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/* NSC -- new scala compiler
* Copyright 2005-2013 LAMP/EPFL
* @author Martin Odersky
*/
package scala
package reflect
package internal
import Variance._
import scala.collection.mutable
import scala.annotation.tailrec
/** See comments at scala.reflect.internal.Variance.
*/
trait Variances {
self: SymbolTable =>
/** Used in Refchecks.
* TODO - eliminate duplication with varianceInType
*/
class VarianceValidator extends Traverser {
private val escapedLocals = mutable.HashSet[Symbol]()
// A flag for when we're in a refinement, meaning method parameter types
// need to be checked.
private var inRefinement = false
@inline private def withinRefinement(body: => Type): Type = {
val saved = inRefinement
inRefinement = true
try body finally inRefinement = saved
}
/** Is every symbol in the owner chain between `site` and the owner of `sym`
* either a term symbol or private[this]? If not, add `sym` to the set of
* escaped locals.
* @pre sym.isLocalToThis
*/
@tailrec final def checkForEscape(sym: Symbol, site: Symbol) {
if (site == sym.owner || site == sym.owner.moduleClass || site.hasPackageFlag) () // done
else if (site.isTerm || site.isPrivateLocal) checkForEscape(sym, site.owner) // ok - recurse to owner
else escapedLocals += sym
}
protected def issueVarianceError(base: Symbol, sym: Symbol, required: Variance): Unit = ()
// Flip occurrences of type parameters and parameters, unless
// - it's a constructor, or case class factory or extractor
// - it's a type parameter of tvar's owner.
def shouldFlip(sym: Symbol, tvar: Symbol) = (
sym.isParameter
&& !(tvar.isTypeParameterOrSkolem && sym.isTypeParameterOrSkolem && tvar.owner == sym.owner)
)
// Is `sym` is local to a term or is private[this] or protected[this]?
def isExemptFromVariance(sym: Symbol): Boolean = !sym.owner.isClass || (
(sym.isLocalToThis || sym.isSuperAccessor) // super accessors are implicitly local #4345
&& !escapedLocals(sym)
)
private object ValidateVarianceMap extends TypeMap(trackVariance = true) {
private var base: Symbol = _
/** The variance of a symbol occurrence of `tvar` seen at the level of the definition of `base`.
* The search proceeds from `base` to the owner of `tvar`.
* Initially the state is covariant, but it might change along the search.
*
* A local alias type is treated as Bivariant;
* this is OK because such aliases are expanded for variance checking.
* However, for an alias which might be externally visible, we must assume Invariant,
* because there may be references to the type parameter that are not checked,
* leading to unsoundness (see SI-6566).
*/
def relativeVariance(tvar: Symbol): Variance = {
def nextVariance(sym: Symbol, v: Variance): Variance = (
if (shouldFlip(sym, tvar)) v.flip
else if (isExemptFromVariance(sym)) Bivariant
else if (sym.isAliasType) (
// Unsound pre-2.11 behavior preserved under -Xsource:2.10
if (settings.isScala211 || sym.isOverridingSymbol) Invariant
else {
currentRun.reporting.deprecationWarning(sym.pos, "Construct depends on unsound variance analysis and will not compile in scala 2.11 and beyond", "2.11.0")
Bivariant
}
)
else v
)
def loop(sym: Symbol, v: Variance): Variance = (
if (sym == tvar.owner || v.isBivariant) v
else loop(sym.owner, nextVariance(sym, v))
)
loop(base, Covariant)
}
def isUncheckedVariance(tp: Type) = tp match {
case AnnotatedType(annots, _) => annots exists (_ matches definitions.uncheckedVarianceClass)
case _ => false
}
private def checkVarianceOfSymbol(sym: Symbol) {
val relative = relativeVariance(sym)
val required = relative * variance
if (!relative.isBivariant) {
def sym_s = s"$sym (${sym.variance}${sym.locationString})"
def base_s = s"$base in ${base.owner}" + (if (base.owner.isClass) "" else " in " + base.owner.enclClass)
log(s"verifying $sym_s is $required at $base_s")
if (sym.variance != required)
issueVarianceError(base, sym, required)
}
}
override def mapOver(decls: Scope): Scope = {
decls foreach (sym => withVariance(if (sym.isAliasType) Invariant else variance)(this(sym.info)))
decls
}
private def resultTypeOnly(tp: Type) = tp match {
case mt: MethodType => !inRefinement
case pt: PolyType => true
case _ => false
}
/** For PolyTypes, type parameters are skipped because they are defined
* explicitly (their TypeDefs will be passed here.) For MethodTypes, the
* same is true of the parameters (ValDefs) unless we are inside a
* refinement, in which case they are checked from here.
*/
def apply(tp: Type): Type = {
tp match {
case _ if isUncheckedVariance(tp) =>
case _ if resultTypeOnly(tp) => this(tp.resultType)
case TypeRef(_, sym, _) if shouldDealias(sym) => this(tp.normalize)
case TypeRef(_, sym, _) if !sym.variance.isInvariant => checkVarianceOfSymbol(sym) ; mapOver(tp)
case RefinedType(_, _) => withinRefinement(mapOver(tp))
case ClassInfoType(parents, _, _) => parents foreach this
case mt @ MethodType(_, result) => flipped(mt.paramTypes foreach this) ; this(result)
case _ => mapOver(tp)
}
// We're using TypeMap here for type traversal only. To avoid wasteful symbol
// cloning during the recursion, it is important to return the input `tp`, rather
// than the result of the pattern match above, which normalizes types.
tp
}
private def shouldDealias(sym: Symbol): Boolean = {
// The RHS of (private|protected)[this] type aliases are excluded from variance checks. This is
// implemented in relativeVariance.
// As such, we need to expand references to them to retain soundness. Example: neg/t8079a.scala
sym.isAliasType && isExemptFromVariance(sym)
}
def validateDefinition(base: Symbol) {
val saved = this.base
this.base = base
try apply(base.info)
finally this.base = saved
}
}
/** Validate variance of info of symbol `base` */
private def validateVariance(base: Symbol) {
ValidateVarianceMap validateDefinition base
}
override def traverse(tree: Tree) {
def sym = tree.symbol
// No variance check for object-private/protected methods/values.
// Or constructors, or case class factory or extractor.
def skip = (
sym == NoSymbol
|| sym.isLocalToThis
|| sym.owner.isConstructor
|| sym.owner.isCaseApplyOrUnapply
)
tree match {
case defn: MemberDef if skip =>
debuglog(s"Skipping variance check of ${sym.defString}")
case ClassDef(_, _, _, _) | TypeDef(_, _, _, _) =>
validateVariance(sym)
super.traverse(tree)
case ModuleDef(_, _, _) =>
validateVariance(sym.moduleClass)
super.traverse(tree)
case ValDef(_, _, _, _) =>
validateVariance(sym)
case DefDef(_, _, tparams, vparamss, _, _) =>
validateVariance(sym)
traverseTrees(tparams)
traverseTreess(vparamss)
case Template(_, _, _) =>
super.traverse(tree)
case CompoundTypeTree(templ) =>
super.traverse(tree)
// SI-7872 These two cases make sure we don't miss variance exploits
// in originals, e.g. in `foo[({type l[+a] = List[a]})#l]`
case tt @ TypeTree() if tt.original != null =>
super.traverse(tt.original)
case tt : TypTree =>
super.traverse(tt)
case _ =>
}
}
}
/** Compute variance of type parameter `tparam` in all types `tps`. */
def varianceInTypes(tps: List[Type])(tparam: Symbol): Variance =
fold(tps map (tp => varianceInType(tp)(tparam)))
/** Compute variance of type parameter `tparam` in type `tp`. */
def varianceInType(tp: Type)(tparam: Symbol): Variance = {
def inArgs(sym: Symbol, args: List[Type]): Variance = fold(map2(args, sym.typeParams)((a, p) => inType(a) * p.variance))
def inSyms(syms: List[Symbol]): Variance = fold(syms map inSym)
def inTypes(tps: List[Type]): Variance = fold(tps map inType)
def inSym(sym: Symbol): Variance = if (sym.isAliasType) inType(sym.info).cut else inType(sym.info)
def inType(tp: Type): Variance = tp match {
case ErrorType | WildcardType | NoType | NoPrefix => Bivariant
case ThisType(_) | ConstantType(_) => Bivariant
case TypeRef(_, `tparam`, _) => Covariant
case BoundedWildcardType(bounds) => inType(bounds)
case NullaryMethodType(restpe) => inType(restpe)
case SingleType(pre, sym) => inType(pre)
case TypeRef(pre, _, _) if tp.isHigherKinded => inType(pre) // a type constructor cannot occur in tp's args
case TypeRef(pre, sym, args) => inType(pre) & inArgs(sym, args)
case TypeBounds(lo, hi) => inType(lo).flip & inType(hi)
case RefinedType(parents, defs) => inTypes(parents) & inSyms(defs.toList)
case MethodType(params, restpe) => inSyms(params).flip & inType(restpe)
case PolyType(tparams, restpe) => inSyms(tparams).flip & inType(restpe)
case ExistentialType(tparams, restpe) => inSyms(tparams) & inType(restpe)
case AnnotatedType(annots, tp) => inTypes(annots map (_.atp)) & inType(tp)
}
inType(tp)
}
}
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