no-sequences.js
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/**
* @fileoverview Rule to flag use of comma operator
* @author Brandon Mills
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = function(context) {
/**
* Parts of the grammar that are required to have parens.
*/
var parenthesized = {
"DoWhileStatement": "test",
"IfStatement": "test",
"SwitchStatement": "discriminant",
"WhileStatement": "test",
"WithStatement": "object"
// 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) {
var previousToken = context.getTokenBefore(node),
nextToken = context.getTokenAfter(node);
return previousToken && nextToken &&
previousToken.value === "(" && previousToken.range[1] <= node.range[0] &&
nextToken.value === ")" && nextToken.range[0] >= node.range[1];
}
/**
* 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) {
var previousToken = context.getTokenBefore(node, 1),
nextToken = context.getTokenAfter(node, 1);
return isParenthesised(node) && previousToken && nextToken &&
previousToken.value === "(" && previousToken.range[1] <= node.range[0] &&
nextToken.value === ")" && nextToken.range[0] >= node.range[1];
}
return {
"SequenceExpression": function(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;
}
}
var child = context.getTokenAfter(node.expressions[0]);
context.report(node, child.loc.start, "Unexpected use of comma operator.");
}
};
};
module.exports.schema = [];