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libgen

★ 84 Open GitHub ↗

Automatic C-bindings generator for the Crystal language

// repository documentation

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# Crystal lib generator

Libgen is a small tool based on the [crystal_lib](https://github.com/crystal-lang/crystal_lib) project that allows to generate [libs](https://crystal-lang.org/docs/syntax_and_semantics/c_bindings/lib.html) following rules specified in config files.

## Overview
This project aims to ease the port of big C libraries and to provide a convinient way to define re-generable bindings.  
Lib generation is parametrized using a YAML or JSON configuration file (_how to generate_).  
Bindings definitions are specified in YAML, JSON or Crystal files or in the generation config file directly (_what to generate_).  
It's possible to split lib's definitions in several files in order to make the binding more readable/easy to maintain.  
There is also an option to perform AST node renaming at generation time.

## Installation
__Debian/Ubuntu__
```bash
# install build dependencies
apt-get install -y build-essential llvm-16-dev libclang-16-dev
# then, build and install
make && make install
```

__macOS__
```bash
# if necessary, install build dependencies
brew install llvm@16
# then, build and install
make && make install
```

## Usage
```bash
usage: libgen [<lib_desc_file>]
```

## Example
A generation config file, [examples/icu/lib.yml](https://github.com/olbat/libgen/blob/master/examples/icu/lib.yml):
```yaml
name: LibICU
cflags: "-DU_COMMON_IMPLEMENTATION"
ldflags: "-licuuc -licudata -licui18n -licuio"
packages: icu-uc icu-i18n icu-io
destdir: src/lib_icu/
includes:
- include/*.yml
- include/*.json
- include/*.cr
definitions:
  ubrk:
    description: Text Boundary Analysis (Break Iteration)
    includes: [ unicode/ubrk.h ]
    prefixes: [ ubrk_ ]
rename:
  rules:
    "*":
    - pattern: _\d+$
      replacement: ""
options:
  import_docstrings: brief
```

A definition file, [examples/icu/include/ucsdet.yml](https://github.com/olbat/libgen/blob/master/examples/icu/include/ucsdet.yml):
```yaml
description: Charset detection
includes:
- unicode/ucsdet.h
prefixes:
- ucsdet_
```

Generation of the lib:
```bash
$ libgen examples/icu/lib.yml
loading library from examples/icu/lib.yml
moving to examples/icu/
loading ubrk definition from lib.yml
loading lib_icu definition from include/lib_icu.yml
loading ucsdet definition from include/ucsdet.yml
loading ucurr definition from include/ucurr.json
loading udat definition from include/udat.cr
generate src/lib_icu/ubrk.cr
generate src/lib_icu/lib_icu.cr
generate src/lib_icu/ucsdet.cr
generate src/lib_icu/ucurr.cr
generate src/lib_icu/udat.cr

# or, using docker-compose
$ docker-compose run --rm -u $UID libgen examples/icu/lib.yml
```

The generated files: [examples/icu/src/lib_icu](https://github.com/olbat/libgen/blob/master/examples/icu/src/lib_icu).

## Specifications

See [SPECS.md](https://github.com/olbat/libgen/blob/master/SPECS.md)

## Development
__How does it work__

To generate Crystal libs from C headers, the `libgen` tool:
1. loads [Library](https://github.com/olbat/libgen/blob/master/src/lib_generator/library.cr) and [Definition](https://github.com/olbat/libgen/blob/master/src/lib_generator/definition.cr) objects from configuration files
2. generates Crystal ASTs (one per Definition) from C headers using [crystal_lib](https://github.com/olbat/libgen/blob/master/https://github.com/crystal-lang/crystal_lib)'s parser (see [Definition#parse_lib](https://github.com/olbat/libgen/blob/master/src/lib_generator/definition.cr))
3. transforms the Crystal ASTs:
    1. applies transformers following the configuration (AST nodes renaming, sorting, ... see [transformers](https://github.com/olbat/libgen/blob/master/src/lib_generator/transformers))
    2. groups AST nodes that are common to several libs into a common lib
    3. adds requires to non-empty libs in the common lib's AST
4. generates and formats the libs from ASTs adding the _@Link/ldflags_ attribute (see [Generator::Lib#generate](https://github.com/olbat/libgen/blob/master/src/lib_generator/generator/lib.cr))
5. saves the generated libs to their respective output files

__Known limitations__
* it's only possible to filter functions to bind by prefix (and not by name, such as in [example](https://github.com/crystal-lang/crystal_lib/blob/master/examples/lib_readline.cr))
* it's not possible to specify the `description` field in definitions written in Crystal
* the `description` field specified in definitions is not used ATM (it should be added as a comment in the generated bindings)

__LLVM versions__

Libgen is [tested](.travis.yml) using the versions of LLVM that are [currently supported](https://crystal-lang.org/docs/installation/from_source_repository.html) by Crystal: LLVM `3.8`→`6.0`.

The tool is not dependent on this versions of LLVM, it may be working with other versions as well but it's not tested/guaranteed.

__Launch the tests__
```
make test

# or, using docker-compose
docker-compose run --rm -u $UID devel make test
```

__Build the Docker image__
```bash
make
docker build .
```

## Projects using libgen
- [icu.cr](https://github.com/olbat/icu.cr)
- [nacl](https://github.com/watzon/nacl)

__Note__: you are using _libgen_ in your project and want to link it here, please [submit a PR](contributing)

## Contributing
1. Fork it ( https://github.com/olbat/libgen/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

## Contributors
- [olbat](https://github.com/olbat) - creator, maintainer

libgen

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