Nested macro_rules with $$ fails to expand

[TimNN]

rust-analyzer version: Current HEAD (7be85a5)

rustc version: rustc 1.61.0 (fe5b13d68 2022-05-18) and rustc 1.63.0-nightly (b2eed72a6 2022-05-22)

Rust Analyzer fails to expand the following code (playground):

#![feature(macro_metavar_expr)]

macro_rules! outer {
    ($outer_name:ident) => {
        macro_rules! inner {
            ($$inner_name:ident) => {
                impl $outer_name {
                    fn $$inner_name() {}
                }
            };
        }
    };
}

struct Hello;

outer!(Hello);
inner!(world);

Replacing the $$ with singular $s fixes the issues (though note that there are macros where the $$ is necessary). $$ is close to being stabilized: rust-lang/rust#95860

I've added a test case in TimNN@856d689, which produces the following results:

$ cargo test -p hir-def nested_double_dollar
    Finished test [unoptimized] target(s) in 0.09s
     Running unittests src/lib.rs (target/debug/deps/hir_def-96fd50c42b79c470)

running 1 test
test macro_expansion_tests::mbe::nested_double_dollar ... FAILED

failures:

---- macro_expansion_tests::mbe::nested_double_dollar stdout ----
thread 'macro_expansion_tests::mbe::nested_double_dollar' panicked at 'called `Result::unwrap()` on an `Err` value: UnresolvedMacro { path: ModPath { kind: Plain, segments: [Name(Text("inner"))] } }', crates/hir-def/src/macro_expansion_tests/mbe.rs:1550:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    macro_expansion_tests::mbe::nested_double_dollar

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 331 filtered out; finished in 0.00s

Again, replacing the $$ with $ makes the test pass.

[Veykril]

We don't support macro_metvar_expr yet, #11952

[TimNN]

Ah, thanks for linking the issue! (Didn’t find anything when I was searching for something like “nested macros”, IIRC).