varugasu / eslint-sequelize-bigint-rule

If DataType is BIGINT, then type must be bigint

A Proof Of Concept of ESLint Custom rules

Using Local Rules

ESLint allows to include custom rules by adding them in the plugins configuration, then referencing the rules in rules.

Because of it, we would need to distribute custom rules as NPM packages. In Monorepo, this works great due to Workspaces. But we have a problem in small codebases.

The following projects cover this later case:

• https://github.com/not-an-aardvark/eslint-plugin-rulesdir
• https://github.com/taskworld/eslint-plugin-local
• https://github.com/cletusw/eslint-plugin-local-rules

From all of them, rulesdir provided the best DX by being plug-n-play. Therefore, this POC uses rulesdir.

Transpiling

ESLint can only run a rule if it is a Javascript file. Therefore, we must transpile all rules before using them.

This can be done in two ways:

• Pre-transpiling
• Transpiling on the fly

When writing a Javascript rule and using rulesdir, we must export the rule with module.exports. For Typescript-ESLint Custom Rules, we can use either modules.exports = rule or export = rule

Pre-transpiling

This method works by running tsc and pointing rulesdir to the dist folder

const rulesDirPlugin = require("eslint-plugin-rulesdir");
rulesDirPlugin.RULES_DIR = "dist/eslint/";

During development, we must use tsc -w for detecting changes. However, this is not a problem for Monorepos.

Also, this provides better perfomance.

Transpiling on the fly

Although, pre-transpiling is not a problem at all, we can use a loader in the eslint config file to transpile rules on the fly.

This can be done with:

• ts-loader
• @babel/node
• tsx (@esbuild-kit/cjs-loader)

By placing:

• require('ts-loader/register'), or
• require("@esbuild-kit/cjs-loader")

At the top of the .eslintrc.cjs, the rules will be transpiled on the fly. This way, we can se our rulesdir to:

require("@esbuild-kit/cjs-loader");

const rulesDirPlugin = require("eslint-plugin-rulesdir");
rulesDirPlugin.RULES_DIR = "eslint/";

Testing

To use RuleTester, we must install:

pnpm add -D @typescript-eslint/rule-tester

Next, we need to setup the .afterAll hook (Github Issue).

With Vitest this can be done with:

import * as vitest from 'vitest';
import { RuleTester } from '@typescript-eslint/rule-tester';

RuleTester.afterAll = vitest.afterAll;
// if you are not using vitest with globals: true
RuleTester.it = vitest.it;
RuleTester.itOnly = vitest.it.only;
RuleTester.describe = vitest.describe;

See tests/check-bigint.test.ts for an example.