Rust Android Gradle Plugin
Cross compile Rust Cargo projects for Android targets.
Usage
Add the plugin to your root build.gradle
, like:
buildscript {
repositories {
maven {
url "https://plugins.gradle.org/m2/"
}
}
dependencies {
classpath 'org.mozilla.rust-android-gradle:plugin:0.9.3'
}
}
or
buildscript {
//...
}
plugins {
id "org.mozilla.rust-android-gradle.rust-android" version "0.9.3"
}
In your project's build.gradle, apply plugin
and add the cargo
configuration:
android { ... }
apply plugin: 'org.mozilla.rust-android-gradle.rust-android'
cargo {
module = "../rust" // Or whatever directory contains your Cargo.toml
libname = "rust" // Or whatever matches Cargo.toml's [package] name.
targets = ["arm", "x86"] // See bellow for a longer list of options
}
Install the rust toolchains for your target platforms:
rustup target add armv7-linux-androideabi # for arm
rustup target add i686-linux-android # for x86
rustup target add aarch64-linux-android # for arm64
rustup target add x86_64-linux-android # for x86_64
rustup target add x86_64-unknown-linux-gnu # for linux-x86-64
rustup target add x86_64-apple-darwin # for darwin x86_64 (if you have an Intel MacOS)
rustup target add aarch64-apple-darwin # for darwin arm64 (if you have a M1 MacOS)
rustup target add x86_64-pc-windows-gnu # for win32-x86-64-gnu
rustup target add x86_64-pc-windows-msvc # for win32-x86-64-msvc
...
Finally, run the cargoBuild
task to cross compile:
./gradlew cargoBuild
Or add it as a dependency to one of your other build tasks, to build your rust code when you normally build your project:
tasks.whenTaskAdded { task ->
if ((task.name == 'javaPreCompileDebug' || task.name == 'javaPreCompileRelease')) {
task.dependsOn 'cargoBuild'
}
}
Configuration
The cargo
Gradle configuration accepts many options.
Linking Java code to native libraries
Generated libraries will be added to the Android jniLibs
source-sets, when correctly referenced in
the cargo
configuration through the libname
and/or targetIncludes
options. The latter
defaults to ["lib${libname}.so", "lib${libname}.dylib", "{$libname}.dll"]
, so the following configuration will
include all libbackend
libraries generated in the Rust project in ../rust
:
cargo {
module = "../rust"
libname = "backend"
}
Now, Java code can reference the native library using, e.g.,
static {
System.loadLibrary("backend");
}
apiLevel
Native The Android NDK also fixes an API level,
which can be specified using the apiLevel
option. This option defaults to the minimum SDK API
level. As of API level 21, 64-bit builds are possible; and conversely, the arm64
and x86_64
targets require apiLevel >= 21
.
Cargo release profile
The profile
option selects between the --debug
and --release
profiles in cargo
. Defaults
to debug
!
Extension reference
module
The path to the Rust library to build with Cargo; required. module
can be absolute; if it is not,
it is interpreted as a path relative to the Gradle projectDir
.
cargo {
// Note: path is either absolute, or relative to the gradle project's `projectDir`.
module = '../rust'
}
libname
The library name produced by Cargo; required.
libname
is used to determine which native libraries to include in the produced AARs and/or APKs.
See also targetIncludes
.
libname
is also used to determine the ELF SONAME to declare in the Android libraries produced by
Cargo. Different versions of the Android system linker
depend on the ELF SONAME.
In Cargo.toml
:
[lib]
name = "test"
In build.gradle
:
cargo {
libname = 'test'
}
targets
A list of Android targets to build with Cargo; required.
Valid targets for Android are:
'arm',
'arm64',
'x86',
'x86_64'
Valid targets for Desktop are:
'linux-x86-64',
'darwin-x86-64',
'darwin-aarch64',
'win32-x86-64-gnu',
'win32-x86-64-msvc'
The desktop targets are useful for testing native code in Android unit tests that run on the host, not on the target device. Better support for this feature is planned.
cargo {
targets = ['arm', 'x86', 'linux-x86-64']
}
prebuiltToolchains
When set to true
(which requires NDK version 19+), use the prebuilt toolchains bundled with the
NDK. When set to false
, generate per-target architecture standalone NDK toolchains using
make_standalone_toolchain.py
. When unset, use the prebuilt toolchains if the NDK version is 19+,
and fall back to generated toolchains for older NDK versions.
Defaults to null
.
cargo {
prebuiltToolchains = true
}
verbose
When set, execute cargo build
with or without the --verbose
flag. When unset, respect the
Gradle log level: execute cargo build
with or without the --verbose
flag according to whether
the log level is at least INFO
. In practice, this makes ./gradlew ... --info
(and ./gradlew ... --debug
) execute cargo build --verbose ...
.
Defaults to null
.
cargo {
verbose = true
}
profile
The Cargo release profile to build.
Defaults to "debug"
.
cargo {
profile = 'release'
}
features
Set the Cargo features.
Defaults to passing no flags to cargo
.
To pass --all-features
, use
cargo {
features {
all()
}
}
To pass an optional list of --features
, use
cargo {
features {
defaultAnd("x")
defaultAnd("x", "y")
}
}
To pass --no-default-features
, and an optional list of replacement --features
, use
cargo {
features {
noDefaultBut()
noDefaultBut("x")
noDefaultBut "x", "y"
}
}
targetDirectory
The target directory into which Cargo writes built outputs. You will likely need to specify this if you are using a cargo virtual workspace, as our default will likely fail to locate the correct target directory.
Defaults to ${module}/target
. targetDirectory
can be absolute; if it is not, it is interpreted
as a path relative to the Gradle projectDir
.
Note that if CARGO_TARGET_DIR
(see https://doc.rust-lang.org/cargo/reference/environment-variables.html)
is specified in the environment, it takes precedence over targetDirectory
, as cargo will output
all build artifacts to it, regardless of what is being built, or where it was invoked.
You may also override CARGO_TARGET_DIR
variable by setting rust.cargoTargetDir
in
local.properties
, however it seems very unlikely that this will be useful, as we don't pass this
information to cargo itself. That said, it can be used to control where we search for the built
library on a per-machine basis.
cargo {
// Note: path is either absolute, or relative to the gradle project's `projectDir`.
targetDirectory = 'path/to/workspace/root/target'
}
targetIncludes
Which Cargo outputs to consider JNI libraries.
Defaults to ["lib${libname}.so", "lib${libname}.dylib", "{$libname}.dll"]
.
cargo {
targetIncludes = ['libnotlibname.so']
}
apiLevel
The Android NDK API level to target. NDK API levels are not the same as SDK API versions; they are updated less frequently. For example, SDK API versions 18, 19, and 20 all target NDK API level 18.
Defaults to the minimum SDK version of the Android project's default configuration.
cargo {
apiLevel = 21
}
You may specify the API level per target in targets
using the apiLevels
option. At most one of
apiLevel
and apiLevels
may be specified. apiLevels
must have an entry for each target in
targets
.
cargo {
targets = ["arm", "x86_64"]
apiLevels = [
"arm": 16,
"x86_64": 21,
]
}
extraCargoBuildArguments
Sometimes, you need to do things that the plugin doesn't anticipate. Use extraCargoBuildArguments
to append a list of additional arguments to each cargo build
invocation.
cargo {
extraCargoBuildArguments = ['a', 'list', 'of', 'strings']
}
exec
This is a callback taking the ExecSpec
we're going to use to invoke cargo build
, and
the relevant toolchain. It's called for each invocation of cargo build
. This generally
is useful for the following scenarios:
- Specifying target-specific environment variables.
- Adding target-specific flags to the command line.
- Removing/modifying environment variables or command line options the rust-android-gradle plugin would provide by default.
cargo {
exec { spec, toolchain ->
if (toolchain.target != "x86_64-apple-darwin") {
// Don't statically link on macOS desktop builds, for some
// entirely hypothetical reason.
spec.environment("EXAMPLELIB_STATIC", "1")
}
}
}
Specifying NDK toolchains
The plugin can either use prebuilt NDK toolchain binaries, or search for (and if missing, build)
NDK toolchains as generated by make_standalone_toolchain.py
.
A prebuilt NDK toolchain will be used if:
rust.prebuiltToolchain=true
in the per-(multi-)project${rootDir}/local.properties
prebuiltToolchain=true
in thecargo { ... }
block (if not overridden bylocal.properties
)- The discovered NDK is version 19 or higher (if not overridden per above)
The toolchains are rooted in a single Android NDK toolchain directory. In order of preference, the toolchain root directory is determined by:
rust.androidNdkToolchainDir
in the per-(multi-)project${rootDir}/local.properties
- the environment variable
ANDROID_NDK_TOOLCHAIN_DIR
${System.getProperty(java.io.tmpdir)}/rust-android-ndk-toolchains
Note that the Java system property java.io.tmpdir
is not necessarily /tmp
, including on macOS hosts.
Each target architecture toolchain is named like $arch-$apiLevel
: for example, arm-16
or arm64-21
.
Specifying local targets
When developing a project that consumes rust-android-gradle
locally, it's often convenient to
temporarily change the set of Rust target architectures. In order of preference, the plugin
determines the per-project targets by:
rust.targets.${project.Name}
for each project in${rootDir}/local.properties
rust.targets
in${rootDir}/local.properties
- the
cargo { targets ... }
block in the per-projectbuild.gradle
The targets are split on ','
. For example:
rust.targets.library=linux-x86-64
rust.targets=arm,linux-x86-64,darwin
Specifying paths to sub-commands (Python, Cargo, and Rustc)
The plugin invokes Python, Cargo and Rustc. In order of preference, the plugin determines what command to invoke for Python by:
- the value of
cargo { pythonCommand = "..." }
, if non-empty rust.pythonCommand
in${rootDir}/local.properties
- the environment variable
RUST_ANDROID_GRADLE_PYTHON_COMMAND
- the default,
python
In order of preference, the plugin determines what command to invoke for Cargo by:
- the value of
cargo { cargoCommand = "..." }
, if non-empty rust.cargoCommand
in${rootDir}/local.properties
- the environment variable
RUST_ANDROID_GRADLE_CARGO_COMMAND
- the default,
cargo
In order of preference, the plugin determines what command to invoke for rustc
by:
- the value of
cargo { rustcCommand = "..." }
, if non-empty rust.rustcCommand
in${rootDir}/local.properties
- the environment variable
RUST_ANDROID_GRADLE_RUSTC_COMMAND
- the default,
rustc
(Note that failure to locate rustc
is not fatal, however it may result in rebuilding the code more often than is necessary).
Paths must be host operating system specific. For example, on Windows:
rust.pythonCommand=c:\Python27\bin\python
On Linux,
env RUST_ANDROID_GRADLE_CARGO_COMMAND=$HOME/.cargo/bin/cargo ./gradlew ...
Specifying Rust channel
Rust is released to three different "channels": stable, beta, and nightly (see
https://rust-lang.github.io/rustup/concepts/channels.html). The rustup
tool, which is how most
people install Rust, allows multiple channels to be installed simultaneously and to specify which
channel to use by invoking cargo +channel ...
.
In order of preference, the plugin determines what channel to invoke cargo
with by:
- the value of
cargo { rustupChannel = "..." }
, if non-empty rust.rustupChannel
in${rootDir}/local.properties
- the environment variable
RUST_ANDROID_GRADLE_RUSTUP_CHANNEL
- the default, no channel specified (which
cargo
installed viarustup
generally defaults to thestable
channel)
The channel should be recognized by cargo
installed via rustup
, i.e.:
"stable"
"beta"
"nightly"
A single leading '+'
will be stripped, if present.
(Note that Cargo installed by a method other than rustup
will generally not understand +channel
and builds will likely fail.)
Passing arguments to cargo
The plugin passes project properties named like RUST_ANDROID_GRADLE_target_..._KEY=VALUE
through
to the Cargo invocation for the given Rust target
as KEY=VALUE
. Target should be upper-case
with "-" replaced by "_". (See the links from this Cargo issue.) So, for example,
project.RUST_ANDROID_GRADLE_I686_LINUX_ANDROID_FOO=BAR
and
./gradlew -PRUST_ANDROID_GRADLE_ARMV7_LINUX_ANDROIDEABI_FOO=BAR ...
and
env ORG_GRADLE_PROJECT_RUST_ANDROID_GRADLE_ARMV7_LINUX_ANDROIDEABI_FOO=BAR ./gradlew ...
all set FOO=BAR
in the cargo
execution environment (for the "armv7-linux-androideabi` Rust
target, corresponding to the "x86" target in the plugin).
Development
At top-level, the publish
Gradle task updates the Maven repository
under build/local-repo
:
$ ./gradlew publish
...
$ ls -al build/local-repo/org/mozilla/rust-android-gradle/org.mozilla.rust-android-gradle.gradle.plugin/0.4.0/org.mozilla.rust-android-gradle.gradle.plugin-0.4.0.pom
-rw-r--r-- 1 nalexander staff 670 18 Sep 10:09
build/local-repo/org/mozilla/rust-android-gradle/org.mozilla.rust-android-gradle.gradle.plugin/0.4.0/org.mozilla.rust-android-gradle.gradle.plugin-0.4.0.pom
Sample projects
The easiest way to get started is to run the sample projects. The sample projects have dependency
substitutions configured so that changes made to plugin/
are reflected in the sample projects
immediately.
$ ./gradlew -p samples/library :assembleDebug
...
$ file samples/library/build/outputs/aar/library-debug.aar
samples/library/build/outputs/aar/library-debug.aar: Zip archive data, at least v1.0 to extract
$ ./gradlew -p samples/app :assembleDebug
...
$ file samples/app/build/outputs/apk/debug/app-debug.apk
samples/app/build/outputs/apk/debug/app-debug.apk: Zip archive data, at least v?[0] to extract
Testing Local changes
An easy way to locally test changes made in this plugin is to simply add this to your project's settings.gradle
:
// Switch this to point to your local plugin dir
includeBuild('../rust-android-gradle') {
dependencySubstitution {
// As required.
substitute module('gradle.plugin.org.mozilla.rust-android-gradle:plugin') with project(':plugin')
}
}
Publishing
Automatically via the Bump version Github Actions workflow
You will need to be a collaborator. First, manually invoke the Bump version Github Actions
workflow. Specify a
version (like "x.y.z", without quotes) and a single line changelog entry. (This entry will have a
dash prepended, so that it would look normal in a list. This is working around the lack of a
multi-line input in Github
Actions.) This will push
a preparatory commit updating version numbers and the changelog like this
one,
and make a draft Github Release with a name like vx.y.z
. After verifying that tests pass,
navigate to the releases panel and edit
the release, finally pressing "Publish release". The release Github workflow will build and publish
the plugin, although it may take some days for it to be reflected on the Gradle plugin portal.
By hand
You will need credentials to publish to the Gradle plugin portal in
the appropriate place for the plugin-publish
to
find them. Usually, that's in ~/.gradle/gradle.properties
.
At top-level, the publishPlugins
Gradle task publishes the plugin for consumption:
$ ./gradlew publishPlugins
...
Publishing plugin org.mozilla.rust-android-gradle.rust-android version 0.8.1
Publishing artifact build/libs/plugin-0.8.1.jar
Publishing artifact build/libs/plugin-0.8.1-sources.jar
Publishing artifact build/libs/plugin-0.8.1-javadoc.jar
Publishing artifact build/publish-generated-resources/pom.xml
Activating plugin org.mozilla.rust-android-gradle.rust-android version 0.8.1
Real projects
To test in a real project, use the local Maven repository in your build.gradle
, like:
buildscript {
repositories {
maven {
url "file:///Users/nalexander/Mozilla/rust-android-gradle/build/local-repo"
}
}
dependencies {
classpath 'org.mozilla.rust-android-gradle:plugin:0.9.0'
}
}