closes #6912

- on category setParent dialog do not show children of current category
- break recursion if category parentCid is equal to child cid to prevent
infinite loop
- dont allow setting the parentCid of a category to one of it's children

public/src/admin/manage/category.js

@@ -240,8 +240,13 @@ define('admin/manage/category', [
 	}
 
 	Category.launchParentSelector = function () {
+		var parents = [parseInt(ajaxify.data.category.cid, 10)];
 		var categories = ajaxify.data.allCategories.filter(function (category) {
-			return category && !category.disabled && parseInt(category.cid, 10) !== parseInt(ajaxify.data.category.cid, 10);
+			var isChild = parents.includes(parseInt(category.parentCid, 10));
+			if (isChild) {
+				parents.push(parseInt(category.cid, 10));
+			}
+			return category && !category.disabled && parseInt(category.cid, 10) !== parseInt(ajaxify.data.category.cid, 10) && !isChild;
 		});
 
 		categorySelector.modal(categories, function (parentCid) {

src/categories/index.js

@@ -2,6 +2,7 @@
 'use strict';
 
 var async = require('async');
+var _ = require('lodash');
 
 var db = require('../database');
 var user = require('../user');
@@ -219,7 +220,13 @@ Categories.getChildren = function (cids, uid, callback) {
 	});
 
 	async.each(categories, function (category, next) {
+		Categories.getCategoryField(category.cid, 'parentCid', function (err, parentCid) {
+			if (err) {
+				return next(err);
+			}
+			category.parentCid = parentCid;
 			getChildrenRecursive(category, uid, next);
+		});
 	}, function (err) {
 		callback(err, categories.map(function (c) {
 			return c && c.children;
@@ -263,12 +270,37 @@ function getChildrenRecursive(category, uid, callback) {
 		},
 		function (next) {
 			async.each(category.children, function (child, next) {
+				if (parseInt(category.parentCid, 10) === parseInt(child.cid, 10)) {
+					return next();
+				}
 				getChildrenRecursive(child, uid, next);
 			}, next);
 		},
 	], callback);
 }
 
+Categories.getChildrenCids = function (rootCid, callback) {
+	function recursive(currentCid, callback) {
+		db.getSortedSetRange('cid:' + currentCid + ':children', 0, -1, function (err, childrenCids) {
+			if (err) {
+				return callback(err);
+			}
+
+			if (!childrenCids.length) {
+				return callback();
+			}
+			async.eachSeries(childrenCids, function (childCid, next) {
+				allCids.push(parseInt(childCid, 10));
+				recursive(childCid, next);
+			}, callback);
+		});
+	}
+	var allCids = [];
+	recursive(rootCid, function (err) {
+		callback(err, _.uniq(allCids));
+	});
+}
+
 Categories.flattenCategories = function (allCategories, categoryData) {
 	categoryData.forEach(function (category) {
 		if (category) {

src/categories/update.js

@@ -92,6 +92,12 @@ module.exports = function (Categories) {
 		}
 		async.waterfall([
 			function (next) {
+				Categories.getChildrenCids(cid, next);
+			},
+			function (childrenCids, next) {
+				if (childrenCids.includes(parseInt(newParent, 10))) {
+					return next(new Error('[[error:cant-set-child-as-parent]]'));
+				}
 				Categories.getCategoryField(cid, 'parentCid', next);
 			},
 			function (oldParent, next) {

test/categories.js

@@ -338,6 +338,31 @@ describe('Categories', function () {
 			});
 		});
 
+		it('should error if you try to set child as parent', function (done) {
+			var child1Cid;
+			var parentCid;
+			async.waterfall([
+				function (next) {
+					Categories.create({ name: 'parent 1', description: 'poor parent' }, next);
+				},
+				function (category, next) {
+					parentCid = category.cid;
+					Categories.create({ name: 'child1', description: 'wanna be parent', parentCid: parentCid }, next);
+				},
+				function (category, next) {
+					child1Cid = category.cid;
+					var updateData = {};
+					updateData[parentCid] = {
+						parentCid: child1Cid,
+					};
+					socketCategories.update({ uid: adminUid }, updateData, function (err) {
+						assert.equal(err.message, '[[error:cant-set-child-as-parent]]');
+						next();
+					});
+				},
+			], done);
+		});
+
 		it('should update category data', function (done) {
 			var updateData = {};
 			updateData[cid] = {