Fix scala-js#2144: Fix ThreadLocalRandom.nextDouble(MinValue, MaxValue).

Author: nicolasstucki

javalib/src/main/scala/java/util/concurrent/ThreadLocalRandom.scala

@@ -106,7 +106,13 @@ class ThreadLocalRandom extends Random {
     if (least >= bound)
       throw new IllegalArgumentException()
 
-    nextDouble() * (bound - least) + least
+    /* Based on documentation for Random.doubles to avoid issue #2144 and other
+     * possible rounding up issues:
+     * https://docs.oracle.com/javase/8/docs/api/java/util/Random.html#doubles-double-double-
+     */
+    val next = nextDouble() * (bound - least) + least
+    if (next < bound) next
+    else Math.nextAfter(bound, Double.NegativeInfinity)
   }
 }
 

test-suite/shared/src/test/require-jdk7/org/scalajs/testsuite/javalib/util/concurrent/ThreadLocalRandomTest.scala

@@ -515,8 +515,7 @@ class ThreadLocalRandomTest {
   @Test def should_return_nextDouble_that_fits_bounds(): Unit = {
     implicit val tlr = ThreadLocalRandom.current()
 
-    // Issue #2144
-    // checkDoubleBounds(Double.MinValue, Double.MaxValue)
+    checkDoubleBounds(Double.MinValue, Double.MaxValue)
     checkDoubleBounds(Double.MinValue, 0L)
     checkDoubleBounds(Double.MaxValue, 0L)
     checkDoubleBounds(0.14303466203185822, 0.7471945354839639)