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When detecting subtyping loops remember problematic cases on the way out
The test causes a subtyping test that loops, which is caught by existing infrastructure (LogPendingSubTypesThreshold). However, before reaching the threshold the subtyping check branches off into two equal cases at every iteration. For details, see the bug report. To avoid having to reach the threshold on every one of these branches, remember the problematic subtyping tests on teh way back.
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-12
lines changed

4 files changed

+37
-12
lines changed

‎project/MimaFilters.scala‎

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Original file line numberDiff line numberDiff line change
@@ -75,6 +75,9 @@ object MimaFilters extends AutoPlugin {
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ProblemFilters.exclude[DirectMissingMethodProblem]("scala.collection.mutable.StringBuilder.getChars"),
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ProblemFilters.exclude[DirectMissingMethodProblem]("scala.runtime.ArrayCharSequence.getChars"),
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ProblemFilters.exclude[DirectMissingMethodProblem]("scala.runtime.SeqCharSequence.getChars"),
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// scala/scala#11124
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ProblemFilters.exclude[DirectMissingMethodProblem]("scala.reflect.runtime.JavaUniverse.knownFalseSubTypes"),
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)
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override val buildSettings = Seq(

‎src/reflect/scala/reflect/internal/tpe/TypeComparers.scala‎

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Original file line numberDiff line numberDiff line change
@@ -30,6 +30,9 @@ trait TypeComparers {
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private[this] val _pendingSubTypes = new mutable.HashSet[SubTypePair]
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def pendingSubTypes = _pendingSubTypes
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private[this] val _knownFalseSubTypes = new mutable.HashMap[Type, Type]
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def knownFalseSubTypes = _knownFalseSubTypes
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final case class SubTypePair(tp1: Type, tp2: Type) {
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// scala/bug#8146 we used to implement equality here in terms of pairwise =:=.
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// But, this was inconsistent with hashCode, which was based on the
@@ -84,9 +87,10 @@ trait TypeComparers {
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}
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} finally {
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subsametypeRecursions -= 1
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// XXX AM TODO: figure out when it is safe and needed to clear the log -- the commented approach below is too eager (it breaks #3281, #3866)
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// it doesn't help to keep separate recursion counts for the three methods that now share it
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// if (subsametypeRecursions == 0) undoLog.clear()
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if (subsametypeRecursions == 0) {
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knownFalseSubTypes.clear()
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// undoLog.clear() // too eager, breaks #3281, #3866
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}
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}
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def isDifferentTypeConstructor(tp1: Type, tp2: Type) = !isSameTypeConstructor(tp1, tp2)
@@ -121,9 +125,10 @@ trait TypeComparers {
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}
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finally {
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subsametypeRecursions -= 1
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// XXX AM TODO: figure out when it is safe and needed to clear the log -- the commented approach below is too eager (it breaks #3281, #3866)
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// it doesn't help to keep separate recursion counts for the three methods that now share it
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// if (subsametypeRecursions == 0) undoLog.clear()
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if (subsametypeRecursions == 0) {
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knownFalseSubTypes.clear()
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// undoLog.clear() // too eager, breaks #3281, #3866
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}
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}
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// @pre: at least one argument has annotations
@@ -291,16 +296,20 @@ trait TypeComparers {
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try result = { // if subtype test fails, it should not affect constraints on typevars
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if (subsametypeRecursions >= LogPendingSubTypesThreshold) {
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val p = new SubTypePair(tp1, tp2)
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if (pendingSubTypes(p))
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val p = SubTypePair(tp1, tp2)
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if (pendingSubTypes(p)) {
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knownFalseSubTypes(tp1) = tp2 // see scala/bug#13119
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false // see neg/t8146-no-finitary*
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else
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} else
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try {
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pendingSubTypes += p
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isSubType1(tp1, tp2, depth)
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} finally {
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pendingSubTypes -= p
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}
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} else if (!knownFalseSubTypes.isEmpty && knownFalseSubTypes.get(tp1).contains(tp2)) {
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// redundant `isEmtpy` check is probably premature optimization, but isSubType is perf sensitive
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false
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} else {
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isSubType1(tp1, tp2, depth)
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}
@@ -309,9 +318,10 @@ trait TypeComparers {
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result
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} finally {
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subsametypeRecursions -= 1
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// XXX AM TODO: figure out when it is safe and needed to clear the log -- the commented approach below is too eager (it breaks #3281, #3866)
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// it doesn't help to keep separate recursion counts for the three methods that now share it
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// if (subsametypeRecursions == 0) undoLog.clear()
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if (subsametypeRecursions == 0) {
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knownFalseSubTypes.clear()
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// undoLog.clear() // too eager, breaks #3281, #3866
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}
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}
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/** Check whether the subtype or type equivalence relationship

‎src/reflect/scala/reflect/runtime/SynchronizedTypes.scala‎

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Original file line numberDiff line numberDiff line change
@@ -69,6 +69,9 @@ private[reflect] trait SynchronizedTypes extends internal.Types { self: SymbolTa
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private lazy val _pendingSubTypes = mkThreadLocalStorage(new mutable.HashSet[SubTypePair])
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override def pendingSubTypes = _pendingSubTypes.get
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private lazy val _knownFalseSubTypes = mkThreadLocalStorage(new mutable.HashMap[Type, Type])
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override def knownFalseSubTypes = _knownFalseSubTypes.get
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private lazy val _basetypeRecursions = mkThreadLocalStorage(0)
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override def basetypeRecursions = _basetypeRecursions.get
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override def basetypeRecursions_=(value: Int) = _basetypeRecursions.set(value)

‎test/files/pos/t13119.scala‎

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@@ -0,0 +1,9 @@
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trait A[T]
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final class C[T, E] extends A[T with E]
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object T {
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def f(x: A[?]): Int = x match {
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case b: C[?, ?] => 0
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case _ => 1
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}
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}

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