155 lines
4.1 KiB
JavaScript
155 lines
4.1 KiB
JavaScript
/**
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* @fileoverview Rule to disallow unused labels.
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* @author Toru Nagashima
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*/
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'use strict';
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//------------------------------------------------------------------------------
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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require('./utils/ast-utils');
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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/** @type {import('../types').Rule.RuleModule} */
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module.exports = {
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Disallow unused labels',
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recommended: true,
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url: 'https://eslint.org/docs/latest/rules/no-unused-labels',
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},
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schema: [],
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fixable: 'code',
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messages: {
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unused: "'{{name}}:' is defined but never used.",
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},
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},
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create(context) {
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const sourceCode = context.sourceCode;
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let scopeInfo = null;
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/**
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* Adds a scope info to the stack.
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* @param {ASTNode} node A node to add. This is a LabeledStatement.
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* @returns {void}
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*/
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function enterLabeledScope(node) {
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scopeInfo = {
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label: node.label.name,
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used: false,
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upper: scopeInfo,
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};
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}
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/**
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* Checks if a `LabeledStatement` node is fixable.
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* For a node to be fixable, there must be no comments between the label and the body.
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* Furthermore, is must be possible to remove the label without turning the body statement into a
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* directive after other fixes are applied.
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* @param {ASTNode} node The node to evaluate.
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* @returns {boolean} Whether or not the node is fixable.
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*/
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function isFixable(node) {
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/*
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* Only perform a fix if there are no comments between the label and the body. This will be the case
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* when there is exactly one token/comment (the ":") between the label and the body.
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*/
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if (
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sourceCode.getTokenAfter(node.label, {
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includeComments: true,
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}) !== sourceCode.getTokenBefore(node.body, { includeComments: true })
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) {
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return false;
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}
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// Looking for the node's deepest ancestor which is not a `LabeledStatement`.
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let ancestor = node.parent;
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while (ancestor.type === 'LabeledStatement') {
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ancestor = ancestor.parent;
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}
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if (
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ancestor.type === 'Program' ||
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(ancestor.type === 'BlockStatement' &&
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astUtils.isFunction(ancestor.parent))
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) {
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const { body } = node;
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if (
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body.type === 'ExpressionStatement' &&
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((body.expression.type === 'Literal' &&
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typeof body.expression.value === 'string') ||
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astUtils.isStaticTemplateLiteral(body.expression))
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) {
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return false; // potential directive
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}
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}
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return true;
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}
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/**
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* Removes the top of the stack.
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* At the same time, this reports the label if it's never used.
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* @param {ASTNode} node A node to report. This is a LabeledStatement.
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* @returns {void}
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*/
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function exitLabeledScope(node) {
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if (!scopeInfo.used) {
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context.report({
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node: node.label,
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messageId: 'unused',
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data: node.label,
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fix:
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isFixable(node) ?
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(fixer) => fixer.removeRange([node.range[0], node.body.range[0]])
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: null,
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});
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}
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scopeInfo = scopeInfo.upper;
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}
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/**
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* Marks the label of a given node as used.
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* @param {ASTNode} node A node to mark. This is a BreakStatement or
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* ContinueStatement.
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* @returns {void}
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*/
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function markAsUsed(node) {
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if (!node.label) {
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return;
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}
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const label = node.label.name;
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let info = scopeInfo;
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while (info) {
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if (info.label === label) {
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info.used = true;
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break;
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}
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info = info.upper;
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}
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}
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return {
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LabeledStatement: enterLabeledScope,
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'LabeledStatement:exit': exitLabeledScope,
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BreakStatement: markAsUsed,
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ContinueStatement: markAsUsed,
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};
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},
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};
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