try_blocks type inference failure suggests illegal code

[joshlf]

I have the following code:

#![feature(try_blocks)]

fn main() {
    println!(
        "{:?}",
        try {
            if true {
                Ok(0usize)
            } else {
                Err(true)
            }
        }
    );
}

I get the following error:

error[[E0282]](https://doc.rust-lang.org/nightly/error-index.html#E0282): type annotations needed
  --> src/main.rs:6:9
   |
6  | /         try {
7  | |             if true {
8  | |                 Ok(0usize)
9  | |             } else {
10 | |                 Err(true)
11 | |             }
12 | |         }
   | |_________^ cannot infer type of the type parameter `T` declared on the associated function `new_debug`
   |
   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider specifying the generic argument
   |
12 |         }::<T>
   |          +++++

If I try to follow the compiler's advice by adding a trailing ::<Result<usize, bool>> on line 12, it results in code that can't be parsed:

error: expected one of `,`, `.`, `?`, `catch`, or an operator, found `::`
  --> src/main.rs:12:10
   |
12 |         }::<Result<usize, bool>>
   |          ^^ expected one of `,`, `.`, `?`, `catch`, or an operator

Version

Current nightly (2022-10-01 57f097e)

[Rageking8]

@rustbot label +T-compiler +D-invalid-suggestion

[kadiwa4]

The suggestion is gone:

error[E0283]: type annotations needed
   --> src/main.rs:6:9
    |
5   |           "{:?}",
    |            ---- required by a bound introduced by this call
6   | /         try {
7   | |             if true {
8   | |                 Ok(0usize)
9   | |             } else {
10  | |                 Err(true)
11  | |             }
12  | |         }
    | |_________^ cannot infer type
    |
    = note: cannot satisfy `_: Debug`
note: required by a bound in `core::fmt::rt::Argument::<'a>::new_debug`
   --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/rt.rs:100:29
    |
100 |     pub fn new_debug<'b, T: Debug>(x: &'b T) -> Argument<'_> {
    |                             ^^^^^ required by this bound in `Argument::<'a>::new_debug`
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0283`.

@rustbot label: +E-needs-test
Unless there's a test for this already.

[scottmcm]

I think I'm just going to close this, even without a test, because now that try blocks work quite differently from 2022, I don't know that a test would provide material value.