First Rust example for issue #9

examples/rust-simple/.cargo/config

@@ -0,0 +1,2 @@
+[build]
+target = "wasm32-unknown-unknown"

examples/rust-simple/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "rust_simple"
+version = "0.1.0"
+
+[lib]
+crate-type = ["cdylib"]

examples/rust-simple/README.md

@@ -0,0 +1,24 @@
+### Example: Rust Simple
+
+This shows a simple example of compiling Rust to WASM and then to the JVM.
+
+The [root build script](../../build.gradle) actually has the build commands to build it. But basically it runs
+`cargo build --release` on this directory which compiles `add_one` from [lib.rs](src/lib.rs) into
+`target/wasm32-unknown-unknown/release/rust_simple.wasm`. Then the build script takes that wasm file and compiles it
+to `asmble.generated.RustSimple` in `build/wasm-classes`. The class is used by
+[Main.java](src/main/java/asmble/examples/rustsimple/Main.java). It is instantiated with a set of memory and then
+`add_one` is invoked with `25` to return `26`.
+
+To run it yourself, run the following from the root `asmble` dir (assuming you have built the Gradle wrapper described
+in the root README's "Building and Testing" section):
+
+    ./gradlew --no-daemon :examples:rust-simple:run
+
+Yes, this does include Rust's std lib, but it's not that big of a deal. The actual method executed for `add_one` looks
+like this decompiled:
+
+```java
+    private int $func0(final int n) {
+        return n + 1;
+    }
+```

examples/rust-simple/src/lib.rs

@@ -0,0 +1,4 @@
+#[no_mangle]
+pub extern "C" fn add_one(x: i32) -> i32 {
+    x + 1
+}

examples/rust-simple/src/main/java/asmble/examples/rustsimple/Main.java

@@ -0,0 +1,14 @@
+package asmble.examples.rustsimple;
+
+import asmble.generated.RustSimple;
+
+class Main {
+    // 20 pages is good for now
+    private static final int PAGE_SIZE = 65536;
+    private static final int MAX_MEMORY = 20 * PAGE_SIZE;
+
+    public static void main(String[] args) {
+        RustSimple simple = new RustSimple(MAX_MEMORY);
+        System.out.println("25 + 1 = " + simple.add_one(25));
+    }
+}