async fn foo(PAT: [u8; 10]) {
    /* ... */
}

==>

fn foo(x: [u8; 10]) -> impl Future<...> {
    // ~~~~~~~~~~~ don't focus on the parameters
    // ... because
    //
    async {
        let PAT = x;
        /* ... */
    }
    // the real problem is coming out of the generator
    // structure here, namely the free variable `x`
    // is represented as a structural "upvar"
    // upvar: `x`
    // and it being moved/copied into the local(s): PAT
}

==>

fn foo(x: [u8; 10]) -> impl Future<...> {
    async {}
}

for closures:

fn foo(y: 3) {
    let f = |z| { ... y ... z ...}
    //      ~~~~~~~~~~~~~~~~~~~~~~
    //        evaluation of this lambda
    //        is what 1. creates/allocates the "environment"
    //        structure and 2. initializes its values/field
    ...
    f(10);
}