no-unused-result

Require Result and ResultAsync values to be used, preventing silently ignored errors.

Severity: error | Fixable: suggestion

Analogous to Rust's #[must_use] attribute and unused_must_use lint.

Rule Details

This rule reports when a Result or ResultAsync value from antithrow is discarded as an expression statement. A discarded Result means the error case is silently ignored, which defeats the purpose of typed error handling.

The rule is type-aware and uses TypeScript's type checker to determine whether an expression produces a Result. Since Result<T, E> is a type alias for Ok<T, E> | Err<T, E>, the rule checks for the underlying Ok, Err, and ResultAsync class types.

Invalid

import { ok, err, okAsync, errAsync, Result } from "antithrow";

// Bare Result constructors
ok(1);
err("x");
okAsync(1);
errAsync("x");

// Chains that still produce a Result
ok(1).map((x) => x + 1);
ok(1).mapErr((e) => e);

// Function returning Result, called as expression statement
function getResult(): Result<number, string> {
  return ok(1);
}
getResult();

// Awaited okAsync produces a Result
async function f() {
  await okAsync(1);
}

Valid

import { ok, err, okAsync, Result, ResultAsync } from "antithrow";

// Assigned to a variable
const x = ok(1);

// Returned from a function
function f() {
  return ok(1);
}

// Passed as an argument
function foo(r: Result<number, never>) {}
foo(ok(1));

// Explicitly discarded with void
void ok(1);

// Chain ending in a non-Result method
ok(1).unwrap();
ok(1).match({ ok: (v) => v, err: (e) => 0 });

// ResultAsync assigned in async function
async function g() {
  const x = await okAsync(1);
}

// Non-Result expressions
42;
console.log("hi");

Suggestions

This rule provides a suggestion to explicitly discard the Result by wrapping the expression with void. The suggestion accounts for operator precedence, adding parentheses when necessary.

For example, ok(1); suggests void ok(1);, while cond ? ok(1) : ok(2); suggests void (cond ? ok(1) : ok(2));.

When Not To Use It

If you intentionally discard Result values in fire-and-forget scenarios and don't want to add void before each one.

Options

This rule has no options.

Type Checking

This rule requires type information to run. You must configure your ESLint setup with parserOptions.projectService or parserOptions.project.