The closest I am aware of is clippy (`cargo clippy` in a standard Rust project will run it with default configurations).

Clippy is essentially a linter; and one of its checks catches cases where different enum variants have a significantly different size; with a suggestion to Box the larger variant.

Since this is just a linter, it doesn't actually have any knowledge of how frequently each variant is actually used. It also doesn't address the situation in the article at all.

Specifically this lint: https://rust-lang.github.io/rust-clippy/master/index.html#la...