Oxlint Typescript Conventions

oxlint TypeScript conventions

This repo runs oxlint --type-aware with correctness: error and perf: error plus the full typescript plugin (see oxlint.config.ts). The husky pre-commit hook runs lint-staged, which invokes oxlint against every staged .ts and rejects the commit on any error. The rules are non-trivially strict; new code that passes tsc will routinely fail oxlint unless it is written with these patterns from the start.

The config/pi/extensions/** tree - plus the shared pi-importing helpers under lib/node/pi/ext/** and their specs under tests/lib/node/pi/ext/** - has a relaxed override (most no-unsafe-* and require-await rules turned off) because those files import from @earendil-works/* (pi runtime / TUI / AI APIs). This skill applies to everything else — lib/node/** (except lib/node/pi/ext/), tests/** (except tests/lib/node/pi/ext/), config/pi/*.ts (e.g. session-usage.ts), and any future top-level *.ts.

When to use this skill

Apply whenever the user asks to:

• Add or edit a .ts file under lib/node/.
• Add or edit a .spec.ts under tests/lib/, tests/config/, or anywhere else vitest picks up.
• Add a TypeScript helper that other extensions consume.

Skip this skill for .ts files inside config/pi/extensions/ (different rule set), *.d.ts type shims, and generated files. The commit-message and lint-and-test-gate skills are still the final word on subject lines and verification — this one only governs the source style.

The pre-commit gate

$ git commit ...
✖ Task killed: oxlint-tsgolint
✖ Task killed: oxfmt --no-error-on-unmatched-pattern
husky - pre-commit script failed (code 1)

Run npx oxlint --type-aware <file-or-dir> against your changes BEFORE git commit. The pre-commit hook does the same thing; running it manually saves the round trip.

For format issues separately: npx oxfmt --check <files> (and npx oxfmt <files> to fix in place).

Patterns that trip the gate

typescript/require-await — async stubs without await

Tests routinely install async callbacks for type compatibility, then never await. oxlint flags this; rewrite as a non-async () => Promise.resolve(...).

// ✗ Fails: async with no await.
installSandboxWrapper(async (cmd) => ({ command: `srt -- ${cmd}`, wrapped: true }));

// ✓ Use Promise.resolve so the function stays non-async.
installSandboxWrapper((cmd) => Promise.resolve({ command: `srt -- ${cmd}`, wrapped: true }));

The rule is keyed off the literal async keyword; an async function with NO await is the trigger. A real async helper that genuinely uses await passes.

typescript/prefer-includes — .test(literal) on a substring

x.includes('foo') is preferred over /foo/.test(x) whenever the regex is just a literal substring with no metacharacters. oxlint flags the .test() form even inside test assertions.

// ✗ Fails: regex carries no metacharacters.
expect(warnings.find((w) => /silently drop/.test(w.reason))).toBeDefined();

// ✓ Substring match.
expect(warnings.find((w) => w.reason.includes('silently drop'))).toBeDefined();

A real regex (anchors, character classes, alternation) is fine — keep /^foo$/.test(s) as-is.

eslint/no-use-before-define — declare before first use

Function and variable declarations must precede their first reference in source order. ESLint's no-use-before-define is on with the default config, which means the standard "helpers at the bottom" Python style does not work.

// ✗ Fails: uniqueSorted used before defined.
export function compileLinuxRules(...) {
  return { paths: uniqueSorted([...paths]), ... };
}

function uniqueSorted(input: string[]): string[] {
  return [...new Set(input)].sort();
}

// ✓ Define helpers above their first call.
function uniqueSorted(input: string[]): string[] {
  return [...new Set(input)].sort();
}

export function compileLinuxRules(...) {
  return { paths: uniqueSorted([...paths]), ... };
}

typescript/explicit-function-return-type — annotate test helpers

allowExpressions: true is set, so arrow functions passed inline (map((x) => x + 1)) are fine. Top-level declarations and named factory helpers in tests are NOT, even when the return type is inferable.

// ✗ Fails: top-level helper.
function makeUI(over = {}) {
  return { hasUI: true, ... };
}

// ✓ Annotate the return type.
function makeUI(over: Partial<UIBridge> = {}): UIBridge {
  return { hasUI: true, ... };
}

// ✗ Fails: test-local factory.
const noop = () => undefined;

// ✓ Annotate.
const noop = (): undefined => undefined;

typescript/no-unsafe-assignment / no-unsafe-member-access — narrow unknown properly

Array.isArray(value) narrows to any[], and JSON.parse(...) returns any. Either widens to a typed shape with an explicit as unknown[] / as Record<string, unknown> step before iterating, or parses through a typed schema.

// ✗ Fails: `value` after Array.isArray() is `any[]`, item is `any`.
if (!Array.isArray(value)) return;
for (let i = 0; i < value.length; i++) {
  const item = value[i];
  if (typeof item !== 'string') continue;
  out.push(item);
}

// ✓ Re-cast through unknown[] so item is `unknown`.
if (!Array.isArray(value)) return;
const arr = value as unknown[];
for (let i = 0; i < arr.length; i++) {
  const item = arr[i];
  if (typeof item !== 'string') continue;
  out.push(item);
}

// ✗ Fails: JSON.parse returns any, .command access is unsafe.
expect(JSON.parse(line).command).toBe('first');

// ✓ Type the parse target.
const rec = JSON.parse(line) as { command: string };
expect(rec.command).toBe('first');

typescript/consistent-indexed-object-style — prefer Record<K, V>

{ [k: symbol]: unknown } index signatures are flagged in favor of Record<symbol, unknown>.

// ✗ Fails.
const g = globalThis as unknown as { [k: symbol]: unknown };

// ✓
const g = globalThis as unknown as Record<symbol, unknown>;

eslint/no-empty-function — sentinel for let cb = () => {}

A bare () => {} placeholder for a callback that's about to be reassigned trips the rule. Either use a named sentinel function (with a comment explaining the unreachability) or restructure to avoid the placeholder.

// ✗ Fails.
let resolveFn: () => void = () => {};
const next = new Promise<void>((resolve) => {
  resolveFn = resolve;
});
return resolveFn;

// ✓ Named sentinel.
function noopResolve(): void {
  /* unreachable - reassigned by Promise ctor */
}
let resolveFn: () => void = noopResolve;
const next = new Promise<void>((resolve) => {
  resolveFn = resolve;
});
return resolveFn;

eslint/no-unused-vars — drop unused imports

Particularly easy to hit when refactoring: an import { foo, bar } line where one of the names is no longer referenced. The rule respects the ^_ ignore prefix for arguments and destructured elements but NOT for imports — drop the unused name from the import list.

Workflow

1. Write the code naturally; run npm run tsc first to confirm types are sound.
2. Run npx oxlint --type-aware <changed-paths> (paths or directories — both work).
3. Fix every error reported. The patterns above cover ~95% of what trips on a fresh helper.
4. Run npx oxfmt --check <changed-paths>; run without --check to format if it complained.
5. Stage and commit. The pre-commit hook re-runs both — your local pass guarantees a clean commit.

Anti-patterns

• Disabling rules with // oxlint-disable-next-line .... Almost never the right answer in this repo; the rules above all have a clean-code form. Reach for the disable comment only when a third- party type forces the unsafe pattern, and document why in the disable comment.
• Casting through Record<string, unknown> reflexively. The as unknown[] / explicit-shape approach narrows correctly without adding a load-bearing assertion. Casts that hide a real bug are a real maintenance hazard — when in doubt, validate the shape with a guard.
• Skipping oxlint locally because "the pre-commit hook will catch it." It will, by aborting your commit mid-message-typing. Run it yourself first.
• Matching the relaxed config/pi/extensions/ posture in lib/ because "extensions get away with it." Lib helpers are the typed surface that extensions consume; tightening lib while extensions stay loose is the deliberate boundary.

References

• oxlint.config.ts — every rule in force, plus the config/pi/extensions/** override.
• oxlint TypeScript rules index — the upstream rule docs for the messages above.
• lint-and-test-gate — when to run lint vs tests vs both.
• commit-message — what to put in the commit subject after the gate is green.