From be9ad6a311a53e9ab8d2a8b69777b73d33b279c3 Mon Sep 17 00:00:00 2001
From: "H. S. Teoh" <hsteoh@quickfur.ath.cx>
Date: Wed, 9 Aug 2017 17:03:47 -0700
Subject: [PATCH 1/2] Fix issue 17661: isInputRange should work with .front
 that returns reference to parameter.

---
 std/range/primitives.d | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/std/range/primitives.d b/std/range/primitives.d
index 99064ba73ec..5587e1578bb 100644
--- a/std/range/primitives.d
+++ b/std/range/primitives.d
@@ -164,7 +164,7 @@ Returns:
 enum bool isInputRange(R) =
     is(typeof(R.init) == R)
     && is(ReturnType!((R r) => r.empty) == bool)
-    && is(typeof((R r) => r.front))
+    && is(typeof((return ref R r) => r.front))
     && !is(ReturnType!((R r) => r.front) == void)
     && is(typeof((R r) => r.popFront));
 

From 4501f5520a65936e1a180d0b37f389d5578fd7af Mon Sep 17 00:00:00 2001
From: "H. S. Teoh" <hsteoh@quickfur.ath.cx>
Date: Wed, 9 Aug 2017 17:16:22 -0700
Subject: [PATCH 2/2] Add unittest.

---
 std/range/primitives.d | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/std/range/primitives.d b/std/range/primitives.d
index 5587e1578bb..3dbde44900a 100644
--- a/std/range/primitives.d
+++ b/std/range/primitives.d
@@ -220,6 +220,31 @@ enum bool isInputRange(R) =
     static assert(!isInputRange!VoidFront);
 }
 
+@safe unittest
+{
+    import std.algorithm.comparison : equal;
+
+    static struct R
+    {
+        static struct Front
+        {
+            R* impl;
+            @property int value() { return impl._front; }
+            alias value this;
+        }
+
+        int _front;
+
+        @property bool empty() { return _front >= 3; }
+        @property auto front() { return Front(&this); }
+        void popFront() { _front++; }
+    }
+    R r;
+
+    static assert(isInputRange!R);
+    assert(r.equal([ 0, 1, 2 ]));
+}
+
 /+
 puts the whole raw element $(D e) into $(D r). doPut will not attempt to
 iterate, slice or transcode $(D e) in any way shape or form. It will $(B only)