Remove dependencies on Boost.StaticAssert.

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

.drone.jsonnet

@@ -454,4 +454,10 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "cppalliance/dronevs2022:1",
         { TOOLSET: 'msvc-14.3', CXXSTD: '14,17,20,latest', ADDRMD: '32,64' },
     ),
+
+    windows_pipeline(
+        "Windows VS2026 msvc-14.5",
+        "cppalliance/dronevs2026:1",
+        { TOOLSET: 'msvc-14.5', CXXSTD: '14,17,20,latest', ADDRMD: '32,64' },
+    ),
 ]

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/core/lightweight_test.hpp

@@ -207,6 +207,16 @@ inline std::string test_output_impl( char const& v )
     }
 }
 
+#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
+
+inline std::string test_output_impl( char8_t const& v )
+{
+    // assume that char is ASCII, compatible with char8_t
+    return test_output_impl( static_cast<char>( v ) );
+}
+
+#endif
+
 // predicates
 
 struct lw_test_eq

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

test/lightweight_test_test6.cpp

@@ -1,6 +1,6 @@
 // Test BOOST_TEST_EQ with character types
 //
-// Copyright 2020 Peter Dimov
+// Copyright 2020, 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
 // https://www.boost.org/LICENSE_1_0.txt
 
@@ -19,14 +19,23 @@ int main()
 
 #if !defined(BOOST_NO_CXX11_CHAR16_T)
 
+    BOOST_TEST_EQ( u'A', u'A' );
     BOOST_TEST_EQ( (char16_t)1, (char16_t)1 );
 
 #endif
 
 #if !defined(BOOST_NO_CXX11_CHAR32_T)
 
+    BOOST_TEST_EQ( U'A', U'A' );
     BOOST_TEST_EQ( (char32_t)1, (char32_t)1 );
 
+#endif
+
+#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
+
+    BOOST_TEST_EQ( u8'A', u8'A' );
+    BOOST_TEST_EQ( (char8_t)1, (char8_t)1 );
+
 #endif
 
     return boost::report_errors();