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/**
* @fileoverview Rule to flag assignment in a conditional statement's test expression
* @author Stephen Murray <spmurrayzzz>
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const TEST_CONDITION_PARENT_TYPES = new Set(["IfStatement", "WhileStatement", "DoWhileStatement", "ForStatement", "ConditionalExpression"]);
const NODE_DESCRIPTIONS = {
DoWhileStatement: "a 'do...while' statement",
ForStatement: "a 'for' statement",
IfStatement: "an 'if' statement",
WhileStatement: "a 'while' statement"
};
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow assignment operators in conditional expressions",
category: "Possible Errors",
recommended: true,
url: "https://eslint.org/docs/rules/no-cond-assign"
},
schema: [
{
enum: ["except-parens", "always"]
}
],
messages: {
unexpected: "Unexpected assignment within {{type}}.",
// must match JSHint's error message
missing: "Expected a conditional expression and instead saw an assignment."
}
},
create(context) {
const prohibitAssign = (context.options[0] || "except-parens");
const sourceCode = context.getSourceCode();
/**
* Check whether an AST node is the test expression for a conditional statement.
* @param {!Object} node The node to test.
* @returns {boolean} `true` if the node is the text expression for a conditional statement; otherwise, `false`.
*/
function isConditionalTestExpression(node) {
return node.parent &&
TEST_CONDITION_PARENT_TYPES.has(node.parent.type) &&
node === node.parent.test;
}
/**
* Given an AST node, perform a bottom-up search for the first ancestor that represents a conditional statement.
* @param {!Object} node The node to use at the start of the search.
* @returns {?Object} The closest ancestor node that represents a conditional statement.
*/
function findConditionalAncestor(node) {
let currentAncestor = node;
do {
if (isConditionalTestExpression(currentAncestor)) {
return currentAncestor.parent;
}
} while ((currentAncestor = currentAncestor.parent) && !astUtils.isFunction(currentAncestor));
return null;
}
/**
* Check whether the code represented by an AST node is enclosed in two sets of parentheses.
* @param {!Object} node The node to test.
* @returns {boolean} `true` if the code is enclosed in two sets of parentheses; otherwise, `false`.
*/
function isParenthesisedTwice(node) {
const previousToken = sourceCode.getTokenBefore(node, 1),
nextToken = sourceCode.getTokenAfter(node, 1);
return astUtils.isParenthesised(sourceCode, node) &&
previousToken && astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] &&
astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1];
}
/**
* Check a conditional statement's test expression for top-level assignments that are not enclosed in parentheses.
* @param {!Object} node The node for the conditional statement.
* @returns {void}
*/
function testForAssign(node) {
if (node.test &&
(node.test.type === "AssignmentExpression") &&
(node.type === "ForStatement"
? !astUtils.isParenthesised(sourceCode, node.test)
: !isParenthesisedTwice(node.test)
)
) {
context.report({
node: node.test,
messageId: "missing"
});
}
}
/**
* Check whether an assignment expression is descended from a conditional statement's test expression.
* @param {!Object} node The node for the assignment expression.
* @returns {void}
*/
function testForConditionalAncestor(node) {
const ancestor = findConditionalAncestor(node);
if (ancestor) {
context.report({
node,
messageId: "unexpected",
data: {
type: NODE_DESCRIPTIONS[ancestor.type] || ancestor.type
}
});
}
}
if (prohibitAssign === "always") {
return {
AssignmentExpression: testForConditionalAncestor
};
}
return {
DoWhileStatement: testForAssign,
ForStatement: testForAssign,
IfStatement: testForAssign,
WhileStatement: testForAssign,
ConditionalExpression: testForAssign
};
}
};
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