Apply `assure` and `forward` directly to expressions

[ErichDonGubler]

Rust 1.45 lifts the restriction that proc-macros cannot be invoked in expression and statement position, which is the restriction referred to as the reason for needing a #[pre] macro on items using #[assure(...)] in the latest (0.2.0) crate docs:

Doing this is currently necessary, because the current (1.44.1) stable rust compiler does not support attribute macros being applied to statements or expressions directly.

What are plans for this crate now that this restriction has been lifted? Is any help needed to, say, lift the constraint that #[pre] needs to be applied to items?

The premise of the question is invalid, but @aticu has left this issue open and renamed it appropriately.

[aticu]

Unfortunately this restriction has only been lifted for function-like proc-macros. pre uses attribute proc-macros, where this restriction still applies.

The following code still fails on 1.45

fn main() {
    unsafe {
        #[test_macro]
        foo()
    }
}

with this error message

error[E0658]: attributes on expressions are experimental
 --> src/main.rs:7:9
  |
7 |         #[test_macro]
  |         ^^^^^^^^^^^^^
  |
  = note: see issue #15701 <https://github.com/rust-lang/rust/issues/15701> for more information

error[E0658]: custom attributes cannot be applied to expressions
 --> src/main.rs:7:9
  |
7 |         #[test_macro]
  |         ^^^^^^^^^^^^^
  |
  = note: see issue #54727 <https://github.com/rust-lang/rust/issues/54727> for more information

error: aborting due to 2 previous errors

I guess this issue could be left open though, until that limitation can be lifted.

[ErichDonGubler]

Ergh, I obviously misunderstood the situation. Thanks for the patient response. :)

[aticu]

Ergh, I obviously misunderstood the situation.

No worries, I had to double check as well, when I read the patch notes.