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A command line tool and library for creating Common Lisp language bindings from C header files

Project description

cl-bindgen

A command line tool and library for creating Common Lisp language bindings from C header files

Features:

  • Generates CFFI bindings for function declarations, enums, variables, unions, and structures.
  • Handles nested and anonymous structures, unions, and enums.
  • Warns when it cannot produce a correct binding.
  • Documentation comments from the C source files are lispified and included with the generated bindings when available.
  • Provides a powerful way to customize how names are translated into lisp symbols.

Installation

cl-bindgen requires libclang, which is not installed with the other Python dependencies and not available on PyPi. It is recommended to install it first before installing cl-bindgen. Use your distribution's package manager to install it.

Once libclang is installed, you can then install cl-bindgen from source or from PyPI.

From PyPI:

pip install cl-bindgen

From source:

git clone --depth=1 https://github.com/sdilts/cl-bindgen
cd cl-bindgen
pip install --user .

Processing individual files

To process individual files, use the f command and specify one or more files to process. By default, output will be printed to stdout, but the output file can be specified with the -o option. To see a full list of options, run cl-bindgen f -h.

# Process test.h and print the results to stdout:
cl-bindgen f test.h
# Process the files test1.h, test2.h, and place the output in output.lisp:
cl-bindgen f -o output.lisp test1.h test2.h

Batch file processing

cl-bindgen can use a yaml file to process many header files with a single invocation. Use the b command to specify one or more batch files to process:

cl-bindgen b my_library.yaml

Batch file format

Batch files use the YAML format. Multiple documents can be contained in each input file.

Required Fields:

  • output : where to place the generated code
  • files : a list of files to process

Optional Fields:

  • package : The name of the Common Lisp package of the generated file
  • arguments : Arguments to pass to clang
  • force : Ignore errors while parsing. Valid values are True or False

To see example batch files, look in the examples directory.

Handling Include Directories and Clang Arguments

If you need to specify additional command line arguments to the clang processor, you can use -a option, and list any clang arguments after.

cl-bindgen b batch_file.yaml -a -I include_dir1 -I include_dir2
# Use -- to stop collecting clang arguments:
cl-bindgen f -a `pkg-config --cflags mylibrary` -- header.h

If a header file isn't found while processing the input files, cl-bindgen will halt and produce no output. This is to avoid producing incorrect bindings: while bindings can still be produced when header files are missing, they are likely to be incorrect. To ignore missing header files and other fatal errors, the -f flag can be used:

cl-bindgen b -f batch_file.yaml
cl-bindgen f -f header.c

System Include Directories

cl-bindgen doesn't currently know where to find system include directories. This will cause any file that includes standard headers to not be processed without specifying the -f option.

To find the system include directory, run the following command, and replace $ANY_C_FILE with any C file.

clang -### $ANY_C_FILE

Find "-resource-dir" in the produced output. There should be a file path listed right after. For example, "/usr/lib64/clang/9.0.1/". Add include to the end of the path to get the system include directory.

Customizing the behavior of cl-bindgen

cl-bindgen attempts to provide a reasonable interface that is usable in most cases. However, if you need to customize how C names are converted into lisp names or embed cl-bindgen into another application, cl-bindgen is available as a library.

The cl_bindgen package is broken up into three modules: the processfile, mangler and util modules. The processfile module provides the functions to generate the lisp bindings, the mangler module provides functions to convert C names into lisp names, and the util module provides functions to use batch files and cl-bingen's command line interface.

The processfile Module

This module exports two functions: process_file and process_files, which work on a single header file or many, respectively. Both functions take two arguments: the file(s) to be processed and an ProcessOptions object.

The ProcessOptionsclass is the way to specify how the processing functions generate their output. It has the following fields:

  • typedef_mangers, enum_manglers, type_manglers, name_manglers and constant_manglers : See the mangler module section for what these do.
  • output : The path of the file where the output is placed. ":stdout" or ":stderr" can be specified to use standard out or standard error.
  • package : If not None, this specifies the package the the generated output should be placed in.
  • arguments : The command line arguments that should be given to the clang processor.
  • force : If true, then ignore errors while parsing the input files.

The mangler Module

cl-bindgen uses a set of classes called manglers to translate C names so that they follow lisp naming conventions. Each mangler class provides one or more transformations to a symbol. For example, the UnderscoreMangler class converts underscores (_) into dashes (-). A series of manglers are applied to each C name to make it follow lisp naming conventions.

To maximize customization, a list of manglers is associated with each type of name that can be converted. Enums, variable names, typedefs, constants, and record types all use a different set of manglers.

Built-in manglers:

  • UnderscoreMangler : Converts underscores to dashes.
  • ConstantMangler : Converts a string to follow Common Lisp's constant style recomendation.
  • KeywordMangler : Adds a : to the beginning of a string to make it a symbol. Doesn't perform any action if the string has a package prefix.
  • RegexSubMangler : Substitutes the substring matched by a regex with the given string.

Mangler Interface

Mangler classes follow a simple interface:

  • can_mangle(string): returns true if the mangler can perform its operations on the given string
  • mangle(string): returns a string with the desired transformations applied.

The util Module

The util module provides two functions: process_batch_file and dispatch_from_arguments.

  • process_batch_file(batch_file, options) : Processes the given batch file using options as the default options.
  • dispatch_from_arguments(arguments, options) : Uses the provided command line arguments to perform the actions of cl-bindgen using options as the default options.

Examples

The best example of how to use cl-bindgen as a library is to look at its main function found in cl_bindgen/__main__.py. In it, cl-bindgen's default options are set, then passed to dispatch_from_arguments to run the utility.

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