Adversarial Rust

An adversarial, architecture-level review-and-refactor pass for Rust. Where a greenfield idiom skill answers "which tool should I reach for now?", this skill takes code that already exists and imported the wrong mental model — objects and interfaces from Java/C#, shared-everything graphs from garbage-collected languages, exceptions, C-style loops and sentinels, detached-promise concurrency — names the paradigm it betrays, and prescribes the refactor that collapses it back to idiomatic Rust.

Every rule is grounded in a single production codebase: the codex-rs workspace (github.com/openai/codex, codex-rs/ at commit f1affbac5e, ~125 crates / ~2,500 Rust files). The Correct side of each rule is what that codebase actually does, the enforcement evidence is its workspace lint config (unwrap_used, redundant_clone, needless_collect, await_holding_lock and ~30 more denied), and the carve-outs are the real exceptions it keeps — so "when NOT to apply" is never hypothetical. There is no rule for things a capable model already gets right.

When to Apply

• Reviewing or refactoring existing Rust for architecture, not just style — "make this actually idiomatic", "why does this feel like Java in Rust"
• Flattening ported ceremony — dependency-injection traits with one implementation, Deref-simulated inheritance, stateless *Manager/*Service structs, getter/setter boilerplate, a builder for every struct
• Untangling fought ownership — .clone() sprinkled until it compiles, Rc<RefCell<T>> object graphs, self-referential struct attempts
• Fixing anemic data — boolean/string state machines, parallel Option fields, raw primitives carrying domain meaning, god-structs of Options escaping the serde boundary
• Removing exception-style flow — unwrap on expected failures, sentinel returns, catch_unwind as try/catch, anyhow on library API surfaces
• Collapsing habitual indirection — Box<dyn Trait> for closed sets, boxed callback parameters, index loops and per-step collect() chains
• Repairing imported concurrency habits — blocking calls inside async fn, guards held across .await, async task fan-out for CPU-bound work, fire-and-forget tokio::spawn

For greenfield "which pattern, which crate, which discipline" decisions while writing new Rust — async cancellation, error enum design, sandboxing, testing architecture — use openai-codex-rust-patterns instead; this skill is its diagnostic, layer-flattening counterpart drawn from the same codebase.

Rule Categories

Quick Reference

1. Enterprise Ceremony & Fake OO

• arch-drop-di-trait-single-impl — delete the DI trait with one implementation; codex-rs ships ModelClient and Session concrete
• arch-no-deref-inheritance — all 18 codex-rs Deref impls are newtypes or smart pointers; zero simulate a hierarchy
• arch-free-functions-over-manager-struct — stateless capability = module functions (git-utils, apply-patch); a *Manager earns its name by owning state
• arch-public-fields-over-getter-ceremony — Config and every protocol type are all-pub; accessors exist only where an invariant lives
• arch-default-literal-over-builder — 1,787 struct literals with ..Default::default() vs 16 builders; a builder needs staged construction to earn itself

2. Ownership Fought, Not Used

• own-restructure-over-clone — surviving clones are designed (Copy IDs, Arc bumps, lock snapshots); a compile-fixing clone forks data
• own-no-rc-refcell-object-graph — zero Rc<RefCell> in ~2,500 files; narrow Mutex fields, channels, or ID maps instead
• own-id-map-over-self-referential — graphs live in HashMap<ThreadId, Arc<CodexThread>>; cross-references are IDs, never references

3. Anemic & Stringly Data

• type-enum-over-bool-string-state — variants own their fields (SandboxPolicy); its external-sandbox variant types even yes/no as NetworkAccess, not bool
• type-result-over-parallel-options — one Option per shape is CodexAuth in denial; found/missing/failed is Result<Option<T>, E>
• type-newtype-parse-dont-validate — parse once into ThreadId/AgentPath; model names stay String because no invariant exists
• type-split-option-god-struct — ConfigToml (91 of 97 fields are Options) is fine on the wire; resolve it once into rich Config

4. Exception-Style Control Flow

• flow-result-over-unwrap-expected — unwrap_used/expect_used denied workspace-wide; escapes carry #[expect] + a written invariant
• flow-option-over-sentinel-values — lookups return Option; -1 exists only at the OS exit-code boundary
• flow-no-catch-unwind-try-catch — every codex-rs production use supervises a foreign fault domain; none catch expected failures
• flow-thiserror-library-anyhow-application — CodexErr/ApiError/TransportError per layer; anyhow at main()

5. Dynamic Dispatch by Habit

• dyn-enum-over-box-dyn-closed-set — Op/EventMsg/TurnItem are enums; dyn is the tool registry others extend at runtime
• dyn-generics-over-boxed-callbacks — generic F: Fn at the API, box only for storage, channels instead of listener registration

6. Imperative Iteration

• iter-combinator-over-index-loop — 13 manual_* lints denied; for survives for awaits, side effects, index-as-data, FFI
• iter-stay-lazy-single-collect — one lazy chain; collect::<Result<Vec<_>, _>>() is the fallible-pipeline idiom (49 production uses)

7. Concurrency From Another Runtime

• conc-spawn-blocking-over-blocking-async — ~50 spawn_blocking sites: git, file locks, zstd, OAuth servers
• conc-narrow-locks-before-await — even tokio guards may not cross .await; snapshot out or #[expect] with an atomicity reason
• conc-blocking-pool-over-async-cpu-fanout — no rayon; CPU fan-out on bounded OS threads behind one spawn_blocking
• conc-own-spawned-task-handles — AbortOnDropHandle + child CancellationToken; interrupt is cancel → grace window → abort

How to Use

Read a reference file when its smell shows up in the code under review. Each rule names the alien pattern, explains why Rust rejects it, and shows the refactor with real codex-rs names and a permalink into the codebase at the pinned commit. Prefer the deepest refactor the change budget allows — redesigning ownership beats sprinkling clone; deleting the DI trait beats mocking through it. Every example compiles on Rust 1.86 (2021 edition).

• Section definitions — category structure and ordering
• Rule template — for adding new rules
• AGENTS.md — auto-built table of contents across all rules

Related Skills

• openai-codex-rust-patterns — the greenfield counterpart distilled from the same codex-rs workspace: which pattern to reach for while writing production Rust (async cancellation, error enum design, sandboxing, testing, workspace layout). Use it for authoring decisions; use this skill for adversarial review and ceremony-flattening refactors. Several rules here hand off to it once the flatten is done (flow-thiserror-library-anyhow-application → its errors- rules, flow-result-over-unwrap-expected → defensive-deny-unwrap-workspace-wide, arch-drop-di-trait-single-impl → its testing seams).

Reference Files