I was looking more into this challenge and I broke the compiler.
thread 'rustc' panicked at 'internal error: entered unreachable code', src/libsyntax/parse/parser.rs:648:22
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports
In the playground: Rust Playground