143 lines
3.6 KiB
JavaScript
143 lines
3.6 KiB
JavaScript
/**
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* @fileoverview Rule to flag blocks with no reason to exist
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* @author Brandon Mills
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*/
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'use strict';
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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 unnecessary nested blocks',
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recommended: false,
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url: 'https://eslint.org/docs/latest/rules/no-lone-blocks',
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},
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schema: [],
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messages: {
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redundantBlock: 'Block is redundant.',
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redundantNestedBlock: 'Nested block is redundant.',
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},
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},
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create(context) {
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// A stack of lone blocks to be checked for block-level bindings
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const loneBlocks = [];
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let ruleDef;
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const sourceCode = context.sourceCode;
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/**
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* Reports a node as invalid.
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* @param {ASTNode} node The node to be reported.
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* @returns {void}
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*/
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function report(node) {
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const messageId =
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(
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node.parent.type === 'BlockStatement' ||
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node.parent.type === 'StaticBlock'
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) ?
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'redundantNestedBlock'
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: 'redundantBlock';
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context.report({
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node,
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messageId,
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});
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}
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/**
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* Checks for any occurrence of a BlockStatement in a place where lists of statements can appear
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* @param {ASTNode} node The node to check
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* @returns {boolean} True if the node is a lone block.
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*/
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function isLoneBlock(node) {
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return (
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node.parent.type === 'BlockStatement' ||
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node.parent.type === 'StaticBlock' ||
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node.parent.type === 'Program' ||
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// Don't report blocks in switch cases if the block is the only statement of the case.
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(node.parent.type === 'SwitchCase' &&
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!(
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node.parent.consequent[0] === node &&
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node.parent.consequent.length === 1
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))
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);
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}
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/**
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* Checks the enclosing block of the current node for block-level bindings,
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* and "marks it" as valid if any.
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* @param {ASTNode} node The current node to check.
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* @returns {void}
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*/
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function markLoneBlock(node) {
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if (loneBlocks.length === 0) {
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return;
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}
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const block = node.parent;
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if (loneBlocks.at(-1) === block) {
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loneBlocks.pop();
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}
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}
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// Default rule definition: report all lone blocks
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ruleDef = {
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BlockStatement(node) {
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if (isLoneBlock(node)) {
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report(node);
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}
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},
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};
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// ES6: report blocks without block-level bindings, or that's only child of another block
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if (context.languageOptions.ecmaVersion >= 2015) {
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ruleDef = {
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BlockStatement(node) {
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if (isLoneBlock(node)) {
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loneBlocks.push(node);
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}
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},
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'BlockStatement:exit'(node) {
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if (loneBlocks.length > 0 && loneBlocks.at(-1) === node) {
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loneBlocks.pop();
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report(node);
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} else if (
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(node.parent.type === 'BlockStatement' ||
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node.parent.type === 'StaticBlock') &&
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node.parent.body.length === 1
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) {
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report(node);
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}
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},
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};
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ruleDef.VariableDeclaration = function (node) {
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if (node.kind !== 'var') {
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markLoneBlock(node);
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}
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};
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ruleDef.FunctionDeclaration = function (node) {
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if (sourceCode.getScope(node).isStrict) {
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markLoneBlock(node);
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}
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};
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ruleDef.ClassDeclaration = markLoneBlock;
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}
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return ruleDef;
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},
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};
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