C++ Language Interface Foundation (CLIF)

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THIS REPO IS NO LONGER UPDATED — DO NOT USE

STALE INFORMATION FOLLOWS

PyCLIF defines a C++ API to be wrapped via a concise
What You See Is What You Get interface file
(example),
with a syntax derived from pytypedecl.

About the name of this repo: CLIF was started as a common foundation for
creating C++ wrapper generators for various languages. However, currently
Python is the only target language, and there is no development activity
for other target languages.

Overview

PyCLIF consists of four parts:

Parser
Matcher
Generator
Runtime

Parser

The parser converts a language-friendly C++ API description to the
language-agnostic internal format and passes it to the Matcher.

Matcher

The matcher parses selected C++ headers with Clang (LLVM’s C++ compiler) and
collects type information. That info is passed to the Generator.

Generator

The generator emits C++ source code for the wrapper.

The generated wrapper needs to be built according with language extension rules.
Usually that wrapper will call into the Runtime.

Runtime

The runtime C++ library holds type conversion routines that are specific to
each target language but are the same for every generated wrapper.

Python CLIF

See complete implementation of a Python wrapper generator in the /python/
subdirectory. Both Python 2 and 3 are supported.

Installation

Prerequisites

We use CMake, so make sure CMake
version 3.5 or later is available.
(For example, Debian 8 only has version 3.0,
so in that case you’ll need to install an up-to-date CMake.)
We use Google
protobuf
for inter-process communication between the CLIF frontend and backend.
Version 3.8.0 or later is required.
Please install protobuf for both C++ and Python from source, as we will
need some protobuf source code later on.
You must have virtualenv
installed.
You must have pyparsing installed, so we can build protobuf. Use
pip install 'pyparsing==2.2.2' to fetch the correct version.
Make sure pkg-config --libs python works (e.g. install python-dev and
pkg-config).
We use Clang (LLVM’s C++ compiler) to parse C++ headers,
so make sure Clang and LLVM version 11 is available. On Ubuntu and
Debian, you can install the prebuilt version from https://apt.llvm.org.
You must have abseil-cpp installed.
We use googletest for unit testing
C++ libraries.

For references, there is a Dockerfile
running an Ubuntu image with all the prerequisites already installed. See the
instructions at the top of the file.

Building

To build and install CLIF to a virtualenv, run:

virtualenv --python=python3.x clif-venv
./INSTALL.sh clif-venv/bin/python

The following outlines the steps in INSTALL.sh for clarification.

Build and install the CLIF backend. If you use
Ninja instead of make your build will go
significantly faster. It is used by Chromium, LLVM et al. Look at
INSTALL.sh for the directory setup and proper …flags… to supply the
cmake command here:
```
mkdir build
cd build
cmake ...flags... $CLIFSRC_DIR
make clif-matcher
make install
```
Replace the cmake and make commands with these to use Ninja:
```
cmake -G Ninja ...flags... $CLIFSRC_DIR
ninja clif-matcher
ninja -j 2 install
```
If you have more than one Python version installed (eg. python3.8 and
python3.9) cmake may have problems finding python libraries for the Python
you specified as INSTALL.sh argument and uses the default Python instead. To
help cmake use the correct Python add the following options to the cmake
command (substitute the correct path for your system):
```
cmake ... \
  -DPYTHON_INCLUDE_DIR="/usr/include/python3.9" \
  -DPYTHON_LIBRARY="/usr/lib/x86_64-linux-gnu/libpython3.9m.so" \
  -DPYTHON_EXECUTABLE="/usr/bin/python3.9" \
  "${CMAKE_G_FLAGS[@]}" "$CLIFSRC_DIR"
```

Get back to your CLIF python checkout and install it using pip.

cd "$CLIFSRC_DIR"
cp "$BUILD_DIR/clif/protos/ast_pb2.py" clif/protos/
cp "$BUILD_DIR/clif/python/utils/proto_util.cc" clif/python/utils/
cp "$BUILD_DIR/clif/python/utils/proto_util_clif.h" clif/python/utils/
cp "$BUILD_DIR/clif/python/utils/proto_util.init.cc" clif/python/utils/
pip install .

That version is guaranteed to work. Older versions likely do not work (they lack
some APIs); later versions might work, at your own risk.

INSTALL.sh will build and install clif-matcher to CMake install directory and
CLIF for Python to the given Python (virtual) environment.

To run Python CLIF use pyclif.

Using your newly built pyclif

First, try some examples:

cd examples
less README.md

Next, read the Python CLIF User Manual.

For more details please refer to:

Disclaimer

This is not an official Google product.