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Infer.scala
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Infer.scala
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/*
* Scala (https://www.scala-lang.org)
*
* Copyright EPFL and Lightbend, Inc.
*
* Licensed under Apache License 2.0
* (http://www.apache.org/licenses/LICENSE-2.0).
*
* See the NOTICE file distributed with this work for
* additional information regarding copyright ownership.
*/
package scala.tools.nsc
package typechecker
import scala.collection.{immutable, mutable}, mutable.ListBuffer
import scala.reflect.internal.Depth
import scala.util.control.ControlThrowable
import symtab.Flags._
import scala.tools.nsc.Reporting.WarningCategory
/** This trait contains methods related to type parameter inference.
*
* @author Martin Odersky
*/
trait Infer extends Checkable {
self: Analyzer =>
import global._
import definitions._
import typeDebug.ptBlock
import typeDebug.str.parentheses
import typingStack.printTyping
/** The formal parameter types corresponding to `formals`.
* If `formals` has a repeated last parameter, a list of
* (numArgs - numFormals + 1) copies of its type is appended
* to the other formals. By-name types are replaced with their
* underlying type.
*
* @param removeByName allows keeping ByName parameters. Used in NamesDefaults.
* @param removeRepeated allows keeping repeated parameter (if there's one argument). Used in NamesDefaults.
*/
def formalTypes(formals: List[Type], numArgs: Int, removeByName: Boolean = true, removeRepeated: Boolean = true): List[Type] = {
val numFormals = formals.length
val formals1 = if (removeByName) formals mapConserve dropByName else formals
val expandLast = (
(removeRepeated || numFormals != numArgs)
&& isVarArgTypes(formals1)
)
if (expandLast) {
// extract the T from T*
val lastType = formals1.last.dealiasWiden.typeArgs.head
val n = numArgs - numFormals + 1
// Optimized version of: formals1.init ::: List.fill(n)(lastType)
val result = mutable.ListBuffer[Type]()
var fs = formals1
while ((fs ne Nil) && (fs.tail ne Nil)) {
result.addOne(fs.head)
fs = fs.tail
}
result.prependToList(fillList(n)(lastType))
} else
formals1
}
// @requires sam == samOf(samTp)
def instantiateSamFromFunction(funTp: Type, samTp: Type, sam: Symbol) = {
val samClassSym = samTp.typeSymbol
// the unknowns
val tparams = samClassSym.typeParams
if (tparams.isEmpty) samTp
else {
// ... as typevars
val tvars = tparams map freshVar
// we're trying to fully define the type arguments for this type constructor
val samTyCon = samClassSym.typeConstructor
val ptVars = appliedType(samTyCon, tvars)
// carry over info from pt
ptVars <:< samTp
val samInfoWithTVars = ptVars.memberInfo(sam)
// use function type subtyping, not method type subtyping (the latter is invariant in argument types)
funTp <:< functionType(samInfoWithTVars.paramTypes, samInfoWithTVars.finalResultType)
// solve constraints tracked by tvars
val targs = solvedTypes(tvars, tparams, varianceInType(sam.info), upper = false, lubDepth(sam.info :: Nil))
debuglog(s"sam infer: $samTp --> ${appliedType(samTyCon, targs)} by ${funTp} <:< $samInfoWithTVars --> $targs for $tparams")
appliedType(samTyCon, targs)
}
}
/** Sorts the alternatives according to the given comparison function.
* Returns a list containing the best alternative as well as any which
* the best fails to improve upon.
*/
private def bestAlternatives(alternatives: List[Symbol])(isBetter: (Symbol, Symbol) => Boolean): List[Symbol] = {
def improves(sym1: Symbol, sym2: Symbol) = (
(sym2 eq NoSymbol)
|| sym2.isError
|| isBetter(sym1, sym2)
)
alternatives sortWith improves match {
case best :: rest if rest.nonEmpty => best :: rest.filterNot(alt => improves(best, alt))
case bests => bests
}
}
// we must not allow CyclicReference to be thrown when sym.info is called
// in checkAccessible, because that would mark the symbol erroneous, which it
// is not. But if it's a true CyclicReference then macro def will report it.
// See comments to TypeSigError for an explanation of this special case.
// [Eugene] is there a better way?
private object CheckAccessibleMacroCycle extends TypeCompleter {
val tree = EmptyTree
override def complete(sym: Symbol) = ()
}
/** A fresh type variable with given type parameter as origin.
*/
def freshVar(tparam: Symbol): TypeVar = TypeVar(tparam)
class NoInstance(msg: String) extends ControlThrowable(msg)
private class DeferredNoInstance(getmsg: () => String) extends NoInstance("") {
override def getMessage(): String = getmsg()
}
private def ifNoInstance[T](f: String => T): PartialFunction[Throwable, T] = {
case x: NoInstance => f(x.getMessage)
}
/** Map every TypeVar to its constraint.inst field.
* throw a NoInstance exception if a NoType or WildcardType is encountered.
*/
object instantiate extends TypeMap {
private var excludedVars = immutable.Set[TypeVar]()
private def applyTypeVar(tv: TypeVar): Type = tv match {
case TypeVar(origin, constr) if !constr.instValid => throw new DeferredNoInstance(() => s"no unique instantiation of type variable $origin could be found")
case _ if excludedVars(tv) => throw new NoInstance("cyclic instantiation")
case TypeVar(_, constr) =>
excludedVars += tv
try apply(constr.inst)
finally excludedVars -= tv
}
def apply(tp: Type): Type = tp match {
case _: ProtoType | NoType => throw new NoInstance("undetermined type")
case tv: TypeVar if !tv.untouchable => applyTypeVar(tv)
case _ => mapOver(tp)
}
}
@inline final def falseIfNoInstance(body: => Boolean): Boolean =
try body catch { case _: NoInstance => false }
/** Is type fully defined, i.e. no embedded anytypes or wildcards in it?
*/
private[typechecker] def isFullyDefined(tp: Type): Boolean = tp match {
case _: ProtoType | NoType => false
case NoPrefix | ThisType(_) | ConstantType(_) => true
case TypeRef(pre, _, args) => isFullyDefined(pre) && (args forall isFullyDefined)
case SingleType(pre, _) => isFullyDefined(pre)
case RefinedType(ts, _) => ts forall isFullyDefined
case TypeVar(_, constr) if constr.inst == NoType => false
case _ => falseIfNoInstance { instantiate(tp); true }
}
/** Solve constraint collected in types `tvars`.
*
* @param tvars All type variables to be instantiated.
* @param tparams The type parameters corresponding to `tvars`
* @param getVariance Function to extract variances of type parameters; we need to reverse
* solution direction for all contravariant variables.
* @param upper When `true` search for max solution else min.
* @throws NoInstance
*/
def solvedTypes(tvars: List[TypeVar], tparams: List[Symbol], getVariance: Variance.Extractor[Symbol], upper: Boolean, depth: Depth): List[Type] = {
if (tvars.isEmpty) Nil else {
printTyping("solving for " + parentheses(map2(tparams, tvars)((p, tv) => s"${p.name}: $tv")))
// !!! What should be done with the return value of "solve", which is at present ignored?
// The historical commentary says "no panic, it's good enough to just guess a solution,
// we'll find out later whether it works", meaning don't issue an error here when types
// don't conform to bounds. That means you can never trust the results of implicit search.
// For an example where this was not being heeded, scala/bug#2421.
solve(tvars, tparams, getVariance, upper, depth)
tvars map instantiate
}
}
def skipImplicit(tp: Type) = tp match {
case mt: MethodType if mt.isImplicit => mt.resultType
case _ => tp
}
private lazy val stdErrorClass = rootMirror.RootClass.newErrorClass(tpnme.ERROR)
private lazy val stdErrorValue = stdErrorClass.newErrorValue(nme.ERROR)
/** The context-dependent inferencer part */
abstract class Inferencer extends InferencerContextErrors with InferCheckable {
def context: Context
import InferErrorGen._
/* -- Error Messages --------------------------------------------------- */
def setError[T <: Tree](tree: T): T = {
// scala/bug#7388, one can incur a cycle calling sym.toString
// (but it'd be nicer if that weren't so)
def name = {
val sym = tree.symbol
val nameStr = try sym.toString catch { case _: CyclicReference => sym.nameString }
newTermName(s"<error: $nameStr>")
}
def errorClass = if (context.reportErrors) context.owner.newErrorClass(name.toTypeName) else stdErrorClass
def errorValue = if (context.reportErrors) context.owner.newErrorValue(name) else stdErrorValue
def errorSym = if (tree.isType) errorClass else errorValue
if (tree.hasSymbolField)
tree setSymbol errorSym
tree setType ErrorType
}
def getContext = context
def explainTypes(tp1: Type, tp2: Type) = {
if (context.reportErrors)
withDisambiguation(List(), tp1, tp2)(global.explainTypes(tp1, tp2))
}
// When filtering sym down to the accessible alternatives leaves us empty handed.
private def checkAccessibleError(tree: Tree, sym: Symbol, pre: Type, site: Tree): Tree = {
if (settings.isDebug) {
Console.println(context)
Console.println(tree)
Console.println("" + pre + " " + sym.owner + " " + context.owner + " " + context.outer.enclClass.owner + " " + sym.owner.thisType + (pre =:= sym.owner.thisType))
}
ErrorUtils.issueTypeError(AccessError(tree, sym, pre, context.enclClass.owner,
if (settings.check.isDefault)
analyzer.lastAccessCheckDetails
else
ptBlock("because of an internal error (no accessible symbol)",
"sym.ownerChain" -> sym.ownerChain,
"underlyingSymbol(sym)" -> underlyingSymbol(sym),
"pre" -> pre,
"site" -> site,
"tree" -> tree,
"sym.accessBoundary(sym.owner)" -> sym.accessBoundary(sym.owner),
"context.owner" -> context.owner,
"context.outer.enclClass.owner" -> context.outer.enclClass.owner
)
))(context)
setError(tree)
}
/* -- Tests & Checks---------------------------------------------------- */
/** Check that `sym` is defined and accessible as a member of
* tree `site` with type `pre` in current context.
* @note PP: In case it's not abundantly obvious to anyone who might read
* this, the method does a lot more than "check" these things, as does
* nearly every method in the compiler, so don't act all shocked.
* This particular example "checks" its way to assigning both the
* symbol and type of the incoming tree, in addition to forcing lots
* of symbol infos on its way to transforming java raw types (but
* only of terms - why?)
*
* Note: pre is not refchecked -- moreover, refchecking the resulting tree may not refcheck pre,
* since pre may not occur in its type (callers should wrap the result in a TypeTreeWithDeferredRefCheck)
*/
def checkAccessible(tree: Tree, sym: Symbol, pre: Type, site: Tree, isJava: Boolean): Tree = {
def malformed(ex: MalformedType, instance: Type): Type = {
val what = if (ex.msg contains "malformed type") "is malformed" else s"contains a ${ex.msg}"
val message = s"\n because its instance type $instance $what"
val error = AccessError(tree, sym, pre, context.enclClass.owner, message)
ErrorUtils.issueTypeError(error)(context)
ErrorType
}
def accessible = sym filter (alt => context.isAccessible(alt, pre, site.isInstanceOf[Super])) match {
case NoSymbol if sym.isJavaDefined && context.unit.isJava => sym // don't try to second guess Java; see #4402
case sym1 => sym1
}
if (context.unit.exists && settings.YtrackDependencies.value)
context.unit.registerDependency(sym.enclosingTopLevelClass)
if (sym.isError)
tree setSymbol sym setType ErrorType
else accessible match {
case NoSymbol => checkAccessibleError(tree, sym, pre, site)
case sym if context.owner.isTermMacro && (sym hasFlag LOCKED) => throw CyclicReference(sym, CheckAccessibleMacroCycle)
case sym =>
val sym1 = if (sym.isTerm) sym.cookJavaRawInfo() else sym // xform java rawtypes into existentials
val owntype = (
try pre memberType sym1
catch { case ex: MalformedType => malformed(ex, pre memberType underlyingSymbol(sym)) }
)
tree setSymbol sym1 setType (
pre match {
// OPT: avoid lambda allocation and Type.map for super constructor calls
case _: SuperType if !sym.isConstructor && !owntype.isInstanceOf[OverloadedType] =>
owntype map ((tp: Type) => if (tp eq pre) site.symbol.thisType else tp)
case _ =>
if ((owntype eq ObjectTpe) && isJava) ObjectTpeJava
else owntype
}
)
}
}
/** "Compatible" means conforming after conversions.
* "Raising to a thunk" is not implicit; therefore, for purposes of applicability and
* specificity, an arg type `A` is considered compatible with cbn formal parameter type `=> A`.
* For this behavior, the type `pt` must have cbn params preserved; for instance, `formalTypes(removeByName = false)`.
*
* `isAsSpecific` no longer prefers A by testing applicability to A for both m(A) and m(=> A)
* since that induces a tie between m(=> A) and m(=> A, B*) [scala/bug#3761]
*/
private def isCompatible(tp: Type, pt: Type): Boolean = {
def isCompatibleByName(tp: Type, pt: Type): Boolean = (
isByNameParamType(pt)
&& !isByNameParamType(tp)
&& isCompatible(tp, dropByName(pt))
)
def isCompatibleSam(tp: Type, pt: Type): Boolean = (definitions.isFunctionType(tp) || tp.isInstanceOf[MethodType] || tp.isInstanceOf[PolyType]) && {
val samFun = samToFunctionType(pt)
(samFun ne NoType) && isCompatible(tp, samFun)
}
// can only compare if both types are repeated or neither is (T* is not actually a first-class type, even though it has a BTS and thus participates in subtyping)
(!isRepeatedParamType(tp) || isRepeatedParamType(pt)) && {
val tp1 = methodToExpressionTp(tp)
((tp1 weak_<:< pt)
|| isCoercible(tp1, pt)
|| isCompatibleByName(tp, pt)
|| isCompatibleSam(tp, pt)
)
}
}
def isCompatibleArgs(tps: List[Type], pts: List[Type]) = {
val res = (tps corresponds pts)(isCompatible)
// println(s"isCompatibleArgs $res : $tps <:< $pts")
res
}
def isWeaklyCompatible(tp: Type, pt: Type): Boolean = {
def isCompatibleNoParamsMethod = tp match {
case MethodType(Nil, restpe) => isCompatible(restpe, pt)
case _ => false
}
( pt.typeSymbol == UnitClass // can perform unit coercion
|| isCompatible(tp, pt)
|| isCompatibleNoParamsMethod // can perform implicit () instantiation
)
}
/* Like weakly compatible but don't apply any implicit conversions yet.
* Used when comparing the result type of a method with its prototype.
*/
def isConservativelyCompatible(tp: Type, pt: Type): Boolean =
context.withImplicitsDisabled(isWeaklyCompatible(tp, pt))
// Overridden at the point of instantiation, where inferView is visible.
def isCoercible(tp: Type, pt: Type): Boolean = false
/* -- Type instantiation------------------------------------------------ */
/** Replace any (possibly bounded) wildcard types in type `tp`
* by existentially bound variables.
*/
def makeFullyDefined(tp: Type): Type = {
object typeMap extends TypeMap {
def tparamsList: List[Symbol] = if (tparams_ == null) Nil else tparams_.toList
private var tparams_ : ListBuffer[Symbol] = null
private var i = 0
private def nextI(): Int = try i finally i += 1
private def addTypeParam(bounds: TypeBounds): Type = {
val tparam = context.owner.newExistential(nme.existentialName(nextI()), context.tree.pos.focus) setInfo bounds
if (tparams_ == null) tparams_ = ListBuffer.empty
tparams_ += tparam
tparam.tpe
}
override def apply(tp: Type): Type = mapOver(tp) match {
case pt: ProtoType => addTypeParam(pt.toBounds)
case t => t
}
}
val tp1 = typeMap(tp)
if (tp eq tp1) tp
else existentialAbstraction(typeMap.tparamsList, tp1)
}
def ensureFullyDefined(tp: Type): Type = if (isFullyDefined(tp)) tp else makeFullyDefined(tp)
/** Return inferred type arguments of polymorphic expression, given
* type vars, its type parameters and result type and a prototype `pt`.
* If the type variables cannot be instantiated such that the type
* conforms to `pt`, return null.
*/
private def exprTypeArgs(tvars: List[TypeVar], tparams: List[Symbol], restpe: Type, pt: Type, useWeaklyCompatible: Boolean): List[Type] = {
val resTpVars = restpe.instantiateTypeParams(tparams, tvars)
if (if (useWeaklyCompatible) isWeaklyCompatible(resTpVars, pt) else isCompatible(resTpVars, pt)) {
// If conforms has just solved a tvar as a singleton type against pt, then we need to
// prevent it from being widened later by adjustTypeArgs
tvars.foreach(_.constr.stopWideningIfPrecluded())
// If the restpe is an implicit method, and the expected type is fully defined
// optimize type variables wrt to the implicit formals only; ignore the result type.
// See test pos/jesper.scala
val variance = restpe match {
case mt: MethodType if mt.isImplicit && isFullyDefined(pt) => MethodType(mt.params, AnyTpe)
case _ => restpe
}
try solvedTypes(tvars, tparams, varianceInType(variance), upper = false, lubDepth(restpe :: pt :: Nil))
catch { case _: NoInstance => null }
} else
null
}
/** Overload which allocates fresh type vars.
* The other one exists because apparently inferExprInstance needs access to the typevars
* after the call, and it's wasteful to return a tuple and throw it away almost every time.
*/
private def exprTypeArgs(tparams: List[Symbol], restpe: Type, pt: Type, useWeaklyCompatible: Boolean): List[Type] =
exprTypeArgs(tparams map freshVar, tparams, restpe, pt, useWeaklyCompatible)
/** Return inferred proto-type arguments of function, given
* its type and value parameters and result type, and a
* prototype `pt` for the function result.
* Type arguments need to be either determined precisely by
* the prototype, or they are maximized, if they occur only covariantly
* in the value parameter list.
* If instantiation of a type parameter fails,
* take WildcardType for the proto-type argument.
*/
def protoTypeArgs(tparams: List[Symbol], formals: List[Type], restpe: Type, pt: Type): List[Type] = {
// Map type variable to its instance, or, if `variance` is variant,
// to its upper or lower bound
def instantiateToBound(tvar: TypeVar, variance: Variance): Type = {
lazy val hiBounds = tvar.constr.hiBounds
lazy val loBounds = tvar.constr.loBounds
lazy val upper = glb(hiBounds)
lazy val lower = lub(loBounds)
def setInst(tp: Type): Type = {
tvar setInst tp
assert(tvar.constr.inst != tvar, tvar.origin)
instantiate(tvar.constr.inst)
}
if (tvar.constr.instValid)
instantiate(tvar.constr.inst)
else if (loBounds.nonEmpty && variance.isContravariant)
setInst(lower)
else if (hiBounds.nonEmpty && (variance.isPositive || loBounds.nonEmpty && upper <:< lower))
setInst(upper)
else
WildcardType
}
val tvars = tparams map freshVar
if (isConservativelyCompatible(restpe.instantiateTypeParams(tparams, tvars), pt))
map2(tparams, tvars)((tparam, tvar) =>
try instantiateToBound(tvar, varianceInTypes(formals)(tparam))
catch { case ex: NoInstance => WildcardType }
)
else
WildcardType.fillList(tvars.length)
}
/** Retract arguments that were inferred to Nothing because inference failed. Correct types for repeated params.
*
* We detect Nothing-due-to-failure by only retracting a parameter if either:
* - it occurs in an invariant/contravariant position in `restpe`
* - `restpe == WildcardType`
*
* Retracted parameters are mapped to None.
* TODO:
* - make sure the performance hit of storing these in a map is acceptable (it's going to be a small map in 90% of the cases, I think)
* - refactor further up the callstack so that we don't have to do this post-factum adjustment?
*
* Rewrite for repeated param types: Map T* entries to Seq[T].
* @return map from tparams to inferred arg, if inference was successful, tparams that map to None are considered left undetermined
* type parameters that are inferred as `scala.Nothing` and that are not covariant in `restpe` are taken to be undetermined
*/
def adjustTypeArgs(tparams: List[Symbol], tvars: List[TypeVar], targs: List[Type], restpe: Type = WildcardType): AdjustedTypeArgs = {
val okParams = ListBuffer[Symbol]()
val okArgs = ListBuffer[Type]()
val undetParams = ListBuffer[Symbol]()
val allArgs = ListBuffer[Type]()
foreach3(tparams, tvars, targs) { (tparam, tvar, targ) =>
val retract = (
targ.typeSymbol == NothingClass // only retract Nothings
&& (restpe.isWildcard || !varianceInType(restpe)(tparam).isPositive) // don't retract covariant occurrences
)
if (retract) {
undetParams += tparam
allArgs += NothingTpe
} else {
val arg =
if (targ.typeSymbol == RepeatedParamClass) targ.baseType(SeqClass)
else if (targ.typeSymbol == JavaRepeatedParamClass) targ.baseType(ArrayClass)
// this infers Foo.type instead of "object Foo" (see also widenIfNecessary)
else if (targ.typeSymbol.isModuleClass || tvar.constr.avoidWiden) targ
else targ.widen
okParams += tparam
okArgs += arg
allArgs += arg
}
}
AdjustedTypeArgs(okParams.toList, okArgs.toList, undetParams.toList, allArgs.toList)
}
/** Return inferred type arguments, given type parameters, formal parameters,
* argument types, result type and expected result type.
* If this is not possible, throw a `NoInstance` exception.
* Undetermined type arguments are represented by `definitions.NothingTpe`.
* No check that inferred parameters conform to their bounds is made here.
*
* @param fn the function for reporting, may be empty
* @param tparams the type parameters of the method
* @param formals the value parameter types of the method
* @param restpe the result type of the method
* @param argtpes the argument types of the application
* @param pt the expected return type of the application
* @return @see adjustTypeArgs
*
* @throws NoInstance
*/
def methTypeArgs(fn: Tree, tparams: List[Symbol], formals: List[Type], restpe: Type,
argtpes: List[Type], pt: Type): AdjustedTypeArgs = {
val tvars = tparams map freshVar
if (!sameLength(formals, argtpes))
throw new NoInstance("parameter lists differ in length")
val restpeInst = restpe.instantiateTypeParams(tparams, tvars)
// first check if typevars can be fully defined from the expected type.
// The return value isn't used so I'm making it obvious that this side
// effects, because a function called "isXXX" is not the most obvious
// side effecter.
isConservativelyCompatible(restpeInst, pt): Unit
// Return value unused with the following explanation:
//
// Just wait and instantiate from the arguments. That way,
// we can try to apply an implicit conversion afterwards.
// This case could happen if restpe is not fully defined, so the
// search for an implicit from restpe => pt fails due to ambiguity.
// See #347. Therefore, the following two lines are commented out.
//
// throw new DeferredNoInstance(() =>
// "result type " + normalize(restpe) + " is incompatible with expected type " + pt)
for (tvar <- tvars)
if (!isFullyDefined(tvar)) tvar.constr.inst = NoType
// Then define remaining type variables from argument types.
foreach2(argtpes, formals) { (argtpe, formal) =>
val tp1 = argtpe.deconst.instantiateTypeParams(tparams, tvars)
val pt1 = formal.instantiateTypeParams(tparams, tvars)
// Note that isCompatible side-effects: subtype checks involving typevars
// are recorded in the typevar's bounds (see TypeConstraint)
if (!isCompatible(tp1, pt1)) {
throw new DeferredNoInstance(() =>
"argument expression's type is not compatible with formal parameter type" + foundReqMsg(tp1, pt1))
}
}
val targs = solvedTypes(tvars, tparams, varianceInTypes(formals), upper = false, lubDepth(formals) max lubDepth(argtpes))
if (settings.warnInferAny && !fn.isEmpty) {
// Can warn about inferring Any/AnyVal/Object as long as they don't appear
// explicitly anywhere amongst the formal, argument, result, or expected type.
// ...or lower bound of a type param, since they're asking for it.
var checked, warning = false
def checkForAny(): Unit = {
val collector = new ContainsAnyCollector(topTypes) {
val seen = mutable.Set.empty[Type]
override def apply(t: Type): Unit = {
def saw(dw: Type): Unit =
if (!result && !seen(dw)) {
seen += dw
if (!dw.typeSymbol.isRefinementClass) super.apply(dw)
}
if (!result && !seen(t)) t.dealiasWidenChain.foreach(saw)
}
}
@`inline` def containsAny(t: Type) = collector.collect(t)
val hasAny = containsAny(pt) || containsAny(restpe) ||
formals.exists(containsAny) ||
argtpes.exists(containsAny) ||
tparams.exists(x => containsAny(x.info.lowerBound))
checked = true
warning = !hasAny
}
def canWarnAboutAny = { if (!checked) checkForAny() ; warning }
targs.foreach(targ => if (topTypes.contains(targ.typeSymbol) && canWarnAboutAny) context.warning(fn.pos, s"a type was inferred to be `${targ.typeSymbol.name}`; this may indicate a programming error.", WarningCategory.LintInferAny))
}
adjustTypeArgs(tparams, tvars, targs, restpe)
}
/** One must step carefully when assessing applicability due to
* complications from varargs, tuple-conversion, named arguments.
* This method is used to filter out inapplicable methods,
* its behavior slightly configurable based on what stage of
* overloading resolution we're at.
*
* This method has boolean parameters, which is usually suboptimal
* but I didn't work out a better way. They don't have defaults,
* and the method's scope is limited.
*/
private[typechecker] def isApplicableBasedOnArity(tpe: Type, argsCount: Int, varargsStar: Boolean, tuplingAllowed: Boolean): Boolean = followApply(tpe) match {
case OverloadedType(pre, alts) =>
// followApply may return an OverloadedType (tpe is a value type with multiple `apply` methods)
alts exists (alt => isApplicableBasedOnArity(pre memberType alt, argsCount, varargsStar, tuplingAllowed))
case _ =>
val paramsCount = tpe.params.length
// simpleMatch implies we're not using defaults
val simpleMatch = paramsCount == argsCount
val varargsTarget = isVarArgsList(tpe.params)
// varargsMatch implies we're not using defaults, as varargs and defaults are mutually exclusive
def varargsMatch = varargsTarget && (paramsCount - 1) <= argsCount
// another reason why auto-tupling is a bad idea: it can hide the use of defaults, so must rule those out explicitly
def tuplingMatch = tuplingAllowed && eligibleForTupleConversion(paramsCount, argsCount, varargsTarget)
// varargs and defaults are mutually exclusive, so not using defaults if `varargsTarget`
// we're not using defaults if there are (at least as many) arguments as parameters (not using exact match to allow for tupling)
def notUsingDefaults = varargsTarget || paramsCount <= argsCount
// A varargs star call, e.g. (x, y:_*) can only match a varargs method
// with the same number of parameters. See scala/bug#5859 for an example of what
// would fail were this not enforced before we arrived at isApplicable.
if (varargsStar)
varargsTarget && simpleMatch
else
simpleMatch || varargsMatch || (tuplingMatch && notUsingDefaults)
}
private[typechecker] def followApply(tp: Type): Type = tp match {
case _ if tp.isError => tp // scala/bug#8228, `ErrorType nonPrivateMember nme.apply` returns an member with an erroneous type!
case NullaryMethodType(restp) =>
val restp1 = followApply(restp)
if (restp1 eq restp) tp else restp1
case _ =>
//OPT cut down on #closures by special casing non-overloaded case
// was: tp.nonPrivateMember(nme.apply) filter (_.isPublic)
tp nonPrivateMember nme.apply match {
case NoSymbol => tp
case sym if !sym.isOverloaded && sym.isPublic => OverloadedType(tp, sym.alternatives)
case sym => OverloadedType(tp, sym.filter(_.isPublic).alternatives)
}
}
/**
* Verifies whether the named application is valid. The logic is very
* similar to the one in NamesDefaults.removeNames.
*
* @return a triple (argtpes1, argPos, namesOk) where
* - argtpes1 the argument types in named application (assignments to
* non-parameter names are treated as assignments, i.e. type Unit)
* - argPos a Function1[Int, Int] mapping arguments from their current
* to the corresponding position in params
* - namesOK is false when there's an invalid use of named arguments
*/
private def checkNames(argtpes: List[Type], params: List[Symbol]): (List[Type], Array[Int], Boolean) = {
val argPos = Array.fill(argtpes.length)(-1)
var positionalAllowed, namesOK = true
var index = 0
val argtpes1 = argtpes map {
case NamedType(name, tp) => // a named argument
var res = tp
val pos = params.indexWhere(p => paramMatchesName(p, name) && !p.isSynthetic)
if (pos == -1) {
if (positionalAllowed) { // treat assignment as positional argument
argPos(index) = index
res = UnitTpe // TODO: this is a bit optimistic, the name may not refer to a mutable variable...
} else // unknown parameter name
namesOK = false
} else if (argPos.contains(pos)) { // parameter specified twice
namesOK = false
} else {
if (index != pos)
positionalAllowed = false
argPos(index) = pos
}
index += 1
res
case tp => // a positional argument
argPos(index) = index
if (!positionalAllowed)
namesOK = false // positional after named
index += 1
tp
}
(argtpes1, argPos, namesOK)
}
/** True if the given parameter list can accept a tupled argument list,
* and the argument list can be tupled (based on its length.)
*/
def eligibleForTupleConversion(paramsCount: Int, argsCount: Int, varargsTarget: Boolean): Boolean = {
def canSendTuple = argsCount match {
case 0 => !varargsTarget // avoid () to (()) conversion - scala/bug#3224
case 1 => false // can't tuple a single argument
case n => n <= MaxTupleArity // <= 22 arguments
}
def canReceiveTuple = paramsCount match {
case 1 => true
case 2 => varargsTarget
case _ => false
}
canSendTuple && canReceiveTuple
}
def eligibleForTupleConversion(formals: List[Type], argsCount: Int): Boolean = formals match {
case p :: Nil => eligibleForTupleConversion(1, argsCount, varargsTarget = isScalaRepeatedParamType(p))
case _ :: p :: Nil if isScalaRepeatedParamType(p) => eligibleForTupleConversion(2, argsCount, varargsTarget = true)
case _ => false
}
/** The type of an argument list after being coerced to a tuple.
* @note Pre-condition: The argument list is eligible for tuple conversion.
*/
private def typeAfterTupleConversion(argtpes: List[Type]): Type =
if (argtpes.isEmpty) UnitTpe // aka "Tuple0"
else tupleType(argtpes map {
case NamedType(name, tp) => UnitTpe // not a named arg - only assignments here
case RepeatedType(tp) => tp // but probably shouldn't be tupling a call containing :_*
case tp => tp
})
/** If the argument list needs to be tupled for the parameter list,
* a list containing the type of the tuple. Otherwise, the original
* argument list.
*
* NOTE: we have to exclude repeated parameter types for overloading resolution like this:
* def f[T](x: T): T = x
* def f[T](x: T, xs: T*): T = x
*
* In the process of deciding which ones is more specific, isApplicableToMethod would otherwise try T' = (T, T*)
*/
def tupleIfNecessary(formals: List[Type], argtpes: List[Type]): List[Type] = {
if (!argtpes.exists(isRepeatedParamType) && eligibleForTupleConversion(formals, argtpes.size))
typeAfterTupleConversion(argtpes) :: Nil
else
argtpes
}
// This is primarily a duplicate of enhanceBounds in typedAppliedTypeTree
// modified to use updateInfo rather than setInfo to avoid wiping out
// type history.
def enhanceBounds(okparams: List[Symbol], okargs: List[Type], undets: List[Symbol]): Unit =
undets.foreach { undet =>
val bounds = undet.info.bounds
val substBounds = bounds.subst(okparams, okargs)
if(bounds ne substBounds)
undet.updateInfo(substBounds)
}
private def isApplicableToMethod(undetparams: List[Symbol], mt: MethodType, argtpes0: List[Type], pt: Type): Boolean = {
val formals = formalTypes(mt.paramTypes, argtpes0.length, removeByName = false)
def missingArgs = missingParams[Type](argtpes0, mt.params, x => Some(x) collect { case NamedType(n, _) => n })
def argsTupled = tupleIfNecessary(mt.paramTypes, argtpes0)
def argsPlusDefaults = missingArgs match {
case (args, _) if args forall (_.hasDefault) => argtpes0 ::: makeNamedTypes(args)
case _ => argsTupled
}
// If args eq the incoming arg types, fail; otherwise recurse with these args.
def tryWithArgs(args: List[Type]) = (
(args ne argtpes0)
&& isApplicableToMethod(undetparams, mt, args, pt) // used to be isApplicable(undetparams, mt, args, pt), knowing mt: MethodType
)
def tryInstantiating(args: List[Type]) = falseIfNoInstance {
val restpe = mt resultType args
val adjusted = methTypeArgs(EmptyTree, undetparams, formals, restpe, args, pt)
import adjusted.{okParams, okArgs, undetParams}
enhanceBounds(okParams, okArgs, undetParams)
val restpeInst = restpe.instantiateTypeParams(okParams, okArgs)
// #2665: must use weak conformance, not regular one (follow the monomorphic case above)
exprTypeArgs(undetParams, restpeInst, pt, useWeaklyCompatible = true) match {
case null => false
case _ => isWithinBounds(NoPrefix, NoSymbol, okParams, okArgs)
}
}
def typesCompatible(args: List[Type]) = undetparams match {
case Nil => isCompatibleArgs(args, formals) && isWeaklyCompatible(mt resultType args, pt)
case _ => tryInstantiating(args)
}
// when using named application, the vararg param has to be specified exactly once
def reorderedTypesCompatible = checkNames(argtpes0, mt.params) match {
case (_, _, false) => false // names are not ok
case (_, pos, _) if !allArgsArePositional(pos) && !sameLength(formals, mt.params) => false // different length lists and all args not positional
case (args, pos, _) => typesCompatible(reorderArgs(args, pos))
}
val res = compareLengths(argtpes0, formals) match {
case 0 if containsNamedType(argtpes0) => reorderedTypesCompatible // right number of args, wrong order
case 0 => typesCompatible(argtpes0) // fast track if no named arguments are used
case x if x > 0 => tryWithArgs(argsTupled) // too many args, try tupling
case _ => tryWithArgs(argsPlusDefaults) // too few args, try adding defaults or tupling
}
// println(s"isApplicableToMethod $res : $mt --> $formals to $argtpes0 for $pt under $undetparams")
res
}
/** Is there an instantiation of free type variables `undetparams` such that
* function type `ftpe` is applicable to `argtpes0` and its result conform to `pt`?
*
* @param ftpe the type of the function (often a MethodType)
* @param argtpes0 the argument types; a NamedType(name, tp) for named
* arguments. For each NamedType, if `name` does not exist in `ftpe`, that
* type is set to `Unit`, i.e. the corresponding argument is treated as
* an assignment expression (@see checkNames).
*/
private def isApplicable(undetparams: List[Symbol], ftpe: Type, argtpes0: List[Type], pt: Type): Boolean = {
val res =
ftpe match {
case OverloadedType(pre, alts) => alts exists (alt => isApplicable(undetparams, pre memberType alt, argtpes0, pt))
case ExistentialType(_, qtpe) => isApplicable(undetparams, qtpe, argtpes0, pt)
case mt@MethodType(_, _) => isApplicableToMethod(undetparams, mt, argtpes0, pt)
case NullaryMethodType(restpe) => isApplicable(undetparams, restpe, argtpes0, pt)
case PolyType(tparams, restpe) => createFromClonedSymbols(tparams, restpe)((tps1, res1) => isApplicable(tps1 ::: undetparams, res1, argtpes0, pt))
case ErrorType => true
case _ => false
}
// println(s"isApplicable $res : $ftpe to $argtpes0 for $pt under $undetparams")
res
}
/**
* Are arguments of the given types applicable to `ftpe`? Type argument inference
* is tried twice: firstly with the given expected type, and secondly with `WildcardType`.
*/
// Todo: Try to make isApplicable always safe (i.e. not cause TypeErrors).
// The chance of TypeErrors should be reduced through context errors
private[typechecker] def isApplicableSafe(undetparams: List[Symbol], ftpe: Type, argtpes0: List[Type], pt: Type): Boolean = {
def applicableExpectingPt(pt: Type): Boolean = {
val silent = context.makeSilent(reportAmbiguousErrors = false)
val result = newTyper(silent).infer.isApplicable(undetparams, ftpe, argtpes0, pt)
if (silent.reporter.hasErrors && !pt.isWildcard)
applicableExpectingPt(WildcardType) // second try
else
result
}
applicableExpectingPt(pt)
}
/** Is type `ftpe1` strictly more specific than type `ftpe2`
* when both are alternatives in an overloaded function?
* @see SLS (sec:overloading-resolution)
*/
def isAsSpecific(ftpe1: Type, ftpe2: Type): Boolean = {
def checkIsApplicable(mt: MethodType) = {
val paramTypes = mt.paramTypes
val aligned =
if (isRepeatedParamType(paramTypes.last) && isVarArgsList(ftpe2.params)) paramTypes.init :+ repeatedToSingle(paramTypes.last)
else paramTypes
isApplicable(Nil, ftpe2, aligned, WildcardType)
}
val res =
ftpe1 match {
case OverloadedType(pre, alts) => alts exists (alt => isAsSpecific(pre memberType alt, ftpe2))
case et: ExistentialType => isAsSpecific(et.skolemizeExistential, ftpe2)
case NullaryMethodType(restpe) => isAsSpecific(restpe, ftpe2)
case mt @ MethodType(_, restpe) if mt.isImplicit => isAsSpecific(restpe, ftpe2)
case mt @ MethodType(params, _) if params.nonEmpty => checkIsApplicable(mt)
case PolyType(tparams, NullaryMethodType(restpe)) => isAsSpecific(PolyType(tparams, restpe), ftpe2)
case PolyType(tparams, mt @ MethodType(_, restpe)) if mt.isImplicit => isAsSpecific(PolyType(tparams, restpe), ftpe2)
case PolyType(_, mt @ MethodType(params, _)) if params.nonEmpty => checkIsApplicable(mt)
case ErrorType => true
case _ =>
ftpe2 match {
case OverloadedType(pre, alts) => alts forall (alt => isAsSpecific(ftpe1, pre memberType alt))
case et: ExistentialType => et.withTypeVars(isAsSpecific(ftpe1, _))
case mt @ MethodType(_, restpe) => !mt.isImplicit || isAsSpecific(ftpe1, restpe)
case NullaryMethodType(res) => isAsSpecific(ftpe1, res)
case PolyType(tparams, NullaryMethodType(restpe)) => isAsSpecific(ftpe1, PolyType(tparams, restpe))
case PolyType(tparams, mt @ MethodType(_, restpe)) => !mt.isImplicit || isAsSpecific(ftpe1, PolyType(tparams, restpe))
case _ => isAsSpecificValueType(ftpe1, ftpe2, Nil, Nil)
}
}
// println(s"isAsSpecific $res $ftpe1 - $ftpe2")
res
}
private def isAsSpecificValueType(tpe1: Type, tpe2: Type, undef1: List[Symbol], undef2: List[Symbol]): Boolean = tpe1 match {
case PolyType(tparams1, rtpe1) =>
isAsSpecificValueType(rtpe1, tpe2, undef1 ::: tparams1, undef2)
case _ =>
tpe2 match {
case PolyType(tparams2, rtpe2) => isAsSpecificValueType(tpe1, rtpe2, undef1, undef2 ::: tparams2)
case _ if !currentRun.isScala3ImplicitResolution => existentialAbstraction(undef1, tpe1) <:< existentialAbstraction(undef2, tpe2)
case _ =>
// Backport of fix for https://github.com/scala/bug/issues/2509
// from Dotty https://github.com/lampepfl/dotty/commit/89540268e6c49fb92b9ca61249e46bb59981bf5a
//
// Note that as of https://github.com/lampepfl/dotty/commit/b9f3084205bc9fcbd2a5181d3f0e539e2a20253a
// Dotty flips variances throughout, not just at the top level. We follow that behaviour here.
val e1 = existentialAbstraction(undef1, tpe1)
val e2 = existentialAbstraction(undef2, tpe2)
val flip = new VariancedTypeMap {
def apply(tp: Type): Type = tp match {
case TypeRef(pre, sym, args) if variance > 0 && sym.typeParams.exists(_.isContravariant) =>
mapOver(TypeRef(pre, sym.flipped, args))
case _ =>
mapOver(tp)
}
}
val bt = e1.baseType(e2.typeSymbol)
val lhs = if(bt != NoType) bt else e1
flip(lhs) <:< flip(e2)
}
}
/** Is sym1 (or its companion class in case it is a module) a subclass of
* sym2 (or its companion class in case it is a module)?
*/
def isProperSubClassOrObject(sym1: Symbol, sym2: Symbol): Boolean = (
(sym1 ne sym2)
&& (sym1 ne NoSymbol)
&& ( (sym1 isSubClass sym2)
|| (sym1.isModuleClass && isProperSubClassOrObject(sym1.linkedClassOfClass, sym2))
|| (sym2.isModuleClass && isProperSubClassOrObject(sym1, sym2.linkedClassOfClass))
)
)
/** is symbol `sym1` defined in a proper subclass of symbol `sym2`?
*/
def isInProperSubClassOrObject(sym1: Symbol, sym2: Symbol) = (
(sym2 eq NoSymbol)
|| isProperSubClassOrObject(sym1.safeOwner, sym2.owner)
)
// Note that this doesn't consider undetparams -- any type params in `ftpe1/2` need to be bound by their type (i.e. in a PolyType)
// since constructors of poly classes do not have their own polytype in their infos, this must be fixed up
// before calling this method (see memberTypeForSpecificity)
def isStrictlyMoreSpecific(ftpe1: Type, ftpe2: Type, sym1: Symbol, sym2: Symbol): Boolean = {
// ftpe1 / ftpe2 are OverloadedTypes (possibly with one single alternative) if they
// denote the type of an "apply" member method (see "followApply")
ftpe1.isError || {
val specificCount = (if (isAsSpecific(ftpe1, ftpe2)) 1 else 0) -
(if (isAsSpecific(ftpe2, ftpe1) &&
// todo: move to isAsSpecific test
// (!ftpe2.isInstanceOf[OverloadedType] || ftpe1.isInstanceOf[OverloadedType]) &&
(!phase.erasedTypes || covariantReturnOverride(ftpe1, ftpe2))) 1 else 0)
val subClassCount = (if (isInProperSubClassOrObject(sym1, sym2)) 1 else 0) -
(if (isInProperSubClassOrObject(sym2, sym1)) 1 else 0)
specificCount + subClassCount > 0
}
}
private def covariantReturnOverride(ftpe1: Type, ftpe2: Type): Boolean = ftpe1 match {
case MethodType(_, rtpe1) =>
ftpe2 match {
case MethodType(_, rtpe2) => rtpe1 <:< rtpe2 || rtpe2.typeSymbol == ObjectClass
case _ => false
}
case _ => false
}
/** error if arguments not within bounds. */
def checkBounds(tree: Tree, pre: Type, owner: Symbol, tparams: List[Symbol], targs: List[Type], prefix: String): Boolean = {
def issueBoundsError() = { NotWithinBounds(tree, prefix, targs, tparams, Nil) ; false }
def issueKindBoundErrors(errs: List[String]) = { KindBoundErrors(tree, prefix, targs, tparams, errs) ; false }
//@M validate variances & bounds of targs wrt variances & bounds of tparams
//@M TODO: better place to check this?
//@M TODO: errors for getters & setters are reported separately
def check() = checkKindBounds(tparams, targs, pre, owner) match {
case Nil => isWithinBounds(pre, owner, tparams, targs) || issueBoundsError()
case errs => (targs contains WildcardType) || issueKindBoundErrors(errs)
}
targs.exists(_.isErroneous) || tparams.exists(_.isErroneous) || check()
}
def checkKindBounds(tparams: List[Symbol], targs: List[Type], pre: Type, owner: Symbol): List[String] = {
checkKindBounds0(tparams, targs, pre, owner, explainErrors = true) map {
case (targ, tparam, kindErrors) =>
kindErrors.errorMessage(targ, tparam)
}
}