[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.

3 files changed, 150 insertions, 0 deletions

diff --git a/backend/cmake/RCCBackendConfig.cmake.in b/backend/cmake/RCCBackendConfig.cmake.in
new file mode 100644
index 0000000..910572b
--- /dev/null
+++ b/backend/cmake/RCCBackendConfig.cmake.in
@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/RCCBackendTargets.cmake")
+
+check_required_components(RCCBackend)
diff --git a/backend/cmake/modules/RCCBackendBuild.cmake b/backend/cmake/modules/RCCBackendBuild.cmake
new file mode 100644
index 0000000..79e7bb1
--- /dev/null
+++ b/backend/cmake/modules/RCCBackendBuild.cmake
@@ -0,0 +1,93 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+function(rcc_backend_initialize_toolchain)
+  string(REGEX MATCH "^[0-9]+" RCCBackendClangMajor "${CMAKE_CXX_COMPILER_VERSION}")
+
+  find_program(
+    RCC_BACKEND_CLANG_FORMAT
+    NAMES "clang-format-${RCCBackendClangMajor}" clang-format
+    REQUIRED
+  )
+  find_program(
+    RCC_BACKEND_CLANG_TIDY
+    NAMES "clang-tidy-${RCCBackendClangMajor}" clang-tidy
+    REQUIRED
+  )
+
+  foreach(Tool IN ITEMS RCC_BACKEND_CLANG_FORMAT RCC_BACKEND_CLANG_TIDY)
+    execute_process(
+      COMMAND "${${Tool}}" --version
+      OUTPUT_VARIABLE ToolVersionOutput
+      ERROR_VARIABLE ToolVersionError
+      RESULT_VARIABLE ToolVersionResult
+    )
+    if(NOT ToolVersionResult EQUAL 0)
+      message(
+        FATAL_ERROR
+          "Unable to query ${Tool}: ${ToolVersionOutput}${ToolVersionError}"
+      )
+    endif()
+
+    string(REGEX MATCH "version[ \t]+([0-9]+)" ToolVersionMatch "${ToolVersionOutput}")
+    if(NOT CMAKE_MATCH_1 STREQUAL RCCBackendClangMajor)
+      message(
+        FATAL_ERROR
+          "${Tool} must have Clang major version ${RCCBackendClangMajor}: "
+          "${ToolVersionOutput}"
+      )
+    endif()
+  endforeach()
+
+  set(RCC_BACKEND_CLANG_FORMAT "${RCC_BACKEND_CLANG_FORMAT}" PARENT_SCOPE)
+  set(RCC_BACKEND_CLANG_TIDY "${RCC_BACKEND_CLANG_TIDY}" PARENT_SCOPE)
+endfunction()
+
+function(rcc_backend_configure_target Target)
+  target_compile_features("${Target}" PUBLIC cxx_std_23)
+  set_target_properties(
+    "${Target}"
+    PROPERTIES
+      CXX_EXTENSIONS OFF
+      CXX_STANDARD 23
+      CXX_STANDARD_REQUIRED ON
+  )
+
+  target_compile_options(
+    "${Target}"
+    PRIVATE
+      -Wall
+      -Wextra
+      -Wpedantic
+      -Wconversion
+      -Wsign-conversion
+      -Wshadow
+      -Wnon-virtual-dtor
+      -Wold-style-cast
+      -Wcast-align
+      -Woverloaded-virtual
+      -Wnull-dereference
+      -Wdouble-promotion
+      -Wformat=2
+  )
+
+  if(RCC_BACKEND_WARNINGS_AS_ERRORS)
+    target_compile_options("${Target}" PRIVATE -Werror)
+  endif()
+
+  if(RCC_BACKEND_ENABLE_CLANG_TIDY)
+    set_target_properties(
+      "${Target}"
+      PROPERTIES
+        CXX_CLANG_TIDY
+          "${RCC_BACKEND_CLANG_TIDY};--warnings-as-errors=*"
+    )
+  endif()
+endfunction()
+
+function(rcc_backend_register_format_files)
+  set_property(GLOBAL APPEND PROPERTY RCC_BACKEND_FORMAT_FILES ${ARGN})
+endfunction()
+
+function(rcc_backend_register_tidy_files)
+  set_property(GLOBAL APPEND PROPERTY RCC_BACKEND_TIDY_FILES ${ARGN})
+endfunction()
diff --git a/backend/cmake/modules/RCCBackendDeveloperTools.cmake b/backend/cmake/modules/RCCBackendDeveloperTools.cmake
new file mode 100644
index 0000000..d3693cd
--- /dev/null
+++ b/backend/cmake/modules/RCCBackendDeveloperTools.cmake
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+function(rcc_backend_add_developer_targets)
+  get_property(FormatFiles GLOBAL PROPERTY RCC_BACKEND_FORMAT_FILES)
+  get_property(TidyFiles GLOBAL PROPERTY RCC_BACKEND_TIDY_FILES)
+
+  if(FormatFiles)
+    list(REMOVE_DUPLICATES FormatFiles)
+
+    add_custom_target(
+      rcc-backend-format
+      COMMAND "${RCC_BACKEND_CLANG_FORMAT}" -i ${FormatFiles}
+      COMMAND_EXPAND_LISTS
+      COMMENT "Formatting RCC Backend C++ sources"
+      VERBATIM
+    )
+
+    add_custom_target(
+      rcc-backend-format-check
+      COMMAND "${RCC_BACKEND_CLANG_FORMAT}" --dry-run --Werror ${FormatFiles}
+      COMMAND_EXPAND_LISTS
+      COMMENT "Checking RCC Backend C++ formatting"
+      VERBATIM
+    )
+  endif()
+
+  if(TidyFiles)
+    list(REMOVE_DUPLICATES TidyFiles)
+
+    add_custom_target(
+      rcc-backend-tidy
+      COMMAND
+        "${RCC_BACKEND_CLANG_TIDY}" --warnings-as-errors=*
+        "-p=${CMAKE_BINARY_DIR}" ${TidyFiles}
+      COMMAND_EXPAND_LISTS
+      COMMENT "Running clang-tidy on RCC Backend"
+      VERBATIM
+    )
+
+    add_custom_target(
+      rcc-backend-analyze
+      COMMAND
+        "${RCC_BACKEND_CLANG_TIDY}" "--checks=-*,clang-analyzer-*"
+        --warnings-as-errors=* "-p=${CMAKE_BINARY_DIR}" ${TidyFiles}
+      COMMAND_EXPAND_LISTS
+      COMMENT "Running Clang Static Analyzer checks on RCC Backend"
+      VERBATIM
+    )
+  endif()
+endfunction()