Merge remote-tracking branch 'upstream/stable' into merge_stable

std/parallelism.d

@@ -1508,7 +1508,7 @@ public:
 
         if (this.size == 0)
         {
-            return rangeLen;
+            return max(rangeLen, 1);
         }
 
         immutable size_t eightSize = 4 * (this.size + 1);
@@ -3644,6 +3644,15 @@ ParallelForeach!R parallel(R)(R range, size_t workUnitSize)
     assert(arrIndex.sum == 10.iota.sum);
 }
 
+// https://issues.dlang.org/show_bug.cgi?id=22745
+@system unittest
+{
+    auto pool = new TaskPool(0);
+    int[] empty;
+    foreach (i; pool.parallel(empty)) {}
+    pool.finish();
+}
+
 // Thrown when a parallel foreach loop is broken from.
 class ParallelForeachError : Error
 {