From d70356e0190d92b5e0f7e2389006911901ccd0f8 Mon Sep 17 00:00:00 2001
From: Infiltrator <lt.infiltrator@gmail.com>
Date: Tue, 8 Dec 2015 17:57:01 +1100
Subject: [PATCH] Fix topN(Range, Range) disrespect of its predicate

---
 std/algorithm/sorting.d | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/std/algorithm/sorting.d b/std/algorithm/sorting.d
index a43a15d05..8c042d3eb 100644
--- a/std/algorithm/sorting.d
+++ b/std/algorithm/sorting.d
@@ -2301,7 +2301,7 @@ auto topN(alias less = "a < b",
 
     static assert(ss == SwapStrategy.unstable,
             "Stable topN not yet implemented");
-    auto heap = BinaryHeap!Range1(r1);
+    auto heap = BinaryHeap!(Range1, less)(r1);
     for (; !r2.empty; r2.popFront())
     {
         heap.conditionalInsert(r2.front);
@@ -2326,6 +2326,16 @@ unittest
     assert(t == [ 0, 1, 2, 2, 3 ]);
 }
 
+// bug 15420
+unittest
+{
+    int[] a = [ 5, 7, 2, 6, 7 ];
+    int[] b = [ 2, 1, 5, 6, 7, 3, 0 ];
+    topN!"a > b"(a, b);
+    sort!"a > b"(a);
+    assert(a == [ 7, 7, 7, 6, 6 ]);
+}
+
 /**
 Copies the top $(D n) elements of the input range $(D source) into the
 random-access range $(D target), where $(D n =