Remove dependencies on Boost.StaticAssert.

Boost.StaticAssert has been merged into Boost.Config, so replace
the dependency accordingly.

doc/changes.qbk

@@ -7,6 +7,12 @@
 
 [section Revision History]
 
+[section Changes in 1.91.0]
+
+* The header [link core.is_placeholder `boost/is_placeholder.hpp`] has been moved from Bind to Core. ([github_issue 90])
+
+[endsect]
+
 [section Changes in 1.90.0]
 
 * The implementation of `BOOST_TEST_THROWS` and `BOOST_TEST_NO_THROW` macros defined in

doc/core.qbk

@@ -61,6 +61,7 @@ criteria for inclusion is that the utility component be:
 [include functor.qbk]
 [include identity.qbk]
 [include ignore_unused.qbk]
+[include is_placeholder.qbk]
 [include is_same.qbk]
 [include launder.qbk]
 [include lightweight_test.qbk]

doc/is_placeholder.qbk

@@ -0,0 +1,69 @@
+[/
+  Copyright 2014, 2025 Peter Dimov
+
+  Distributed under the Boost Software License, Version 1.0.
+
+  See accompanying file LICENSE_1_0.txt
+  or copy at http://boost.org/LICENSE_1_0.txt
+]
+
+[section:is_placeholder is_placeholder]
+
+[simplesect Authors]
+
+* Peter Dimov
+
+[endsimplesect]
+
+[section Header <boost/is_placeholder.hpp>]
+
+The header `<boost/is_placeholder.hpp>` defines the class template
+`boost::is_placeholder<T>`. It defines a nested integral constant
+`value` which is `0` when `T` is not a `boost::bind` placeholder
+type, and a positive value corresponding to the placeholder index
+otherwise.
+
+That is, `is_placeholder<_1>::value` is `1`,
+`is_placeholder<_2>::value` is `2`, and so on.
+
+`is_placeholder` can be specialized for user types. If it is,
+`boost::bind` will recognize these types as placeholders.
+
+[section Synopsis]
+
+``
+namespace boost
+{
+    template<class T> struct is_placeholder;
+}
+``
+
+[endsect]
+
+[section Example]
+
+``
+#include <boost/is_placeholder.hpp>
+#include <boost/bind.hpp>
+
+struct arg1_type {};
+constexpr arg1_type arg1{};
+
+template<> struct boost::is_placeholder<arg1_type>
+{
+    static constexpr int value = 1;
+};
+
+int f( int x ) { return x + 1; }
+
+int main()
+{
+    return boost::bind( f, arg1 )( -1 );
+}
+``
+
+[endsect]
+
+[endsect]
+
+[endsect]

include/boost/is_placeholder.hpp

@@ -0,0 +1,31 @@
+#ifndef BOOST_IS_PLACEHOLDER_HPP_INCLUDED
+#define BOOST_IS_PLACEHOLDER_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined( _MSC_VER ) && ( _MSC_VER >= 1020 )
+# pragma once
+#endif
+
+
+//  is_placeholder.hpp - TR1 is_placeholder metafunction
+//
+//  Copyright (c) 2006 Peter Dimov
+//
+//  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
+
+
+namespace boost
+{
+
+template< class T > struct is_placeholder
+{
+    enum _vt { value = 0 };
+};
+
+} // namespace boost
+
+#endif // #ifndef BOOST_IS_PLACEHOLDER_HPP_INCLUDED

test/CMakeLists.txt

@@ -6,7 +6,7 @@ include(BoostTestJamfile OPTIONAL RESULT_VARIABLE HAVE_BOOST_TEST)
 
 if(HAVE_BOOST_TEST)
 
-boost_test_jamfile(FILE Jamfile.v2 LINK_LIBRARIES Boost::core Boost::static_assert Boost::type_traits)
+boost_test_jamfile(FILE Jamfile.v2 LINK_LIBRARIES Boost::core Boost::config Boost::type_traits)
 
 set(BOOST_TEST_LINK_LIBRARIES Boost::core Boost::throw_exception)
 

test/Jamfile.v2

@@ -14,7 +14,7 @@ import testing ;
 
 project : requirements
   <library>/boost/core//boost_core
-  <library>/boost/static_assert//boost_static_assert
+  <library>/boost/config//boost_config
   <library>/boost/type_traits//boost_type_traits
   <warnings>extra
   <toolset>msvc:<warnings-as-errors>on