Move fclose_deleter and null_deleter to their own namespaces to block ADL.

This prevents bringing namespace boost into ADL when the deleters are used
in template parameters, e.g. in std::unique_ptr.

doc/changes.qbk

@@ -11,6 +11,15 @@
 
 * Added a new [link core.functor `boost/core/functor.hpp`] header with a `functor` class template
   for wrapping a raw function into a function object class.
+* Changed [link core.null_deleter `null_deleter`] and [link core.fclose_deleter `fclose_deleter`]
+  definitions so that they don't bring namespace `boost` into argument-dependent lookup in cases
+  like this:
+  ```
+  std::unique_ptr< std::FILE, boost::fclose_deleter > p1, p2;
+  swap(p1, p2); // no longer looks for boost::swap as part of ADL
+  ```
+  Users may need to either explicitly qualify the namespace of the called function or add a
+  `using`-declaration.
 
 [endsect]
 

include/boost/core/fclose_deleter.hpp

@@ -26,6 +26,9 @@
 
 namespace boost {
 
+// Block unintended ADL
+namespace fclose_deleter_ns {
+
 //! A function object that closes a file
 struct fclose_deleter
 {
@@ -41,6 +44,10 @@ struct fclose_deleter
     }
 };
 
+} // namespace fclose_deleter_ns
+
+using fclose_deleter_ns::fclose_deleter;
+
 } // namespace boost
 
 #endif // BOOST_CORE_FCLOSE_DELETER_HPP

include/boost/core/null_deleter.hpp

@@ -27,6 +27,9 @@
 
 namespace boost {
 
+// Block unintended ADL
+namespace null_deleter_ns {
+
 //! A function object that does nothing and can be used as an empty deleter for \c shared_ptr
 struct null_deleter
 {
@@ -39,6 +42,10 @@ struct null_deleter
     void operator() (T*) const BOOST_NOEXCEPT {}
 };
 
+} // namespace null_deleter_ns
+
+using null_deleter_ns::null_deleter;
+
 } // namespace boost
 
 #endif // BOOST_CORE_NULL_DELETER_HPP

test/Jamfile.v2

@@ -187,7 +187,12 @@ compile-fail scoped_enum_compile_fail_conv_to_int.cpp
 
 run underlying_type.cpp ;
 
+compile-fail null_deleter_compile_fail_adl.cpp
+  : $(warnings-as-errors-off) ;
+
 run fclose_deleter_test.cpp : : : <target-os>windows:<define>_CRT_SECURE_NO_WARNINGS <target-os>windows:<define>_CRT_SECURE_NO_DEPRECATE ;
+compile-fail fclose_deleter_compile_fail_adl.cpp
+  : <target-os>windows:<define>_CRT_SECURE_NO_WARNINGS <target-os>windows:<define>_CRT_SECURE_NO_DEPRECATE $(warnings-as-errors-off) ;
 
 run functor_test.cpp ;
 

test/fclose_deleter_compile_fail_adl.cpp

@@ -0,0 +1,30 @@
+/*
+ *             Copyright Andrey Semashev 2024.
+ * 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)
+ */
+/*!
+ * \file   fclose_deleter_compile_fail_adl.cpp
+ * \author Andrey Semashev
+ * \date   02.02.2024
+ *
+ * This file tests that \c boost::fclose_deleter doesn't bring namespace
+ * boost into ADL.
+ */
+
+#include <boost/core/fclose_deleter.hpp>
+
+namespace boost {
+
+void check_adl(fclose_deleter const&)
+{
+}
+
+} // namespace boost
+
+int main()
+{
+    // Must not find boost::check_adl
+    check_adl(boost::fclose_deleter());
+}

test/null_deleter_compile_fail_adl.cpp

@@ -0,0 +1,30 @@
+/*
+ *             Copyright Andrey Semashev 2024.
+ * 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)
+ */
+/*!
+ * \file   fclose_deleter_compile_fail_adl.cpp
+ * \author Andrey Semashev
+ * \date   02.02.2024
+ *
+ * This file tests that \c boost::null_deleter doesn't bring namespace
+ * boost into ADL.
+ */
+
+#include <boost/core/null_deleter.hpp>
+
+namespace boost {
+
+void check_adl(null_deleter const&)
+{
+}
+
+} // namespace boost
+
+int main()
+{
+    // Must not find boost::check_adl
+    check_adl(boost::null_deleter());
+}