[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.

2 files changed, 68 insertions, 0 deletions

diff --git a/backend/lib/Support/CMakeLists.txt b/backend/lib/Support/CMakeLists.txt
new file mode 100644
index 0000000..88c959d
--- /dev/null
+++ b/backend/lib/Support/CMakeLists.txt
@@ -0,0 +1,40 @@
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set(RCCBackendSupportSources Error.cpp)
+set(
+  RCCBackendSupportHeaders
+  "${RCC_BACKEND_SOURCE_DIR}/include/rcc/Support/Error.h"
+)
+
+add_library(RCCBackendSupport ${RCCBackendSupportSources})
+add_library(RCCBackend::Support ALIAS RCCBackendSupport)
+
+rcc_backend_configure_target(RCCBackendSupport)
+
+target_include_directories(
+  RCCBackendSupport
+  PUBLIC
+    "$<BUILD_INTERFACE:${RCC_BACKEND_SOURCE_DIR}/include>"
+    "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
+)
+
+set_target_properties(
+  RCCBackendSupport
+  PROPERTIES
+    EXPORT_NAME Support
+    OUTPUT_NAME RCCBackendSupport
+)
+
+install(
+  TARGETS RCCBackendSupport
+  EXPORT RCCBackendTargets
+  ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+  LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
+  RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
+)
+
+rcc_backend_register_format_files(
+  "${CMAKE_CURRENT_SOURCE_DIR}/Error.cpp"
+  ${RCCBackendSupportHeaders}
+)
+rcc_backend_register_tidy_files("${CMAKE_CURRENT_SOURCE_DIR}/Error.cpp")
diff --git a/backend/lib/Support/Error.cpp b/backend/lib/Support/Error.cpp
new file mode 100644
index 0000000..dc7d590
--- /dev/null
+++ b/backend/lib/Support/Error.cpp
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "rcc/Support/Error.h"
+
+namespace rcc {
+
+std::string_view getErrorCodeName(ErrorCode Code) noexcept {
+  switch (Code) {
+  case ErrorCode::InvalidArgument:
+    return "invalid argument";
+  case ErrorCode::ParseError:
+    return "parse error";
+  case ErrorCode::VerificationError:
+    return "verification error";
+  case ErrorCode::Unsupported:
+    return "unsupported";
+  case ErrorCode::IoError:
+    return "I/O error";
+  case ErrorCode::InternalError:
+    return "internal error";
+  }
+
+  return "unknown error";
+}
+
+Error::Error(ErrorCode Code, std::string Message) : Code(Code), Message(std::move(Message)) {}
+
+} // namespace rcc