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app_vue/node_modules/eslint/lib/rules/for-direction.js

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+/**
+ * @fileoverview enforce "for" loop update clause moving the counter in the right direction.(for-direction)
+ * @author Aladdin-ADD<hh_2013@foxmail.com>
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        type: "problem",
+
+        docs: {
+            description: "enforce \"for\" loop update clause moving the counter in the right direction.",
+            category: "Possible Errors",
+            recommended: true,
+            url: "https://eslint.org/docs/rules/for-direction"
+        },
+
+        fixable: null,
+        schema: [],
+
+        messages: {
+            incorrectDirection: "The update clause in this loop moves the variable in the wrong direction."
+        }
+    },
+
+    create(context) {
+
+        /**
+         * report an error.
+         * @param {ASTNode} node the node to report.
+         * @returns {void}
+         */
+        function report(node) {
+            context.report({
+                node,
+                messageId: "incorrectDirection"
+            });
+        }
+
+        /**
+         * check the right side of the assignment
+         * @param {ASTNode} update UpdateExpression to check
+         * @param {int} dir expected direction that could either be turned around or invalidated
+         * @returns {int} return dir, the negated dir or zero if it's not clear for identifiers
+         */
+        function getRightDirection(update, dir) {
+            if (update.right.type === "UnaryExpression") {
+                if (update.right.operator === "-") {
+                    return -dir;
+                }
+            } else if (update.right.type === "Identifier") {
+                return 0;
+            }
+            return dir;
+        }
+
+        /**
+         * check UpdateExpression add/sub the counter
+         * @param {ASTNode} update UpdateExpression to check
+         * @param {string} counter variable name to check
+         * @returns {int} if add return 1, if sub return -1, if nochange, return 0
+         */
+        function getUpdateDirection(update, counter) {
+            if (update.argument.type === "Identifier" && update.argument.name === counter) {
+                if (update.operator === "++") {
+                    return 1;
+                }
+                if (update.operator === "--") {
+                    return -1;
+                }
+            }
+            return 0;
+        }
+
+        /**
+         * check AssignmentExpression add/sub the counter
+         * @param {ASTNode} update AssignmentExpression to check
+         * @param {string} counter variable name to check
+         * @returns {int} if add return 1, if sub return -1, if nochange, return 0
+         */
+        function getAssignmentDirection(update, counter) {
+            if (update.left.name === counter) {
+                if (update.operator === "+=") {
+                    return getRightDirection(update, 1);
+                }
+                if (update.operator === "-=") {
+                    return getRightDirection(update, -1);
+                }
+            }
+            return 0;
+        }
+        return {
+            ForStatement(node) {
+
+                if (node.test && node.test.type === "BinaryExpression" && node.test.left.type === "Identifier" && node.update) {
+                    const counter = node.test.left.name;
+                    const operator = node.test.operator;
+                    const update = node.update;
+
+                    let wrongDirection;
+
+                    if (operator === "<" || operator === "<=") {
+                        wrongDirection = -1;
+                    } else if (operator === ">" || operator === ">=") {
+                        wrongDirection = 1;
+                    } else {
+                        return;
+                    }
+
+                    if (update.type === "UpdateExpression") {
+                        if (getUpdateDirection(update, counter) === wrongDirection) {
+                            report(node);
+                        }
+                    } else if (update.type === "AssignmentExpression" && getAssignmentDirection(update, counter) === wrongDirection) {
+                        report(node);
+                    }
+                }
+            }
+        };
+    }
+};