Why is the Rust compiler so slow?

    andy@bark ~/d/andrewkelley.me (master)> zig build --watch -fincremental
    Build Summary: 3/3 steps succeeded
    install success
    └─ run exe compile success 57ms MaxRSS:3M
       └─ compile exe compile Debug native success 331ms
    Build Summary: 3/3 steps succeeded
    install success
    └─ run exe compile success 56ms MaxRSS:3M
       └─ compile exe compile Debug native success 17ms
    watching 75 directories, 1 processes

All Zig code is built in a single compilation unit and everything is compiled from scratch every time you change something, including all dependencies and all the parts of the stdlib that you use in your project.

So you've been comparing Zig rebuilds that do all the work every time with Rust rebuilds that cache all dependencies.

Once incremental is fully released you will see instant rebuilds.