package dotty.tools
package dotc
package typer
import core._
import ast.{Trees, untpd, tpd, TreeInfo}
import util.Positions._
import Trees.Untyped
import Mode.ImplicitsDisabled
import Contexts._
import Types._
import Flags._
import Denotations._
import NameOps._
import Symbols._
import Types._
import Decorators._
import Names._
import StdNames._
import Constants._
import Inferencing._
import collection.mutable
import language.implicitConversions
object Applications {
private val isNamedArg = (arg: Any) => arg.isInstanceOf[Trees.NamedArg[_]]
def hasNamedArg(args: List[Any]) = args exists isNamedArg
/** A trait defining an `isCompatible` method. */
trait Compatibility {
/** Is there an implicit conversion from `tp` to `pt`? */
def viewExists(tp: Type, pt: Type)(implicit ctx: Context): Boolean
/** A type `tp` is compatible with a type `pt` if one of the following holds:
* 1. `tp` is a subtype of `pt`
* 2. `pt` is by name parameter type, and `tp` is compatible with its underlying type
* 3. there is an implicit conversion from `tp` to `pt`.
*/
def isCompatible(tp: Type, pt: Type)(implicit ctx: Context): Boolean = (
tp <:< pt
|| pt.typeSymbol == defn.ByNameParamClass && tp <:< pt.typeArgs.head
|| viewExists(tp, pt)
)
}
/** The normalized form of a type
* - unwraps polymorphic types, tracking their parameters in the current constraint
* - skips implicit parameters
* - converts non-dependent method types to the corresponding function types
* - dereferences parameterless method types
*/
def normalize(tp: Type)(implicit ctx: Context): Type = tp.widen match {
case pt: PolyType => normalize(ctx.track(pt).resultType)
case mt: MethodType if !mt.isDependent =>
if (mt.isImplicit) mt.resultType
else defn.FunctionType(mt.paramTypes, mt.resultType)
case et: ExprType => et.resultType
case _ => tp
}
}
import Applications._
trait Applications extends Compatibility{ self: Typer =>
import Applications._
import Trees._
private def state(implicit ctx: Context) = ctx.typerState
def lift(defs: mutable.ListBuffer[tpd.Tree], expr: tpd.Tree, prefix: String = "")(implicit ctx: Context): tpd.Tree =
if (TreeInfo.isIdempotentExpr(expr)) expr
else {
val name = ctx.freshName(prefix).toTermName
val sym = ctx.newSymbol(ctx.owner, name, EmptyFlags, expr.tpe, coord = positionCoord(expr.pos))
defs += tpd.ValDef(sym, expr)
tpd.Ident(sym.symRef)
}
def liftArgs(defs: mutable.ListBuffer[tpd.Tree], methType: Type, args: List[tpd.Tree])(implicit ctx: Context) = {
val paramPrefixes = methType match {
case MethodType(paramNames, _) => paramNames map (_.toString)
case _ => args map (_ => "")
}
for ((arg, prefix) <- args zip paramPrefixes) yield lift(defs, arg, prefix)
}
def liftApp(defs: mutable.ListBuffer[tpd.Tree], tree: tpd.Tree)(implicit ctx: Context): tpd.Tree = tree match {
case Apply(fn, args) =>
tree.derivedApply(liftApp(defs, fn), liftArgs(defs, fn.tpe, args))
case TypeApply(fn, targs) =>
tree.derivedTypeApply(liftApp(defs, fn), targs)
case Select(pre, name) =>
tree.derivedSelect(lift(defs, pre), name)
case Ident(name) =>
lift(defs, tree)
case Block(stats, expr) =>
liftApp(defs ++= stats, expr)
case _ =>
tree
}
/**
* @param Arg the type of arguments, could be tpd.Tree, untpd.Tree, or Type
* @param methRef the reference to the method of the application
* @param funType the type of the function part of the application
* @param args the arguments of the application
* @param resultType the expected result type of the application
*/
abstract class Application[Arg](methRef: TermRef, funType: Type, args: List[Arg], resultType: Type)(implicit ctx: Context) {
/** The type of typed arguments: either tpd.Tree or Type */
type TypedArg
/** Given an original argument and the type of the corresponding formal
* parameter, produce a typed argument.
*/
protected def typedArg(arg: Arg, formal: Type): TypedArg
/** Turn a typed tree into an argument */
protected def treeToArg(arg: tpd.Tree): Arg
/** Check that argument corresponds to type `formal` and
* possibly add it to the list of adapted arguments
*/
protected def addArg(arg: TypedArg, formal: Type): Unit
/** Is this an argument of the form `expr: _*` or a RepeatedParamType
* derived from such an argument?
*/
protected def isVarArg(arg: Arg): Boolean
/** If constructing trees, turn last `n` processed arguments into a
* `SeqLiteral` tree with element type `elemFormal`.
*/
protected def makeVarArg(n: Int, elemFormal: Type): Unit
/** Signal failure with given message at position of given argument */
protected def fail(msg: => String, arg: Arg): Unit
/** Signal failure with given message at position of the application itself */
protected def fail(msg: => String): Unit
/** If constructing trees, the current function part, which might be
* affected by lifting. EmptyTree otherwise.
*/
protected def normalizedFun: tpd.Tree
/** If constructing trees, pull out all parts of the function
* which are not idempotent into separate prefix definitions
*/
protected def liftFun(): Unit = ()
/** A flag signalling that the application was so far succesful */
protected var ok = true
/** The function's type after widening and instantiating polytypes
* with polyparams or typevars in constraint set
*/
val methType = funType.widen match {
case funType: MethodType => funType
case funType: PolyType => ctx.track(funType).resultType
case _ => funType
}
/** The arguments re-ordered so that each named argument matches the
* same-named formal parameter.
*/
val orderedArgs =
if (hasNamedArg(args))
reorder(args.asInstanceOf[List[untpd.Tree]]).asInstanceOf[List[Arg]]
else
args
methType match {
case methType: MethodType =>
// apply the result type constraint, unless method type is dependent
if (!methType.isDependent)
ok = ok && constrainResult(methType.resultType, resultType)
// match all arguments with corresponding formal parameters
matchArgs(orderedArgs, methType.paramTypes, 0)
case _ =>
if (methType.isError) ok = false
else fail(s"$methString does not take parameters")
}
/** The application was succesful */
def success = ok
private def state = ctx.typerState
protected def methodType = methType.asInstanceOf[MethodType]
private def methString: String = s"method ${methRef.name}: ${methType.show}"
/** Re-order arguments to correctly align named arguments */
def reorder[T >: Untyped](args: List[Tree[T]]): List[Tree[T]] = {
var namedToArg: Map[Name, Tree[T]] =
(for (NamedArg(name, arg1) <- args) yield (name, arg1)).toMap
def badNamedArg(arg: Tree[_ >: Untyped]): Unit = {
val NamedArg(name, _) = arg
def msg =
if (methodType.paramNames contains name)
s"parameter $name of $methString is already instantiated"
else
s"$methString does not have a parameter $name"
fail(msg, arg.asInstanceOf[Arg])
}
def recur(pnames: List[Name], args: List[Tree[T]]): List[Tree[T]] = pnames match {
case pname :: pnames1 =>
namedToArg get pname match {
case Some(arg) =>
namedToArg -= pname
arg :: recur(pnames1, args)
case None =>
args match {
case (arg @ NamedArg(aname, _)) :: args1 =>
if (namedToArg contains aname)
emptyTree[T]() :: recur(pnames1, args)
else {
badNamedArg(arg)
recur(pnames1, args1)
}
case arg :: args1 =>
arg :: recur(pnames1, args1)
case Nil =>
recur(pnames1, args)
}
}
case nil =>
if (hasNamedArg(args)) {
val (namedArgs, otherArgs) = args partition isNamedArg
namedArgs foreach badNamedArg
otherArgs
}
else args
}
recur(methodType.paramNames, args)
}
/** Splice new method reference into existing application */
def spliceMeth(meth: tpd.Tree, app: tpd.Tree): tpd.Tree = app match {
case Apply(fn, args) => tpd.Apply(spliceMeth(meth, fn), args)
case TypeApply(fn, targs) => tpd.TypeApply(spliceMeth(meth, fn), targs)
case _ => meth
}
/** Find reference to default parameter getter for parameter #n in current
* parameter list, or NoType if none was found
*/
def findDefaultGetter(n: Int)(implicit ctx: Context): Type = {
def getterName = methRef.name.toTermName.defaultGetterName(n)
def ref(pre: Type, sym: Symbol): Type =
if (pre.exists && sym.isTerm) TermRef.withSym(pre, sym.asTerm) else NoType
val meth = methRef.symbol
if (meth.hasDefaultParams)
methRef.prefix match {
case NoPrefix =>
def findDefault(cx: Context): Type = {
if (cx eq NoContext) NoType
else if (cx.scope != cx.outer.scope &&
cx.lookup(methRef.name)
.filterWithPredicate(_.symbol == meth).exists) {
val denot = cx.lookup(getterName).toDenot(NoPrefix)
NamedType(NoPrefix, getterName).withDenot(denot)
} else findDefault(cx.outer)
}
findDefault(ctx)
case mpre =>
val cls = meth.owner
val pre =
if (meth.isClassConstructor) {
mpre.baseType(cls) match {
case TypeRef(clspre, _) => ref(clspre, cls.companionModule)
case _ => NoType
}
} else mpre
ref(pre, pre.member(getterName).symbol)
}
else NoType
}
/** Match re-ordered arguments against formal parameters
* @param n The position of the first parameter in formals in `methType`.
*/
def matchArgs(args: List[Arg], formals: List[Type], n: Int): Unit = {
if (success) formals match {
case formal :: formals1 =>
def addTyped(arg: Arg, formal: Type) =
addArg(typedArg(arg, formal), formal)
def missingArg(n: Int): Unit = {
val pname = methodType.paramNames(n)
fail(
if (pname contains '$') s"not enough arguments for $methString"
else s"missing argument for parameter $pname of $methString")
}
def tryDefault(n: Int, args1: List[Arg]): Unit = {
findDefaultGetter(n + TreeInfo.numArgs(normalizedFun)) match {
case dref: NamedType =>
liftFun()
addTyped(treeToArg(spliceMeth(tpd.Ident(dref), normalizedFun)), formal)
matchArgs(args1, formals1, n + 1)
case _ =>
missingArg(n)
}
}
if (formal.isRepeatedParam)
args match {
case arg :: Nil if isVarArg(arg) =>
addTyped(arg, formal)
case _ =>
val elemFormal = formal.typeArgs.head
args foreach (addTyped(_, elemFormal))
makeVarArg(args.length, elemFormal)
}
else args match {
case EmptyTree :: args1 =>
tryDefault(n, args1)
case arg :: args1 =>
addTyped(arg, formal)
matchArgs(args1, formals1, n + 1)
case nil =>
tryDefault(n, args)
}
case nil =>
args match {
case arg :: args1 => fail(s"too many arguments for $methString", arg)
case nil =>
}
}
}
/** Take into account that the result type of the current method
* must fit the given expected result type.
*/
def constrainResult(mt: Type, pt: Type): Boolean = pt match {
case FunProtoType(_, result) =>
mt match {
case mt: MethodType if !mt.isDependent =>
constrainResult(mt.resultType, pt.resultType)
case _ =>
true
}
case pt: ValueType =>
mt match {
case mt: ImplicitMethodType if !mt.isDependent =>
constrainResult(mt.resultType, pt)
case _ =>
isCompatible(mt, pt)
}
case _ =>
true
}
}
/** Subclass of Application for the cases where we are interested only
* in a "can/cannot apply" answer, without needing to construct trees or
* issue error messages.
*/
abstract class TestApplication[Arg](methRef: TermRef, funType: Type, args: List[Arg], resultType: Type)(implicit ctx: Context)
extends Application[Arg](methRef, funType, args, resultType) {
type TypedArg = Arg
type Result = Unit
/** The type of the given argument */
protected def argType(arg: Arg): Type
def typedArg(arg: Arg, formal: Type): Arg = arg
def addArg(arg: TypedArg, formal: Type) =
ok = ok & isCompatible(argType(arg), formal)
def makeVarArg(n: Int, elemFormal: Type) = {}
def fail(msg: => String, arg: Arg) =
ok = false
def fail(msg: => String) =
ok = false
def normalizedFun = tpd.EmptyTree
}
/** Subtrait of Application for the cases where arguments are (typed or
* untyped) trees.
*/
trait TreeApplication[T >: Untyped] extends Application[Tree[T]] {
type TypeArg = tpd.Tree
def isVarArg(arg: Tree[T]): Boolean = TreeInfo.isWildcardStarArg(arg)
}
/** Subclass of Application for applicability tests with trees as arguments. */
class ApplicableToTrees(methRef: TermRef, args: List[tpd.Tree], resultType: Type)(implicit ctx: Context)
extends TestApplication(methRef, methRef, args, resultType) with TreeApplication[Type] {
def argType(arg: tpd.Tree): Type = normalize(arg.tpe)
def treeToArg(arg: tpd.Tree): tpd.Tree = arg
}
/** Subclass of Application for applicability tests with types as arguments. */
class ApplicableToTypes(methRef: TermRef, args: List[Type], resultType: Type)(implicit ctx: Context)
extends TestApplication(methRef, methRef, args, resultType) {
def argType(arg: Type): Type = arg
def treeToArg(arg: tpd.Tree): Type = arg.tpe
def isVarArg(arg: Type): Boolean = arg.isRepeatedParam
}
/** Subclass of Application for type checking an Apply node, where
* types of arguments are either known or unknown.
*/
abstract class TypedApply[T >: Untyped](
app: untpd.Apply, fun: tpd.Tree, methRef: TermRef, args: List[Tree[T]], resultType: Type)(implicit ctx: Context)
extends Application(methRef, fun.tpe, args, resultType) with TreeApplication[T] {
type TypedArg = tpd.Tree
private var typedArgBuf = new mutable.ListBuffer[tpd.Tree]
private var liftedDefs: mutable.ListBuffer[tpd.Tree] = null
private var myNormalizedFun: tpd.Tree = fun
def addArg(arg: tpd.Tree, formal: Type): Unit =
typedArgBuf += adapt(arg, formal)
def makeVarArg(n: Int, elemFormal: Type): Unit = {
val args = typedArgBuf.takeRight(n).toList
typedArgBuf.trimEnd(n)
typedArgBuf += SeqLiteral(TypeTree(elemFormal), args)
}
def fail(msg: => String, arg: Tree[T]) = {
ctx.error(msg, arg.pos)
ok = false
}
def fail(msg: => String) = {
ctx.error(msg, app.pos)
ok = false
}
def normalizedFun = myNormalizedFun
override def liftFun(): Unit =
if (liftedDefs == null) {
liftedDefs = new mutable.ListBuffer[tpd.Tree]
myNormalizedFun = liftApp(liftedDefs, myNormalizedFun)
}
/** The index of the first difference between lists of trees `xs` and `ys`,
* where `EmptyTree`s in the second list are skipped.
* -1 if there are no differences.
*/
private def firstDiff[T <: Tree[_]](xs: List[T], ys: List[T], n: Int = 0): Int = xs match {
case x :: xs1 =>
ys match {
case EmptyTree :: ys1 => firstDiff(xs1, ys1, n)
case y :: ys1 => if (x ne y) n else firstDiff(xs1, ys1, n + 1)
case nil => n
}
case nil =>
ys match {
case EmptyTree :: ys1 => firstDiff(xs, ys1, n)
case y :: ys1 => n
case nil => -1
}
}
def sameSeq[T <: Tree[_]](xs: List[T], ys: List[T]): Boolean = firstDiff(xs, ys) < 0
val result: tpd.Tree =
if (!success) app withType ErrorType
else {
var typedArgs = typedArgBuf.toList
if (!sameSeq(app.args, orderedArgs)) {
// need to lift arguments to maintain evaluation order in the
// presence of argument reorderings.
liftFun()
val eqSuffixLength = firstDiff(app.args.reverse, orderedArgs.reverse)
val (liftable, rest) = typedArgs splitAt (typedArgs.length - eqSuffixLength)
typedArgs = liftArgs(liftedDefs, methType, liftable) ++ rest
}
if (sameSeq(typedArgs, args)) // trick to cut down on tree copying
typedArgs = args.asInstanceOf[List[tpd.Tree]]
val app1 = app.withType(methodType.instantiate(typedArgs map (_.tpe)))
.derivedApply(normalizedFun, typedArgs)
if (liftedDefs != null && liftedDefs.nonEmpty) tpd.Block(liftedDefs.toList, app1)
else app1
}
}
/** Subclass of Application for type checking an Apply node with untyped arguments. */
class ApplyToUntyped(app: untpd.Apply, fun: tpd.Tree, methRef: TermRef, args: List[untpd.Tree], resultType: Type)(implicit ctx: Context)
extends TypedApply(app, fun, methRef, args, resultType) {
def typedArg(arg: untpd.Tree, formal: Type): TypedArg = typed(arg, formal)
def treeToArg(arg: tpd.Tree): untpd.Tree = untpd.TypedSplice(arg)
}
/** Subclass of Application for type checking an Apply node with typed arguments. */
class ApplyToTyped(app: untpd.Apply, fun: tpd.Tree, methRef: TermRef, args: List[tpd.Tree], resultType: Type)(implicit ctx: Context)
extends TypedApply(app, fun, methRef, args, resultType) {
def typedArg(arg: tpd.Tree, formal: Type): TypedArg = arg
def treeToArg(arg: tpd.Tree): tpd.Tree = arg
}
def typedApply(app: untpd.Apply, fun: tpd.Tree, methRef: TermRef, args: List[tpd.Tree], resultType: Type)(implicit ctx: Context): tpd.Tree =
new ApplyToTyped(app, fun, methRef, args, resultType).result
def typedApply(fun: tpd.Tree, methRef: TermRef, args: List[tpd.Tree], resultType: Type)(implicit ctx: Context): tpd.Tree =
typedApply(Apply(untpd.TypedSplice(fun), Nil), fun, methRef, args, resultType)
/** Is given method reference applicable to argument types `args`?
* @param resultType The expected result type of the application
*/
def isApplicableToTrees(methRef: TermRef, args: List[tpd.Tree], resultType: Type)(implicit ctx: Context) =
new ApplicableToTrees(methRef, args, resultType)(ctx.fresh.withNewTyperState).success
/** Is given method reference applicable to arguments `args`?
* @param resultType The expected result type of the application
*/
def isApplicableToTypes(methRef: TermRef, args: List[Type], resultType: Type = WildcardType)(implicit ctx: Context) =
new ApplicableToTypes(methRef, args, resultType)(ctx.fresh.withNewTyperState).success
/** Is `tp` a subtype of `pt`? */
def testCompatible(tp: Type, pt: Type)(implicit ctx: Context) =
isCompatible(tp, pt)(ctx.fresh.withNewTyperState)
/** In a set of overloaded applicable alternatives, is `alt1` at least as good as
* `alt2`? `alt1` and `alt2` are nonoverloaded references.
*/
def isAsGood(alt1: TermRef, alt2: TermRef)(implicit ctx: Context): Boolean = {
/** Is class or module class `sym1` derived from class or module class `sym2`? */
def isDerived(sym1: Symbol, sym2: Symbol): Boolean =
if (sym1 isSubClass sym2) true
else if (sym2 is Module) isDerived(sym1, sym2.companionClass)
else (sym1 is Module) && isDerived(sym1.companionClass, sym2)
/** Is alternative `alt1` with type `tp1` as specific as alternative
* `alt2` with type `tp2` ? This is the case if `tp2` can be applied to
* `tp1` (without intervention of implicits) or `tp2' is a supertype of `tp1`.
*/
def isAsSpecific(alt1: TermRef, tp1: Type, alt2: TermRef, tp2: Type): Boolean = tp1 match {
case tp1: PolyType =>
def bounds(tparamRefs: List[TypeRef]) = tp1.paramBounds map (_.substParams(tp1, tparamRefs))
val tparams = ctx.newTypeParams(alt1.symbol.owner, tp1.paramNames, EmptyFlags, bounds)
isAsSpecific(alt1, tp1.instantiate(tparams map (_.symRef)), alt2, tp2)
case tp1: MethodType =>
isApplicableToTypes(alt2, tp1.paramTypes)(ctx)
case _ =>
testCompatible(tp1, tp2)(ctx)
}
val owner1 = alt1.symbol.owner
val owner2 = alt2.symbol.owner
val tp1 = alt1.widen
val tp2 = alt2.widen
def winsOwner1 = isDerived(owner1, owner2)
def winsType1 = isAsSpecific(alt1, tp1, alt2, tp2)
def winsOwner2 = isDerived(owner2, owner1)
def winsType2 = isAsSpecific(alt2, tp2, alt1, tp1)
// Assume the following probabilities:
//
// P(winsOwnerX) = 2/3
// P(winsTypeX) = 1/3
//
// Then the call probabilities of the 4 basic operations are as follows:
//
// winsOwner1: 1/1
// winsOwner2: 1/1
// winsType1 : 7/9
// winsType2 : 4/9
if (winsOwner1) /* 6/9 */ !winsOwner2 || /* 4/9 */ winsType1 || /* 8/27 */ !winsType2
else if (winsOwner2) /* 2/9 */ winsType1 && /* 2/27 */ !winsType2
else /* 1/9 */ winsType1 || /* 2/27 */ !winsType2
}
def narrowMostSpecific(alts: List[TermRef])(implicit ctx: Context): List[TermRef] = (alts: @unchecked) match {
case alt :: alts1 =>
def winner(bestSoFar: TermRef, alts: List[TermRef]): TermRef = alts match {
case alt :: alts1 =>
winner(if (isAsGood(alt, bestSoFar)) alt else bestSoFar, alts1)
case nil =>
bestSoFar
}
val best = winner(alt, alts1)
def asGood(alts: List[TermRef]): List[TermRef] = alts match {
case alt :: alts1 =>
if ((alt eq best) || !isAsGood(alt, best)) asGood(alts1)
else alt :: asGood(alts1)
case nil =>
Nil
}
best :: asGood(alts1)
}
private val dummyTree = Literal(Constant(null))
def dummyTreeOfType(tp: Type): tpd.Tree = dummyTree withType tp
/** Resolve overloaded alternative `alts`, given expected type `pt`. */
def resolveOverloaded(alts: List[TermRef], pt: Type)(implicit ctx: Context): List[TermRef] = {
def isDetermined(alts: List[TermRef]) = alts.isEmpty || alts.tail.isEmpty
/** The shape of given tree as a type; cannot handle named arguments. */
def typeShape(tree: untpd.Tree): Type = tree match {
case untpd.Function(args, body) =>
defn.FunctionType(args map Function.const(defn.AnyType), typeShape(body))
case _ =>
defn.NothingType
}
/** The shape of given tree as a type; is more expensive than
* typeShape but can can handle named arguments.
*/
def treeShape(tree: untpd.Tree): tpd.Tree = tree match {
case NamedArg(name, arg) =>
val argShape = treeShape(arg)
tree.withType(argShape.tpe).derivedNamedArg(name, argShape)
case _ =>
dummyTreeOfType(typeShape(tree))
}
def narrowByTypes(alts: List[TermRef], argTypes: List[Type], resultType: Type): List[TermRef] =
alts filter (isApplicableToTypes(_, argTypes, resultType))
val candidates = pt match {
case pt @ FunProtoType(args, resultType) =>
val numArgs = args.length
def sizeFits(alt: TermRef, tp: Type): Boolean = tp match {
case tp: PolyType => sizeFits(alt, tp.resultType)
case MethodType(_, ptypes) =>
val numParams = ptypes.length
def isVarArgs = ptypes.nonEmpty && ptypes.last.isRepeatedParam
def hasDefault = alt.symbol.hasDefaultParams
if (numParams == numArgs) true
else if (numParams < numArgs) isVarArgs
else if (numParams > numArgs + 1) hasDefault
else isVarArgs || hasDefault
}
def narrowBySize(alts: List[TermRef]): List[TermRef] =
alts filter (alt => sizeFits(alt, alt.widen))
def narrowByShapes(alts: List[TermRef]): List[TermRef] =
if (args exists (_.isInstanceOf[untpd.Function]))
if (args exists (_.isInstanceOf[NamedArg[_]]))
narrowByTrees(alts, args map treeShape, resultType)
else
narrowByTypes(alts, args map typeShape, resultType)
else
alts
def narrowByTrees(alts: List[TermRef], args: List[tpd.Tree], resultType: Type): List[TermRef] =
alts filter (isApplicableToTrees(_, args, resultType))
val alts1 = narrowBySize(alts)
if (isDetermined(alts1)) alts1
else {
val alts2 = narrowByShapes(alts1)
if (isDetermined(alts2)) alts2
else narrowByTrees(alts2, pt.typedArgs, resultType)
}
case defn.FunctionType(args, resultType) =>
narrowByTypes(alts, args, resultType)
case tp =>
alts filter (alt => testCompatible(normalize(alt), tp))
}
if (isDetermined(candidates)) candidates
else narrowMostSpecific(candidates)(ctx.addMode(ImplicitsDisabled))
}
}
