Do not set target_compile_features

Author: ClausKlein

CMakeLists.txt

@@ -3,8 +3,6 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 # cmake-format: on
 
-set(CMAKE_SKIP_TEST_ALL_DEPENDENCY FALSE)
-
 cmake_minimum_required(VERSION 3.25...3.31)
 
 project(
@@ -19,6 +17,23 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
     message(FATAL_ERROR "In-source builds are not allowed!")
 endif()
 
+# Require C++20, but let a parent project ask for something higher
+if(DEFINED CMAKE_CXX_STANDARD)
+    if(CMAKE_CXX_STANDARD EQUAL 98 OR CMAKE_CXX_STANDARD LESS 20)
+        message(FATAL_ERROR "This project requires at least C++23")
+    endif()
+else()
+    set(CMAKE_CXX_STANDARD 23)
+endif()
+
+# Always enforce the language constraint
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# We don't need compiler extensions, but let a parent ask for them
+if(NOT DEFINED CMAKE_CXX_EXTENSIONS)
+    set(CMAKE_CXX_EXTENSIONS OFF)
+endif()
+
 # [CMAKE.SKIP_EXAMPLES]
 option(
     BEMAN_EXEMPLAR_BUILD_EXAMPLES
@@ -55,7 +70,6 @@ set_target_properties(
     beman.inplace_vector
     PROPERTIES VERIFY_INTERFACE_HEADER_SETS ON
 )
-target_compile_features(beman.inplace_vector INTERFACE cxx_std_23)
 
 set(TARGET_PACKAGE_NAME ${PROJECT_NAME}-config)
 set(TARGETS_EXPORT_NAME ${PROJECT_NAME}-targets)