Library to parse and work with the C++ AST
Library interface to the C++ AST — parse source files, synthesize entities, get documentation comments and generate code.
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.
libclang-parser
for a list;See tool/main.cpp for a simple application of the library that prints the AST.
TODO, refer to documentation comments in header file.
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.
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.
llvm
and clang
with choco install llvm
clang.exe --version
git clone https://github.com/llvm/llvm-project
git checkout llvmorg-7.0.1
cd llvm-project && mkdir build && cd build
to prep the build environment.cmake -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_TARGETS_TO_BUILD="X86" -G "Visual Studio 15 2017" -Thost=x64 ..\llvm
LLVM.sln
solution, and set the build type to be "Release".Tools/llvm-config
target.build\Release\bin\llvm-config.exe
to C:\Program Files\LLVM\bin\llvm-config.exe
llvm-config.exe
, it should return with it's help message.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.
There are three class hierarchies that represent the AST:
cpp_entity
: This is the base class for all C++ entities, i.e. declarations/definitions or things like static_assert()
and function parameters;cpp_type
: This is the base class for the C++ type hierachy. It is used in the cpp_entity
hierachy, i.e. cpp_type_alias
contains an underlying_type()
. Derived classes are, for example, cpp_builtin_type
or cpp_pointer_type
;cpp_expression
: This is the base class for all C++ expressions. It is used in the cpp_entity
hierarchy, i.e. cpp_function_parameter
contains a default_value()
as expression. Derived classes are currently only cpp_literal_expression
and cpp_unexposed_expression
;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:
cpp_entity_index
: This is only required to resolve cross-references in the AST (i.e. if you want to get the cpp_class
referenced in the return type of a cpp_function
); it does not own the entities;compile_config
: It stores the compilation flags used for compiling the file, it needs to match the parser, i.e. use libclang_compile_config
with libclang_parser
;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.