# Strict tsconfig + OXC

The canonical ultra-strict config. Copy-paste, then add your own paths.

---

## tsconfig.json

```jsonc
{
  "compilerOptions": {
    // ── Strict core ──────────────────────────────────────────
    "strict": true,                            // enables all strict* flags below
    // strict includes: strictNullChecks, strictFunctionTypes,
    // strictBindCallApply, strictPropertyInitialization,
    // noImplicitAny, noImplicitThis, alwaysStrict, useUnknownInCatchVariables

    // ── Additional strict flags (NOT included in "strict") ──
    "noUncheckedIndexedAccess": true,           // obj[key] is T | undefined, not T
    "exactOptionalPropertyTypes": true,         // { x?: string } !== { x: string | undefined }
    "noFallthroughCasesInSwitch": true,         // switch fall-through is an error
    "noPropertyAccessFromIndexSignature": true, // forces bracket notation for index sigs
    "forceConsistentCasingInFileNames": true,   // prevents case-sensitivity bugs on macOS/Win

    // ── Module system ────────────────────────────────────────
    "module": "ESNext",
    "moduleResolution": "bundler",
    "verbatimModuleSyntax": true,               // forces `import type` for type-only imports
    "isolatedModules": true,                    // safe for esbuild / swc / Bun transpilation
    "esModuleInterop": true,
    "resolveJsonModule": true,

    // ── Target ───────────────────────────────────────────────
    "target": "ESNext",
    "lib": ["ESNext"],

    // ── Emit ─────────────────────────────────────────────────
    "declaration": true,
    "declarationMap": true,
    "sourceMap": true,
    "outDir": "dist",
    "rootDir": "src",

    // ── Performance ──────────────────────────────────────────
    "skipLibCheck": true,                       // skip checking .d.ts files for speed
    "incremental": true
  },
  "include": ["src"],
  "exclude": ["node_modules", "dist"]
}
```

### What each extra flag catches

| Flag | What it prevents |
|---|---|
| `noUncheckedIndexedAccess` | `arr[0]` is `T \| undefined`, not `T`. Forces you to check before using. |
| `exactOptionalPropertyTypes` | `{ x?: string }` means "missing or string", NOT "string \| undefined". Assigns `undefined` explicitly? Type error. |
| `noFallthroughCasesInSwitch` | Forgetting `break` / `return` in a switch case. |
| `noPropertyAccessFromIndexSignature` | `obj.foo` on `Record<string, X>` is an error. Use `obj["foo"]`. |
| `verbatimModuleSyntax` | Forces `import type { X }` for type-only imports. Prevents runtime import of types. |

### Bun-specific additions

For Bun projects, add to `compilerOptions`:
```jsonc
{
  "types": ["bun-types"],
  "moduleDetection": "force"
}
```

---

## oxlint + oxfmt

Use [oxc-lint.md](oxc-lint.md) for the complete `.oxlintrc.json`, `.oxfmtrc.json`, and local JS plugin. It maps the strictness intent to verified oxlint rules, adds the two t3code copy rules, and documents type-aware support. Retain ESLint, Prettier, or Biome only in repositories already using them.

---

## CI gate

```bash
bunx oxlint --type-aware --deny-warnings
bunx oxfmt --check
bunx tsc --noEmit
bun test
```

---

## Sources

- TypeScript: [tsconfig reference](https://www.typescriptlang.org/tsconfig)
- OXC: [oxlint configuration](https://oxc.rs/docs/guide/usage/linter/config.html) and [oxfmt configuration](https://oxc.rs/docs/guide/usage/formatter/config.html)
- Total TypeScript: [tsconfig cheat sheet](https://www.totaltypescript.com/tsconfig-cheat-sheet)