rust

name	rust
description	Use for ALL Rust questions including errors, design, patterns, and coding. Triggers on: Rust, cargo, rustc, Cargo.toml, compiler errors (E0382, E0597, E0277, E0308, E0499, E0502, E0506, E0507), ownership, borrowing, lifetimes, traits, generics, async/await, tokio, concurrency, Result, Option, Error, thiserror, anyhow, Box, Rc, Arc, RefCell, performance, profiling, clippy, code review, anti-pattern, idiomatic Rust, code style, best practice
globs	["**/Cargo.toml","**/*.rs"]

Rust

Project Defaults

When creating new Rust projects or Cargo.toml files:

[package]
edition = "2024"
rust-version = "1.85"

[lints.rust]
unsafe_code = "warn"

[lints.clippy]
all = "warn"
pedantic = "warn"

Error Code Routing

When the user has a compiler error, read the relevant reference file for detailed guidance.

Error Code	Topic	Reference
E0382	Use of moved value	ref/ownership.md
E0597	Lifetime too short	ref/ownership.md
E0506	Cannot assign to borrowed	ref/ownership.md
E0507	Cannot move out of borrowed	ref/ownership.md
E0515	Return local reference	ref/ownership.md
E0716	Temporary value dropped	ref/ownership.md
E0106	Missing lifetime specifier	ref/ownership.md
E0596	Cannot borrow as mutable	ref/ownership.md
E0499	Multiple mutable borrows	ref/ownership.md
E0502	Borrow conflict	ref/ownership.md
E0277	Trait bound not satisfied	ref/types-and-traits.md (or ref/concurrency.md if Send/Sync)
E0308	Type mismatch	ref/types-and-traits.md
E0599	No method found	ref/types-and-traits.md
E0038	Trait not object-safe	ref/types-and-traits.md
E0433	Cannot find crate/module	ref/ecosystem.md
E0603	Private item access	ref/ecosystem.md

Keyword Routing

When the user asks about a topic, read the relevant reference file for detailed guidance.

Topic Keywords	Reference
ownership, borrow, lifetime, move, clone, Copy, 'a, 'static	ref/ownership.md
Box, Rc, Arc, Weak, RefCell, Cell, smart pointer, heap	ref/ownership.md
mut, interior mutability, borrow conflict	ref/ownership.md
generic, trait, impl, dyn, monomorphization, dispatch	ref/types-and-traits.md
type state, PhantomData, newtype, builder, sealed trait	ref/types-and-traits.md
Result, Option, Error, ?, unwrap, expect, panic, anyhow, thiserror	ref/error-handling.md
domain error, retry, fallback, circuit breaker, recovery	ref/error-handling.md
async, await, Send, Sync, thread, channel, Mutex, tokio, deadlock	ref/concurrency.md
domain model, DDD, entity, value object, aggregate, repository	ref/design-patterns.md
RAII, Drop, lifecycle, connection pool, OnceLock, LazyLock	ref/design-patterns.md
performance, optimization, benchmark, profiling, flamegraph	ref/performance.md
crate, cargo, dependency, feature flag, workspace, interop	ref/ecosystem.md
naming, formatting, clippy, code style, best practice	ref/ecosystem.md
anti-pattern, code smell, common mistake, idiomatic	ref/anti-patterns.md
mental model, learning Rust, coming from Java/Python/C++	ref/anti-patterns.md

For code examples, read the relevant file from examples/.

Domain Detection

When domain keywords are present alongside a Rust question, also load the domain-specific skill:

Domain Keywords	Also Load
Web, HTTP, axum, CLI, clap, kubernetes, gRPC, embedded, no_std, fintech, trading, IoT, MQTT, ML, tensor	rust-domain skill

Functional Routing

Pattern	Route To
unsafe, FFI, extern, raw pointer, transmute	rust-unsafe skill
project structure, list structs/traits, call graph, refactor	rust-lsp skill

Quick Decision Trees

Ownership: Who Should Own This Data?

Is the data shared?
├─ No (single owner)
│  ├─ Needs heap? → Box<T>
│  └─ Stack is fine → owned value (default)
├─ Yes, immutable sharing
│  ├─ Single-thread → Rc<T>
│  └─ Multi-thread → Arc<T>
└─ Yes, mutable sharing
   ├─ Single-thread → Rc<RefCell<T>>
   └─ Multi-thread → Arc<Mutex<T>> or Arc<RwLock<T>>

Concurrency: What Model?

What type of work?
├─ CPU-bound → std::thread or rayon
├─ I/O-bound → async/await (tokio)
└─ Mixed → spawn_blocking for CPU parts

Need to share data?
├─ No → message passing (channels)
├─ Immutable → Arc<T>
└─ Mutable → Arc<Mutex<T>> or channels

Error Handling: What Strategy?

Is failure expected?
├─ Yes
│  ├─ Absence only → Option<T>
│  └─ Real errors → Result<T, E>
│     ├─ Library code → thiserror (typed errors)
│     └─ Application code → anyhow (ergonomic)
└─ No (bug/invariant violation) → panic!, assert!

Static vs Dynamic Dispatch

Is the type known at compile time?
├─ Yes → generics / impl Trait (zero-cost)
└─ No → dyn Trait (vtable)
   ├─ Heterogeneous collection → Vec<Box<dyn Trait>>
   └─ Plugin architecture → Box<dyn Trait>

Style Quick Reference

Rule	Guideline
No get_ prefix	fn name() not fn get_name()
Conversion naming	as_ (cheap &), to_ (expensive), into_ (ownership)
Iterator convention	iter() / iter_mut() / into_iter()
Prefer ? over unwrap	Use expect() only when value guaranteed
Use newtypes	struct Email(String) for domain semantics
Meaningful lifetimes	'src, 'ctx not just 'a

Deprecated Patterns

Deprecated	Better	Since
lazy_static!	std::sync::OnceLock	1.70
once_cell::Lazy	std::sync::LazyLock	1.80
failure/error-chain	thiserror/anyhow	-
try!()	? operator	2018
extern crate	Just use	2018
#[macro_use]	Explicit import	2018

Preferences

Standard	Preferred	Why
std::sync::mpsc	crossbeam::channel	MPMC support, select! macro