Cross compile Rust Cargo projects for Android targets.
To begin you must first 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 macOS (darwin)
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
...
Add the plugin to your root build.gradle
, like:
buildscript {
repositories {
maven {
url "https://plugins.gradle.org/m2/"
}
}
dependencies {
classpath 'gradle.plugin.org.mozilla.rust-android-gradle:plugin:0.8.1'
}
}
Next add the cargo
configuration to android project. Point to your cargo project using module
and add targets. Currently supported targets are arm
, arm64
, x86
, x86_64
, and
linux-x86-64
, darwin
, win32-x86-64-gnu
, and win32-x86-64-msvc
.
cargo {
module = "../rust"
targets = ["arm", "x86"]
}
Run the cargoBuild
task to cross compile
./gradlew cargoBuild
The cargo
Gradle configuration accepts many options.
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");
}
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
.
The profile
option selects between the --debug
and --release
profiles in cargo
. Defaults
to debug
!
The path to the Rust library to build with Cargo; required. module
is interpreted as a relative
path to the Gradle projectDir
.
cargo {
module = '../rust'
}
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'
}
A list of Android targets to build with Cargo; required.
Valid targets are arm
, arm64
, x86
, x86_64
(Android), and 'linux-x86-64'
, 'darwin'
,
'win32-x86-64-gnu'
, and 'win32-x86-64-msvc'
(Desktop).
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']
}
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
}
The Cargo release profile to build.
Defaults to "debug"
.
cargo {
profile = 'release'
}
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 {
noDefaultFeatures()
noDefaultFeatures("x")
noDefaultFeatures "x", "y"
}
}
The target directory into which Cargo writes built outputs.
Defaults to ${module}/target
. targetDirectory
is interpreted as a relative path to the Gradle
projectDir
.
cargo {
targetDirectory = 'release'
}
Which Cargo outputs to consider JNI libraries.
Defaults to ["lib${libname}.so", "lib${libname}.dylib", "{$libname}.dll"]
.
cargo {
targetIncludes = ['libnotlibname.so']
}
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
}
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']
}
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")
}
}
}
The plugin looks for (and will generate) per-target architecture standalone NDK toolchains as
generated by make_standalone_toolchain.py
.
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
.
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${rootDir}/local.properties
- the
cargo { targets ... }
block in the per-projectbuild.gradle
The targets are split on ','
. For example:
rust.targets.library=linux-x86-64
rust.targets=arm,linux-x86-64,darwin
The plugin invokes Python and Cargo. In order of preference, the plugin determines what command to invoke for Python by:
rust.pythonCommand
in${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:
rust.cargoCommand
in${rootDir}/local.properties
- the environment variable
RUST_ANDROID_GRADLE_CARGO_COMMAND
- the default,
cargo
Paths must be host operating system specific. For example, on Windows:
rust.pythonCommand=c:\Python27\bin\python
On Linux,
env RUST_ANDROID_GRADLE_CARGO_COMMAND=$HOME/.cargo/bin/cargo ./gradlew ...
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).
At top-level, the publish
Gradle task updates the Maven repository
under samples
:
$ ./gradlew publish
...
$ ls -al samples/maven-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
samples/maven-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
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
To run the sample projects:
$ ./gradlew -p samples/library :assembleDebug
...
$ ls -al samples/library/build//outputs/aar/library-debug.aar
-rw-r--r-- 1 nalexander staff 8926315 18 Sep 10:22 samples/library/build//outputs/aar/library-debug.aar
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/samples/maven-repo"
}
}
dependencies {
classpath 'org.mozilla.rust-android-gradle:plugin:0.3.0'
}
}