rust-analyzer is mostly the opposite of "finishing what we started" implementation-wise, but it fits in the overall "maturity of tooling" theme. The biggest thing that happened is that we proved that it is possible to expand macros and solve traits to provide correct instant completions for Rust, in principle ( ).

So far, this was mostly an independent of rustc experiment, but now I think we should push harder on making rustc work along the lines of rust-analyzer. I am proud of the first step in this direction: rust-analyzer and rustc now actually share the same lexer. Now we only need to split the rest of the compiler into libraries