diff options
Diffstat (limited to 'src')
4 files changed, 39 insertions, 6 deletions
diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala index c55693d60e..4d236b226d 100644 --- a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala +++ b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala @@ -30,7 +30,7 @@ trait ScalaSettings extends AbsScalaSettings protected def defaultClasspath = sys.env.getOrElse("CLASSPATH", ".") /** Enabled under -Xexperimental. */ - protected def experimentalSettings = List[BooleanSetting](YmethodInfer, overrideObjects, overrideVars) + protected def experimentalSettings = List[BooleanSetting](YpartialUnification) /** Enabled under -Xfuture. */ protected def futureSettings = List[BooleanSetting]() @@ -201,6 +201,7 @@ trait ScalaSettings extends AbsScalaSettings val etaExpandKeepsStar = BooleanSetting ("-Yeta-expand-keeps-star", "Eta-expand varargs methods to T* rather than Seq[T]. This is a temporary option to ease transition.").withDeprecationMessage(removalIn212) val inferByName = BooleanSetting ("-Yinfer-by-name", "Allow inference of by-name types. This is a temporary option to ease transition. See SI-7899.").withDeprecationMessage(removalIn212) val YdisableFlatCpCaching = BooleanSetting ("-YdisableFlatCpCaching", "Do not cache flat classpath representation of classpath elements from jars across compiler instances.") + val YpartialUnification = BooleanSetting ("-Ypartial-unification", "Enable partial unification in type constructor inference") val exposeEmptyPackage = BooleanSetting ("-Yexpose-empty-package", "Internal only: expose the empty package.").internalOnly() val Ydelambdafy = ChoiceSetting ("-Ydelambdafy", "strategy", "Strategy used for translating lambdas into JVM code.", List("inline", "method"), "method") diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala index de82a6a0b2..a649f6f926 100644 --- a/src/reflect/scala/reflect/internal/Types.scala +++ b/src/reflect/scala/reflect/internal/Types.scala @@ -3131,13 +3131,43 @@ trait Types */ def unifyFull(tpe: Type): Boolean = { def unifySpecific(tp: Type) = { - sameLength(typeArgs, tp.typeArgs) && { - val lhs = if (isLowerBound) tp.typeArgs else typeArgs - val rhs = if (isLowerBound) typeArgs else tp.typeArgs + val tpTypeArgs = tp.typeArgs + val arityDelta = compareLengths(typeArgs, tpTypeArgs) + if (arityDelta == 0) { + val lhs = if (isLowerBound) tpTypeArgs else typeArgs + val rhs = if (isLowerBound) typeArgs else tpTypeArgs // This is a higher-kinded type var with same arity as tp. // If so (see SI-7517), side effect: adds the type constructor itself as a bound. - isSubArgs(lhs, rhs, params, AnyDepth) && { addBound(tp.typeConstructor); true } - } + isSubArgs(lhs, rhs, params, AnyDepth) && {addBound(tp.typeConstructor); true} + } else if (settings.YpartialUnification && arityDelta < 0 && typeArgs.nonEmpty) { + // Simple algorithm as suggested by Paul Chiusano in the comments on SI-2712 + // + // https://issues.scala-lang.org/browse/SI-2712?focusedCommentId=61270 + // + // Treat the type constructor as curried and partially applied, we treat a prefix + // as constants and solve for the suffix. For the example in the ticket, unifying + // M[A] with Int => Int this unifies as, + // + // M[t] = [t][Int => t] --> abstract on the right to match the expected arity + // A = Int --> capture the remainder on the left + // + // A more "natural" unifier might be M[t] = [t][t => t]. There's lots of scope for + // experimenting with alternatives here. + val numCaptured = tpTypeArgs.length - typeArgs.length + val (captured, abstractedArgs) = tpTypeArgs.splitAt(numCaptured) + + val (lhs, rhs) = + if (isLowerBound) (abstractedArgs, typeArgs) + else (typeArgs, abstractedArgs) + + isSubArgs(lhs, rhs, params, AnyDepth) && { + val tpSym = tp.typeSymbolDirect + val abstractedTypeParams = tpSym.typeParams.drop(numCaptured).map(_.cloneSymbol(tpSym)) + + addBound(PolyType(abstractedTypeParams, appliedType(tp.typeConstructor, captured ++ abstractedTypeParams.map(_.tpeHK)))) + true + } + } else false } // The type with which we can successfully unify can be hidden // behind singleton types and type aliases. diff --git a/src/reflect/scala/reflect/internal/settings/MutableSettings.scala b/src/reflect/scala/reflect/internal/settings/MutableSettings.scala index e75b3dff3d..5a2c802476 100644 --- a/src/reflect/scala/reflect/internal/settings/MutableSettings.scala +++ b/src/reflect/scala/reflect/internal/settings/MutableSettings.scala @@ -53,6 +53,7 @@ abstract class MutableSettings extends AbsSettings { def printtypes: BooleanSetting def uniqid: BooleanSetting def verbose: BooleanSetting + def YpartialUnification: BooleanSetting def Yrecursion: IntSetting def maxClassfileName: IntSetting diff --git a/src/reflect/scala/reflect/runtime/Settings.scala b/src/reflect/scala/reflect/runtime/Settings.scala index b1d7fde1b4..3b33f089e1 100644 --- a/src/reflect/scala/reflect/runtime/Settings.scala +++ b/src/reflect/scala/reflect/runtime/Settings.scala @@ -47,6 +47,7 @@ private[reflect] class Settings extends MutableSettings { val printtypes = new BooleanSetting(false) val uniqid = new BooleanSetting(false) val verbose = new BooleanSetting(false) + val YpartialUnification = new BooleanSetting(false) val Yrecursion = new IntSetting(0) val maxClassfileName = new IntSetting(255) |