Usage of inline const for static assertions

[hinto-janai]

What

Rust 1.79 brought inline const expressions.

These can be used to conditionally make static assertions (among other things).

Why

Turns runtime panics into compile time errors.

Where/How

Certain runtime panics can be replaced with these new inline const expressions, e.g.:

cuprate/storage/database/src/env.rs

Lines 126 to 128 in 929d19c

	fn resize_map(&self, resize_algorithm: Option<ResizeAlgorithm>) -> NonZeroUsize {
	unreachable!()
	}

Can be turned into:

fn resize_map(&self, resize_algorithm: Option<ResizeAlgorithm>) -> NonZeroUsize {
    const {
        assert!(
            Self::MANUAL_RESIZE,
            "This function should not be called as this database backend automatically resizes.",
        )
    }
}

This will make calling resize() from database backends that shouldn't be calling resize_map() in the first place to fail at compile time instead of at runtime.

The const expression will only be evaluated if resize() is called, e.g.:

fn main() {}

fn f<const B: bool>() {
    const {
        assert!(B);
    }
}

This program will only fail if f::<false>() is called. It is commented out (not called) so it compiles fine.

[antonio-hickey]

Hello, anyone working on this?

I'll take it on if not

[SyntheticBird45]

Hi @antonio-hickey, No one is working on it. You are welcome to take it.