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