Merge pull request #910 from AurelienRichez/fix/fix-909

fix wrong match in shrinker (fixes #909)

Author: rossabaker

core/shared/src/main/scala/org/scalacheck/Prop.scala

@@ -773,7 +773,7 @@ object Prop {
     /*
      * Returns the first failed result in Left or success in Right.
      */
-    def getFirstFailure(xs: Stream[T], exceptionFilter: Option[Class[_]]): Either[(T,Result),(T,Result)] = {
+    def getFirstFailure(xs: Stream[T], exceptionFilter: Option[Class[_ <: Throwable]]): Either[(T,Result),(T,Result)] = {
       assert(!xs.isEmpty, "Stream cannot be empty")
       val results = xs.map(x => (x, result(x)))
       results.dropWhile {
@@ -788,7 +788,7 @@ object Prop {
     def shrinker(x: T, r: Result, shrinks: Int, orig: T): Result = {
       val xs = shrink(x)
       val res = r.addArg(Arg(labels,x,shrinks,orig,pp(x),pp(orig)))
-      val originalException = Some(r.status).collect { case NonFatal(e) => e.getClass() }
+      val originalException = Some(r.status).collect { case Prop.Exception(e) => e.getClass }
       if(xs.isEmpty) res else getFirstFailure(xs, originalException) match {
         case Right((x2,r2)) => res
         case Left((x2,r2)) => shrinker(x2, replOrig(r,r2), shrinks+1, orig)

core/shared/src/test/scala/org/scalacheck/PropSpecification.scala

@@ -269,6 +269,30 @@ object PropSpecification extends Properties("Prop") {
     })
   }
 
+  property("shrinking process always take the first value returned by the Shrink[T]") = {
+    // this shrinker split a string in 2
+    implicit val stringShrink: Shrink[String] = Shrink[String] {
+      def split(s: String): Stream[String] = {
+        if (s.length == 1) Stream.empty
+        else {
+          s.take(s.length / 2) #:: s.drop(s.length / 2)  #:: Stream.empty
+        }
+      }
+      split
+    }
+
+    // shrinked value will be "1234", then shrinked to "12" because it also fails, and finally "1"
+    val prop = forAll(Gen.const("12345678")) { (a: String) =>
+      throw new RuntimeException("expected exception")
+    }
+
+    val result = prop(Gen.Parameters.default)
+    Prop(result.status match {
+      case Exception(_) => result.args.head.arg == "1"
+      case _ => false
+    })
+  }
+
   // make sure the two forAlls are seeing independent values
   property("regression #530: failure to slide seed") =
     forAll((x: Int) => (x >= 0) ==> true) &&