Added a test for compatibility of boost::distance between Range and Iterator.

This functionality is used in core Boost components, so it is preferable
to test it in Boost.Iterator, even if it's already tested in Boost.Range,
to discover problems as early as possible.

The test verifies that boost::distance implemented in Boost.Range can invoke
boost::distance in Boost.Iterator (i.e. the function lookup succeeds).

include/boost/iterator/advance.hpp

@@ -77,7 +77,7 @@ namespace iterators {
 
 } // namespace iterators
 
-using iterators::advance;
+using namespace iterators::advance_adl_barrier;
 
 } // namespace boost
 

include/boost/iterator/distance.hpp

@@ -58,7 +58,7 @@ namespace iterators {
 
 } // namespace iterators
 
-using iterators::distance;
+using namespace iterators::distance_adl_barrier;
 
 } // namespace boost
 

test/Jamfile.v2

@@ -59,6 +59,8 @@ test-suite iterator
     [ run next_prior_test.cpp ]
     [ run advance_test.cpp ]
     [ run distance_test.cpp ]
+    [ compile adl_test.cpp ]
+    [ compile range_distance_compat_test.cpp ]
 
     [ run shared_iterator_test.cpp ]
 ;

test/adl_test.cpp

@@ -0,0 +1,25 @@
+// Copyright (C) 2017 Michel Morin.
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <vector>
+#include <boost/array.hpp>
+#include <boost/iterator/advance.hpp>
+#include <boost/iterator/distance.hpp>
+
+int main()
+{
+    // Test that boost::advance/distance are not found by ADL.
+    // (https://github.com/boostorg/iterator/issues/43)
+
+    typedef boost::array<int, 1> boost_type;
+    std::vector<boost_type> std_boost(2);
+    std::vector<boost_type>::iterator it = std_boost.begin();
+
+    advance(it, 2);
+    (void)distance(it, it);
+
+    return 0;
+}

test/range_distance_compat_test.cpp

@@ -0,0 +1,22 @@
+// Copyright (C) 2018 Andrey Semashev
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <boost/range/distance.hpp>
+#include <boost/range/iterator_range_core.hpp>
+#include <boost/iterator/distance.hpp>
+
+int main()
+{
+    // Test that boost::distance from Boost.Range works with boost::distance from Boost.Iterator
+    // (https://github.com/boostorg/iterator/commit/b844c8df530c474ec1856870b9b0de5f487b84d4#commitcomment-30603668)
+
+    typedef boost::iterator_range<const char*> range_type;
+    range_type range;
+
+    (void)boost::distance(range);
+
+    return 0;
+}