The minimal example of the Docker multi-stage build with BuildKit caching for Rust

1. first build

$ DOCKER_BUILDKIT=1 docker build .
[+] Building 51.7s (17/17) FINISHED
...

2. modify src/main.rs like

7c7
<     println!("{}", y);
---
>     // println!("{}", y);

3. second build

$ DOCKER_BUILDKIT=1 docker build .
[+] Building 5.5s (17/17) FINISHED
...

The build time was reduced by 89%: 51.7s -> 5.5s