/**
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* @fileoverview Rule to disallow duplicate conditions in if-else-if chains
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* @author Milos Djermanovic
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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("./utils/ast-utils");
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//------------------------------------------------------------------------------
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// Helpers
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//------------------------------------------------------------------------------
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/**
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* Determines whether the first given array is a subset of the second given array.
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* @param {Function} comparator A function to compare two elements, should return `true` if they are equal.
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* @param {Array} arrA The array to compare from.
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* @param {Array} arrB The array to compare against.
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* @returns {boolean} `true` if the array `arrA` is a subset of the array `arrB`.
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*/
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function isSubsetByComparator(comparator, arrA, arrB) {
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return arrA.every(a => arrB.some(b => comparator(a, b)));
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}
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/**
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* Splits the given node by the given logical operator.
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* @param {string} operator Logical operator `||` or `&&`.
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* @param {ASTNode} node The node to split.
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* @returns {ASTNode[]} Array of conditions that makes the node when joined by the operator.
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*/
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function splitByLogicalOperator(operator, node) {
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if (node.type === "LogicalExpression" && node.operator === operator) {
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return [...splitByLogicalOperator(operator, node.left), ...splitByLogicalOperator(operator, node.right)];
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}
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return [node];
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}
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const splitByOr = splitByLogicalOperator.bind(null, "||");
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const splitByAnd = splitByLogicalOperator.bind(null, "&&");
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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: "problem",
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docs: {
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description: "disallow duplicate conditions in if-else-if chains",
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category: "Possible Errors",
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recommended: true,
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url: "https://eslint.org/docs/rules/no-dupe-else-if"
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},
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schema: [],
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messages: {
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unexpected: "This branch can never execute. Its condition is a duplicate or covered by previous conditions in the if-else-if chain."
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}
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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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* Determines whether the two given nodes are considered to be equal. In particular, given that the nodes
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* represent expressions in a boolean context, `||` and `&&` can be considered as commutative operators.
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* @param {ASTNode} a First node.
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* @param {ASTNode} b Second node.
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* @returns {boolean} `true` if the nodes are considered to be equal.
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*/
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function equal(a, b) {
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if (a.type !== b.type) {
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return false;
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}
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if (
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a.type === "LogicalExpression" &&
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(a.operator === "||" || a.operator === "&&") &&
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a.operator === b.operator
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) {
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return equal(a.left, b.left) && equal(a.right, b.right) ||
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equal(a.left, b.right) && equal(a.right, b.left);
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}
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return astUtils.equalTokens(a, b, sourceCode);
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}
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const isSubset = isSubsetByComparator.bind(null, equal);
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return {
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IfStatement(node) {
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const test = node.test,
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conditionsToCheck = test.type === "LogicalExpression" && test.operator === "&&"
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? [test, ...splitByAnd(test)]
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: [test];
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let current = node,
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listToCheck = conditionsToCheck.map(c => splitByOr(c).map(splitByAnd));
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while (current.parent && current.parent.type === "IfStatement" && current.parent.alternate === current) {
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current = current.parent;
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const currentOrOperands = splitByOr(current.test).map(splitByAnd);
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listToCheck = listToCheck.map(orOperands => orOperands.filter(
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orOperand => !currentOrOperands.some(currentOrOperand => isSubset(currentOrOperand, orOperand))
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));
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if (listToCheck.some(orOperands => orOperands.length === 0)) {
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context.report({ node: test, messageId: "unexpected" });
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break;
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}
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}
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}
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};
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}
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};
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