Macro expansion: concat!() macro with single quotes escapes special characters while rustc does not

[azerupi]

rust-analyzer version: rust-analyzer version: 0.3.1148-standalone (2b472f6 2022-07-31)

rustc version: rustc 1.60.0 (7737e0b5c 2022-04-04) and rustc 1.62.0-nightly (90ca44752 2022-04-11)

We discovered an inconsistency between rust-analyzer's expansion of concat! and rustc when using single quotes. So '\n' gets expanded to "\'\\n\'" instead of "\n". And '\0' gets expanded to \'\\0\' instead of \u{0}.

Examples to reproduce

Source code

fn main() {
    let s = concat!("Hello, World!", '\n');
}

rust-analyzer

fn main() {
    let s = "Hello, World!\'\\n\'";
}

cargo-expand

fn main() {
    let s = "Hello, World!\n";
}

---

Source code

fn main() {
    let s = concat!("Hello, World!", '\0');
}

rust-analyzer

fn main() {
    let s = "Hello, World!\'\\0\'";
}

cargo-expand

fn main() {
    let s = "Hello, World!\u{0}";
}