Setup and validate compiler versions

Author: Bill-hbrhbr

CMakeLists.txt

@@ -1,7 +1,14 @@
 cmake_minimum_required(VERSION 3.23)
 
+# Toolchain setup must come before the first project() call in the entire CMake buildsystem.
+# If ystdlib is not the top-level project, the following setup has no effect.
+include("${CMAKE_CURRENT_SOURCE_DIR}/cmake/Toolchains/utils.cmake")
+setup_toolchains()
+
 project(ystdlib VERSION "0.1.0" LANGUAGES CXX)
 
+validate_compiler_versions()
+
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}/cmake")
 include(CMakePackageConfigHelpers)
 include(GNUInstallDirs)
@@ -10,28 +17,6 @@ include(ystdlib-helpers)
 option(BUILD_SHARED_LIBS "Build using shared libraries." OFF)
 option(ystdlib_BUILD_TESTING "Build the testing tree for ystdlib." ON)
 
-# Require compiler versions that support the C++17 features necessary for compiling ystdlib
-# See also: https://en.cppreference.com/w/cpp/compiler_support/17
-if("AppleClang" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
-    set(ystdlib_CMAKE_CXX_COMPILER_MIN_VERSION "15")
-elseif("Clang" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
-    set(ystdlib_CMAKE_CXX_COMPILER_MIN_VERSION "15")
-elseif("GNU" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
-    set(ystdlib_CMAKE_CXX_COMPILER_MIN_VERSION "11")
-else()
-    message(
-        FATAL_ERROR
-        "Unsupported compiler: ${CMAKE_CXX_COMPILER_ID}. Please use AppleClang, Clang, or GNU."
-    )
-endif()
-if("${CMAKE_CXX_COMPILER_VERSION}" VERSION_LESS "${ystdlib_CMAKE_CXX_COMPILER_MIN_VERSION}")
-    message(
-        FATAL_ERROR
-        "${CMAKE_CXX_COMPILER_ID} version ${CMAKE_CXX_COMPILER_VERSION} is too low. Must be at \
-        least ${ystdlib_CMAKE_CXX_COMPILER_MIN_VERSION}."
-    )
-endif()
-
 set(CMAKE_EXPORT_COMPILE_COMMANDS
     ON
     CACHE BOOL

cmake/Toolchains/llvm-clang-15-toolchain.cmake

@@ -0,0 +1,21 @@
+message(STATUS "Setting up LLVM v15 toolchain...")
+
+execute_process(
+    COMMAND
+        "brew" "--prefix" "llvm@15"
+    RESULT_VARIABLE BREW_RESULT
+    OUTPUT_VARIABLE LLVM_TOOLCHAIN_PREFIX
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+)
+if(NOT 0 EQUAL BREW_RESULT)
+    message(
+        FATAL_ERROR
+        "Failed to locate LLVM v15 using Homebrew. Please ensure llvm@15 is installed: 'brew \
+        install llvm@15'"
+    )
+endif()
+
+set(CMAKE_C_COMPILER "${LLVM_TOOLCHAIN_PREFIX}/bin/clang")
+set(CMAKE_CXX_COMPILER "${LLVM_TOOLCHAIN_PREFIX}/bin/clang++")
+set(CMAKE_AR "${LLVM_TOOLCHAIN_PREFIX}/bin/llvm-ar")
+set(CMAKE_RANLIB "${LLVM_TOOLCHAIN_PREFIX}/bin/llvm-ranlib")

cmake/Toolchains/utils.cmake

@@ -0,0 +1,49 @@
+# This file contains utility functions for setting up toolchains and validating toolchain versions
+# to ensure compatibility with the C++20 features required by the project.
+
+# Sets up the appropriate toolchain file based on the host system.
+function(setup_toolchains)
+    # For macOS versions below 15, use the LLVM 15 Clang toolchain.
+    if("Darwin" STREQUAL "${CMAKE_HOST_SYSTEM_NAME}")
+        execute_process(
+            COMMAND
+                "sw_vers" "--productVersion"
+            OUTPUT_VARIABLE MACOS_VERSION
+            OUTPUT_STRIP_TRAILING_WHITESPACE
+        )
+        if("${MACOS_VERSION}" VERSION_LESS "15")
+            set(CMAKE_TOOLCHAIN_FILE
+                "${CMAKE_CURRENT_SOURCE_DIR}/cmake/Toolchains/llvm-clang-15-toolchain.cmake"
+                CACHE STRING
+                "Toolchain file"
+            )
+        endif()
+    endif()
+endfunction()
+
+# Checks if the compiler ID and version meet the minimum requirements to support C++20 features
+# required by the project:
+# - AppleClang: version 15+
+# - Clang: version 15+
+# - GNU: version 11+
+function(validate_compiler_versions)
+    if("AppleClang" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
+        set(CXX_COMPILER_MIN_VERSION "15")
+    elseif("Clang" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
+        set(CXX_COMPILER_MIN_VERSION "15")
+    elseif("GNU" STREQUAL "${CMAKE_CXX_COMPILER_ID}")
+        set(CXX_COMPILER_MIN_VERSION "11")
+    else()
+        message(
+            FATAL_ERROR
+            "Unsupported compiler: ${CMAKE_CXX_COMPILER_ID}. Please use AppleClang, Clang, or GNU."
+        )
+    endif()
+    if("${CMAKE_CXX_COMPILER_VERSION}" VERSION_LESS "${CXX_COMPILER_MIN_VERSION}")
+        message(
+            FATAL_ERROR
+            "${CMAKE_CXX_COMPILER_ID} version ${CMAKE_CXX_COMPILER_VERSION} is too low. Must be at \
+			least ${CXX_COMPILER_MIN_VERSION}."
+        )
+    endif()
+endfunction()