Merge pull request #4191 from dotty-staging/add-overload-test

Add overload resolution test corresponding to scala/scala #6275.

Author: smarter

tests/pos/overloaded_ho_fun.scala

@@ -0,0 +1,106 @@
+import scala.math.Ordering
+import scala.reflect.ClassTag
+
+trait Sam { def apply(x: Int): String }
+trait SamP[U] { def apply(x: Int): U }
+
+class OverloadedFun[T](x: T) {
+  // def foo(f: T => String): String = f(x)    Can't unify - need just type equality
+  def foo(f: Any => String): String = f(x)
+  def foo(f: Any => T): T = f("a")
+
+  def poly[U](f: Int => String): String = f(1)
+  def poly[U](f: Int => U): U = f(1)
+
+//  def polySam[U](f: Sam): String = f(1)      Only function types supported for pretype-args
+//  def polySam[U](f: SamP[U]): U = f(1)
+
+  // check that we properly instantiate java.util.function.Function's type param to String
+  def polyJavaSam(f: String => String) = 1
+  def polyJavaSam(f: java.util.function.Function[String, String]) = 2
+}
+
+class StringLike(xs: String) {
+  def map[A](f: Char => A): Array[A] = ???
+  def map(f: Char => Char): String = ???
+}
+
+object Test {
+  val of = new OverloadedFun[Int](1)
+
+  of.foo(_.toString)
+
+  of.poly(x => x / 2 )
+  //of.polySam(x => x / 2 )
+  of.polyJavaSam(x => x)
+
+  val sl = new StringLike("a")
+  sl.map(_ == 'a')  // : Array[Boolean]
+  sl.map(x => 'a')  // : String
+}
+
+object sorting {
+  def stableSort[K: ClassTag](a: Seq[K], f: (K, K) => Boolean): Array[K] = ???
+  def stableSort[L: ClassTag](a: Array[L], f: (L, L) => Boolean): Unit = ???
+
+  stableSort(??? : Seq[Boolean], (x: Boolean, y: Boolean) => x && !y)
+}
+
+// trait Bijection[A, B] extends (A => B) {
+//   def andThen[C](g: Bijection[B, C]): Bijection[A, C] = ???
+//   def compose[T](g: Bijection[T, A]) = g andThen this
+// }
+
+object SI10194 {
+  trait X[A] {
+    def map[B](f: A => B): Unit
+  }
+
+  trait Y[A] extends X[A] {
+    def map[B](f: A => B)(implicit ordering: Ordering[B]): Unit
+  }
+
+  trait Z[A] extends Y[A]
+
+  (null: Y[Int]).map(x => x.toString) // compiled
+  (null: Z[Int]).map(x => x.toString) // didn't compile
+}
+
+// Perform eta-expansion of methods passed as functions to overloaded functions
+trait A { def map[T](f: Int => T): Unit = () }
+object B extends A {
+  def noover(f: SAM[Int, Any]): Unit = ()
+  def map[T: scala.reflect.ClassTag](f: Int => T): Unit = ()
+  def f(x: Int) = x
+  noover(f)
+  noover(identity)
+  map(f) // same param type, monomorphic method
+  map(identity) // same param type, polymorphic method
+
+  // must not lub to an incompatible function type
+  object t { def f(x: Int => Int): Int = 0; def f(y: String => Int): String = "1" }
+  def fun(x: Int) = x
+  def fun2[T] = (x: T) => 42
+  t.f(fun) // different param type, monomorphic method
+  //t.f(fun2) // different param type, polymorphic method - not possible
+}
+
+// The same for SAM types
+trait SAM[-T, +R] { def apply(x: T): R }
+trait A2 { def map[T](f: SAM[Int, T]): Unit = () }
+object B2 extends A2 {
+  def noover(f: SAM[Int, Any]): Unit = ()
+  def map[T: scala.reflect.ClassTag](f: SAM[Int, T]): Unit = ()
+  def f(x: Int) = x
+  noover(f)
+  noover(identity)
+  map(f) // same param type, monomorphic method
+  //map(identity) // same param type, polymorphic method - not possible for SAMs
+
+  // must not lub to an incompatible function type
+  object t { def f(x: SAM[Int, Int]): Int = 0; def f(y: SAM[String, Int]): String = "1" }
+  def fun(x: Int) = x
+  def fun2[T] = (x: T) => 42
+  t.f(fun) // different param type, monomorphic method
+  //t.f(fun2) // different param type, polymorphic method - not possible
+}