typed-builder

typed-builder is a Rust derive macro that generates builder types with compile-time required field checking. It automates the typestate builder pattern from type-driven-development: .build() only exists as a method when all required fields have been set, producing a compile error if any are missing.

The bon crate extends this concept to function arguments, providing the same compile-time guarantees for function call sites. Both crates add proc-macro compile overhead but eliminate the manual boilerplate of typestate builders (one type per field-state combination). See typestate-pattern for the underlying mechanism.