Add smoke test for std::regex compatibility

Author: Flamefire

test/Jamfile.v2

@@ -43,6 +43,7 @@ run test_ios_info.cpp ;
 run test_ios_prop.cpp ;
 run test_codecvt.cpp ;
 run test_codepage_converter.cpp ;
+run test_std_regex.cpp ;
 run test_stream_io.cpp ;
 run test_message.cpp : $(BOOST_ROOT)/libs/locale/test ;
 run test_generator.cpp ;

test/test_std_regex.cpp

@@ -0,0 +1,60 @@
+//
+// Copyright (c) 2025 Alexander Grund
+//
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/locale/generator.hpp>
+#include <boost/locale/localization_backend.hpp>
+#include "boostLocale/test/tools.hpp"
+#include <boost/core/detail/string_view.hpp>
+#include <regex>
+
+/// Smoke test that std::regex works with generated locales
+template<typename CharType>
+void test_by_char(const std::locale& l)
+{
+    using string_type = std::basic_string<CharType>;
+    std::basic_regex<CharType> pattern;
+    pattern.imbue(l);
+    pattern = ascii_to<CharType>("[[:alnum:]]+");
+    const string_type text = ascii_to<CharType>("ab12cd");
+    std::match_results<typename string_type::const_iterator> pieces;
+    if TEST(std::regex_match(text, pieces, pattern)) {
+        TEST_EQ(pieces.size(), 1u);
+        TEST_EQ(pieces[0].str(), text);
+    }
+}
+
+void test_main(int /*argc*/, char** /*argv*/)
+{
+    for(const std::string& backend_name : boost::locale::localization_backend_manager::global().get_all_backends()) {
+        TEST_CONTEXT("Backend: " << backend_name);
+        boost::locale::localization_backend_manager tmp_backend = boost::locale::localization_backend_manager::global();
+        tmp_backend.select(backend_name);
+        boost::locale::localization_backend_manager::global(tmp_backend);
+
+        boost::locale::generator gen;
+        const std::locale loc = gen("en_US.UTF-8");
+        gen.categories(gen.categories() ^ boost::locale::category_t::collation);
+        const std::locale loc_no_collation = gen("en_US.UTF-8");
+        gen.categories(boost::locale::category_t::collation);
+        const std::locale loc_collation = gen("en_US.UTF-8");
+        {
+            TEST_CONTEXT("char");
+            test_by_char<char>(loc);
+            {
+                TEST_CONTEXT("without collation");
+                test_by_char<char>(loc_no_collation);
+            }
+            {
+                TEST_CONTEXT("just collation");
+                test_by_char<char>(loc_collation);
+            }
+        }
+        {
+            TEST_CONTEXT("wchar_t");
+            test_by_char<wchar_t>(loc);
+        }
+    }
+}