From 289149a2f1e582d8fcbe74dbead47c1a01f8201c Mon Sep 17 00:00:00 2001
From: Vladimir Panteleev <git@thecybershadow.net>
Date: Wed, 25 Sep 2019 07:50:24 +0000
Subject: [PATCH] Fix Issue 20241 - BitArray.bitsSet ignores length

---
 std/bitmanip.d | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/std/bitmanip.d b/std/bitmanip.d
index 5e3e15d80..adc3defc0 100644
--- a/std/bitmanip.d
+++ b/std/bitmanip.d
@@ -2585,12 +2585,16 @@ public:
     @property auto bitsSet() const nothrow
     {
         import std.algorithm.iteration : filter, map, joiner;
-        import std.range : iota;
+        import std.range : iota, chain;
 
-        return iota(dim).
-               filter!(i => _ptr[i])().
-               map!(i => BitsSet!size_t(_ptr[i], i * bitsPerSizeT))().
-               joiner();
+        return chain(
+            iota(fullWords)
+                .filter!(i => _ptr[i])()
+                .map!(i => BitsSet!size_t(_ptr[i], i * bitsPerSizeT))()
+                .joiner(),
+            iota(fullWords * bitsPerSizeT, _len)
+                .filter!(i => this[i])()
+        );
     }
 
     ///
@@ -2630,6 +2634,16 @@ public:
         assert(b.bitsSet.equal(iota(wordBits * 2)));
     }
 
+    // Issue 20241
+    @system unittest
+    {
+        BitArray ba;
+        ba.length = 2;
+        ba[1] = 1;
+        ba.length = 1;
+        assert(ba.bitsSet.empty);
+    }
+
     private void formatBitString(Writer)(auto ref Writer sink) const
     {
         if (!length)