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buildfiles/app/node_modules/eslint/lib/rules/no-dupe-else-if.js

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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: true,
+            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;
+                    }
+                }
+            }
+        };
+    }
+};