Declare the public CMake target's C++17 requirement

CMakeLists.txt

@@ -18,6 +18,8 @@ add_library(robin_map INTERFACE)
 # Use tsl::robin_map as target, more consistent with other libraries conventions (Boost, Qt, ...)
 add_library(tsl::robin_map ALIAS robin_map)
 
+target_compile_features(robin_map INTERFACE cxx_std_17)
+
 target_include_directories(robin_map INTERFACE
                            "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
                            "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>")

tests/CMakeLists.txt

@@ -24,3 +24,11 @@ target_link_libraries(tsl_robin_map_tests PRIVATE Boost::unit_test_framework)
 # tsl::robin_map
 add_subdirectory(../ ${CMAKE_CURRENT_BINARY_DIR}/tsl)
 target_link_libraries(tsl_robin_map_tests PRIVATE tsl::robin_map)  
+
+# The public target must raise a consumer's lower requested language standard.
+add_executable(tsl_robin_map_cmake_test "cmake_target_test.cpp")
+set_target_properties(tsl_robin_map_cmake_test PROPERTIES
+                      CXX_STANDARD 14
+                      CXX_STANDARD_REQUIRED ON
+                      CXX_EXTENSIONS OFF)
+target_link_libraries(tsl_robin_map_cmake_test PRIVATE tsl::robin_map)

tests/cmake_target_test.cpp

@@ -0,0 +1,11 @@
+#include <tsl/robin_map.h>
+#include <tsl/robin_set.h>
+
+int main() {
+  tsl::robin_map<int, int> values;
+  values[7] = 42;
+  tsl::robin_set<int> keys;
+  keys.insert(7);
+
+  return values.at(7) == 42 && keys.count(7) == 1 ? 0 : 1;
+}