prefer-optional-catch-binding.js

'use strict';
const getDocumentationUrl = require('./utils/get-documentation-url');
const {findVariable, isOpeningParenToken, isClosingParenToken} = require('eslint-utils');

const ERROR_MESSAGE_ID = 'error';

const selector = [
	'CatchClause',
	'>',
	'Identifier.param'
].join('');

const create = context => {
	return {
		[selector]: node => {
			const scope = context.getScope();
			const variable = findVariable(scope, node);

			if (variable.references.length !== 0) {
				return;
			}

			const {name} = node;

			context.report({
				node,
				messageId: ERROR_MESSAGE_ID,
				data: {name},
				fix: fixer => {
					const tokenBefore = context.getTokenBefore(node);
					const tokenAfter = context.getTokenAfter(node);

					/* istanbul ignore next */
					if (!isOpeningParenToken(tokenBefore) || !isClosingParenToken(tokenAfter)) {
						throw new Error('Unexpected token.');
					}

					return [
						tokenBefore,
						node,
						tokenAfter
					].map(nodeOrToken => fixer.remove(nodeOrToken));
				}
			});
		}
	};
};

module.exports = {
	create,
	meta: {
		type: 'suggestion',
		docs: {
			url: getDocumentationUrl(__filename)
		},
		fixable: 'code',
		messages: {
			[ERROR_MESSAGE_ID]: 'Remove unused catch binding paramter `{{name}}`.'
		}
	}
};