Prepare use of CMAKE_CXX_MODULE_STD

.github/workflows/ci_tests.yml

@@ -27,8 +27,8 @@ jobs:
       - name: Setup build environment
         uses: lukka/get-cmake@latest
         with:
-          cmakeVersion: "~3.28.0"
-          ninjaVersion: "^1.11.1"
+          cmakeVersion: latest
+          ninjaVersion: latest
       - name: Setup MSVC
         if: startsWith(matrix.presets.platform, 'windows')
         uses: TheMrMilchmann/setup-msvc-dev@v3
@@ -80,8 +80,8 @@ jobs:
       - name: Install Ninja
         uses: lukka/get-cmake@latest
         with:
-          cmakeVersion: "~4.0.0"
-          ninjaVersion: "^1.11.1"
+          cmakeVersion: latest
+          ninjaVersion: latest
       - name: Setup MSVC
         if: startsWith(matrix.platform.os, 'windows')
         uses: TheMrMilchmann/setup-msvc-dev@v3
@@ -139,8 +139,8 @@ jobs:
       - name: Setup build environment
         uses: lukka/get-cmake@latest
         with:
-          cmakeVersion: "~3.28.0"
-          ninjaVersion: "^1.11.1"
+          cmakeVersion: latest
+          ninjaVersion: latest
       - name: Print installed softwares
         run: |
           cmake --version
@@ -183,8 +183,8 @@ jobs:
       - name: Setup build environment
         uses: lukka/get-cmake@latest
         with:
-          cmakeVersion: "~4.0.0"
-          ninjaVersion: "^1.11.1"
+          cmakeVersion: latest
+          ninjaVersion: latest
       - name: Install Compiler
         id: install-compiler
         run: |

.gitignore

@@ -1,6 +1,8 @@
 # ignore temp build files
 /compile_commands.json
 /build
+**/_deps/
+**/CMakeFiles/
 
 # ignore emacs temp files
 *~

CMakeLists.txt

@@ -1,6 +1,23 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-cmake_minimum_required(VERSION 3.28)
+if(CMAKE_CXX_STANDARD GREATER_EQUAL 23)
+    if(CMAKE_CXX_MODULE_STD)
+        if(CMAKE_VERSION VERSION_EQUAL 4.0.2)
+            set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
+                "a9e1cf81-9932-4810-974b-6eccaf14e457"
+            )
+        else()
+            set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
+                "d0edc3af-4c50-42ea-a356-e2862fe7a444"
+            )
+        endif()
+        set(CMAKE_CXX_SCAN_FOR_MODULES 1)
+        add_definitions(-DHAS_STDLIB_MODULES)
+    endif()
+    set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+endif()
+
+cmake_minimum_required(VERSION 4.0)
 
 project(
     beman.scope
@@ -12,15 +29,45 @@ project(
 # gersemi: off
 
 # 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)
-    set(CMAKE_CXX_SCAN_FOR_MODULES 1)
-elseif()
+if(CMAKE_CXX_STANDARD GREATER_EQUAL 23)
+    if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19)
+        if(APPLE AND CMAKE_CXX_COMPILER_VERSION VERSION_EQUAL 20.1.5)
+            execute_process(OUTPUT_VARIABLE LLVM_PREFIX COMMAND brew --prefix llvm@20 COMMAND_ECHO STDOUT)
+            string(STRIP ${LLVM_PREFIX} LLVM_PREFIX)
+            file(REAL_PATH ${LLVM_PREFIX} LLVM_ROOT)
+            set(LLVM_ROOT ${LLVM_ROOT} CACHE PATH "")
+            message(STATUS "LLVM_ROOT=${LLVM_ROOT}")
+
+            add_compile_options(-fexperimental-library)
+            add_link_options(-L${LLVM_ROOT}/lib/c++ -lc++experimental)
+            add_compile_options(-stdlib=libc++)
+            add_link_options(-stdlib=libc++)
+        endif()
+        set(CMAKE_CXX_SCAN_FOR_MODULES 1)
+    elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 15)
+        set(CMAKE_CXX_SCAN_FOR_MODULES 1)
+    endif()
+else()
     set(CMAKE_CXX_SCAN_FOR_MODULES 0)
 endif()
 
-set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+if(CMAKE_CXX_SCAN_FOR_MODULES)
+    set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+endif()
+
+set(CMAKE_EXPORT_COMPILE_COMMANDS OFF)
+if(CMAKE_EXPORT_COMPILE_COMMANDS)
+    set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
+    find_program(CLANG_TIDY_EXE NAMES clang-tidy clang-tidy-20 DOC "Path to clang-tidy executable")
+endif()
+
+include(CMakePrintHelpers)
+cmake_print_variables(
+    CMAKE_CXX_STANDARD
+    CMAKE_CXX_SCAN_FOR_MODULES
+    CMAKE_CXX_MODULE_STD
+    CMAKE_CXX_COMPILER_IMPORT_STD
+)
 
 # [CMAKE.SKIP_TESTS]
 option(
@@ -42,12 +89,8 @@ 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)
@@ -62,6 +105,8 @@ if(CMAKE_CXX_SCAN_FOR_MODULES)
             BASE_DIRS include
             FILES include/beman/scope/beman.scope.cppm
     )
+    # prevent "not include "cxx_std_20" (or newer) among its `target_compile_features`; no C++ standard found"
+    target_compile_features(beman.scope PUBLIC cxx_std_23)
 else()
     add_library(beman.scope INTERFACE)
     target_sources(
@@ -71,6 +116,7 @@ else()
             BASE_DIRS include
             FILES include/beman/scope/scope.hpp
     )
+    target_compile_features(beman.scope INTERFACE cxx_std_20)
 endif()
 
 add_library(beman::scope ALIAS beman.scope)
@@ -90,7 +136,7 @@ install(
     EXPORT beman.scope-targets
 
     FILE_SET CXX_MODULES
-        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
     FILE_SET HEADERS
 )
 
@@ -116,7 +162,8 @@ 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()
@@ -127,5 +174,11 @@ if(BEMAN_SCOPE_BUILD_TESTS)
 endif()
 
 if(BEMAN_SCOPE_BUILD_EXAMPLES)
+    if(CLANG_TIDY_EXE)
+        message(STATUS "clang-tidy found: ${CLANG_TIDY_EXE}")
+        set(CMAKE_CXX_CLANG_TIDY
+            "${CLANG_TIDY_EXE};-extra-arg=--Wno-error=unknown-argument"
+        )
+    endif()
     add_subdirectory(examples)
 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);
-
 }