regression: attributes on expressions are experimental

[Mark-Simulacrum]

Seems like something about our detection here changed, doesn't look like the cases here should be errors at a glance.

• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/gh/emily-signet.sleepyhead-kdl/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/gh/mozilla.rust-parsepatch/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/gh/sampersand.quest2/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/over-0.6.5/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/parsepatch-0.2.9/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/rlxc-0.1.0/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/snapshots-0.2.8/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/cismute-0.1.2/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.65-2/beta-2022-10-11/reg/vipers-2.0.6/log.txt

[ehuss]

This seems to be caused by #100232 (cc @cjgillot).

Here's a little repro:

macro_rules! foo {
    () => {
        #[allow(unreachable_patterns)]
        {
            123i32
        }
    };
}

fn main() {
    let _ = foo!().abs();
}

Technically the error is correct, the attribute is being used in an expression in this example. Due to the strange rules for when attributes are allowed on expressions, I'm guessing that self was previously being rewritten to be an argument, which does allow attributes.

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-critical