From 403eadd0f10cf6e493b81913148b0b9065e80699 Mon Sep 17 00:00:00 2001 From: Jason Zaugg Date: Wed, 29 May 2013 23:44:21 +0200 Subject: SI-7517 Fix higher kinded type inference regression - Discovered in 2.10.2-RC1 - Ostensibly regressed in 7e52fb910b, which conceptually reverted part of 0cde930b so that (mutable) TypeVars don't use structural equality. - But, does *not* fail if 7e52fb910b is cherry-picked directly after 0cde930b, suggesting that it shone a light on a behaviour change in some other commit in between the two. - Indeed, the true regression came in https://github.com/scala/scala/commit/e5da30b843#L5L3176 - A targeted revert of e5da30b843 is undesirable, as we'd like SI-6846 to stay fixed What's happening here? In the enclosed test case, higher kinded type inference explores two possibilities: Composed.this.Split[A] K[[T]A[B[T]]] // `Split[A]` dealiased The difference in the flow of type inference can be seen from the diff below. Notice how now we no longer register `?K.addBound(Composed.this.Split)`, we instead only register `?K.addBound(K)` ```patch --- sandbox/old.log 2013-05-30 00:27:34.000000000 +0200 +++ sandbox/new.log 2013-05-30 00:28:28.000000000 +0200 @@ -1,55 +1,114 @@ ?K.unifyFull(Composed.this.Split[A]) ?K.unifySpecific(Composed.this.Split[A]) - ?K.addBound(Composed.this.Split) ?B.unifyFull(T) ?B.unifySpecific(T) `-> false ?B.unifyFull(Any) ?B.unifySpecific(Any) `-> false `-> false ?K.unifySpecific(L[[T]A[B[T]]]) - ?K.addBound(L) ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true + ?K.addBound(L) `-> true ?K.unifyFull(Composed.this.Split[A]) ?K.unifySpecific(Composed.this.Split[A]) - ?K.addBound(Composed.this.Split) ?B.unifyFull(x) ?B.unifySpecific(x) `-> false `-> false ?K.unifySpecific(L[[T]A[B[T]]]) + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true ?K.addBound(L) + `-> true +?K.unifyFull(Composed.this.Split[A]) + ?K.unifySpecific(Composed.this.Split[A]) + ?B.unifyFull(T) + ?B.unifySpecific(T) + `-> false + ?B.unifyFull(Any) + ?B.unifySpecific(Any) + `-> false + `-> false + ?K.unifySpecific(L[[T]A[B[T]]]) ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true ?B.unifyFull(B[T]) ?B.unifySpecific(B[T]) ?B.addBound(B) `-> true + ?K.addBound(L) + `-> true +?K.unifyFull(Composed.this.Split[A]) + ?K.unifySpecific(Composed.this.Split[A]) + ?B.unifyFull(x) + ?B.unifySpecific(x) + `-> false + `-> false + ?K.unifySpecific(L[[T]A[B[T]]]) + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?B.unifyFull(B[T]) + ?B.unifySpecific(B[T]) + ?B.addBound(B) + `-> true + ?K.addBound(L) + `-> true +?K.unifyFull(L[A]) + ?K.unifySpecific(L[A]) + ?K.addBound(L) + `-> true +?K.unifyFull(L[A]) + ?K.unifySpecific(L[A]) + ?K.addBound(L) `-> true ``` --- src/reflect/scala/reflect/internal/Types.scala | 7 +++---- test/files/pos/t7517.scala | 22 ++++++++++++++++++++++ 2 files changed, 25 insertions(+), 4 deletions(-) create mode 100644 test/files/pos/t7517.scala diff --git a/src/reflect/scala/reflect/internal/Types.scala b/src/reflect/scala/reflect/internal/Types.scala index ee584bed2c..0cc2b91a44 100644 --- a/src/reflect/scala/reflect/internal/Types.scala +++ b/src/reflect/scala/reflect/internal/Types.scala @@ -3218,10 +3218,9 @@ trait Types extends api.Types { self: SymbolTable => sameLength(typeArgs, tp.typeArgs) && { val lhs = if (isLowerBound) tp.typeArgs else typeArgs val rhs = if (isLowerBound) typeArgs else tp.typeArgs - // this is a higher-kinded type var with same arity as tp. - // side effect: adds the type constructor itself as a bound - addBound(tp.typeConstructor) - isSubArgs(lhs, rhs, params, AnyDepth) + // 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 } } } // The type with which we can successfully unify can be hidden diff --git a/test/files/pos/t7517.scala b/test/files/pos/t7517.scala new file mode 100644 index 0000000000..7ce4c6b13e --- /dev/null +++ b/test/files/pos/t7517.scala @@ -0,0 +1,22 @@ +trait Box[ K[A[x]] ] + +object Box { + // type constructor composition + sealed trait ∙[A[_], B[_]] { type l[T] = A[B[T]] } + + // composes type constructors inside K + type SplitBox[K[A[x]], B[x]] = Box[ ({ type l[A[x]] = K[ (A ∙ B)#l] })#l ] + + def split[ K[A[x]], B[x] ](base: Box[K]): SplitBox[K,B] = ??? + + class Composed[B[_], L[A[x]] ] { + val box: Box[L] = ??? + + type Split[ A[x] ] = L[ (A ∙ B)#l ] + val a: Box[Split] = Box.split(box) + + //Either of these work: + val a1: Box[Split] = Box.split[L,B](box) + val a2: Box[ ({ type l[A[x]] = L[ (A ∙ B)#l ] })#l ] = Box.split(box) + } +} \ No newline at end of file -- cgit v1.2.3