CMake Rust Demo

A C CMake demo using Rust static library components and building Rust executables. The notable feature of this project is cmake/FindRust.cmake

Usage

Add FindRust.cmake to your project's cmake directory and use the following to enable Rust support:

find_package(Rust REQUIRED)

Rust-based C-style Static Libraries

To build a rust library and link it into your app, use:

add_rust_library(TARGET yourlib
  SOURCE_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
  BINARY_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
)

add_executable(yourexe)
target_sources(yourexe PRIVATE yourexe.c)
target_link_libraries(yourexe yourlib)

Rust Library Unit Tests

For unit test support, you can use the add_rust_test() function, like this:

add_rust_library(TARGET yourlib
  SOURCE_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
  BINARY_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
)
add_rust_test(NAME yourlib
  SOURCE_DIRECTORY "${CMAKE_SOURCE_DIR}/path/to/yourlib"
  BINARY_DIRECTORY "${CMAKE_BINARY_DIR}/path/to/yourlib"
)

And don't forget to enable CTest early in your top-level CMakeLists.txt file:

# Enable CTest
if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
    include(CTest)
    enable_testing()
endif()

Rust-based Executables

To build a rust executable use:

add_rust_executable(TARGET yourexe
  SOURCE_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
  BINARY_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
)
add_executable(YourProject::yourexe ALIAS yourexe)

Minimum Rust version

You may set the CMake variable RUSTC_MINIMUM_REQUIRED to enforce a minimum Rust version, such as "1.56" for the 2021 edition support.

cbindgen and bindgen FFI generation

This project demonstrates using bindgen and cbindgen within the <src>/lib/rust/build.rs script to generate the API's at build time.

cbindgen is used to generate a demorust.h C binding for the Rust exports every time you build. It'll be dropped in the build directory.

bindgen, on the otherhand, generates a sys.rs Rust binding for the C exports required by the Rust code. Unfortunately, bindgen depends on libclang for some features that aren't readily available on all systems. So we only run bindgen if you set the MAINTAINER_MODE CMake parameter to ON. That works out okay, as the sys.rs file is dropped into the source directory, not the build directory. But that means you have to remember to build with MAINTAINER_MODE=ON any time you change the internal C API's used by the Rust library.

The cbindgen and bindgen programs don't need to be pre-installed. Cargo.toml will pull them in during the build.

Building this project

Requirements:

• CMake 3.18+
• The Rust toolchain (Cargo, etc)

Run:

mkdir build && cd build
cmake .. \
  -D MAINTAINER_MODE=ON \
  -D CMAKE_INSTALL_PREFIX=install
cmake --build .
ctest -V
cmake --build . --target install

Vendoring dependencies

For building a source package with CPack (E.g., the TGZ package archive generator), you may wish to vendor the Cargo dependencies so your users can do offline builds when using your source package.

The FindRust.cmake module makes that easy. Simply define VENDOR_DEPENDENCIES=ON and it will run cargo vendor during the configuration stage. The dependencies and assocaited config.toml file, instructing cargo to use the vendored dependencies, will be placed in a .cargo directory next to each of your Cargo.toml files.

Example building a source tarball with vendored dependencies:

mkdir build && cd build
cmake .. -D VENDOR_DEPENDENCIES=ON && cpack --config CPackSourceConfig.cmake

Afterwards, you should have a source package (E.g., cmake-rust-0.1.0.tar.gz) containing the project with vendored dependencies in your working directory, and if you run git status, you'll see the .cargo directories:

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        ../common/gen_uuid/.cargo/
        ../lib/colorlog/.cargo/

At this point you could do something like this, to see it build w/out downloading the crates:

tar xzf cmake-rust-0.1.0.tar.gz
cd cmake-rust-0.1.0
mkdir build && cd build
cmake .. && cmake --build . && ctest

You'll note that the vendored dependencies appear in your source directory. To remove them, you can do this:

rm -rf **/.cargo

Installing Rust binaries with CMake

C static libraries don't link in other static libraries. Fully-static builds of projects that are composed of a few different static libraries will result in a collection of static libraries. If you're only providing an application, then you can link them into the app and only install the app. But if you provide a library for others to consume then you may need to install all of the static libraries that compose the features of "the library" you provide for downstream projects.

For example, let's say you've got a C library that may be built as a shared lib AND as a static lib, and you're slowly porting the C code into a Rust static library. You will link your Rust static library into the C library to maintain the original C API for your downstream users. With a shared-build of the C library, the Rust static library will get linked into the shared library and the downstream users never have to know it exists. Buf for a static-build of the C library, the C library is linked against your Rust library but they remain two separate libs that must both be linked with the downstream applications. You will need to install both the C static library and the Rust static library.

Projects built with CMake can use CMake to install the software directly (e.g. under /usr/local) or via a packager like WiX Toolset (Windows) or .deb / .rpm / .pkg packages.

Rust binaries aren't treated quite the same by CMake as native C binaries, but you can use CMake to install them.

How to install Rust binaries with CMake

The first thing you'll probably need if you want to use CMake to install stuff, whether or not you bundle in some Rust binaries, is to include the GNUEInstallDirs module somewhere at the top of your top-level CMakeLists.txt:

include(GNUInstallDirs)

Now with a regular C library or executable CMake target, you might configure them for installation like this:

install(TARGETS demo DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT libraries)

or:

install(TARGETS app DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT programs)

Rust library CMake targets aren't normal CMake binary targets though. They're "custom" targets, which means you will instead have to use install(FILES instead of install(TARGETS, and then point CMake at the specific file you need installed instead of at a target. Our FindRust.cmake's add_rust_library() function makes this easy. When you add a Rust library, it sets the target properties such that you can simply use CMake's $<TARGET_FILE:target> generator expression to provide the file path.

In this demo, we configure installation for our demorust Rust static library like this:

install(FILES $<TARGET_FILE:demorust> DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT libraries)

And for our app_rust Rust executable, we install like this:

get_target_property(app_rust_EXECUTABLE app_rust IMPORTED_LOCATION)
install(PROGRAMS ${app_rust_EXECUTABLE} DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT programs)

Note that we have to get the IMPORTED_LOCATION manually for the executable.

License

This project is dual-licensed under MIT and Apache 2.0.

Contribute

This project could use your help testing build support for various targets on various operating systems. Please feel free to help work on the outstanding issues too!