Sorry, I'm not going to merge anything C++17 anytime soon. C++11 is okay, though. We need to be intentionally very conservative with support.

The attribute is not effective unless -std=c++17 is supplied. Actually there are many unused variables.

Sorry, I'm not going to merge anything C++17 anytime soon. C++11 is okay, though. We need to be intentionally very conservative with support.

Good call.

I think the fallback case should be to use nothing. (evaluate UNUSED(x) to `` --nothing--). #2376

Besides [[maybe_unused]] is only for C++17, the keyword is not for that™.
[[maybe_unused]] is mainly for generic code or macros, if constexpr, etc.

An unused variable shouldn't be named in the first place.
At most have a commented name f(double /*unused x*/) (Linters recommend that).
There is nothing wrong with not naming the unusued variable, there is no need to make acrobatics with unused attributes.

The original motivation is to replace UNUSED macro with [[maybe_unused]] attribute, so this does not fix all of the warning on unused parameters.

Now the unused parameters are commented out as far as clang-tidy does.