diff options
Diffstat (limited to 'src/reflect/scala/reflect/internal/Types.scala')
| -rw-r--r-- | src/reflect/scala/reflect/internal/Types.scala | 40 |
1 files changed, 35 insertions, 5 deletions
diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala index 9697e16da7..98510825c0 100644 --- a/src/reflect/scala/reflect/internal/Types.scala +++ b/src/reflect/scala/reflect/internal/Types.scala @@ -3076,13 +3076,43 @@ 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. |