Matt Pocock 工程方法论 - codebase-design

codebase-design：mattpocock/skills 方法论: engineering/codebase-design，适用于工程实践、代码质量与开发流程优化。

Skill Documentation

Matt Pocock 工程方法论 - codebase-design

摘要

codebase-design：mattpocock/skills 方法论: engineering/codebase-design，适用于工程实践、代码质量与开发流程优化。

> 来源: mattpocock/skills (141k stars) — Total TypeScript 创始人 Matt Pocock

> 类目: 工程方法论

> 原文件: skills/engineering/codebase-design/SKILL.md

> 模型推荐: gpt-4.1 (代码工程)

这个 skill 是干嘛的

Matt Pocock (Total TypeScript, 141k stars) 沉淀下来的"日常代码工程动作"skill 模板。

每一个对应一个具体动作(代码评审 / TDD / 重构 / 文档对齐 / 任务交接),不是工具,是"该怎么干这件事"的工作流模板。

michael 强调"skill 要有相应的指导功能,指导用户使用",所以这里加了下面两节让 Agent 和用户对接。

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🤖 Agent 使用说明

1. 接到任务后先按这个 skill 的检查清单走一遍

2. 清单里如果出现"先做 X 才能做 Y"的红线 → 必须先完成 X

3. 跑完清单后开始动手(改代码 / 写文档 / 评审)

4. 完工前用 `verification-before-completion`(superpowers) 或 `verification` 类 step 自检

5. 任务量大时考虑用 `dispatching-parallel-agents`(superpowers) 或 `wayfinder`(mattpocock) 拆解

👤 用户需要做什么?

1. 告诉 Agent 你要做什么(一句话即可)

2. Agent 跑 skill 清单时不要打断 — 它可能在收集上下文

3. 如果 Agent 主动问你"代码评审要不要安排一个 reviewer"等决策点 → 直接回答

4. 完工后让 Agent 跑一遍自检再交回

5. 整个过程 Agent 自动化,不需要手工介入

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原 skill 内容(mattpocock/skills/engineering/codebase-design/SKILL.md)

---

name: codebase-design

description: Shared vocabulary for designing deep modules. Use when the user wants to design or improve a module's interface, find deepening opportunities, decide where a seam goes, make code more testable or AI-navigable, or when another skill needs the deep-module vocabulary.

---

Codebase Design

Design **deep modules**: a lot of behaviour behind a small interface, placed at a clean seam, testable through that interface. Use this language and these principles wherever code is being designed or restructured. The aim is leverage for callers, locality for maintainers, and testability for everyone.

Glossary

Use these terms exactly — don't substitute "component," "service," "API," or "boundary." Consistent language is the whole point.

**Module** — anything with an interface and an implementation. Deliberately scale-agnostic: a function, class, package, or tier-spanning slice. _Avoid_: unit, component, service.

**Interface** — everything a caller must know to use the module correctly: the type signature, but also invariants, ordering constraints, error modes, required configuration, and performance characteristics. _Avoid_: API, signature (too narrow — they refer only to the type-level surface).

**Implementation** — what's inside a module, its body of code. Distinct from **Adapter**: a thing can be a small adapter with a large implementation (a Postgres repo) or a large adapter with a small implementation (an in-memory fake). Reach for "adapter" when the seam is the topic; "implementation" otherwise.

**Depth** — leverage at the interface: the amount of behaviour a caller (or test) can exercise per unit of interface they have to learn. A module is **deep** when a large amount of behaviour sits behind a small interface, **shallow** when the interface is nearly as complex as the implementation.

**Seam** _(Michael Feathers)_ — a place where you can alter behaviour without editing in that place; the *location* at which a module's interface lives. Where to put the seam is its own design decision, distinct from what goes behind it. _Avoid_: boundary (overloaded with DDD's bounded context).

**Adapter** — a concrete thing that satisfies an interface at a seam. Describes *role* (what slot it fills), not substance (what's inside).

**Leverage** — what callers get from depth: more capability per unit of interface they learn. One implementation pays back across N call sites and M tests.

**Locality** — what maintainers get from depth: change, bugs, knowledge, and verification concentrate in one place rather than spreading across callers. Fix once, fixed everywhere.

Deep vs shallow

**Deep module** = small interface + lots of implementation:

┌─────────────────────┐
│   Small Interface   │  ← Few methods, simple params
├─────────────────────┤
│                     │
│  Deep Implementation│  ← Complex logic hidden
│                     │
└─────────────────────┘

**Shallow module** = large interface + little implementation (avoid):

┌─────────────────────────────────┐
│       Large Interface           │  ← Many methods, complex params
├─────────────────────────────────┤
│  Thin Implementation            │  ← Just passes through
└─────────────────────────────────┘

When designing an interface, ask:

• Can I reduce the number of methods?
• Can I simplify the parameters?
• Can I hide more complexity inside?

Principles

• **Depth is a property of the interface, not the implementation.** A deep module can be internally composed of small, mockable, swappable parts — they just aren't part of the interface. A module can have **internal seams** (private to its implementation, used by its own tests) as well as the **external seam** at its interface.
• **The deletion test.** Imagine deleting the module. If complexity vanishes, it was a pass-through. If complexity reappears across N callers, it was earning its keep.
• **The interface is the test surface.** Callers and tests cross the same seam. If you want to test *past* the interface, the module is probably the wrong shape.
• **One adapter means a hypothetical seam. Two adapters means a real one.** Don't introduce a seam unless something actually varies across it.

Designing for testability

Good interfaces make testing natural:

1. **Accept dependencies, don't create them.**

   // Testable
   function processOrder(order, paymentGateway) {}

   // Hard to test
   function processOrder(order) {
     const gateway = new StripeGateway();
   }

2. **Return results, don't produce side effects.**

   // Testable
   function calculateDiscount(cart): Discount {}

   // Hard to test
   function applyDiscount(cart): void {
     cart.total -= discount;
   }

3. **Small surface area.** Fewer methods = fewer tests needed. Fewer params = simpler test setup.

Relationships

• A **Module** has exactly one **Interface** (the surface it presents to callers and tests).
• **Depth** is a property of a **Module**, measured against its **Interface**.
• A **Seam** is where a **Module**'s **Interface** lives.
• An **Adapter** sits at a **Seam** and satisfies the **Interface**.
• **Depth** produces **Leverage** for callers and **Locality** for maintainers.

Rejected framings

• **Depth as ratio of implementation-lines to interface-lines** (Ousterhout): rewards padding the implementation. We use depth-as-leverage instead.
• **"Interface" as the TypeScript `interface` keyword or a class's public methods**: too narrow — interface here includes every fact a caller must know.
• **"Boundary"**: overloaded with DDD's bounded context. Say **seam** or **interface**.

Going deeper

• **Deepening a cluster given its dependencies** — see [DEEPENING.md](DEEPENING.md): dependency categories, seam discipline, and replace-don't-layer testing.
• **Exploring alternative interfaces** — see [DESIGN-IT-TWICE.md](DESIGN-IT-TWICE.md): spin up parallel sub-agents to design the interface several radically different ways, then compare on depth, locality, and seam placement.

常见问题（FAQ）

使用「codebase-desig」这个 skill 能解决什么问题?

本 skill 专注于codebase-desig，mattpocock/skills 方法论: engineering/codebase-design。它将相关流程标准化，帮助用户更快拿到可靠结果，减少重复手工操作。

什么情况下适合使用「codebase-desig」?

当你需要在codebase-design相关工作中获得稳定、可复用的产出时最适合——无论是单次任务还是纳入日常工作流，都能直接调用。

使用「codebase-desig」前需要准备什么?

需要一个具体的项目或任务上下文，最好带有代码仓库或需求文档。