An analysis of semver compliance in Rust finds accidental semver violations are common even in the most popular crates. Human error is not the cause, and better tooling is the way forward.
To do it 100% probably isn’t possible, something something halting problem. However, you’d catch a lot of basic mistakes with proper typing. In your example, the first function should be typed like this: fn third_planet_from_sun() -> Planet, where Planet is an enum. De/serializing it still has the same problem of interpreting an arbitrary string, but at least for deserializing it, you can be loose in what you allow and just lowercase it before matching it to the enum.
To do it 100% probably isn’t possible, something something halting problem. However, you’d catch a lot of basic mistakes with proper typing. In your example, the first function should be typed like this:
fn third_planet_from_sun() -> Planet, wherePlanetis an enum. De/serializing it still has the same problem of interpreting an arbitrary string, but at least for deserializing it, you can be loose in what you allow and just lowercase it before matching it to the enum.