Test case for SI-8372: issue with ArrayOps.unzip

This commit merely documents current (suboptimal) error message printed
for the code reported in SI-8372. The next commit will fix the problem.

test/files/neg/t8372.check

@@ -0,0 +1,7 @@
+t8372.scala:7: error: tpe T1 is an unresolved spliceable type
+  def unzip[T1, T2](a: Array[(T1, T2)]) = a.unzip
+                                            ^
+t8372.scala:9: error: tpe T1 is an unresolved spliceable type
+  def unzip3[T1, T2, T3](a: Array[(T1, T2, T3)]): (Array[T1], Array[T2], Array[T3]) = a.unzip3
+                                                                                        ^
+two errors found

test/files/neg/t8372.scala

@@ -0,0 +1,10 @@
+class t8372 {
+  // failed with "error: tpe T1 is an unresolved spliceable type"; that was caused by
+  // misguided type inference of type parameters in ArrayOps.unzip
+  // the type inference failed because the order of implicit arguments was wrong
+  // the evidence that T <: (T1, T2) came as last argument so it couldn't guide the
+  // type inference early enough
+  def unzip[T1, T2](a: Array[(T1, T2)]) = a.unzip
+  // the same as above
+  def unzip3[T1, T2, T3](a: Array[(T1, T2, T3)]): (Array[T1], Array[T2], Array[T3]) = a.unzip3
+}