node_modules/eslint/lib/rules/default-case.js

/**
 * @fileoverview require default case in switch statements
 * @author Aliaksei Shytkin
 */
"use strict";

const DEFAULT_COMMENT_PATTERN = /^no default$/iu;

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../types').Rule.RuleModule} */
module.exports = {
	meta: {
		type: "suggestion",

		defaultOptions: [{}],

		docs: {
			description: "Require `default` cases in `switch` statements",
			recommended: false,
			url: "https://eslint.org/docs/latest/rules/default-case",
		},

		schema: [
			{
				type: "object",
				properties: {
					commentPattern: {
						type: "string",
					},
				},
				additionalProperties: false,
			},
		],

		messages: {
			missingDefaultCase: "Expected a default case.",
		},
	},

	create(context) {
		const [options] = context.options;
		const commentPattern = options.commentPattern
			? new RegExp(options.commentPattern, "u")
			: DEFAULT_COMMENT_PATTERN;

		const sourceCode = context.sourceCode;

		//--------------------------------------------------------------------------
		// Helpers
		//--------------------------------------------------------------------------

		/**
		 * Shortcut to get last element of array
		 * @param {*[]} collection Array
		 * @returns {any} Last element
		 */
		function last(collection) {
			return collection.at(-1);
		}

		//--------------------------------------------------------------------------
		// Public
		//--------------------------------------------------------------------------

		return {
			SwitchStatement(node) {
				if (!node.cases.length) {
					/*
					 * skip check of empty switch because there is no easy way
					 * to extract comments inside it now
					 */
					return;
				}

				const hasDefault = node.cases.some(v => v.test === null);

				if (!hasDefault) {
					let comment;

					const lastCase = last(node.cases);
					const comments = sourceCode.getCommentsAfter(lastCase);

					if (comments.length) {
						comment = last(comments);
					}

					if (
						!comment ||
						!commentPattern.test(comment.value.trim())
					) {
						context.report({
							node,
							messageId: "missingDefaultCase",
						});
					}
				}
			},
		};
	},
};