async fn forgets the mutability of the arguments

[taiki-e]

Code:

#![feature(async_await)]

async fn foo(n: u32, mut vec: Vec<u32>) {
    vec.push(n);
}

Error:

error[E0596]: cannot borrow `vec` as mutable, as it is not declared as mutable
 --> code\src\lib.rs:4:5
  |
3 | async fn foo(n: u32, mut vec: Vec<u32>) {
  |                      ------- help: consider changing this to be mutable: `mut vec`
4 |     vec.push(n);
  |     ^^^ cannot borrow as mutable

Rustc version: rustc 1.36.0-nightly (08bfe16 2019-05-02)

[taiki-e]

@rustbot modify labels: A-async-await and T-compiler.

[cramertj]

@davidtwco I wonder if this is related to the drop order fix desugaring?

[davidtwco]

@cramertj Oops, looks like it is. Thanks @taiki-e for the fix.