no-magic-numbers.ts

/**
 * @fileoverview Rule to flag statements that use magic numbers (adapted from https://github.com/danielstjules/buddy.js)
 * @author Scott O'Hara
 */

import { TSESTree, AST_NODE_TYPES } from '@typescript-eslint/typescript-estree';
import baseRule from 'eslint/lib/rules/no-magic-numbers';
import * as util from '../util';
import { JSONSchema4 } from 'json-schema';

type Options = util.InferOptionsTypeFromRule<typeof baseRule>;
type MessageIds = util.InferMessageIdsTypeFromRule<typeof baseRule>;

// Original schema properties from the base rule
const {properties} = (baseRule.meta.schema as JSONSchema4[])[0];

// Extend base schema with additional property to ignore TS numeric literal types
if (properties) {
  properties.ignoreNumericLiteralTypes = {
    type: "boolean",
  };
}

export default util.createRule<Options, MessageIds>({
  name: 'no-magic-numbers',
  meta: {
    type: 'suggestion',
    docs: {
      description: "Disallow magic numbers",
      category: "Best Practices",
      recommended: false,
    },
    schema: baseRule.meta.schema,
    messages: baseRule.meta.messages,
  },
  defaultOptions: [
    {
      ignore: [],
      ignoreArrayIndexes: false,
      enforceConst: false,
      detectObjects: false,
      ignoreNumericLiteralTypes: false,
    },
  ],
  create(context, [options]) {
    const rules = baseRule.create(context);

    /**
     * Returns whether the node is number literal
     * @param node the node literal being evaluated
     * @returns true if the node is a number literal
     */
    function isNumber(node: TSESTree.Literal): boolean {
      return typeof node.value === "number";
    }

    /**
     * Checks if the node grandparent is a Typescript type alias declaration
     * @param node the node to be validated.
     * @returns true if the node grandparent is a Typescript type alias declaration
     * @private
     */
    function isGrandparentTSTypeAliasDeclaration(node: TSESTree.Node): boolean {
      return node.parent && node.parent.parent ? AST_NODE_TYPES.TSTypeAliasDeclaration === node.parent.parent.type : false;
    }

    /**
     * Checks if the node grandparent is a Typescript union type and its parent is a type alias declaration
     * @param node the node to be validated.
     * @returns true if the node grandparent is a Typescript untion type and its parent is a type alias declaration
     * @private
     */
    function isGrandparentTSUnionType(node: TSESTree.Node): boolean {
      if (node.parent && node.parent.parent && AST_NODE_TYPES.TSUnionType === node.parent.parent.type) {
        return isGrandparentTSTypeAliasDeclaration(node.parent);
      }

      return false;
    }

    /**
     * Checks if the node parent is a Typescript literal type
     * @param node the node to be validated.
     * @returns true if the node parent is a Typescript literal type
     * @private
     */
    function isParentTSLiteralType(node: TSESTree.Node): boolean {
      return node.parent ? AST_NODE_TYPES.TSLiteralType === node.parent.type : false;
    }

    /**
     * Checks if the node is a valid TypeScript numeric literal type.
     * @param node the node to be validated.
     * @returns true if the node is a TypeScript numeric literal type.
     * @private
     */
    function isTSNumericLiteralType(node: TSESTree.Node): boolean {
      // For negative numbers, update the parent node
      if (node.parent && node.parent.type === AST_NODE_TYPES.UnaryExpression && node.parent.operator === "-") {
        node = node.parent;
      }

      // If the parent node is not a TSLiteralType, early return
      if (!isParentTSLiteralType(node)) {
        return false;
      }

      // If the grandparent is a TSTypeAliasDeclaration, ignore
      if (isGrandparentTSTypeAliasDeclaration(node)) {
        return true;
      }

      // If the grandparent is a TSUnionType and it's parent is a TSTypeAliasDeclaration, ignore
      if (isGrandparentTSUnionType(node)) {
        return true;
      }

      return false;
    }

    return {
      Literal(node) {
        // Check TypeScript specific nodes
        if (options.ignoreNumericLiteralTypes &&
          isNumber(node) &&
          isTSNumericLiteralType(node)
        ) {
          return;
        }

        // Let the base rule deal with the rest
        rules.Literal(node);
      },
    };
  },
});