Elarnon / cbindgen

A project for generating C bindings from Rust code

cbindgen  

This project can be used to generate C bindings for Rust code. It is currently being developed to support creating bindings for WebRender, but has been designed to support any project.

Features

• Builds bindings for a crate, its mods, its dependent crates, and their mods
• Only the necessary types for exposed functions are given bindings
• Can specify annotations for controlling some aspects of binding
• Support for generic structs and unions
• Support for exporting constants and statics
• Customizable formatting, can be used in C or C++ projects
• Support for generating #ifdef's for #[cfg] attributes
• Support for #[repr(sized)] tagged enum's

Use

Command line

cbindgen crate/ -o crate/bindings.h

See cbindgen --help for more options.

build.rs

cbindgen can also be used in build scripts. How this fits into compiling the native code depends on your project.

Here's an example build.rs script:

extern crate cbindgen;

use std::env;

fn main() {
    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();

    cbindgen::Builder::new()
      .with_crate(crate_dir)
      .generate()
      .expect("Unable to generate bindings")
      .write_to_file("bindings.h");
}

Configuration

There are some options that can be used to configure the binding generation.

For the command line, they can be specified by creating a cbindgen.toml with the options. This can be placed in the binding crate root or at a path manually specified.

For build scripts, options can be specified on the builder or by writing a cbindgen.toml and using the helper function cbindgen::generate.

Here is a description of the options available in a config.

# An optional string of text to output at the beginning of the generated file
header = "/* Text to put at the beginning of the generated file. Probably a license. */"
# An optional string of text to output at the end of the generated file
trailer = "/* Text to put at the end of the generated file */"
# An optional name to use as an include guard
include_guard = "mozilla_wr_bindings_h"
# An optional string of text to output between major sections of the generated
# file as a warning against manual editing
autogen_warning = "/* Warning, this file is autogenerated by cbindgen. Don't modify this manually. */"
# Whether to include a comment with the version of cbindgen used to generate the
# file
include_version = true
# An optional namespace to output around the generated bindings
namespace = "ffi"
# An optional list of namespaces to output around the generated bindings
namespaces = ["mozilla", "wr"]
# The style to use for curly braces
braces = "[SameLine|NextLine]"
# The desired length of a line to use when formatting lines
line_length = 80
# The amount of spaces in a tab
tab_width = 2
# The language to output bindings in
language = "[C|C++]"
# A rule to use to select style of declaration in C, tagname vs typedef
style = "[Both|Type|Tag]"

[parse]
# Whether to parse dependent crates and include their types in the generated
# bindings
parse_deps = true
# A white list of crate names that are allowed to be parsed
include = ["webrender", "webrender_traits"]
# A black list of crate names that are not allowed to be parsed
exclude = ["libc"]
# Whether to use a new temporary target directory when running `rustc --pretty=expanded`.
# This may be required for some build processes.
clean = false

[parse.expand]
# A list of crate names that should be run through `cargo expand` before
# parsing to expand any macros
crates = ["euclid"]
# If enabled,  use the `--all-features` option when expanding. Ignored when
# `expand_features` is set. Disabled by default, except when using the
# `expand = ["euclid"]` shorthand for backwards-compatibility.
all_features = false
# When `enable_all_features` is disabled and this is also disabled, use the
# `--no-default-features` option when expanding. Enabled by default.
default_features = true
# A list of feature names that should be used when running `cargo expand`. This
# combines with `default_features` like in `Cargo.toml`. Note that the features
# listed here are features for the current crate being built, *not* the crates
# being expanded. The crate's `Cargo.toml` must take care of enabling the
# appropriate features in its dependencies
features = ["cbindgen"]

[export]
# A list of additional items not used by exported functions to include in
# the generated bindings
include = ["Foo", "Bar"]
# A list of items to not include in the generated bindings
exclude = ["Bad"]
# A prefix to add before the name of every item
prefix = "CAPI_"
# Types of items that we'll generate.
item_types = ["constants", "globals", "enums", "structs", "unions", "typedefs", "opaque", "functions"]

# Table of name conversions to apply to item names
[export.rename]
"Struct" = "CAPI_Struct"

[fn]
# An optional prefix to put before every function declaration
prefix = "string"
# An optional postfix to put after any function declaration
postfix = "string"
# How to format function arguments
args = "[Auto|Vertical|Horizontal]"
# A rule to use to rename function argument names
rename_args = "[None|GeckoCase|LowerCase|UpperCase|PascalCase|CamelCase|SnakeCase|ScreamingSnakeCase|QualifiedScreamingSnakeCase]"

[struct]
# A rule to use to rename field names
rename_fields = "[None|GeckoCase|LowerCase|UpperCase|PascalCase|CamelCase|SnakeCase|ScreamingSnakeCase|QualifiedScreamingSnakeCase]"
# Whether to derive an operator== for all structs
derive_eq = false
# Whether to derive an operator!= for all structs
derive_neq = false
# Whether to derive an operator< for all structs
derive_lt = false
# Whether to derive an operator<= for all structs
derive_lte = false
# Whether to derive an operator> for all structs
derive_gt = false
# Whether to derive an operator>= for all structs
derive_gte = false

[enum]
# A rule to use to rename enum variants
rename_variants = "[None|GeckoCase|LowerCase|UpperCase|PascalCase|CamelCase|SnakeCase|ScreamingSnakeCase|QualifiedScreamingSnakeCase]"

Examples

See tests/rust/ for some examples of rust source that can be handled.

Major differences between cbindgen and rusty-cheddar

1. cbindgen supports generics
2. cbindgen supports C++ output using enum class and template specialization
3. cbindgen supports generating bindings including multiple modules and crates

There may be other differences, but those are the ones that I know of. Please correct me if I misrepresented anything.

Prominent users

• milksnake
• webrender

If you're using cbindgen and would like to be added to this list, please open a pull request!