Using ClangSharp and libclang for C# Reflection Code Generation and Meta‑Attribute Support

This article explains how to build an offline reflection tool for C# by leveraging libclang and the ClangSharp C# bindings. It covers the entire workflow, from parsing C++ headers into an AST, traversing the AST with ClangSharp, generating structured AST data, and using Liquid templates for code generation.

Key steps include:

Creating a temporary source file that includes all target headers and parsing it with CXTranslationUnit.TryParse while handling include paths (-I) and macros (-D).

Processing diagnostics to detect fatal errors before proceeding.

Understanding the two main AST components: CXCursor (structure) and CXType (type information).

Recursively visiting children using CXCursor.VisitChildren and a custom visitor callback to collect node details.

Implementing a C# version of clang -cc1 -ast-dump (AstDumpTool) that formats each cursor into readable strings.

Building a higher‑level ClangAST structure that aggregates namespaces, classes, enums, typedefs, and template specializations for easy multi‑pass processing.

Introducing a meta‑attribute mechanism based on the C++ annotate attribute, wrapped in macros (e.g., RCLASS_LUA(...) ) that embed custom key‑value strings.

Parsing these annotation strings in C# with a custom CustomAttributeTool to drive code‑generation decisions (e.g., skipping export, adding runtime metadata, protobuf support).

The article also discusses the advantages of a structured AST (filtering irrelevant nodes, fast look‑ups, extensibility) and shows how meta‑attributes can replace external configuration files, enabling fine‑grained control over what gets exported and providing runtime metadata for C++ systems.