Prepare use of CMAKE_CXX_MODULE_STD

We need at least cmake v3.28!

We need to set CMAKE_CXX_SCAN_FOR_MODULES too!

Fix compiler program name for apple-clang

Prevent unintended define of HAS_STDLIB_MODULES

Make it more readable

The final cleanup

Prepare run-clang-tidy too

Author: ClausKlein

CMakeLists.txt

@@ -1,6 +1,17 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-cmake_minimum_required(VERSION 3.28)
+if(CMAKE_CXX_STANDARD STREQUAL 26)
+    if(CMAKE_CXX_MODULE_STD)
+        set(CMAKE_CXX_SCAN_FOR_MODULES 1)
+        set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
+            "d0edc3af-4c50-42ea-a356-e2862fe7a444"
+        )
+        add_definitions(-DHAS_STDLIB_MODULES)
+    endif()
+    set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+endif()
+
+cmake_minimum_required(VERSION 3.28...4.0)
 
 project(
     beman.scope
@@ -14,13 +25,27 @@ project(
 # Modules opt in only on compilers that support g++-15 and clang-19+
 if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19)
     set(CMAKE_CXX_SCAN_FOR_MODULES 1)
-elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 15)
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 15)
     set(CMAKE_CXX_SCAN_FOR_MODULES 1)
-elseif()
+else()
     set(CMAKE_CXX_SCAN_FOR_MODULES 0)
 endif()
 
+if(CMAKE_CXX_SCAN_FOR_MODULES)
+    set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+endif()
+
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+if(CMAKE_EXPORT_COMPILE_COMMANDS)
+  set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
+endif()
+
+include(CMakePrintHelpers)
+cmake_print_variables(
+    CMAKE_CXX_SCAN_FOR_MODULES
+    CMAKE_CXX_MODULE_STD
+    CMAKE_CXX_COMPILER_IMPORT_STD
+)
 
 # [CMAKE.SKIP_TESTS]
 option(
@@ -42,12 +67,8 @@ option(
     ${PROJECT_IS_TOP_LEVEL}
 )
 
-message(
-    "Compiler is: ${CMAKE_CXX_COMPILER_ID} version:  ${CMAKE_CXX_COMPILER_VERSION}"
-)
-message(
-    "cmake is: ${CMAKE_VERSION} modules scan :  ${CMAKE_CXX_SCAN_FOR_MODULES}"
-)
+message(STATUS "Compiler is: ${CMAKE_CXX_COMPILER_ID} version: ${CMAKE_CXX_COMPILER_VERSION}")
+message(STATUS "CMake is: ${CMAKE_VERSION} modules scan: ${CMAKE_CXX_SCAN_FOR_MODULES}")
 
 if(CMAKE_CXX_SCAN_FOR_MODULES)
     add_library(beman.scope)
@@ -90,7 +111,7 @@ install(
     EXPORT beman.scope-targets
 
     FILE_SET CXX_MODULES
-        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
     FILE_SET HEADERS
 )
 
@@ -116,7 +137,8 @@ if(BEMAN_SCOPE_INSTALL_CONFIG_FILE_PACKAGE)
         EXPORT beman.scope-targets
         DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/beman.scope
         NAMESPACE beman::
-        CXX_MODULES_DIRECTORY cxx-modules
+        CXX_MODULES_DIRECTORY
+        cxx-modules
         COMPONENT beman.scope
     )
 endif()

cmake/appleclang-toolchain.cmake

@@ -16,8 +16,8 @@
 
 include_guard(GLOBAL)
 
-set(CMAKE_C_COMPILER clang)
-set(CMAKE_CXX_COMPILER clang++)
+set(CMAKE_C_COMPILER cc)
+set(CMAKE_CXX_COMPILER c++)
 
 if(BEMAN_BUILDSYS_SANITIZER STREQUAL "MaxSan")
     set(SANITIZER_FLAGS

tests/CMakeLists.txt

@@ -5,18 +5,18 @@ include(FetchContent)
 FetchContent_Declare(
     Catch2
     GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-    GIT_TAG v3.8.0
+    GIT_TAG v3.8.1
+    SYSTEM
+    # FIXME: FIND_PACKAGE_ARGS 3.8.1
 )
 FetchContent_MakeAvailable(Catch2)
 
-# module tests will only compile with gcc15 or clang20 and above
+set(ALL_TESTNAMES scope_success scope_exit scope_fail unique_resource)
 if(CMAKE_CXX_SCAN_FOR_MODULES)
-    set(ALL_TESTNAMES scope_success scope_exit scope_fail unique_resource module)
-else()
-    set(ALL_TESTNAMES scope_success scope_exit scope_fail unique_resource)
+    list(APPEND ALL_TESTNAMES module)
 endif()
 
-message("Tests to be built: ${ALL_TESTNAMES}")
+message(DEBUG "Tests to be built: ${ALL_TESTNAMES}")
 
 include(Catch)
 

tests/module.test.cpp

@@ -4,6 +4,9 @@
 #include <catch2/catch_all.hpp>
 
 // for g++-15 the order is important -- import after includes
+#ifdef HAS_STDLIB_MODULES
+import std;
+#endif
 import beman.scope;
 
 struct DummyResource {
@@ -33,5 +36,4 @@ TEST_CASE("module-test", "[scope_module_test]") {
     REQUIRE(success_ran == true);
     REQUIRE(fail_ran == false);
     REQUIRE(cleaned == true);
-
 }