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oderskyodersky
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Make ApproxState a value class
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+30
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‎compiler/src/dotty/tools/dotc/core/TypeComparer.scala

+30-18
Original file line numberDiff line numberDiff line change
@@ -107,7 +107,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
107107
assert(isSatisfiable, constraint.show)
108108
}
109109

110-
protected def isSubType(tp1: Type, tp2: Type): Boolean = isSubType(tp1, tp2, Precise)
110+
protected def isSubType(tp1: Type, tp2: Type): Boolean = isSubType(tp1, tp2, NoApprox)
111111

112112
protected def isSubType(tp1: Type, tp2: Type, approx: ApproxState): Boolean = trace(s"isSubType ${traceInfo(tp1, tp2)} $approx", subtyping) {
113113

@@ -273,7 +273,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
273273
def compareTypeParamRef =
274274
ctx.mode.is(Mode.TypevarsMissContext) ||
275275
isSubTypeWhenFrozen(bounds(tp1).hi, tp2) || {
276-
if (canConstrain(tp1) && (approx & HiApprox) == 0)
276+
if (canConstrain(tp1) && !approx.high)
277277
addConstraint(tp1, tp2, fromBelow = false) && flagNothingBound
278278
else thirdTry
279279
}
@@ -339,8 +339,8 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
339339
GADTusage(tp2.symbol)
340340
}
341341
val tryLowerFirst = frozenConstraint || !isCappable(tp1)
342-
if (tryLowerFirst) isSubType(tp1, lo2, approx | HiApprox) || compareGADT || fourthTry
343-
else compareGADT || fourthTry || isSubType(tp1, lo2, approx | HiApprox)
342+
if (tryLowerFirst) isSubType(tp1, lo2, approx.addHigh) || compareGADT || fourthTry
343+
else compareGADT || fourthTry || isSubType(tp1, lo2, approx.addHigh)
344344

345345
case _ =>
346346
val cls2 = tp2.symbol
@@ -354,7 +354,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
354354
// If `cls2` is parameterized, we are seeing a raw type, so we need to compare only the symbol
355355
return base.typeSymbol == cls2
356356
if (base ne tp1)
357-
return isSubType(base, tp2, if (tp1.isRef(cls2)) approx else approx | LoApprox)
357+
return isSubType(base, tp2, if (tp1.isRef(cls2)) approx else approx.addLow)
358358
}
359359
if (cls2 == defn.SingletonClass && tp1.isStable) return true
360360
}
@@ -381,7 +381,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
381381
if (frozenConstraint) isSubType(tp1, bounds(tp2).lo)
382382
else isSubTypeWhenFrozen(tp1, tp2)
383383
alwaysTrue || {
384-
if (canConstrain(tp2) && (approx & LoApprox) == 0)
384+
if (canConstrain(tp2) && !approx.low)
385385
addConstraint(tp2, tp1.widenExpr, fromBelow = true)
386386
else fourthTry
387387
}
@@ -548,7 +548,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
548548
narrowGADTBounds(tp1, tp2, approx, isUpper = true)) &&
549549
GADTusage(tp1.symbol)
550550
}
551-
isSubType(hi1, tp2, approx | LoApprox) || compareGADT
551+
isSubType(hi1, tp2, approx.addLow) || compareGADT
552552
case _ =>
553553
def isNullable(tp: Type): Boolean = tp.widenDealias match {
554554
case tp: TypeRef => tp.symbol.isNullableClass
@@ -727,7 +727,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
727727
* @param tyconLo The type constructor's lower approximation.
728728
*/
729729
def fallback(tyconLo: Type) =
730-
either(fourthTry, isSubType(tp1, tyconLo.applyIfParameterized(args2), approx | HiApprox))
730+
either(fourthTry, isSubType(tp1, tyconLo.applyIfParameterized(args2), approx.addHigh))
731731

732732
/** Let `tycon2bounds` be the bounds of the RHS type constructor `tycon2`.
733733
* Let `app2 = tp2` where the type constructor of `tp2` is replaced by
@@ -741,7 +741,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
741741
def compareLower(tycon2bounds: TypeBounds, tyconIsTypeRef: Boolean): Boolean =
742742
if (tycon2bounds.lo eq tycon2bounds.hi)
743743
if (tyconIsTypeRef) recur(tp1, tp2.superType)
744-
else isSubType(tp1, tycon2bounds.lo.applyIfParameterized(args2), approx | HiApprox)
744+
else isSubType(tp1, tycon2bounds.lo.applyIfParameterized(args2), approx.addHigh)
745745
else
746746
fallback(tycon2bounds.lo)
747747

@@ -758,7 +758,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
758758
case info2: ClassInfo =>
759759
val base = tp1.baseType(info2.cls)
760760
if (base.exists && base.ne(tp1))
761-
isSubType(base, tp2, if (tp1.isRef(info2.cls)) approx else approx | LoApprox)
761+
isSubType(base, tp2, if (tp1.isRef(info2.cls)) approx else approx.addLow)
762762
else fourthTry
763763
case _ =>
764764
fourthTry
@@ -785,7 +785,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
785785
false
786786
}
787787
canConstrain(param1) && canInstantiate ||
788-
isSubType(bounds(param1).hi.applyIfParameterized(args1), tp2, approx | LoApprox)
788+
isSubType(bounds(param1).hi.applyIfParameterized(args1), tp2, approx.addLow)
789789
case tycon1: TypeRef if tycon1.symbol.isClass =>
790790
false
791791
case tycon1: TypeProxy =>
@@ -801,7 +801,7 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
801801
if (isCovered(tp1) && isCovered(tp2)) {
802802
//println(s"useless subtype: $tp1 <:< $tp2")
803803
false
804-
} else isSubType(tp1, tp2, approx | LoApprox)
804+
} else isSubType(tp1, tp2, approx.addLow)
805805

806806
def recur(tp1: Type, tp2: Type) = isSubType(tp1, tp2, approx)
807807

@@ -1083,8 +1083,8 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
10831083
* Test that the resulting bounds are still satisfiable.
10841084
*/
10851085
private def narrowGADTBounds(tr: NamedType, bound: Type, approx: ApproxState, isUpper: Boolean): Boolean = {
1086-
val boundIsPrecise = (approx & (if (isUpper) HiApprox else LoApprox)) == 0
1087-
ctx.mode.is(Mode.GADTflexible) && !frozenConstraint && boundIsPrecise && {
1086+
val boundImprecise = if (isUpper) approx.high else approx.low
1087+
ctx.mode.is(Mode.GADTflexible) && !frozenConstraint && !boundImprecise && {
10881088
val tparam = tr.symbol
10891089
gadts.println(i"narrow gadt bound of $tparam: ${tparam.info} from ${if (isUpper) "above" else "below"} to $bound ${bound.toString} ${bound.isRef(tparam)}")
10901090
if (bound.isRef(tparam)) false
@@ -1605,10 +1605,22 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
16051605

16061606
object TypeComparer {
16071607

1608-
type ApproxState = Int
1609-
val Precise = 0
1610-
val LoApprox = 1
1611-
val HiApprox = 2
1608+
private val LoApprox = 1
1609+
private val HiApprox = 2
1610+
1611+
class ApproxState(private val bits: Int) extends AnyVal {
1612+
override def toString = {
1613+
val lo = if ((bits & LoApprox) != 0) "LoApprox" else ""
1614+
val hi = if ((bits & HiApprox) != 0) "HiApprox" else ""
1615+
lo ++ hi
1616+
}
1617+
def addLow = new ApproxState(bits | LoApprox)
1618+
def addHigh = new ApproxState(bits | HiApprox)
1619+
def low = (bits & LoApprox) != 0
1620+
def high = (bits & HiApprox) != 0
1621+
}
1622+
1623+
val NoApprox = new ApproxState(0)
16121624

16131625
/** Show trace of comparison operations when performing `op` as result string */
16141626
def explained[T](op: Context => T)(implicit ctx: Context): String = {

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