Fix #5765: Add regression test

tests/pos/i5765.scala

@@ -0,0 +1,41 @@
+import scala.language.higherKinds
+
+trait LogDSL[L]
+
+object LogDSL {
+  implicit object LogRecsLogDSL extends LogDSL[String]
+  def runLog(ls: String): String = ???
+}
+
+trait Direction[D] {
+  def north: D
+}
+
+object Direction {
+  // needs both instances to trigger the bug
+  implicit def logDirection[L](implicit L: LogDSL[L]): Direction[L] = ???
+  implicit def RotateDirection[D](implicit D: Direction[D]): Direction[Rotate.Rotation[D]] = ???
+}
+
+trait Rotate[R] {
+  def rotate(r: R): R
+}
+
+object Rotate {
+  implicit def logRotate[L](implicit L: LogDSL[L]): Rotate[L] = ???
+
+  opaque type Rotation[T] = Int => T
+}
+
+object Main {
+  // the instances have to be acquired through implicit resolution to cause the crash
+  def north[D](implicit D: Direction[D]): D = ???
+  def rotate[R](r: R)(implicit RR: Rotate[R]): R = ???
+
+  def main(args: Array[String]): Unit = {
+    // commenting out either the first or the second of these lines removes the compiler crash
+    // removing the wrapping println call abolishes the crash
+    println(LogDSL.runLog(rotate(north)))
+    println(LogDSL.runLog(rotate(north)))
+  }
+}