Special case suggestion for missing tail expression when dealing with Ok(()) and Some(())

[estebank]

The suggestion in the following code isn't great:

error[E0308]: mismatched types
  --> src/main.rs:72:5
   |
72 | /     while let Some(i) = x.try_next().await? {
73 | |         println!("{:?}", i);
74 | |     }
   | |_____^ expected enum `Option`, found `()`
   |
   = note:   expected enum `Option<()>`
           found unit type `()`
help: try using a variant of the expected enum
   |
72 ~     Some(while let Some(i) = x.try_next().await? {
73 +         println!("{:?}", i);
74 +     })
   |

It makes sense why it happens: the while let expression resolves to type (), it's the tail expression of an async fn that returns Option<()>, so wrapping the expression in Some(()) would make the type checker happy, but suggesting that seems almost always wrong? I think I would prefer it if we special cased this and didn't gave a suggestion for Result<(), _> or Option<()>.

[m-ou-se]

How about something like this?

[m-ou-se]

(Just need to figure out a way to detect whether the expression was the final one in a block.)

[estebank]

That looks good!

[m-ou-se]

Re-opening this, because it doesn't work yet for for loops:

help: try wrapping the expression in `Ok`
  |
4 ~     Ok(for _ in x {
5 |         ...
6 ~     })
  |