Add dependency on native Rust project

README.md

@@ -0,0 +1,10 @@
+# Building
+
+Make sure the required Android NDK platforms are installed, and the environment
+variable `ANDROID_NDK_TOOLCHAIN_DIR` is configured correctly.
+
+On Windows, this might be a path such as the following (NDK "Side by side" SDK tool):
+
+```
+%LOCALAPPDATA%\Android\Sdk\ndk\25.1.8937393\toolchains\llvm\prebuilt\windows-x86_64\bin
+```

app/build.gradle

@@ -1,6 +1,7 @@
 plugins {
     id 'com.android.application'
     id 'org.jetbrains.kotlin.android'
+    id "org.mozilla.rust-android-gradle.rust-android"
 }
 
 android {
@@ -44,6 +45,7 @@ android {
             excludes += '/META-INF/{AL2.0,LGPL2.1}'
         }
     }
+    ndkVersion '25.1.8937393'
 }
 
 dependencies {
@@ -62,3 +64,17 @@ dependencies {
     debugImplementation "androidx.compose.ui:ui-tooling:$compose_ui_version"
     debugImplementation "androidx.compose.ui:ui-test-manifest:$compose_ui_version"
 }
+
+// See https://github.com/mozilla/rust-android-gradle for other targets and required toolchains
+cargo {
+    module = "../native"
+    libname = "talaria"
+    targets = ["arm64", "arm", "x86"]
+    profile = 'release'
+}
+
+tasks.whenTaskAdded { task ->
+    if ((task.name == 'javaPreCompileDebug' || task.name == 'javaPreCompileRelease')) {
+        task.dependsOn 'cargoBuild'
+    }
+}

build.gradle

@@ -7,4 +7,5 @@ plugins {
     id 'com.android.application' version '7.3.0' apply false
     id 'com.android.library' version '7.3.0' apply false
     id 'org.jetbrains.kotlin.android' version '1.6.10' apply false
+    id "org.mozilla.rust-android-gradle.rust-android" version "0.9.3"
 }

native/.gitignore

@@ -0,0 +1,14 @@
+# Generated by Cargo
+# will have compiled files and executables
+debug/
+target/
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb

native/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "talaria"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "talaria"
+crate-type = ["cdylib"]
+
+[dependencies]
+jni = { version = "0.10.2", default-features = false }
+
+[profile.release]
+lto = true

native/src/lib.rs

@@ -0,0 +1,20 @@
+#![cfg(target_os = "android")]
+#![allow(non_snake_case)]
+
+use std::ffi::{CStr, CString};
+
+use jni::JNIEnv;
+use jni::objects::{JObject, JString};
+use jni::sys::jstring;
+
+#[no_mangle]
+pub unsafe extern fn Java_dev_lonami_talaria_MainActivity_hello(env: JNIEnv, _: JObject, j_recipient: JString) -> jstring {
+    let recipient = CString::from(
+        CStr::from_ptr(
+            env.get_string(j_recipient).unwrap().as_ptr()
+        )
+    );
+
+    let output = env.new_string("Hello ".to_owned() + recipient.to_str().unwrap()).unwrap();
+    output.into_inner()
+}