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E. FLS Background¶
E:1 The FLS is a document describing aspects of the Rust language for Rust toolchain qualification purposes.
E:2 It was created by Ferrous Systems, in an original joint effort with AdaCore, as one of the prerequisites for qualifying Ferrocene, a Rust toolchain qualified for safety-critical environments. The FLS is compiled of existing Rust documentation, but presented with a rigorous structure in order to meet the requirements of qualification.
E:3 The FLS is not intended to be used as the normative specification of the Rust language (see the Rust Reference), nor is it meant to replace the decision-making processes of the Rust project. Any difference between the FLS and the behavior of the Rust compiler is considered an error on our part and the FLS will be updated accordingly.
E:4 The FLS text is licensed under either the MIT or
Apache-2.0 licenses, at your option. Individual files might have different
licensing. Licensing metadata is present in each file, and the full licenses
text is present in the LICENSES/ directory.
E.1. Acknowledging Ferrous Systems¶
E.1:1 The Rust Project would like to thank Ferrous Systems for donating the FLS (formerly the Ferrocene Language Specification) to the Rust Project for its continued maintenance and development.
E.1:2 As a brief history, the FLS is a description of the Rust programming language, developed by Ferrous Systems and AdaCore in July 2022 as part of Ferrocene, a Rust compiler and toolchain designed for safety-critical and regulated industries. The FLS provides a structured and detailed reference for Rust’s syntax, semantics, and behavior, serving as a foundation for verification, compliance, and standardization efforts. The FLS represented a major step toward describing Rust in a way that aligns with industry requirements, particularly in high-assurance domains. Until its transfer in April 2025, Ferrous Systems had been the sole steward of the FLS since July 2023.