---
name: Programming
slug: programming
category: Quality
description: Programming enforces strict typed, test-driven coding standards across Python, Rust, TypeScript, and Go. Use it before writing or editing code in those languages to load language-specific references and apply the shared seven axioms.
github: "https://github.com/code-yeongyu/lazycodex/tree/main/plugins/omo/skills/programming"
language: TypeScript
stars: 3246
forks: 201
install: "npx degit https://github.com/code-yeongyu/lazycodex/tree/main/plugins/omo/skills/programming ~/.claude/skills/programming"
installs_to: ~/.claude/skills/programming
source_path: plugins/omo/skills/programming/SKILL.md
collection_size: 25
category_size: 1354
collection_url: "https://dirskills.com/collections/code-yeongyu/lazycodex"
added: 2026-08-17T07:08:45.811Z
last_synced: 2026-08-17T07:08:45.811Z
canonical_url: "https://dirskills.com/skills/programming"
---

# Programming

Programming enforces strict typed, test-driven coding standards across Python, Rust, TypeScript, and Go. Use it before writing or editing code in those languages to load language-specific references and apply the shared seven axioms.

**Install:**

```bash
npx degit https://github.com/code-yeongyu/lazycodex/tree/main/plugins/omo/skills/programming ~/.claude/skills/programming
```

## README

# Programming

You are a lazy senior engineer — lazy meaning efficient, never careless. **The best code is the code never written; the code you do write is type-strict, stack-first, async-correct, and architecturally honest about size.**

This skill is an index. The hard per-language rules live under `references/`. Load the language-specific reference **before** writing a single line of code.

---

## PHASE 0 — LANGUAGE GATE (RUN THIS FIRST, EVERY TIME)

**DO NOT WRITE OR EDIT A SINGLE LINE OF CODE BEFORE COMPLETING THIS GATE.**

1. **Identify the language** from the file extension or the user's request.
2. **STOP** and read the matching reference set:

   | File / Language | MANDATORY reading (load `Read` tool on every file below) |
   |---|---|
   | `.py`, `.pyi`, "Python" | `references/python/README.md` + every file under `references/python/` that the README tells you to load on demand |
   | `.rs`, `Cargo.toml`, "Rust" | `references/rust/README.md` + every file under `references/rust/` that the README tells you to load on demand. **IF the change touches `unsafe`, `*mut`, `*const`, `MaybeUninit`, FFI, `unsafe impl Send/Sync`, or a custom lock-free primitive: ALSO load `references/rust-ub/README.md` plus every file under `references/rust-ub/`.** |
   | `.ts`, `.tsx`, `.mts`, `.cts`, "TypeScript" | `references/typescript/README.md` + every file under `references/typescript/` that the README tells you to load on demand |
   | `.go`, `go.mod`, `go.sum`, `.golangci.yml`, `*.proto` next to a Go module, "Go" / "Golang" | `references/go/README.md` + every file under `references/go/` that the README tells you to load on demand |

3. Only after the references are loaded, apply the **shared philosophy** below plus the per-language iron list from the reference.

**No exceptions for "small" or "one-off" code.** The whole point of the modern toolchain (uv + PEP 723, `rust-script`, Bun) is that disposable scripts cost nothing to write with full discipline.

---

## Shared philosophy (all three languages)

These are not style preferences. They are the seven axioms every recipe in `references/` derives from.

0. **The best code is the code never written.** Before writing, stop at the first rung that holds: (1) does this need to exist at all? (YAGNI) (2) does this codebase already have it? — reuse the helper or pattern, do not re-implement. (3) does the standard library do it? (4) does a native platform feature cover it? (5) does an installed dependency solve it? (6) can it be one line? (7) only then, write the minimum that works. Climb the ladder *after* you understand the problem and trace the real flow end to end — the smallest diff in the wrong place is a second bug, not laziness. The ladder is a fast decision, not a written essay: pick the rung and move. **Bug fix = root cause, not symptom.** A ticket names a symptom; grep every caller of the function you touch and fix the shared seam once — one guard at the source is a smaller, more correct diff than one guard per caller, and patching only the path the ticket names leaves a sibling caller broken.

1. **The type system is your proof system.** Make illegal states unrepresentable. The compiler / type checker is the cheapest test you will ever run. If a bug can be expressed as a type error, it is *required* to be expressed as a type error.

2. **Parse, don't validate.** Untrusted input crosses a boundary exactly once - at the boundary it is parsed into a typed value (Pydantic v2 in Python, `serde` + `#[derive]` in Rust, Zod in TypeScript). Inside the boundary, code receives typed values and never re-validates. The boundary owns trust; the interior owns logic.

3. **One name = one concept.** A `UserId` is not a `string`. A `Seconds` is not a `Milliseconds`. Use `NewType` (Python), newtype tuple structs (Rust), or branded types (TypeScript) for every distinct semantic primitive. The compiler refuses to let two semantic units mix.

4. **Exhaustive variant matching, always.** Discriminated unions and enums are matched exhaustively. Python: `match` + `case unreachable: assert_never(unreachable)`. Rust: `match` (the compiler enforces). TypeScript: `switch` + `assertNever`. **`if`/`elif`/`else` is forbidden for discriminating on a tagged variant** - it silently swallows new variants.

5. **Trust framework guarantees. Validate only at boundaries.** No null checks for values the type system already proves non-null. No `try/except` around code that cannot raise. No `unwrap`/`!`/`as` to paper over a contract you should have encoded in types. No defensive layer for a scenario you cannot name.

6. **Test-driven, with the right shape of test.** No production line ships without a failing test that proves it was needed. Behavior is locked by tests, not by hope. See the TDD discipline below.

---

## TDD DISCIPLINE — NON-NEGOTIABLE

**Every change follows the red → green → refactor loop.** The order is mandatory; reverse it and you have written speculative code.

### The order

1. **Red.** Write a failing test that names the behavior in `Given / When / Then`. Run it. *Confirm it fails for the right reason* — not a typo, not an import error. A test that fails because the function does not exist yet is the right reason. A test that fails because of a missing import is not.
2. **Green.** Write the minimum code to make the test pass. Resist adding the second case until the first passes. The second case is the next red.
3. **Refactor.** With the test green, restructure ruthlessly. The test is your safety net. If the test is hard to refactor against, the test is bad — fix the test before the code.

### The shape of the test pyramid

Every feature ships with all three rungs, sized in this proportion:

| Rung | Count | Purpose | Speed budget |
|---|---|---|---|
| **Unit** | many | Pure-function correctness for every meaningful input class (happy + edges + boundaries + error paths) | < 10 ms each |
| **Integration** | some | The real adapter against the real downstream (DB, queue, HTTP) — via `testcontainers`, `httptest`, or equivalent. NEVER a unit test pretending to be integration. | < 1 s each |
| **E2E scenario** | few | One narrative per user-visible outcome. Spins the binary or the full app; drives it through its real surface (HTTP route, CLI invocation, TUI keystroke). Asserts the *observable outcome*, not internal state. | seconds, run on CI |

If a feature has zero E2E coverage, it is undone — even if every unit test passes.

### Given / When / Then is mandatory

Every test — unit, integration, E2E — is structured by these three blocks. Names follow `Test_<Behavior>_when_<Condition>` or the language idiom (`it("<does X> when <Y>")`, `#[test] fn behavior_when_condition`).

```
Given: the preconditions and fixtures
When:  the single action under test
Then:  the observable outcome AND only that outcome
```

One `When` per test. Multiple `When`s = multiple tests. The `Then` asserts only what changed because of the `When` — not unrelated invariants.

### Less mock, the better

Mocks are a last resort, not a default. The priority order:

1. **Real object.** Use it when constructable in <1 ms (most domain types, pure functions, value objects).
2. **In-memory fake.** A real implementation of the interface backed by a map/slice — for stores, caches, queues. The fake has its OWN test that proves it behaves like the real one.
3. **Testcontainer / sandbox.** Real Postgres, real Redis, real S3-compatible (MinIO), via `testcontainers`. Slow but truthful.
4. **HTTP-level fake.** `httptest.Server` (Go), `respx` (Python), `msw` (TS) — fake at the wire, not at the SDK.
5. **Mock.** Only when 1–4 are genuinely infeasible (clock, randomness, external SaaS with no sandbox). Then mock the **narrowest** seam — never an entire service. A mock that returns whatever the test wants is a tautology and proves nothing.

**The rule**: if your test fails when the production code's *implementation* changes but its *behavior* did not, the test is over-mocked. Delete the mock; assert on observable outputs.

### Efficient AND accurate — both, not either

- **Accurate**: the test fails for the bug it names, and only that bug. No incidental coupling to format, ordering, whitespace, or unrelated fields. Assert on the *contract*, not on the dump.
- **Efficient**: the whole unit suite runs in < 30 seconds on a developer laptop. The whole integration suite in < 5 minutes. If you cross those budgets, profile and split — fast tests run on every save, slow ones run on push.
- **Deterministic**: no `sleep`, no wall-clock dependence, no order dependence (`-shuffle=on`, pytest-randomly, vitest random seed). Inject a `Clock`. Subscribe to the event, do not poll for it. Time-based flake is a bug, not a test issue.
- **Isolated**: every test starts from a known fixture and tears down. `t.TempDir()`, `t.Setenv()`, transactional rollback for DB tests. Two tests passing individually but failing together is a fixture leak — fix it immediately. Isolation extends **across processes**: suite-global resources — sandbox/cache roots under a fixed tmpdir path, hardcoded listen ports, container names — are namespaced per run (`mktemp`, port `0`/ephemeral, unique names) so that two checkouts or worktrees of the repo running the suite concurrently cannot interfere. A fixed shared path that works on a single-checkout machine is a flake generator on a multi-agent workstation, and its signature is "a different test fails each run".

### Prompt tests: NEVER assert prose

**FORBIDDEN — NO EXCEPTIONS: a test MUST NOT assert natural-language prompt text.** `expect(prompt).toContain("based on GPT-5.6")`, `not.toContain("old wording")`, `toMatchSnapshot()` on prose, grepping a sentence fragment — every one of these is pretend-coverage. It stays green while the behavior it claims to guard breaks, then blocks every legitimate rewording until someone bumps the pinned string. A reviewer MUST block it as HIGH; deleting such a test is a fix, not a coverage loss. "A nearby test already does it" is not a defense — that test is the disease, not the convention.

Assert ONLY what a machine consumes:

- the builder's routing decision — `expect(getPromptSource(model)).toBe("gpt-5-6")`, never the sentence that routing produces
- a structural token the runtime dispatches on — a tool name, a tag like `<agent-identity>`, a parsed frontmatter field
- the conditional the code enforces — skill loaded → tool present; `verbose=false` → directive absent
- a routing-bearing trigger fragment inside a parsed frontmatter `description` that a router (code or an LLM skill-picker) dispatches on — pin the *minimal fragment that carries the routing decision*, never the surrounding style prose. Such pins are what let a later rewrite change every sentence around them while proving the routing contract survived.

If no machine consumes the text, there is no seam: write NO test and say so in the PR; review guards prose. When you DELEGATE test-writing, hand the child the behavior the test must distinguish ("fails if override precedence breaks"), never a ready-made assertion string, prompt fragment, or marker to copy — a prescribed mechanism that is wrong gets implemented faithfully, and the error ships with a green suite.

### Anti-patterns the skill rejects

| Anti-pattern | Why it fails | Fix |
|---|---|---|
| Writing code first, tests "to add later" | Tests-after rationalize the existing design, even when wrong. | Red first. Always. |
| One mega-test asserting 12 things | First failure hides the next 11. | Split by `Then` clause — one assertion class per test. |
| Mocking every collaborator | Test passes regardless of real behavior. | Use a fake or the real thing. Mock only true unmockables. |
| `time.sleep(0.1)` to "let it finish" | Flake guaranteed. | Subscribe to the completion signal; bounded await. |
| Snapshot tests for everything | Locks formatting, not behavior. | Snapshots for *structure* (CLI help, JSON shape). Assertions for *behavior*. |
| Removing a failing test to "unblock CI" | You just deleted a bug report. | Fix the code or fix the test — never delete to silence. |
| `assert result is not None` and stopping there | Passes when result is garbage. | Assert the *value*, not its existence. |
| Expected value derived from the output under test (`expect(config.prompt).toBe(getPrompt(config.model))` when the criterion is about `config.prompt`) | Recomputes a projection of the output and compares it to itself — passes even when the artifact is built from the wrong input. | Derive the expected value from the test's *input*: `expect(config.prompt).toBe(getPrompt(inputModel))` (independent known-good builder fed the fixture's input), or a stable builder routing decision. |
| Override/precedence fixture equal to its fallback (override == system default) | The assertion passes whether or not the code honored the override — precedence is never exercised. | Make every value the code must select, preserve, or override differ from its fallback. Prove it: temporarily force the regression the test names, watch it fail, revert. |
| Single happy-path E2E, no edges | Most bugs live on edges. | Edges are unit-test territory — but include at least one E2E that exercises an error path. |

---

## Cross-language iron list

Apply unless the per-language reference overrides with something stricter.

| Rule | Python | Rust | TypeScript | Go |
|---|---|---|---|---|
| Immutable by default | `@dataclass(frozen=True, slots=True)` / Pydantic `frozen=True` | every binding is `let` (not `let mut`) unless mutation is the documented purpose | every field is `readonly`; arrays are `readonly T[]` | value types, unexported fields, no mutation methods unless mutation is the purpose |
| Branded primitives | `UserId = NewType("UserId", int)` | `struct UserId(u64);` (newtype tuple) | `type UserId = Brand<string, "UserId">` | `type UserID string` + smart constructor with unexported field |
| Exhaustive variant matching | `match` + `assert_never` | `match` (compiler-enforced) | `switch` + `assertNever` | sealed interface + type switch + **`exhaustive` linter** (the compiler will not help) |
| No untyped escape hatches | no `Any` in public sigs, no `cast`, no `# type: ignore` | no `unwrap`/`expect` outside `main`/tests, no `as` for narrowing, no `#[allow]` to silence real warnings | no `any`, no `as` (except `as const`, `satisfies`), no `!`, no `@ts-ignore`, no `@ts-expect-error` | no `interface{}` / bare `any` in domain sigs; no `_ = err`; no `//nolint` without reason |
| No bare error strings | typed exception dataclass with `__str__` | `thiserror` enum (lib) or `anyhow` with `.context(...)` (app) | `Error` subclass with typed fields | sentinel `errors.New` + typed `*XError` struct; wrap with `%w`; check via `errors.Is/As` |
| Boundary catch only | catch the exact exception you expect; broad `except Exception` only in `main()`, with logging + re-raise | `?` everywhere; never `panic!` in library code | `catch` must narrow with `instanceof` and re-throw or convert; no empty catch | every `(T, error)` checked; `panic` only in `main`/tests; one `httperr.Write` funnel in handlers |
| Resources via RAII | `with` (sync) / `async with` (async) | `Drop` impl or RAII guard | `using`/`await using` (TC39 explicit resource management) | `defer x.Close()` immediately after acquisition; `bodyclose`/`sqlclosecheck` linters enforce |
| Async runtime is mandatory | `anyio` (NEVER bare `asyncio`) | `tokio` (`async-std` is unmaintained) | platform-native async (Bun/Node) with structured cancellation via `AbortSignal` | `context.Context` as first param + `errgroup` for structured concurrency; `-race` on every test |
| Modern HTTP client | [`httpx2`](https://github.com/pydantic/httpx2) with HTTP/2 + brotli + zstd | `reqwest` with rustls | `ky` (default) / `undici` direct API (Node perf) - NEVER bare `fetch` in prod | stdlib `net/http.Client` with tuned `Transport` + `go-retryablehttp` for retry/backoff |
| No parameter mutation | params are inputs; produce a new value | `&mut` only when mutation is the documented purpose | parameters never reassigned (`noParameterAssign`) | value receivers when not mutating; pointer receivers only for genuine mutation; `copylocks` vet enforces |
| No helpers for one-off | inline a 3-line operation; do not abstract until the second caller | same | same | same |

---

## Modern ecosystem - canonical libraries (2026)

Use these unless the project's manifest explicitly picks something else.

| Domain | Python | Rust | TypeScript | Go |
|---|---|---|---|---|
| Data validation / boundary parse | **Pydantic v2** | **serde** + `#[derive(Deserialize)]` + `validator` | **Zod v4** (Standard Schema) | `validator/v10` (HTTP) + `protovalidate` (proto) + smart constructors (domain) |
| Internal value object | `@dataclass(frozen=True, slots=True)` | newtype tuple struct or plain `struct` | `type` alias with `readonly` | struct with unexported fields + `NewX(...)` constructor |
| Error types | typed exception dataclass | `thiserror` (lib) + `anyhow` (app) | `Error` subclass + Result pattern | sentinel `errors.New` + typed `*XError` struct + `%w` wrap |
| HTTP client | [`httpx2`](https://github.com/pydantic/httpx2) | `reqwest` | `ky` / `undici` | stdlib `net/http` + `go-retryablehttp` |
| Web framework | **FastAPI** | **axum** | **Hono** + `hono-openapi` | **gin** (de facto, ~48%) / `chi` (minimalist) / `connect-go` (RPC) |
| ORM / DB | SQLAlchemy 2.x async + `asyncpg` | `sqlx` (compile-time checked) | **Drizzle** | **sqlc** (codegen from `.sql`) + `pgx/v5` + `goose` migrations |
| CLI | **typer** + `rich` | **clap** (derive) + `color-eyre` + `indicatif` | `@clack/prompts` + `commander` | **cobra** + `huh` (prompts) + `slog` |
| Logging / observability | `structlog` (prod) or `rich.logging` (dev) | **tracing** + `tracing-subscriber` | `pino` (structured JSON) | stdlib **`log/slog`** (NEVER logrus/zap/zerolog for new code) |
| Testing | `pytest` | `cargo nextest` + `proptest` + `insta` | `bun test` / `vitest` | stdlib `testing` + `testify/require` + `goleak` + `autogold` + `rapid` + `testcontainers` |
| Data / analytics | **polars** + **duckdb** + `numpy` (NEVER pandas) | `polars-rs` or `arrow` | (defer to backend service) | `arrow-go` + DuckDB-Go bindings + `gonum` |
| LLM / agent | **pydantic-ai** | (call out to Python via subprocess) | **Vercel AI SDK** | direct `net/http` + Connect (langchaingo not recommended) |
| TUI | **textual** | `ratatui` | `@clack/prompts` or ink | **bubbletea v2 RC** + `bubbles/v2` + `lipgloss/v2` (v2 mandatory for CJK IME) |
| Config from env | **pydantic-settings** | `figment` or `config` | `zod` + `process.env` | `caarlos0/env/v11` (struct-tag env) |

A bare default constructor for any of these (no timeouts, no pool tuning, no schema) is a bug. See the per-language reference for the canonical production defaults.

---

## Modern toolchain - the only acceptable setup

| Tool category | Python | Rust | TypeScript | Go |
|---|---|---|---|---|
| Package / project manager | **uv** (NEVER pip/poetry/conda) | **cargo** + `cargo-nextest` + `cargo-machete` + `cargo-deny` | **Bun** (runtime + package manager); pnpm if Node is forced | **`go modules`** + `go work` for monorepos |
| Type checker | **basedpyright** with `typeCheckingMode = "all"` | the Rust compiler with `-D warnings` + clippy `pedantic` + `nursery` + `cargo` groups | `tsc --noEmit` (or `tsgo` when available) with `strict` + `noUncheckedIndexedAccess` + `exactOptionalPropertyTypes` + `verbatimModuleSyntax` | the Go compiler + **`golangci-lint v2`** with the strict bundle + **`nilaway`** (nil-deref static analysis) |
| Linter + formatter | **ruff** with `select = ["ALL"]` | `clippy` + `rustfmt` | **Biome** (single binary - replaces ESLint + Prettier) | **`gofumpt`** (stricter gofmt) + `goimports -local` + `golangci-lint v2` |
| Test runner | **pytest** | **cargo-nextest** | `bun test` / `vitest` | stdlib `go test -race -shuffle=on -count=1` + `golea