From c96cfb6c1818bbc15fd26a54f03de7facd629f39 Mon Sep 17 00:00:00 2001
From: Andrey Semashev <andrey.semashev@gmail.com>
Date: Thu, 19 Jun 2025 04:22:30 +0300
Subject: [PATCH] Relax C++11 type_traits requirements.

This replaces the cxx11_hdr_type_traits requirement with a local
configure-time check for the presence of only those type traits
which are used in the library. This enables testing of gcc 4.8 and
4.9, which was previously silently skipped.
---
 build.jam                                   | 30 ++++++++--------
 config/Jamfile                              |  9 +++++
 config/has_sufficient_cxx11_type_traits.cpp | 38 +++++++++++++++++++++
 3 files changed, 63 insertions(+), 14 deletions(-)
 create mode 100644 config/Jamfile
 create mode 100644 config/has_sufficient_cxx11_type_traits.cpp

diff --git a/build.jam b/build.jam
index e25a0ae..3fc2867 100644
--- a/build.jam
+++ b/build.jam
@@ -16,20 +16,22 @@ constant boost_dependencies :
     /boost/core//boost_core
     /boost/type_traits//boost_type_traits ;
 
-local cxx_requirements = [ requires
-    exceptions
-    sfinae_expr
-    cxx11_constexpr
-    cxx11_noexcept
-    cxx11_decltype
-    cxx11_rvalue_references
-    cxx11_template_aliases
-    cxx11_variadic_templates
-    cxx11_defaulted_functions
-    cxx11_deleted_functions
-    cxx11_function_template_default_args
-    cxx11_hdr_type_traits
-] ;
+local cxx_requirements =
+    [ requires
+        exceptions
+        sfinae_expr
+        cxx11_constexpr
+        cxx11_noexcept
+        cxx11_decltype
+        cxx11_rvalue_references
+        cxx11_template_aliases
+        cxx11_variadic_templates
+        cxx11_defaulted_functions
+        cxx11_deleted_functions
+        cxx11_function_template_default_args
+    ]
+    [ check-target-builds config//has_sufficient_cxx11_type_traits "has <type_traits> sufficient for Boost.Scope" : : <build>no ]
+    ;
 
 project /boost/scope
     : common-requirements
diff --git a/config/Jamfile b/config/Jamfile
new file mode 100644
index 0000000..48badef
--- /dev/null
+++ b/config/Jamfile
@@ -0,0 +1,9 @@
+#
+#             Copyright Andrey Semashev 2025.
+# 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)
+#
+
+obj has_sufficient_cxx11_type_traits : has_sufficient_cxx11_type_traits.cpp : <library>/boost/config//boost_config ;
+explicit has_sufficient_cxx11_type_traits ;
diff --git a/config/has_sufficient_cxx11_type_traits.cpp b/config/has_sufficient_cxx11_type_traits.cpp
new file mode 100644
index 0000000..6197592
--- /dev/null
+++ b/config/has_sufficient_cxx11_type_traits.cpp
@@ -0,0 +1,38 @@
+/*
+ *             Copyright Andrey Semashev 2025.
+ * 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)
+ */
+
+// The test verifies that the compiler provides a <type_traits> header that is
+// sufficient for Boost.Scope needs.
+
+#include <type_traits>
+
+int main(int, char*[])
+{
+    using std::integral_constant;
+    using std::true_type;
+    using std::false_type;
+    using std::conditional;
+    using std::enable_if;
+
+    using std::decay;
+
+    using std::is_class;
+    using std::is_reference;
+
+    using std::is_constructible;
+    using std::is_nothrow_constructible;
+    using std::is_move_constructible;
+    using std::is_nothrow_move_constructible;
+    using std::is_default_constructible;
+    using std::is_nothrow_default_constructible;
+    using std::is_assignable;
+    using std::is_nothrow_assignable;
+    using std::is_move_assignable;
+    using std::is_nothrow_move_assignable;
+
+    return 0;
+}