rust/tests/ui/async-await/async-block-control-flow-static-semantics.rs

// Test that `async { .. }` blocks:
// 1. do not allow `break` expressions.
// 2. get targeted by `return` and not the parent function.
// 3. get targeted by `?` and not the parent function.
//
//@ edition:2018

fn main() {}

use core::future::Future;

fn return_targets_async_block_not_fn() -> u8 {
    //~^ ERROR mismatched types
    let block = async {
        return 0u8;
    };
    let _: &dyn Future<Output = ()> = &block;
    //~^ ERROR to be a future that resolves to `()`, but it resolves to `u8`
}

async fn return_targets_async_block_not_async_fn() -> u8 {
    //~^ ERROR mismatched types [E0308]
    let block = async {
        return 0u8;
    };
    let _: &dyn Future<Output = ()> = &block;
    //~^ ERROR to be a future that resolves to `()`, but it resolves to `u8`
}

fn no_break_in_async_block() {
    async {
        break 0u8; //~ ERROR `break` inside `async` block
    };
}

fn no_break_in_async_block_even_with_outer_loop() {
    loop {
        async {
            break 0u8; //~ ERROR `break` inside `async` block
        };
    }
}

struct MyErr;
fn err() -> Result<u8, MyErr> {
    Err(MyErr)
}

fn rethrow_targets_async_block_not_fn() -> Result<u8, MyErr> {
    //~^ ERROR mismatched types
    let block = async {
        err()?;
        Ok(())
    };
    let _: &dyn Future<Output = Result<(), MyErr>> = &block;
}

fn rethrow_targets_async_block_not_async_fn() -> Result<u8, MyErr> {
    //~^ ERROR mismatched types
    let block = async {
        err()?;
        Ok(())
    };
    let _: &dyn Future<Output = Result<(), MyErr>> = &block;
}