Ecosystem Integration
Layer 2: Design Choices
Core Question
What's the right crate for this job, and how should it integrate?
Before adding dependencies:
-
Is there a standard solution?
-
What's the maintenance status?
-
What's the API stability?
Integration Decision → Implementation
Need Choice Crates
Serialization Derive-based serde, serde_json
Async runtime tokio or async-std tokio (most popular)
HTTP client Ergonomic reqwest
HTTP server Modern axum, actix-web
Database SQL or ORM sqlx, diesel
CLI parsing Derive-based clap
Error handling App vs lib anyhow, thiserror
Logging Facade tracing, log
Thinking Prompt
Before adding a dependency:
Is it well-maintained?
-
Recent commits?
-
Active issue response?
-
Breaking changes frequency?
What's the scope?
-
Do you need the full crate or just a feature?
-
Can feature flags reduce bloat?
How does it integrate?
-
Trait-based or concrete types?
-
Sync or async?
-
What bounds does it require?
Trace Up ↑
To domain constraints (Layer 3):
"Which HTTP framework should I use?" ↑ Ask: What are the performance requirements? ↑ Check: domain-web (latency, throughput needs) ↑ Check: Team expertise (familiarity with framework)
Question Trace To Ask
Framework choice domain-* What constraints matter?
Library vs build domain-* What's the deployment model?
API design domain-* Who are the consumers?
Trace Down ↓
To implementation (Layer 1):
"Integrate external crate" ↓ m04-zero-cost: Trait bounds and generics ↓ m06-error-handling: Error type compatibility
"FFI integration" ↓ unsafe-checker: Safety requirements ↓ m12-lifecycle: Resource cleanup
Quick Reference
Language Interop
Integration Crate/Tool Use Case
C/C++ → Rust bindgen
Auto-generate bindings
Rust → C cbindgen
Export C headers
Python ↔ Rust pyo3
Python extensions
Node.js ↔ Rust napi-rs
Node addons
WebAssembly wasm-bindgen
Browser/WASI
Cargo Features
Feature Purpose
[features]
Optional functionality
default = [...]
Default features
feature = "serde"
Conditional deps
[workspace]
Multi-crate projects
Error Code Reference
Error Cause Fix
E0433 Can't find crate Add to Cargo.toml
E0603 Private item Check crate docs
Feature not enabled Optional feature Enable in features
Version conflict Incompatible deps cargo update or pin
Duplicate types Different crate versions Unify in workspace
Crate Selection Criteria
Criterion Good Sign Warning Sign
Maintenance Recent commits Years inactive
Community Active issues/PRs No response
Documentation Examples, API docs Minimal docs
Stability Semantic versioning Frequent breaking
Dependencies Minimal, well-known Heavy, obscure
Anti-Patterns
Anti-Pattern Why Bad Better
extern crate
Outdated (2018+) Just use
#[macro_use]
Global pollution Explicit import
Wildcard deps *
Unpredictable Specific versions
Too many deps Supply chain risk Evaluate necessity
Vendoring everything Maintenance burden Trust crates.io
Related Skills
When See
Error type design m06-error-handling
Trait integration m04-zero-cost
FFI safety unsafe-checker
Resource management m12-lifecycle