Fix SI-2712

Allows partially instantiated types as type constrictors when inferring higher-kinded
types.

7 files changed, 79 insertions, 4 deletions

diff --git a/tests/neg/i94-nada.scala b/tests/neg/i94-nada.scala
new file mode 100644
index 000000000..8ca104e06
--- /dev/null
+++ b/tests/neg/i94-nada.scala
@@ -0,0 +1,11 @@
+trait Test1 {
+  trait Monad[MX] {
+    def x: MX
+  }
+  sealed abstract class Either[A,B]
+  case class Left[A,B](x: A) extends Either[A,B] with Monad[A]
+  case class Right[A,B](x: B) extends Either[A,B] with Monad[B]
+  def flatMap[FX,FY,M[FMX]<:Monad[FMX]](m: M[FX], f: FX => M[FY]): M[FY] = f(m.x)
+  println(flatMap(Left(1), {x: Int => Left(x)})) // error: Left does not conform to [X] -> Monad[X]
+
+}
diff --git a/tests/pickling/i94-nada.scala b/tests/pickling/i94-nada.scala
index ce8dc98ad..cf39ee2ae 100644
--- a/tests/pickling/i94-nada.scala
+++ b/tests/pickling/i94-nada.scala
@@ -27,7 +27,7 @@ trait Test1 {
   case class Left[A,B](x: A) extends Either[A,B] with Monad[A]
   case class Right[A,B](x: B) extends Either[A,B] with Monad[B]
   def flatMap[X,Y,M[X]<:Monad[X]](m: M[X], f: X => M[Y]): M[Y] = f(m.x)
-  println(flatMap(Left(1), {x: Int => Left(x)}))
+  println(flatMap(Right(1), {x: Int => Right(x)}))
 }
 trait Test2 {
   trait Monad[X] {
@@ -37,7 +37,7 @@ trait Test2 {
   case class Left[A,B](x: A) extends Either[A,B] with Monad[A]
   case class Right[A,B](x: B) extends Either[A,B] with Monad[B]
   def flatMap[X,Y,M[X]](m: M[X], f: X => M[Y]): M[Y]
-  println(flatMap(Left(1), {x: Int => Left(x)}))
+  println(flatMap(Right(1), {x: Int => Right(x)}))
 }
 trait Test3 {
   def flatMap[X,Y,M[X]](m: M[X], f: X => M[Y]): M[Y]
diff --git a/tests/pos/i94-nada.scala b/tests/pos/i94-nada.scala
index f8263ccf2..1c7d88a10 100644
--- a/tests/pos/i94-nada.scala
+++ b/tests/pos/i94-nada.scala
@@ -25,7 +25,7 @@ trait Test1 {
   case class Left[A,B](x: A) extends Either[A,B] with Monad[A]
   case class Right[A,B](x: B) extends Either[A,B] with Monad[B]
   def flatMap[X,Y,M[X]<:Monad[X]](m: M[X], f: X => M[Y]): M[Y] = f(m.x)
-  println(flatMap(Left(1), {x: Int => Left(x)}))
+  println(flatMap(Right(1), {x: Int => Right(x)}))
 }
 trait Test2 {
   trait Monad[X] {
@@ -35,7 +35,7 @@ trait Test2 {
   case class Left[A,B](x: A) extends Either[A,B] with Monad[A]
   case class Right[A,B](x: B) extends Either[A,B] with Monad[B]
   def flatMap[X,Y,M[X]](m: M[X], f: X => M[Y]): M[Y]
-  println(flatMap(Left(1), {x: Int => Left(x)}))
+  println(flatMap(Right(1), {x: Int => Right(x)}))
 }
 trait Test3 {
   def flatMap[X,Y,M[X]](m: M[X], f: X => M[Y]): M[Y]
diff --git a/tests/pos/t2712-1.scala b/tests/pos/t2712-1.scala
new file mode 100644
index 000000000..4f84c9df5
--- /dev/null
+++ b/tests/pos/t2712-1.scala
@@ -0,0 +1,9 @@
+package test
+
+// Original test case from,
+//
+//   https://issues.scala-lang.org/browse/SI-2712
+object Test {
+  def meh[M[_], A](x: M[A]): M[A] = x
+  meh{(x: Int) => x} // solves ?M = [X] Int => X and ?A = Int ...
+}
diff --git a/tests/pos/t2712-4.scala b/tests/pos/t2712-4.scala
new file mode 100644
index 000000000..3e2e5cdda
--- /dev/null
+++ b/tests/pos/t2712-4.scala
@@ -0,0 +1,17 @@
+package test
+
+object Test1 {
+  trait X
+  trait Y extends X
+  class Foo[T, U <: X]
+  def meh[M[_ <: A], A](x: M[A]): M[A] = x
+  meh(new Foo[Int, Y])
+}
+
+object Test2 {
+  trait X
+  trait Y extends X
+  class Foo[T, U >: Y]
+  def meh[M[_ >: A], A](x: M[A]): M[A] = x
+  meh(new Foo[Int, X])
+}
diff --git a/tests/pos/t2712-7.scala b/tests/pos/t2712-7.scala
new file mode 100644
index 000000000..d9c5243f1
--- /dev/null
+++ b/tests/pos/t2712-7.scala
@@ -0,0 +1,15 @@
+package test
+
+// Cats Xor, Scalaz \/, scala.util.Either
+sealed abstract class Xor[+A, +B] extends Product with Serializable
+object Xor {
+  final case class Left[+A](a: A) extends (A Xor Nothing)
+  final case class Right[+B](b: B) extends (Nothing Xor B)
+}
+
+object TestXor {
+  import Xor._
+  def meh[F[_], A, B](fa: F[A])(f: A => B): F[B] = ???
+  meh(new Right(23): Xor[Boolean, Int])(_ < 13)
+  meh(new Left(true): Xor[Boolean, Int])(_ < 13)
+}
diff --git a/tests/pos/t5683.scala b/tests/pos/t5683.scala
new file mode 100644
index 000000000..05ab03579
--- /dev/null
+++ b/tests/pos/t5683.scala
@@ -0,0 +1,23 @@
+object Test {
+  trait NT[X]
+  trait W[W, A] extends NT[Int]
+  type StringW[T] = W[String, T]
+  trait K[M[_], A, B]
+
+  def k[M[_], B](f: Int => M[B]): K[M, Int, B] = null
+
+  val okay1: K[StringW,Int,Int] = k{ (y: Int) => null: StringW[Int] }
+  val okay2 = k[StringW,Int]{ (y: Int) => null: W[String, Int] }
+
+  val crash: K[StringW,Int,Int] = k{ (y: Int) => null: W[String, Int] }
+
+  // remove `extends NT[Int]`, and the last line gives an inference error
+  // rather than a crash.
+  //   test/files/pos/t5683.scala:12: error: no type parameters for method k: (f: Int => M[B])Test.K[M,Int,B] exist so that it can be applied to arguments (Int => Test.W[String,Int])
+  //  --- because ---
+  // argument expression's type is not compatible with formal parameter type;
+  //  found   : Int => Test.W[String,Int]
+  //  required: Int => ?M[?B]
+  //   val crash: K[StringW,Int,Int] = k{ (y: Int) => null: W[String, Int] }
+  //                                   ^
+}