async functions fail to move values into generated futures in the latest nightly

[sfackler]

This simple async function fails to compile on the newest nightly: https://github.com/sfackler/rust-postgres/blob/2cc5bbf21b654c26bfd8b1e80b1e5c7cbd81235f/tokio-postgres/src/lib.rs#L163-L172

error[E0597]: `config` does not live long enough
   --> tokio-postgres/src/lib.rs:171:5
    |
171 |     config.connect(tls).await
    |     ^^^^^^-------------
    |     |
    |     borrowed value does not live long enough
    |     a temporary with access to the borrow is created here ...
172 | }
    | -
    | |
    | `config` dropped here while still borrowed
    | ... and the borrow might be used here, when that temporary is dropped and runs the destructor for type `impl core::future::future::Future`
    |
    = note: The temporary is part of an expression at the end of a block. Consider forcing this temporary to be dropped sooner, before the block's local variables are dropped. For example, you could save the expression's value in a new local variable `x` and then make `x` be the expression at the end of the block.

I'm guessing this was caused by #64292 (cc @davidtwco)

[sfackler]

This can be hacked around via an async move {} block:

diff --git a/tokio-postgres/src/lib.rs b/tokio-postgres/src/lib.rs
index 98c245f..eaf43f1 100644
--- a/tokio-postgres/src/lib.rs
+++ b/tokio-postgres/src/lib.rs
@@ -168,7 +168,9 @@ where
     T: MakeTlsConnect<Socket>,
 {
     let config = config.parse::<Config>()?;
-    config.connect(tls).await
+    async move {
+        config.connect(tls).await
+    }.await
 }

[nikomatsakis]

I think the root cause of this is #46413 -- feels like we ought to have more test cases covering these patterns, but oh well.

I haven't tried to look closely enough to decide what possible solution is.

[nikomatsakis]

I can confirm that this is actually a duplicate of #64512, so this is a genuine bug. An alternative workaround is return config.connect(tls).await

[nikomatsakis]

Minimized test case is just this:

async fn add(x: u32, y: u32) -> u32 {
    async { x + y }.await
}

fn main() { }