Fix GCC-7 compilation after cmcstl2 upgrade (which compiles with stdc++20)

pylene/CMakeLists.txt

@@ -51,11 +51,11 @@ target_sources(Pylene PRIVATE
 # Compiler configurations
 target_compile_features(Pylene PUBLIC cxx_std_17)
 
-# Add concepts support for gcc > 7.2 with -fconcepts
-if (CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 7.2)
-  target_compile_options(Pylene PUBLIC -fconcepts)
+# Add concepts support for gcc > 8 with -fconcepts
+if (CMAKE_COMPILER_IS_GNUCXX AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 8)
+  set(PYLENE_CONCEPT_TS_ENABLED True PARENT_SCOPE)
   find_package(cmcstl2 REQUIRED)
-  target_link_libraries(Pylene PUBLIC stl2)
+  target_link_libraries(Pylene PUBLIC stl2) # This add appropriate -fconcept flags
   target_compile_definitions(Pylene PUBLIC PYLENE_CONCEPT_TS_ENABLED)
 endif ()
 

pylene/include/mln/core/rangev3/view/zip_with.hpp

@@ -83,7 +83,7 @@ namespace mln::ranges
       void next() requires (mln::concepts::stl::ForwardRange<Rngs> && ...)
       // clang-format on
 #else
-      template <typename U = void, typename = std::enable_if_t<(::ranges::ForwardRange<Rngs>() && ...)>>
+      template <typename U = void, typename = std::enable_if_t<(::ranges::ForwardRange<Rngs>() && ...), U>>
       void next()
 #endif
       {
@@ -94,30 +94,13 @@ namespace mln::ranges
       // clang-format off
       void prev() requires (mln::concepts::stl::BidirectionalRange<Rngs> && ...)
       // clang-format on
-      {
-        std::apply([](auto&... rng_it) { (--rng_it, ...); }, begins_);
-      }
 #else
-      // Clunky SFINAE doesn't work
-      /*
-      template <typename U = void, typename = std::enable_if_t<(::ranges::BidirectionalRange<Rngs>() && ...)>>
+      template <class U = void, class = std::enable_if_t<(::ranges::BidirectionalRange<Rngs>() && ...), U>>
       void prev()
+#endif
       {
         std::apply([](auto&... rng_it) { (--rng_it, ...); }, begins_);
       }
-      */
-      void prev()
-      {
-        if constexpr (are_bidir_rngs_)
-        {
-          std::apply([](auto&... rng_it) { (--rng_it, ...); }, begins_);
-        }
-        else
-        {
-          static_assert(are_bidir_rngs_, "Cannot traverse non-bidirectional range backward");
-        }
-      }
-#endif
     };
 
     cursor begin_cursor()

tests/core/CMakeLists.txt

@@ -89,7 +89,7 @@ add_core_test(${test_prefix}mask2d             se/mask2d.cpp)
 
 # test Concepts
 # Add concepts support for gcc > 7.2 with -fconcepts
-if (CMAKE_COMPILER_IS_GNUCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 7.2)
+if (PYLENE_CONCEPT_TS_ENABLED)
   add_core_test(${test_prefix}concept_values            concept/values.cpp)
   add_core_test(${test_prefix}concept_points            concept/points.cpp)
   add_core_test(${test_prefix}concept_pixels            concept/pixels.cpp)