Rust has inheritance and polymorphism.

Rust has trait inheritance, but not object inheritance. Servo uses code generation and macros to get around this. (I’m literally writing an operating system in Rust, I know what I’m talking about.)

Could you elaborate on how trait inheritance is different from object inheritance?

"Trait" inheritance is just interface inheritance, which is indistinguishable from composition+delegation. It doesn't have the pitfalls of actual implementation inheritance, which essentially involves an extra "trick" of dispatching on the actual type of your object even when calling base-class methods. It's not that Rust cannot do this - heck, people do it all the time in C. But it has to be done by writing things out explicitly, it's not automatic in any sense. And for good reason - letting base-class code access methods that have been redefined in a derived class can create all sorts of pitfalls when you're not very careful about what that implies.