create a patch

.gitignore

@@ -0,0 +1 @@
+/vendor/

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Mariusz Łopuch
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,26 @@
+# Instalation
+
+Fix for https://github.com/magento/magento2/issues/31007
+
+1. Install package by composer:
+
+`composer require alex-79/magento2-page-save-fixes`
+
+2. Extend composer.json:
+
+```
+    "extra": {
+        "enable-patching": true,
+        "magento-force": "override",
+        "composer-exit-on-patch-failure": true,
+        "patches": {
+            "magento/module-cms": {
+                "Fix for https://github.com/magento/magento2/issues/31007": "vendor/alex-79/magento2-cms-save-fixes/vendorPatch/magento/module-cms/Model/PageRepository.patch",
+            }
+        }
+    }
+```
+
+3. composer install
+
+`composer install`

composer.json

@@ -0,0 +1,16 @@
+{
+    "name": "alex-79/magento2-page-save-fixes",
+    "description": "Magento 2 fixes: CMS Page saving fails with 'The value specified in the URL Key field would generate a URL that already exists.'",
+    "version": "1.0.0",
+    "minimum-stability": "dev",
+    "require": {
+        "cweagans/composer-patches": "^1.7"
+    },
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "Alexander Bobylev",
+            "email": "alexander.bobylev@gmail.com"
+        }
+    ]
+}

vendorPatch/magento/module-cms/Model/PageRepository.patch

@@ -0,0 +1,16 @@
+diff --git a/magento/module-cms/Model/PageRepository.php b/magento/module-cms/Model/PageRepository.php
+index 2816b4c..6508aa2 100644
+--- a/magento/module-cms/Model/PageRepository.php
++++ b/magento/module-cms/Model/PageRepository.php
+@@ -188,7 +188,7 @@ class PageRepository implements PageRepositoryInterface
+                 $page->setStoreId($storeId);
+             }
+             $this->validateLayoutUpdate($page);
+-            $this->validateRoutesDuplication($page);
++            // $this->validateRoutesDuplication($page);
+             $this->resource->save($page);
+             $this->identityMap->add($page);
+         } catch (LocalizedException $exception) {
+-- 
+2.20.1
+

vendorPatch/magento/module-cms/Model/PageRepository.php

@@ -0,0 +1,312 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+namespace Magento\Cms\Model;
+
+use Magento\Cms\Api\Data;
+use Magento\Cms\Api\Data\PageInterface;
+use Magento\Cms\Api\Data\PageInterfaceFactory;
+use Magento\Cms\Api\Data\PageSearchResultsInterface;
+use Magento\Cms\Api\PageRepositoryInterface;
+use Magento\Cms\Model\Api\SearchCriteria\PageCollectionProcessor;
+use Magento\Cms\Model\Page\IdentityMap;
+use Magento\Cms\Model\ResourceModel\Page as ResourcePage;
+use Magento\Cms\Model\ResourceModel\Page\CollectionFactory as PageCollectionFactory;
+use Magento\Framework\Api\DataObjectHelper;
+use Magento\Framework\Api\SearchCriteria\CollectionProcessorInterface;
+use Magento\Framework\Api\SearchCriteriaInterface;
+use Magento\Framework\App\ObjectManager;
+use Magento\Framework\App\Route\Config;
+use Magento\Framework\Exception\CouldNotDeleteException;
+use Magento\Framework\Exception\CouldNotSaveException;
+use Magento\Framework\Exception\LocalizedException;
+use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Framework\Reflection\DataObjectProcessor;
+use Magento\Store\Model\StoreManagerInterface;
+use Magento\Framework\EntityManager\HydratorInterface;
+
+/**
+ * Cms page repository
+ * @SuppressWarnings(PHPMD.CouplingBetweenObjects)
+ */
+class PageRepository implements PageRepositoryInterface
+{
+    /**
+     * @var ResourcePage
+     */
+    protected $resource;
+
+    /**
+     * @var PageFactory
+     */
+    protected $pageFactory;
+
+    /**
+     * @var PageCollectionFactory
+     */
+    protected $pageCollectionFactory;
+
+    /**
+     * @var Data\PageSearchResultsInterfaceFactory
+     */
+    protected $searchResultsFactory;
+
+    /**
+     * @var DataObjectHelper
+     */
+    protected $dataObjectHelper;
+
+    /**
+     * @var DataObjectProcessor
+     */
+    protected $dataObjectProcessor;
+
+    /**
+     * @var PageInterfaceFactory
+     */
+    protected $dataPageFactory;
+
+    /**
+     * @var StoreManagerInterface
+     */
+    private $storeManager;
+
+    /**
+     * @var CollectionProcessorInterface
+     */
+    private $collectionProcessor;
+
+    /**
+     * @var IdentityMap
+     */
+    private $identityMap;
+
+    /**
+     * @var Config
+     */
+    private $routeConfig;
+
+    /**
+     * @var HydratorInterface
+     */
+    private $hydrator;
+
+    /**
+     * @param ResourcePage $resource
+     * @param PageFactory $pageFactory
+     * @param PageInterfaceFactory $dataPageFactory
+     * @param PageCollectionFactory $pageCollectionFactory
+     * @param Data\PageSearchResultsInterfaceFactory $searchResultsFactory
+     * @param DataObjectHelper $dataObjectHelper
+     * @param DataObjectProcessor $dataObjectProcessor
+     * @param StoreManagerInterface $storeManager
+     * @param CollectionProcessorInterface $collectionProcessor
+     * @param IdentityMap|null $identityMap
+     * @param Config|null $routeConfig
+     * @param HydratorInterface|null $hydrator
+     * @SuppressWarnings(PHPMD.ExcessiveParameterList)
+     */
+    public function __construct(
+        ResourcePage $resource,
+        PageFactory $pageFactory,
+        PageInterfaceFactory $dataPageFactory,
+        PageCollectionFactory $pageCollectionFactory,
+        Data\PageSearchResultsInterfaceFactory $searchResultsFactory,
+        DataObjectHelper $dataObjectHelper,
+        DataObjectProcessor $dataObjectProcessor,
+        StoreManagerInterface $storeManager,
+        CollectionProcessorInterface $collectionProcessor = null,
+        ?IdentityMap $identityMap = null,
+        ?Config $routeConfig = null,
+        ?HydratorInterface $hydrator = null
+    ) {
+        $this->resource = $resource;
+        $this->pageFactory = $pageFactory;
+        $this->pageCollectionFactory = $pageCollectionFactory;
+        $this->searchResultsFactory = $searchResultsFactory;
+        $this->dataObjectHelper = $dataObjectHelper;
+        $this->dataPageFactory = $dataPageFactory;
+        $this->dataObjectProcessor = $dataObjectProcessor;
+        $this->storeManager = $storeManager;
+        $this->collectionProcessor = $collectionProcessor ?: $this->getCollectionProcessor();
+        $this->identityMap = $identityMap ?? ObjectManager::getInstance()
+                ->get(IdentityMap::class);
+        $this->routeConfig = $routeConfig ?? ObjectManager::getInstance()
+                ->get(Config::class);
+        $this->hydrator = $hydrator ?: ObjectManager::getInstance()->get(HydratorInterface::class);
+    }
+
+    /**
+     * Validate new layout update values.
+     *
+     * @param PageInterface $page
+     * @return void
+     * @throws \InvalidArgumentException
+     */
+    private function validateLayoutUpdate(PageInterface $page): void
+    {
+        //Persisted data
+        $oldData = null;
+        if ($page->getId() && $page instanceof Page) {
+            $oldData = $page->getOrigData();
+        }
+        //Custom layout update can be removed or kept as is.
+        if ($page->getCustomLayoutUpdateXml()
+            && (
+                !$oldData
+                || $page->getCustomLayoutUpdateXml() !== $oldData[Data\PageInterface::CUSTOM_LAYOUT_UPDATE_XML]
+            )
+        ) {
+            throw new \InvalidArgumentException('Custom layout updates must be selected from a file');
+        }
+        if ($page->getLayoutUpdateXml()
+            && (!$oldData || $page->getLayoutUpdateXml() !== $oldData[Data\PageInterface::LAYOUT_UPDATE_XML])
+        ) {
+            throw new \InvalidArgumentException('Custom layout updates must be selected from a file');
+        }
+    }
+
+    /**
+     * Save Page data
+     *
+     * @param PageInterface|Page $page
+     * @return Page
+     * @throws CouldNotSaveException
+     */
+    public function save(PageInterface $page)
+    {
+        try {
+            $pageId = $page->getId();
+            if ($pageId && !($page instanceof Page && $page->getOrigData())) {
+                $page = $this->hydrator->hydrate($this->getById($pageId), $this->hydrator->extract($page));
+            }
+            if ($page->getStoreId() === null) {
+                $storeId = $this->storeManager->getStore()->getId();
+                $page->setStoreId($storeId);
+            }
+            $this->validateLayoutUpdate($page);
+            // $this->validateRoutesDuplication($page);
+            $this->resource->save($page);
+            $this->identityMap->add($page);
+        } catch (LocalizedException $exception) {
+            throw new CouldNotSaveException(
+                __('Could not save the page: %1', $exception->getMessage()),
+                $exception
+            );
+        } catch (\Throwable $exception) {
+            throw new CouldNotSaveException(
+                __('Could not save the page: %1', __('Something went wrong while saving the page.')),
+                $exception
+            );
+        }
+        return $page;
+    }
+
+    /**
+     * Load Page data by given Page Identity
+     *
+     * @param string $pageId
+     * @return Page
+     * @throws NoSuchEntityException
+     */
+    public function getById($pageId)
+    {
+        $page = $this->pageFactory->create();
+        $page->load($pageId);
+        if (!$page->getId()) {
+            throw new NoSuchEntityException(__('The CMS page with the "%1" ID doesn\'t exist.', $pageId));
+        }
+        $this->identityMap->add($page);
+
+        return $page;
+    }
+
+    /**
+     * Load Page data collection by given search criteria
+     *
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
+     * @SuppressWarnings(PHPMD.NPathComplexity)
+     * @param SearchCriteriaInterface $criteria
+     * @return PageSearchResultsInterface
+     */
+    public function getList(SearchCriteriaInterface $criteria)
+    {
+        $collection = $this->pageCollectionFactory->create();
+
+        $this->collectionProcessor->process($criteria, $collection);
+
+        $searchResults = $this->searchResultsFactory->create();
+        $searchResults->setSearchCriteria($criteria);
+        $searchResults->setItems($collection->getItems());
+        $searchResults->setTotalCount($collection->getSize());
+        return $searchResults;
+    }
+
+    /**
+     * Delete Page
+     *
+     * @param PageInterface $page
+     * @return bool
+     * @throws CouldNotDeleteException
+     */
+    public function delete(PageInterface $page)
+    {
+        try {
+            $this->resource->delete($page);
+            $this->identityMap->remove($page->getId());
+        } catch (\Exception $exception) {
+            throw new CouldNotDeleteException(
+                __('Could not delete the page: %1', $exception->getMessage())
+            );
+        }
+        return true;
+    }
+
+    /**
+     * Delete Page by given Page Identity
+     *
+     * @param string $pageId
+     * @return bool
+     * @throws CouldNotDeleteException
+     * @throws NoSuchEntityException
+     */
+    public function deleteById($pageId)
+    {
+        return $this->delete($this->getById($pageId));
+    }
+
+    /**
+     * Retrieve collection processor
+     *
+     * @deprecated 102.0.0
+     * @return CollectionProcessorInterface
+     */
+    private function getCollectionProcessor()
+    {
+        if (!$this->collectionProcessor) {
+            // phpstan:ignore "Class Magento\Cms\Model\Api\SearchCriteria\PageCollectionProcessor not found."
+            $this->collectionProcessor = ObjectManager::getInstance()
+                ->get(PageCollectionProcessor::class);
+        }
+        return $this->collectionProcessor;
+    }
+
+    /**
+     * Checks that page identifier doesn't duplicate existed routes
+     *
+     * @param PageInterface $page
+     * @return void
+     * @throws CouldNotSaveException
+     */
+    private function validateRoutesDuplication($page): void
+    {
+        if ($this->routeConfig->getRouteByFrontName($page->getIdentifier(), 'frontend')) {
+            throw new CouldNotSaveException(
+                __('The value specified in the URL Key field would generate a URL that already exists.')
+            );
+        }
+    }
+}