2 * @fileoverview Rule to flag assignment in a conditional statement's test expression
3 * @author Stephen Murray <spmurrayzzz>
8 //------------------------------------------------------------------------------
10 //------------------------------------------------------------------------------
12 const astUtils = require("./utils/ast-utils");
14 //------------------------------------------------------------------------------
16 //------------------------------------------------------------------------------
18 const TEST_CONDITION_PARENT_TYPES = new Set(["IfStatement", "WhileStatement", "DoWhileStatement", "ForStatement", "ConditionalExpression"]);
20 const NODE_DESCRIPTIONS = {
21 DoWhileStatement: "a 'do...while' statement",
22 ForStatement: "a 'for' statement",
23 IfStatement: "an 'if' statement",
24 WhileStatement: "a 'while' statement"
27 //------------------------------------------------------------------------------
29 //------------------------------------------------------------------------------
36 description: "disallow assignment operators in conditional expressions",
37 category: "Possible Errors",
39 url: "https://eslint.org/docs/rules/no-cond-assign"
44 enum: ["except-parens", "always"]
49 unexpected: "Unexpected assignment within {{type}}.",
51 // must match JSHint's error message
52 missing: "Expected a conditional expression and instead saw an assignment."
58 const prohibitAssign = (context.options[0] || "except-parens");
60 const sourceCode = context.getSourceCode();
63 * Check whether an AST node is the test expression for a conditional statement.
64 * @param {!Object} node The node to test.
65 * @returns {boolean} `true` if the node is the text expression for a conditional statement; otherwise, `false`.
67 function isConditionalTestExpression(node) {
69 TEST_CONDITION_PARENT_TYPES.has(node.parent.type) &&
70 node === node.parent.test;
74 * Given an AST node, perform a bottom-up search for the first ancestor that represents a conditional statement.
75 * @param {!Object} node The node to use at the start of the search.
76 * @returns {?Object} The closest ancestor node that represents a conditional statement.
78 function findConditionalAncestor(node) {
79 let currentAncestor = node;
82 if (isConditionalTestExpression(currentAncestor)) {
83 return currentAncestor.parent;
85 } while ((currentAncestor = currentAncestor.parent) && !astUtils.isFunction(currentAncestor));
91 * Check whether the code represented by an AST node is enclosed in two sets of parentheses.
92 * @param {!Object} node The node to test.
93 * @returns {boolean} `true` if the code is enclosed in two sets of parentheses; otherwise, `false`.
95 function isParenthesisedTwice(node) {
96 const previousToken = sourceCode.getTokenBefore(node, 1),
97 nextToken = sourceCode.getTokenAfter(node, 1);
99 return astUtils.isParenthesised(sourceCode, node) &&
100 previousToken && astUtils.isOpeningParenToken(previousToken) && previousToken.range[1] <= node.range[0] &&
101 astUtils.isClosingParenToken(nextToken) && nextToken.range[0] >= node.range[1];
105 * Check a conditional statement's test expression for top-level assignments that are not enclosed in parentheses.
106 * @param {!Object} node The node for the conditional statement.
109 function testForAssign(node) {
111 (node.test.type === "AssignmentExpression") &&
112 (node.type === "ForStatement"
113 ? !astUtils.isParenthesised(sourceCode, node.test)
114 : !isParenthesisedTwice(node.test)
126 * Check whether an assignment expression is descended from a conditional statement's test expression.
127 * @param {!Object} node The node for the assignment expression.
130 function testForConditionalAncestor(node) {
131 const ancestor = findConditionalAncestor(node);
136 messageId: "unexpected",
138 type: NODE_DESCRIPTIONS[ancestor.type] || ancestor.type
144 if (prohibitAssign === "always") {
146 AssignmentExpression: testForConditionalAncestor
151 DoWhileStatement: testForAssign,
152 ForStatement: testForAssign,
153 IfStatement: testForAssign,
154 WhileStatement: testForAssign,
155 ConditionalExpression: testForAssign