Contract Rust Template

This is a minimal template for a Rust contract targeting pallet_revive. This is a low- level way to write contracts, so we don't expect it to be used for implementing high-level contract logic. Instead, we expect that Rust will be used to implement libraries that are then called by Solidity, similar to Python, where performance-critical code is written in C.

Components

In terms of code, this template is very bare bones. main.rs is just a few lines of code. Most of the files in this repo deal with compiling the code to PolkaVM in a rust-analyzer-friendly way. We included a rust-toolchain.toml and a .cargo/config.toml so that all tools automatically select the correct target and toolchain (we need a relatively new nightly).

The call_from_sol.sol file demonstrates how to call the example in main.rs from Solidity.

Memory Allocation

The contract depends on the pallet-revive-uapi crate, which is a thin (but safe) wrapper around all available host functions. It only includes the absolute minimum. This means we also don't include a memory allocator. If you want to use alloc, you need to define a global allocator. Note that we don't support dynamic memory allocations in pallet_revive yet. Therefore, the allocator would need to operate on a static buffer.

How to Build

You can build this project with cargo build. However, to generate a valid contract, you also need to link it. Linking means taking the ELF file outputted by the Rust compiler and transforming it into a PolkaVM module.

# Make sure to have the latest polkatool installed
$ cargo install polkatool

# This will build the project and then use polkatool to link it
$ make

The build result is placed as contract.polkavm in the repository root. This is the final artifact that can be deployed as-is.

How to Inspect the Contract

$ polkatool stats contract.polkavm
$ polkatool disassemble contract.polkavm

Examples

The test fixtures for pallet_revive are written in the same way as this template and might be useful as examples.