Merge pull request #835 from kadzuya/fix_arbitrary_char

Fix Arbitrary[Char] generates 0xFFFE (not a character in Unicode)

Author: ashawley

jvm/src/test/scala/org/scalacheck/ArbitrarySpecification.scala

@@ -9,9 +9,10 @@
 
 package org.scalacheck
 
+import java.util.concurrent.TimeUnit
+
 import Prop._
 import Arbitrary._
-import java.util.concurrent.TimeUnit
 
 object ArbitrarySpecification extends Properties("Arbitrary") {
   val genOptionUnits =
@@ -23,6 +24,11 @@ object ArbitrarySpecification extends Properties("Arbitrary") {
   property("arbOption coverage") =
     exists(genOptionUnits) { case (a, b) => a.isDefined != b.isDefined }
 
+  property("arbChar") =
+    Prop.forAll { (c: Char) =>
+      0x0000 <= c && c <= 0xD7FF || 0xE000 <= c && c <= 0xFFFD
+    }
+
   property("arbString") =
     Prop.forAll { (s: String) =>
       s ne new String(s)

src/main/scala/org/scalacheck/Arbitrary.scala

@@ -152,8 +152,8 @@ private[scalacheck] sealed trait ArbitraryLowPriority {
   implicit lazy val arbChar: Arbitrary[Char] = Arbitrary {
     // valid ranges are [0x0000, 0xD7FF] and [0xE000, 0xFFFD].
     //
-    // ((0xFFFD + 1) - 0xE000) + ((0xD7FF + 1) - 0x0000)
-    choose(0, 63486).map { i =>
+    // ((0xFFFD + 1) - 0xE000) + ((0xD7FF + 1) - 0x0000) - 1
+    choose(0, 63485).map { i =>
       if (i <= 0xD7FF) i.toChar
       else (i + 2048).toChar
     }