[profile.dev.package.'*']
opt-level = 3

The problem: on WASM and android its not really easy to organize main loop like this:

fn main() {
    // do some initilization
    
    // start main loop
    loop {
        // handle input 

        // update logic

        // draw frame
    }
}

It is fixable on Android with threads, but on web there is not way to "pause" and "resume" WASM execution, so no WASM code should block ever. While that loop is blocking for the entire game execution! The C++ solution for that problem: https://kripken.github.io/blog/wasm/2019/07/16/asyncify.html

But in Rust we have async/await. Rust's futures is basically a continuations - future's stack may be store into a variable to later pause/resume execution of future's code.

async/await in macroquad is used without any external dependencies - no runtime, executor or even futures-rs are involved. It's just a way to preserve main's stack on WASM and keep the code cross platform without any WASM-specific main loop.