Design Principles

Strict Superset

Every valid Rust program is a valid Rs program. This is a hard constraint, not a goal. Compatibility is verified by compiling the top 1000 no_std crates from crates.io with rsc on every CI run.

Valid Rust ⊂ Valid Rs

Rs adds constructs. It never changes the meaning of existing Rust constructs.

Edition-Gated Restrictions

Rs introduces an rs edition. When active, certain Rust features are restricted or enhanced:

# Cargo.toml
[package]
edition = "rs"

In rs edition:

• Heap allocation primitives (Box, Vec, String) produce compile errors unless explicitly opted-in via #[allow(rs::heap)]
• Non-deterministic collections (HashMap, HashSet) produce compile errors unless opted-in via #[allow(rs::nondeterministic)]
• dyn Trait produces a compile error unless opted-in via #[allow(rs::dyn_dispatch)]
• panic!() with unwinding produces a compile error; only abort mode is permitted
• Floating point types (f32, f64) are forbidden inside #[deterministic] functions
• All async fn must have a deadline

In standard Rust editions (2021, 2024), none of these restrictions apply. Rs extensions are still available but optional.

Zero New Keywords

Rs introduces zero new keywords. All extensions use:

• Attributes (#[register], #[deterministic], #[step], #[bounded_async])
• Derive macros (#[derive(Addressed)])
• Declarative macros (cell! { })

The async(duration) shorthand syntax is available inside cell! blocks (parsed by the macro). Outside cells, #[bounded_async(duration)] is standard Rust attribute syntax.

This ensures no conflict with any existing or future Rust syntax.