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cppast

Library interface to the C++ AST — parse source files, synthesize entities, get documentation comments and generate code.

Motivation

If you're writing a tool that needs access to the C++ AST (i.e. documentation generator, reflection library, …), your only option apart from writing your own parser is to use clang. It offers three interfaces for tools, but the only one that really works for standalone applications is libclang. However, libclang has various limitations and does not expose the entire AST.

So there is no feasible option — except for this library. It was originally a part of the standardese documentation generator, but has been extracted into an independent library.

See this blog post for more information about the motiviation and design.

Features

Missing features

Example

See tool/main.cpp for a simple application of the library that prints the AST.

Documentation

TODO, refer to documentation comments in header file.

Installation

The library can be used as CMake subdirectory, download it and call add_subdirectory(path/to/cppast), then link to the cppast target and enable C++11 or higher.

The parser needs libclang and the clang++ binary, at least version 4.0.0. The clang++ binary will be found in PATH and in the same directory as the program that is being executed.

Note: The project will drop support for older LLVM versions very soon; this minimizes the workaround code when the libclang API catches up.

The CMake code requires llvm-config, you may need to install llvm and not just clang to get it (e.g. on ArchLinux). If llvm-config is in your path and the version is compatible, it should just work out of the box. Else you need to set the CMake variable LLVM_CONFIG_BINARY to the proper path.

If you don't have a proper clang version installed, it can also be downloaded. For that you need to set LLVM_DOWNLOAD_OS_NAME. This is the name of the operating system used on the LLVM pre-built binary archive, e.g. x86_64-linux-gnu-ubuntu-16.10 for Ubuntu 16.10.

You can also set LLVM_DOWNLOAD_URL to a custom url, to download a specific version or from a mirror.

If you don't have llvm-config, you need to pass the locations explictly. For that set the option LLVM_VERSION_EXPLICIT to the version you're using, LIBCLANG_LIBRARY to the location of the libclang library file, LIBCLANG_INCLUDE_DIR to the directory where the header files are located (so they can be included with clang-c/Index.h), and CLANG_BINARY to the full path of the clang++ exectuable.

The other dependencies like type_safe are installed automatically with FetchContent, if they're not installed already.

If you run into any issues with the installation, please report them.

Installation on Windows

Similar to the above instructions for cppast, there are a couple extra requirements for Windows.

The LLVM team does not currently distribute llvm-config.exe as part of the release binaries, so the only way to get it is through manual compilation or from 3rd parties. To prevent version mismatches, it's best to compile LLVM, libclang, and llvm-config.exe from source to ensure proper version matching. However, this is a non-trivial task, requiring a lot of time. The easiest way to work with LLVM and llvm-config.exe is to leverage the Chocolatey llvm package, and then compile the llvm-config.exe tool as a standalone binary.

In your cppast based project, if you run into issues with cmake not finding libclang, set LIBCLANG_LIBRARY to be C:/Program Files/LLVM/lib in your CMakeLists.txt file.

Quick API Overview

There are three class hierarchies that represent the AST:

In order to parse a C++ source file, you need an implementation of parser. The library provides one, libclang_parser, but you could also write one yourself. Parsing is as simple as calling the parse() member function passing it three things:

It returns nullptr on failure and prints diagnostics using a given diagnostic_logger — note that it will only return nullptr on fatal parse errors, else it will just skip the one where the error occured. If everything went succesful, it returns a std::unique_ptr<cpp_file> which is the top-level AST entity of the current file. You can then work with it.