Corrosion

Corrosion, formerly known as cmake-cargo, is a tool for integrating Rust into an existing CMake project. Corrosion is capable of importing executables, static libraries, and dynamic libraries from a crate.

Features

• Automatic Import of Executable, Static, and Shared Libraries from Rust Crate
• Easy Installation of Rust Executables
• Trivially Link Rust Executables to C++ Libraries in Tree
• Multi-Config Generator Support
• Simple Cross-Compilation

Sample Usage

cmake_minimum_required(VERSION 3.15)
project(MyCoolProject LANGUAGES CXX)

find_package(Corrosion REQUIRED)

corrosion_import_crate(MANIFEST_PATH rust-lib/Cargo.toml)

add_executable(cpp-exe main.cpp)
target_link_libraries(cpp-exe PUBLIC rust-lib)

Documentation

Table of Contents

• Corrosion
  • Features
  • Sample Usage
• Documentation
  • Table of Contents
  • Installation
    • Package Manager
    • CMake Install
    • FetchContent
    • Subdirectory
  • Usage
    • Corrosion Options
      • Developer/Maintainer Options
    • Information provided by Corrosion
    • Adding crate targets
    • Per Target options
    • Selecting a custom cargo profile
    • Importing C-Style Libraries Written in Rust
      • Generate Bindings to Rust Library Automatically
    • Importing Libraries Written in C and C++ Into Rust
    • Cross Compiling
      • Windows-to-Windows
      • Linux-to-Linux
      • Android

Installation

There are two fundamental installation methods that are supported by Corrosion - installation as a CMake package or using it as a subdirectory in an existing CMake project. For CMake versions below 3.19 Corrosion strongly recommends installing the package, either via a package manager or manually using CMake's installation facilities.

Installation will pre-build all of Corrosion's native tooling (required only for CMake versions below 3.19). Using Corrosion as a subdirectory with CMake versions before 3.19 will result in the native tooling for Corrosion to be re-built every time you configure a new build directory, which could be a non-trivial cost for some projects. It also may result in issues with large, complex projects with many git submodules that each individually may use Corrosion. This can unnecessarily exacerbate diamond dependency problems that wouldn't otherwise occur using an externally installed Corrosion. On CMake >= 3.19 installing Corrosion does not offer any advantages, unless the native tooling option is explicitly enabled.

Package Manager

Coming soon...

CMake Install

First, download and install Corrosion:

git clone https://github.com/corrosion-rs/corrosion.git
# Optionally, specify -DCMAKE_INSTALL_PREFIX=<target-install-path>. You can install Corrosion anyway
cmake -Scorrosion -Bbuild -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release
# This next step may require sudo or admin privileges if you're installing to a system location,
# which is the default.
cmake --install build --config Release

You'll want to ensure that the install directory is available in your PATH or CMAKE_PREFIX_PATH environment variable. This is likely to already be the case by default on a Unix system, but on Windows it will install to C:\Program Files (x86)\Corrosion by default, which will not be in your PATH or CMAKE_PREFIX_PATH by default.

Once Corrosion is installed and you've ensured the package is available in your PATH, you can use it from your own project like any other package from your CMakeLists.txt:

find_package(Corrosion REQUIRED)

FetchContent

If you are using CMake >= 3.19 or installation is difficult or not feasible in your environment, you can use the FetchContent module to include Corrosion. This will download Corrosion and use it as if it were a subdirectory at configure time.

In your CMakeLists.txt:

include(FetchContent)

FetchContent_Declare(
    Corrosion
    GIT_REPOSITORY https://github.com/corrosion-rs/corrosion.git
    GIT_TAG v0.2.1 # Optionally specify a commit hash, version tag or branch here
)

FetchContent_MakeAvailable(Corrosion)

Subdirectory

Corrosion can also be used directly as a subdirectory. This solution may work well for small projects, but it's discouraged for large projects with many dependencies, especially those which may themselves use Corrosion. Either copy the Corrosion library into your source tree, being sure to preserve the LICENSE file, or add this repository as a git submodule:

git submodule add https://github.com/corrosion-rs/corrosion.git

From there, using Corrosion is easy. In your CMakeLists.txt:

add_subdirectory(path/to/corrosion)

Usage

Corrosion Options

All of the following variables are evaluated automatically in most cases. In typical cases you shouldn't need to alter any of these. If you do want to specify them manually, make sure to set them before find_package(Corrosion REQUIRED).

• Rust_TOOLCHAIN:STRING - Specify a named rustup toolchain to use. Changes to this variable resets all other options. Default: If the first-found rustc is a rustup proxy, then the default rustup toolchain (see rustup show) is used. Otherwise, the variable is unset by default.
• Rust_ROOT:STRING - CMake provided. Path to a Rust toolchain to use. This is an alternative if you want to select a specific Rust toolchain, but it's not managed by rustup. Default: Nothing
• Rust_COMPILER:STRING - Path to an actual rustc. If set to a rustup proxy, it will be replaced by a path to an actual rustc. Default: The rustc in the first-found toolchain, either from rustup, or from a toolchain available in the user's PATH.
• Rust_CARGO:STRING - Path to an actual cargo. Default: the cargo installed next to ${Rust_COMPILER}.
• Rust_CARGO_TARGET:STRING - The default target triple to build for. Alter for cross-compiling. Default: On Visual Studio Generator, the matching triple for CMAKE_VS_PLATFORM_NAME. Otherwise, the default target triple reported by ${Rust_COMPILER} --version --verbose.
• CORROSION_NATIVE_TOOLING:BOOL - Use a native tool (written in Rust) as part of Corrosion. This option increases the configure-time significantly unless Corrosion is installed. Default: OFF if CMake >= 3.19.0. Forced ON for CMake < 3.19.

Developer/Maintainer Options

These options are not used in the course of normal Corrosion usage, but are used to configure how Corrosion is built and installed. Only applies to Corrosion builds and subdirectory uses.

• CORROSION_DEV_MODE:BOOL - Indicates that Corrosion is being actively developed. Default: OFF if Corrosion is a subdirectory, ON if it is the top-level project
• CORROSION_BUILD_TESTS:BOOL - Build the Corrosion tests. Default: Off if Corrosion is a subdirectory, ON if it is the top-level project
• CORROSION_GENERATOR_EXECUTABLE:STRING - Specify a path to the corrosion-generator executable. This is to support scenarios where it's easier to build corrosion-generator outside of the normal bootstrap path, such as in the case of package managers that make it very easy to import Rust crates for fully reproducible, offline builds.
• CORROSION_INSTALL_EXECUTABLE:BOOL - Controls whether corrosion-generator is installed with the package. Default: ON with CORROSION_GENERATOR_EXECUTABLE unset, otherwise OFF

Information provided by Corrosion

For your convenience, Corrosion sets a number of variables which contain information about the version of the rust toolchain. You can use the CMake version comparison operators (e.g. VERSION_GREATER_EQUAL) on the main variable (e.g. if(Rust_VERSION VERSION_GREATER_EQUAL "1.57.0")), or you can inspect the major, minor and patch versions individually.

• Rust_VERSION<_MAJOR|_MINOR|_PATCH> - The version of rustc.
• Rust_CARGO_VERSION<_MAJOR|_MINOR|_PATCH> - The cargo version.
• Rust_LLVM_VERSION<_MAJOR|_MINOR|_PATCH> - The LLVM version used by rustc.
• Rust_IS_NIGHTLY - 1 if a nightly toolchain is used, otherwise 0. Useful for selecting an unstable feature for a crate, that is only available on nightly toolchains.

Adding crate targets

In order to integrate a Rust crate into CMake, you first need to import a crate or Workspace:

corrosion_import_crate(MANIFEST_PATH <path/to/cargo.toml>
        # Equivalent to --all-features passed to cargo build
        [ALL_FEATURES]
        # Equivalent to --no-default-features passed to cargo build
        [NO_DEFAULT_FEATURES]
        # Disable linking of standard libraries (required for no_std crates).
        [NO_STD]
        # Specify  cargo build profile (e.g. release or a custom profile)
        [PROFILE <cargo-profile>]
        # Only import the specified crates from a workspace
        [CRATES <crate1> ... <crateN>]
        # Enable the specified features
        [FEATURES <feature1> ... <featureN>]
        # Pass additional arguments to `cargo build`
        [FLAGS <flag1> ... <flagN>]
)

This will add a cmake target for each imported crate. Many of the options can also be set per target, see Per Target options for details.

Per Target options

Some configuration options can be specified individually for each target. You can set them via the corrosion_set_xxx() functions specified below:

• corrosion_set_env_vars(<target_name> <key1=value1> [... <keyN=valueN>]): Define environment variables that should be set during the invocation of cargo build for the specified target. Please note that the environment variable will only be set for direct builds of the target via cmake, and not for any build where cargo built the crate in question as a dependency for another target. The environment variables may contain generator expressions.
• corrosion_add_target_rustflags(<target_name> <rustflag> [... <rustflagN>]): When building the target, the RUSTFLAGS environment variable will contain the flags added via this function. Please note that any dependencies (built by cargo) will also see these flags. In the future corrosion may offer a second function to allow specifying flags only for the target in question, utilizing cargo rustc instead of cargo build.
• corrosion_add_target_local_rustflags(target_name rustc_flag [more_flags ...]): Support setting rustflags for only the main target (crate ) and none of it's dependencies. This is useful in cases where you only need rustflags on the main-crate, but need to set different flags for different targets. Without "local" Rustflags this would require rebuilds of the dependencies when switching targets.
• corrosion_set_hostbuild(<target_name>): The target should be compiled for the Host target and ignore any cross-compile configuration.
• corrosion_set_features(<target_name> [ALL_FEATURES <Bool>] [NO_DEFAULT_FEATURES] [FEATURES <feature1> ... ]): For a given target, enable specific features via FEATURES, toggle ALL_FEATURES on or off or disable all features via NO_DEFAULT_FEATURES. For more information on features, please see also the cargo reference.
• corrosion_set_flags(<target_name> <flag1> ...]): For a given target, add options and flags at the end of cargo build invocation. This will be appended after any arguments passed through the FLAGS during the crate import.
• corrosion_set_linker(target_name linker): Use linker to link the target. Please note that this only has an effect for targets where the final linker invocation is done by cargo, i.e. targets where foreign code is linked into rust code and not the other way around. Please also note that if you are cross-compiling and specify a linker such as clang, you are responsible for also adding a rustflag which adds the necessary --target= argument for the linker.

Selecting a custom cargo profile

Rust 1.57 stabilized the support for custom profiles. If you are using a sufficiently new rust toolchain, you may select a custom profile by adding the optional argument PROFILE <profile_name> to corrosion_import_crate(). If you do not specify a profile, or you use an older toolchain, corrosion will select the standard dev profile if the CMake config is either Debug or unspecified. In all other cases the release profile is chosen for cargo.

Importing C-Style Libraries Written in Rust

Corrosion makes it completely trivial to import a crate into an existing CMake project. Consider a project called rust2cpp with the following file structure:

rust2cpp/
    rust/
        src/
            lib.rs
        Cargo.lock
        Cargo.toml
    CMakeLists.txt
    main.cpp

This project defines a simple Rust lib crate, like so, in rust2cpp/rust/Cargo.toml:

[package]
name = "rust-lib"
version = "0.1.0"
authors = ["Andrew Gaspar <andrew.gaspar@outlook.com>"]
license = "MIT"
edition = "2018"

[dependencies]

[lib]
crate-type=["staticlib"]

In addition to "staticlib", you can also use "cdylib". In fact, you can define both with a single crate and switch between which is used using the standard BUILD_SHARED_LIBS variable.

This crate defines a simple crate called rust-lib. Importing this crate into your CMakeLists.txt is trivial:

# Note: you must have already included Corrosion for `corrosion_import_crate` to be available. See # the `Installation` section above.

corrosion_import_crate(MANIFEST_PATH rust/Cargo.toml)

Now that you've imported the crate into CMake, all of the executables, static libraries, and dynamic libraries defined in the Rust can be directly referenced. So, merely define your C++ executable as normal in CMake and add your crate's library using target_link_libraries:

add_executable(cpp-exe main.cpp)
target_link_libraries(cpp-exe PUBLIC rust-lib)

That's it! You're now linking your Rust library to your C++ library.

Generate Bindings to Rust Library Automatically

Currently, you must manually declare bindings in your C or C++ program to the exported routines and types in your Rust project. You can see boths sides of this in the Rust code and in the C++ code.

Integration with cbindgen is planned for the future.

Importing Libraries Written in C and C++ Into Rust

TODO

Cross Compiling

Corrosion attempts to support cross-compiling as generally as possible, though not all configurations are tested. Cross-compiling is explicitly supported in the following scenarios.

In all cases, you will need to install the standard library for the Rust target triple. When using Rustup, you can use it to install the target standard library:

rustup target add <target-rust-triple>

If the target triple is automatically derived, Corrosion will print the target during configuration. For example:

-- Rust Target: aarch64-linux-android

Windows-to-Windows

Corrosion supports cross-compiling between arbitrary Windows architectures using the Visual Studio Generator. For example, to cross-compile for ARM64 from any platform, simply set the -A architecture flag:

cmake -S. -Bbuild-arm64 -A ARM64
cmake --build build-arm64

Please note that for projects containing a build-script at least Rust 1.54 is required due to a bug in previous cargo versions, which causes the build-script to incorrectly be built for the target platform.

Linux-to-Linux

In order to cross-compile on Linux, you will need to install a cross-compiler. For example, on Ubuntu, to cross compile for 64-bit Little-Endian PowerPC Little-Endian, install g++-powerpc64le-linux-gnu from apt-get:

sudo apt install g++-powerpc64le-linux-gnu

Currently, Corrosion does not automatically determine the target triple while cross-compiling on Linux, so you'll need to specify a matching Rust_CARGO_TARGET.

cmake -S. -Bbuild-ppc64le -DRust_CARGO_TARGET=powerpc64le-unknown-linux-gnu -DCMAKE_CXX_COMPILER=powerpc64le-linux-gnu-g++
cmake --build build-ppc64le

Android

Cross-compiling for Android is supported on all platforms with the Makefile and Ninja generators, and the Rust target triple will automatically be selected. The CMake cross-compiling instructions for Android apply here. For example, to build for ARM64:

cmake -S. -Bbuild-android-arm64 -GNinja -DCMAKE_SYSTEM_NAME=Android \
      -DCMAKE_ANDROID_NDK=/path/to/android-ndk-rxxd -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a

Important note: The Android SDK ships with CMake 3.10 at newest, which Android Studio will prefer over any CMake you've installed locally. CMake 3.10 is insufficient for using Corrosion, which requires a minimum of CMake 3.15. If you're using Android Studio to build your project, follow the instructions in the Android Studio documentation for using a specific version of CMake.