ESLint plugin: must use

This is a plugin for Typescript/ESLint that enables you to enforce the usage of values of a certain type. It works much like the #must_use attribute in Rust.

For example, let's say you have a Result<A, E> type, that represents a success (A) or a failure (E) in your code. You want every instance of Result to be used within your code, so even when the successful value of a result is void, ESLint will force developers to use the result, if only to check that it was successful.

In this case, you would pass Result as a type to the plugin in your ESLint config file:

import { defineConfig } from "eslint/config";
import mustUse from "@mconst/eslint-plugin-must-use";

export default defineConfig([
  {
    // ...
    plugins: {
      // ...
      "@mustUse": mustUse,
      // ...
    },
    // ...
    rules: {
      "@mustUse/mustUse": ["error", { types: ["Result"] }],
    },
  }
]);

After this, your code will be valid if every instance of Result is used:

declare function computeResult(): Result<void, Error>;

// the result is stored in a constant -> valid code
const result = computeResult();

// the result is ignored -> invalid code
computeResult();