ICE with macro_rules! inside macro_rules!

[comex]

#[feature(macro_rules)];

macro_rules! foo(
    () => (macro_rules! bar(
        () => (5)
    ))
)

fn main() {
    foo!();
}

results in:

task 'rustc' failed at 'not allowed to compare these idents: &ast::Ident{name: 76u, ctxt: 20u}, &ast::Ident{name: 2u, ctxt: 0u}.
                    Probably related to issue #6993', /usr/src/rust/src/libsyntax/ast.rs:50
error: internal compiler error: unexpected failure
This message reflects a bug in the Rust compiler. 
We would appreciate a bug report: https://github.com/mozilla/rust/wiki/HOWTO-submit-a-Rust-bug-report
note: the compiler hit an unexpected failure path. this is a bug
note: try running with RUST_LOG=rustc=1 to get further details and report the results to github.com/mozilla/rust/issues
task '<main>' failed at 'explicit failure', /usr/src/rust/src/librustc/lib.rs:396

This works if foo! is used at global scope.

Tested on 2c9e56f.

[klutzy]

Still an issue. (revision 6720977)
Similar case:

#[feature(macro_rules)];
fn main() {
    assert!({ macro_rules! bar( () => (5)) });
}

[jbclements]

Wow! Didn't see this. Thanks for bringing this to my attention.

[erickt]

visiting for triage. Still reproducible.

[lilyball]

Trivial reproduction:

pub fn main() {
    assert!({foo! bar})
}

Backtrace is a bit different between this and the macro_rules! nested inside macro_rules!, but both end up failing inside parse_stmt().