Rust → JVM Toolchain 🚀

Welcome! This project provides a toolchain for compiling Rust code into Java bytecode, allowing it to run on the JVM.

How It Works

The toolchain follows these steps:

1. Parsing & MIR Generation

   • Rust code is first parsed and converted into MIR (Mid-level Intermediate Representation) using rustc.

2. MIR to Java Bytecode

   • The MIR for each crate is translated into a Java Classfile (containing JVM bytecode) via rustc_codegen_jvm, which is the core of this repository.
   • Source code for this component is located in the src folder.

3. Linking & .jar Generation

   • Java Classfiles for all crates used in a library or executable are linked into a single .jar file, making it ready to run on the JVM.
   • This step is handled by java-linker-rs, a custom-built linker in this repository (found in the java-linker folder).

Current Capabilities

• ✅ Compiling a minimal no_std & no_core Rust program with an empty main function.
• ✅ Simple mathematical operations on i32s: addition, subtraction, and returning () or an i32.

Next Milestone:

🚧 Full support for the core crate is in progress!

How to Use the Toolchain

Prerequisites

• Ensure you're on the latest nightly build of Rust.
• Install necessary Rust components:

  rustup component add rust-src rustc-dev llvm-tools-preview

• Run the setup script:

  chmod +x setup.sh && ./setup.sh

Compiling Rust to JVM Bytecode

To use the toolchain for compiling your Rust project:
```

1. Update the Target JSON
   • Modify jvm-unknown-unknown.json, replacing the ../../.. (relative path to the project root from a test folder) part of the linker and default-codegen-backend lines to the absolute or relative path of where you cloned this repo.
2. Build Your Project

   cargo build --target /path/to/rustc_codegen_jvm/jvm-unknown-unknown.json

3. Find & Run the Generated .jar
   • The compiled .jar file will be in:

     target/jvm-unknown-unknown/debug/[cratename].jar
     

   • If it's a binary (not a library), run it using:

     java -jar target/jvm-unknown-unknown/debug/[cratename].jar

Running Tests

• If you modified the target JSON file, revert the changes before running tests.
• Execute the test script:

  python3 Tester.py

• Look for a success message 🎉