I don't believe your comment is fair or correct, and even very naive. Considering GCC's case, what makes a parser complex is not the language grammar itself, but all the requirements set onto the compiler to enable it to churn out intelligible warnings and error messages, which means supporting typical errors as extensions of the language grammar.
Furthermore, GCC's C++ parser support half a dozen different versions of C++ and all the error and warning messages that come with targetting a language standard but using a feature not supported by it. Rust has no such requirement, nor it will have any time soon.
Your comment strikes me as the old and faded tendency to throw baseless complains about tried and true technology by pointing out how green and untested tech is somehow better because it's yet to satisfy real-world requirements.