From 6a61e172d9de912c74af50e49f0057fbe8d4e500 Mon Sep 17 00:00:00 2001 From: Adriaan Moors Date: Sat, 23 Mar 2013 15:06:22 +0100 Subject: SI-7289 Less strict type application for TypeVar. When a type constructor variable is applied to the wrong number of arguments, return a new type variable whose instance is `ErrorType`. Dissection of the reported test case by @retronym: Define the first implicit: scala> trait Schtroumpf[T] defined trait Schtroumpf scala> implicit def schtroumpf[T, U <: Coll[T], Coll[X] <: Traversable[X]] | (implicit minorSchtroumpf: Schtroumpf[T]): Schtroumpf[U] = ??? schtroumpf: [T, U <: Coll[T], Coll[X] <: Traversable[X]](implicit minorSchtroumpf: Schtroumpf[T])Schtroumpf[U] Call it explicitly => kind error during type inference reported. scala> schtroumpf(null): Schtroumpf[Int] :10: error: inferred kinds of the type arguments (Nothing,Int,Int) do not conform to the expected kinds of the type parameters (type T,type U,type Coll). Int's type parameters do not match type Coll's expected parameters: class Int has no type parameters, but type Coll has one schtroumpf(null): Schtroumpf[Int] ^ :10: error: type mismatch; found : Schtroumpf[U] required: Schtroumpf[Int] schtroumpf(null): Schtroumpf[Int] ^ Add another implicit, and let implicit search weigh them up. scala> implicitly[Schtroumpf[Int]] :10: error: diverging implicit expansion for type Schtroumpf[Int] starting with method schtroumpf implicitly[Schtroumpf[Int]] ^ scala> implicit val qoo = new Schtroumpf[Int]{} qoo: Schtroumpf[Int] = $anon$1@c1b9b03 scala> implicitly[Schtroumpf[Int]] Implicit search compares the two in-scope implicits in `isStrictlyMoreSpecific`, which constructs an existential type: type ET = Schtroumpf[U] forSome { type T; type U <: Coll[T]; type Coll[_] <: Traversable[_] } A subsequent subtype check `ET <:< Schtroumpf[Int]` gets to `withTypeVars`, which replaces the quantified types with type variables, checks conformance of that substitued underlying type against `Schtroumpf[Int]`, and then tries to solve the collected type constraints. The type var trace looks like: [ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ create] ?U ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ create] ?Coll ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ setInst] Nothing ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Nothing ) [ setInst] scala.collection.immutable.Nil.type( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], U=scala.collection.immutable.Nil.type ) [ setInst] =?scala.collection.immutable.Nil.type( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], Coll==?scala.collection.immutable.Nil.type ) [ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ setInst] Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Int ) [ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ create] ?U ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ create] ?Coll ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) [ setInst] Nothing ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Nothing ) [ setInst] Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], U=Int ) [ setInst] =?Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], Coll==?Int ) The problematic part is when `?Int` (the type var originated from `U`) is registered as a lower bound for `Coll`. That happens in `solveOne`: for (tparam2 <- tparams) tparam2.info.bounds.hi.dealias match { case TypeRef(_, `tparam`, _) => log(s"$tvar addLoBound $tparam2.tpeHK.instantiateTypeParams($tparams, $tvars)") tvar addLoBound tparam2.tpeHK.instantiateTypeParams(tparams, tvars) case _ => } --- test/files/neg/t7289.check | 4 ++++ test/files/neg/t7289.scala | 39 +++++++++++++++++++++++++++++++++++ test/files/neg/t7289_status_quo.check | 22 ++++++++++++++++++++ test/files/neg/t7289_status_quo.scala | 23 +++++++++++++++++++++ 4 files changed, 88 insertions(+) create mode 100644 test/files/neg/t7289.check create mode 100644 test/files/neg/t7289.scala create mode 100644 test/files/neg/t7289_status_quo.check create mode 100644 test/files/neg/t7289_status_quo.scala (limited to 'test') diff --git a/test/files/neg/t7289.check b/test/files/neg/t7289.check new file mode 100644 index 0000000000..e4aeebbc6c --- /dev/null +++ b/test/files/neg/t7289.check @@ -0,0 +1,4 @@ +t7289.scala:8: error: could not find implicit value for parameter e: Test.Schtroumpf[scala.collection.immutable.Nil.type] + implicitly[Schtroumpf[Nil.type]] + ^ +one error found diff --git a/test/files/neg/t7289.scala b/test/files/neg/t7289.scala new file mode 100644 index 0000000000..f4ed3daf76 --- /dev/null +++ b/test/files/neg/t7289.scala @@ -0,0 +1,39 @@ +object Test extends App { + trait Schtroumpf[T] + + implicit def schtroumpf[T, U <: Coll[T], Coll[X] <: Traversable[X]] + (implicit minorSchtroumpf: Schtroumpf[T]): Schtroumpf[U] = ??? + + implicit val qoo: Schtroumpf[Int] = new Schtroumpf[Int]{} + implicitly[Schtroumpf[Nil.type]] +} + +/* +info1 = {scala.tools.nsc.typechecker.Implicits$ImplicitInfo@3468}"qoo: => Test.Schtroumpf[Int]" +info2 = {scala.tools.nsc.typechecker.Implicits$ImplicitInfo@3469}"schtroumpf: [T, U <: Coll[T], Coll[_] <: Traversable[_]](implicit minorSchtroumpf: Test.Schtroumpf[T])Test.Schtroumpf[U]" +isStrictlyMoreSpecific(info1, info2) + isSubType(Test.Schtroumpf[Int], Test.Schtroumpf[U] forSome { T; U <: Coll[T]; Coll[_] <: Traversable[_] }) + isAsSpecificValueType(Test.Schtroumpf[Int], Test.Schtroumpf[U], undef2 = List(type T, type U, type Coll)) + + val et: ExistentialType = Test.Schtroumpf[U] forSome { T; U <: Coll[T]; Coll[_] <: Traversable[_] } + val tp1 = Test.Schtroumpf[Int] + et.withTypeVars(isSubType(tp1, _, depth)) + solve() + tvars = tList(=?Nothing, =?Int, =?=?Int) + + +[ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ create] ?U ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ create] ?Coll ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ setInst] Nothing ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Nothing ) +[ setInst] scala.collection.immutable.Nil.type( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], U=scala.collection.immutable.Nil.type ) +[ setInst] =?scala.collection.immutable.Nil.type( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], Coll==?scala.collection.immutable.Nil.type ) +[ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ setInst] Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Int ) +[ create] ?T ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ create] ?U ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ create] ?Coll ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]] ) +[ setInst] Nothing ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], T=Nothing ) +[ setInst] Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], U=Int ) +[ setInst] =?Int ( In Test#schtroumpf[T,U <: Coll[T],Coll[_] <: Traversable[_]], Coll==?Int ) +*/ \ No newline at end of file diff --git a/test/files/neg/t7289_status_quo.check b/test/files/neg/t7289_status_quo.check new file mode 100644 index 0000000000..31c072e969 --- /dev/null +++ b/test/files/neg/t7289_status_quo.check @@ -0,0 +1,22 @@ +t7289_status_quo.scala:9: error: could not find implicit value for parameter e: Test1.Ext[List[Int]] + implicitly[Ext[List[Int]]] // fails - not found + ^ +t7289_status_quo.scala:11: error: could not find implicit value for parameter e: Test1.Ext[List[List[List[Int]]]] + implicitly[Ext[List[List[List[Int]]]]] // fails - not found + ^ +t7289_status_quo.scala:15: error: ambiguous implicit values: + both method f in object Test1 of type [A, Coll <: CC[A], CC[X] <: Traversable[X]](implicit xi: Test1.Ext[A])Test1.Ext[Coll] + and value m in object Test1 of type => Test1.Ext[List[List[Int]]] + match expected type Test1.Ext[_ <: List[List[Int]]] + implicitly[Ext[_ <: List[List[Int]]]] // fails - ambiguous + ^ +t7289_status_quo.scala:20: error: could not find implicit value for parameter e: Test1.ExtCov[List[Int]] + implicitly[ExtCov[List[Int]]] // fails - not found + ^ +t7289_status_quo.scala:21: error: could not find implicit value for parameter e: Test1.ExtCov[List[List[Int]]] + implicitly[ExtCov[List[List[Int]]]] // fails - not found + ^ +t7289_status_quo.scala:22: error: could not find implicit value for parameter e: Test1.ExtCov[List[List[List[Int]]]] + implicitly[ExtCov[List[List[List[Int]]]]] // fails - not found + ^ +6 errors found diff --git a/test/files/neg/t7289_status_quo.scala b/test/files/neg/t7289_status_quo.scala new file mode 100644 index 0000000000..39621429a1 --- /dev/null +++ b/test/files/neg/t7289_status_quo.scala @@ -0,0 +1,23 @@ +// record the status quo after this fix +// not clear to @adriaanm why an upper-bounded existential in an invariant position +// is different from putting that upper bound in a covariant position +object Test1 { + trait Ext[T] + implicit def f[A, Coll <: CC[A], CC[X] <: Traversable[X]](implicit xi: Ext[A]): Ext[Coll] = ??? + implicit val m: Ext[List[List[Int]]] = new Ext[List[List[Int]]]{} + + implicitly[Ext[List[Int]]] // fails - not found + implicitly[Ext[List[List[Int]]]] // compiles + implicitly[Ext[List[List[List[Int]]]]] // fails - not found + + // Making Ext[+T] should incur the same behavior as these. (so says @paulp) + implicitly[Ext[_ <: List[Int]]] // compiles + implicitly[Ext[_ <: List[List[Int]]]] // fails - ambiguous + implicitly[Ext[_ <: List[List[List[Int]]]]] // compiles + + // But, we currently get: + trait ExtCov[+T] + implicitly[ExtCov[List[Int]]] // fails - not found + implicitly[ExtCov[List[List[Int]]]] // fails - not found + implicitly[ExtCov[List[List[List[Int]]]]] // fails - not found +} \ No newline at end of file -- cgit v1.2.3