " ==> " + result);//debug
}
case _ =>
}
case _ =>
}
result = super.transform(result);
localTyper = savedLocalTyper;
result
} catch {
case ex: TypeError =>
if (settings.debug.value) ex.printStackTrace();
unit.error(tree.pos, ex.getMessage());
tree
}
}
}