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