feat: make side strategy configurable

Author: barendgehrels

include/boost/geometry/core/config.hpp

@@ -15,4 +15,18 @@
 
 #include <boost/config.hpp>
 
+#if    defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_BY_TRIANGLE) \
+    && defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_ROBUST)
+#error "Both BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_BY_TRIANGLE" \
+    " and BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_ROBUST are defined." \
+    " Only one of them should be defined."
+#endif
+
+// Define default side strategy, if not defined by the user.
+// Until Boost 1.88.0, the default strategy is side_by_triangle.
+#if    ! defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_BY_TRIANGLE) \
+    && ! defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_ROBUST)
+#define BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_BY_TRIANGLE
+#endif
+
 #endif // BOOST_GEOMETRY_CORE_CONFIG_HPP

include/boost/geometry/strategy/cartesian/side_by_triangle.hpp

@@ -243,7 +243,7 @@ public :
 };
 
 #ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
-
+#if defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_BY_TRIANGLE)
 namespace services
 {
 
@@ -253,9 +253,9 @@ struct default_strategy<cartesian_tag, CalculationType>
     using type = side_by_triangle<CalculationType>;
 };
 
-}
-
+} // namespace services
 #endif
+#endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
 
 }} // namespace strategy::side
 

include/boost/geometry/strategy/cartesian/side_robust.hpp

@@ -178,6 +178,21 @@ struct side_robust
 
 };
 
+#ifndef DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
+#if defined(BOOST_GEOMETRY_DEFAULT_STRATEGY_SIDE_USE_SIDE_ROBUST)
+namespace services
+{
+
+template <typename CalculationType>
+struct default_strategy<cartesian_tag, CalculationType>
+{
+    using type = side_robust<CalculationType>;
+};
+
+} // namespace services
+#endif
+#endif // DOXYGEN_NO_STRATEGY_SPECIALIZATIONS
+
 }} // namespace strategy::side
 
 }} // namespace boost::geometry

test/geometry_test_common.hpp

@@ -20,6 +20,7 @@
 #define GEOMETRY_TEST_GEOMETRY_TEST_COMMON_HPP
 
 #include <boost/config.hpp>
+#include <boost/core/demangle.hpp>
 
 // Determine debug/release mode
 // (it would be convenient if Boost.Config or Boost.Test would define this)
@@ -94,6 +95,7 @@
 #include <boost/geometry/core/closure.hpp>
 #include <boost/geometry/core/point_order.hpp>
 #include <boost/geometry/core/tag.hpp>
+#include <boost/geometry/strategies/strategies.hpp>
 namespace bg = boost::geometry;
 
 
@@ -210,6 +212,13 @@ inline void BoostGeometryWriteTestConfiguration()
     std::cout << "  - Including failing test cases" << std::endl;
 #endif
     std::cout << "  - Default test type: " << string_from_type<default_test_type>::name() << std::endl;
+
+    using side_strategy = typename bg::strategy::side::services::default_strategy
+        <
+            bg::cartesian_tag
+        >::type;
+    std::cout << "  - Side strategy: " << boost::core::demangle(typeid(side_strategy).name()) << std::endl;
+
     std::cout << std::endl;
 }