[Backend] Establish standalone build infrastructure

Add the thin monorepo CMake entry point and an independently configurable backend project. Enforce the Clang/C++23 toolchain, expose Make/Ninja-neutral tests and developer checks, export an installable RCCBackend package, and introduce the first Support error abstraction.

1 files changed, 85 insertions, 0 deletions

diff --git a/backend/CMakeLists.txt b/backend/CMakeLists.txt
new file mode 100644
index 0000000..2d5cc82
--- /dev/null
+++ b/backend/CMakeLists.txt
@@ -0,0 +1,85 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+cmake_minimum_required(VERSION 3.25)
+
+set(RCC_BACKEND_VERSION 0.1.0)
+set(RCC_BACKEND_IS_STANDALONE OFF)
+set(RCC_BACKEND_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
+set(RCC_BACKEND_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}")
+
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  project(
+    RCCBackend
+    VERSION ${RCC_BACKEND_VERSION}
+    DESCRIPTION "Independent RCC machine-code backend"
+    LANGUAGES CXX
+  )
+  set(RCC_BACKEND_IS_STANDALONE ON)
+  include(CTest)
+endif()
+
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES "^(Apple)?Clang$")
+  message(
+    FATAL_ERROR
+      "RCC Backend must be compiled with Clang; found '${CMAKE_CXX_COMPILER_ID}'"
+  )
+endif()
+
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
+  message(
+    FATAL_ERROR
+      "RCC Backend does not support in-source builds. Configure a separate build directory."
+  )
+endif()
+
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+list(PREPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
+
+include(GNUInstallDirs)
+include(CMakePackageConfigHelpers)
+include(RCCBackendBuild)
+include(RCCBackendDeveloperTools)
+
+option(RCC_BACKEND_BUILD_TESTS "Build RCC Backend tests" "${BUILD_TESTING}")
+option(RCC_BACKEND_WARNINGS_AS_ERRORS "Treat compiler warnings as errors" OFF)
+option(RCC_BACKEND_ENABLE_CLANG_TIDY "Run clang-tidy during each compilation" OFF)
+
+rcc_backend_initialize_toolchain()
+
+add_subdirectory(lib)
+
+if(RCC_BACKEND_BUILD_TESTS)
+  enable_testing()
+  add_subdirectory(unittests)
+endif()
+
+rcc_backend_add_developer_targets()
+
+install(DIRECTORY include/ DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}")
+
+configure_package_config_file(
+  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/RCCBackendConfig.cmake.in"
+  "${CMAKE_CURRENT_BINARY_DIR}/RCCBackendConfig.cmake"
+  INSTALL_DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/RCCBackend"
+)
+
+write_basic_package_version_file(
+  "${CMAKE_CURRENT_BINARY_DIR}/RCCBackendConfigVersion.cmake"
+  VERSION "${RCC_BACKEND_VERSION}"
+  COMPATIBILITY SameMajorVersion
+)
+
+install(
+  EXPORT RCCBackendTargets
+  FILE RCCBackendTargets.cmake
+  NAMESPACE RCCBackend::
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/RCCBackend"
+)
+
+install(
+  FILES
+    "${CMAKE_CURRENT_BINARY_DIR}/RCCBackendConfig.cmake"
+    "${CMAKE_CURRENT_BINARY_DIR}/RCCBackendConfigVersion.cmake"
+  DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/RCCBackend"
+)