rustc 1.83 lexing regression in the 2015 edition: 'r#x'y

[mattheww]

rustc 1.82 accepts forms like 'r#x'y in the 2015 edition, but rustc 1.83 (beta) rejects them.

As I understand it, #126452 wasn't intended to have any effect on the 2015 edition.

playground

macro_rules! lexes {($($_:tt)*) => {}}

fn main() {
    lexes!('r#x'y);
}

I think this is fallout from the beta-backport of #132341.

[compiler-errors]

I'm tempted to say that this is a purely theoretical regression, and we should perhaps fix it in 1.84 but it's possibly a bit too late for 1.83? Especially because I'm not certain how to prepare a fix for this other than perhaps reverting raw lifetime functionality altogether.

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium