[FEATURE] Page module: Show notice "Content is also shown on:"

If a page is selected in page module which content is also shown on
other pages, now a notice is shown with the titles and pid of these pages.

Resolves: #69572
Releases: master
Change-Id: Ie66564da98160825f5759c6ac4937fbbeaafdce0
Reviewed-on: https://review.typo3.org/51049

Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>

typo3/sysext/backend/Classes/Controller/PageLayoutController.php

@@ -644,10 +644,50 @@ class PageLayoutController
                 'state' => InfoboxViewHelper::STATE_INFO
             ]);
             $content .= $view->render();
+        } else {
+            $links = $this->getPageLinksWhereContentIsAlsoShownOn($this->pageinfo['uid']);
+            if (!empty($links)) {
+                $message = sprintf($lang->getLL('content_on_pid_title'), $links);
+                $view->assignMultiple([
+                    'title' => '',
+                    'message' => $message,
+                    'state' => InfoboxViewHelper::STATE_INFO
+                ]);
+                $content .= $view->render();
+            }
         }
         return $content;
     }
 
+    /**
+     * Get all pages with links where the content of a page $pageId is also shown on
+     *
+     * @param int $pageId
+     * @return string
+     */
+    protected function getPageLinksWhereContentIsAlsoShownOn($pageId)
+    {
+        $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)->getQueryBuilderForTable('pages');
+        $queryBuilder->getRestrictions()->removeAll();
+        $queryBuilder->getRestrictions()->add(GeneralUtility::makeInstance(DeletedRestriction::class));
+        $queryBuilder
+            ->select('*')
+            ->from('pages')
+            ->where($queryBuilder->expr()->eq('content_from_pid', $queryBuilder->createNamedParameter($pageId, \PDO::PARAM_INT)));
+
+        $links = [];
+        $rows = $queryBuilder->execute()->fetchAll();
+        if (!empty($rows)) {
+            foreach ($rows as $row) {
+                $linkToPid = $this->local_linkThisScript(['id' => $row['uid']]);
+                $title = BackendUtility::getRecordTitle('pages', $row);
+                $link = '<a href="' . htmlspecialchars($linkToPid) . '">' . htmlspecialchars($title) . ' (PID ' . (int)$row['uid'] . ')</a>';
+                $links[] = $link;
+            }
+        }
+        return implode(', ', $links);
+    }
+
     /**
      *
      * @return string $title

typo3/sysext/backend/Resources/Private/Language/locallang_layout.xlf

@@ -282,6 +282,9 @@
 			<trans-unit id="content_from_pid_title">
 				<source>Page uses content from this page: %s</source>
 			</trans-unit>
+			<trans-unit id="content_on_pid_title">
+				<source>This content is also shown on: %s</source>
+			</trans-unit>
 			<trans-unit id="pageIsExternalLinkMessage">
 				<source>Page is a link to the following external URL: %s</source>
 			</trans-unit>

typo3/sysext/core/Documentation/Changelog/master/Feature-69572-PageModuleNoticeContentIsAlsoShownOn.rst

+.. include:: ../../Includes.txt
+
+================================================================
+Feature: #69572 - Page module Notice "Content is also shown on:"
+================================================================
+
+See :issue:`69572`
+
+Description
+===========
+
+When page content is inherited from different page via "Show content from page" there is a notice displayed on the page.
+
+This feature does the opposite and displays a notice on pages that are inherited elsewhere:
+"This content is also shown on:"
+
+
+Impact
+======
+
+On pages that are inherited elsewhere you see a notice with links to the pages where the content is inherited.
+
+.. index:: Backend
\ No newline at end of file