115 lines
3.9 KiB
JavaScript
115 lines
3.9 KiB
JavaScript
/**
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* @fileoverview Rule to flag use of comma operator
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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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// Requirements
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//------------------------------------------------------------------------------
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const astUtils = require("../util/ast-utils");
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//------------------------------------------------------------------------------
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// Rule Definition
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//------------------------------------------------------------------------------
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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 comma operators",
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category: "Best Practices",
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recommended: false,
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url: "https://eslint.org/docs/rules/no-sequences"
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},
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schema: []
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},
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create(context) {
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const sourceCode = context.getSourceCode();
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/**
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* Parts of the grammar that are required to have parens.
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*/
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const parenthesized = {
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DoWhileStatement: "test",
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IfStatement: "test",
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SwitchStatement: "discriminant",
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WhileStatement: "test",
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WithStatement: "object",
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ArrowFunctionExpression: "body"
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/*
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* Omitting CallExpression - commas are parsed as argument separators
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* Omitting NewExpression - commas are parsed as argument separators
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* Omitting ForInStatement - parts aren't individually parenthesised
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* Omitting ForStatement - parts aren't individually parenthesised
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*/
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};
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/**
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* Determines whether a node is required by the grammar to be wrapped in
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* parens, e.g. the test of an if statement.
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* @param {ASTNode} node - The AST node
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* @returns {boolean} True if parens around node belong to parent node.
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*/
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function requiresExtraParens(node) {
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return node.parent && parenthesized[node.parent.type] &&
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node === node.parent[parenthesized[node.parent.type]];
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}
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/**
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* Check if a node is wrapped in parens.
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* @param {ASTNode} node - The AST node
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* @returns {boolean} True if the node has a paren on each side.
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*/
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function isParenthesised(node) {
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return astUtils.isParenthesised(sourceCode, node);
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}
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/**
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* Check if a node is wrapped in two levels of parens.
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* @param {ASTNode} node - The AST node
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* @returns {boolean} True if two parens surround the node on each side.
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*/
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function isParenthesisedTwice(node) {
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const previousToken = sourceCode.getTokenBefore(node, 1),
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nextToken = sourceCode.getTokenAfter(node, 1);
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return isParenthesised(node) && previousToken && nextToken &&
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astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] &&
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astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1];
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}
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return {
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SequenceExpression(node) {
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// Always allow sequences in for statement update
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if (node.parent.type === "ForStatement" &&
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(node === node.parent.init || node === node.parent.update)) {
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return;
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}
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// Wrapping a sequence in extra parens indicates intent
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if (requiresExtraParens(node)) {
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if (isParenthesisedTwice(node)) {
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return;
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}
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} else {
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if (isParenthesised(node)) {
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return;
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}
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}
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const child = sourceCode.getTokenAfter(node.expressions[0]);
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context.report({ node, loc: child.loc.start, message: "Unexpected use of comma operator." });
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}
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};
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}
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};
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