Fix SI-2712

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

1 files changed, 23 insertions, 0 deletions

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] }
+  //                                   ^
+}