[FEATURE] Use the ckeditor plugin editorplaceholder

Enable the ckeditor plugin editorplaceholder which is available since
the update of ckeditor to version 4.15.0 with #92412 and fill it with
the placeholder information provided by the TCA.

Resolves: #92423
Releases: master
Change-Id: Ie392073d200a193b2be5f245042f0914f7665cdd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65899
Tested-by: Torben Hansen <derhansen@gmail.com>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>

typo3/sysext/core/Documentation/Changelog/master/Feature-92423-EnablePlaceholderConfigForCkeditor.rst

@@ -0,0 +1,37 @@
+.. include:: ../../Includes.txt
+
+========================================================
+Feature: #92423 - Enable placeholder config for ckeditor
+========================================================
+
+See :issue:`92423`
+
+Description
+===========
+
+After the update of ckeditor to version 4.15.0, a new ckeditor plugin, called
+**Editor Placeholder**, is now available. More information along with an example
+can be found in the official documentation_.
+
+The placeholder configuration of TCA type `text` is now fed into the ckeditor plugin:
+
+.. code-block:: php
+
+    'bodytext' => [
+        'label' => 'LLL:EXT:core/Resources/Private/Language/locallang_general.xlf:LGL.text',
+        'config' => [
+            'placeholder' => 'This is a placeholder',
+            'type' => 'text',
+            'enableRichtext' => true,
+        ]
+    ]
+
+
+Impact
+======
+
+Editors can now be supported by providing a placeholder text also for the ckeditor.
+
+.. _documentation: https://ckeditor.com/docs/ckeditor4/latest/examples/editorplaceholder.html
+
+.. index:: Backend, ext:rte_ckeditor

typo3/sysext/rte_ckeditor/Classes/Form/Element/RichTextElement.php

@@ -218,6 +218,9 @@ protected function getCkEditorRequireJsModuleCode(string $fieldId): string
                 }
             }
             $configuration['extraPlugins'] .= ',' . $extraPluginName;
+            if (isset($this->data['parameterArray']['fieldConf']['config']['placeholder'])) {
+                $configuration['editorplaceholder'] = (string)$this->data['parameterArray']['fieldConf']['config']['placeholder'];
+            }
 
             $externalPlugins .= 'CKEDITOR.plugins.addExternal(';
             $externalPlugins .= GeneralUtility::quoteJSvalue($extraPluginName) . ',';

typo3/sysext/rte_ckeditor/Configuration/RTE/Default.yaml

@@ -31,6 +31,7 @@ editor:
     extraPlugins:
       - justify
       - autolink
+      - editorplaceholder
 
     removePlugins:
       - image

typo3/sysext/rte_ckeditor/Configuration/RTE/Full.yaml

@@ -55,6 +55,7 @@ editor:
       - selectall
       - autolink
       - wordcount
+      - editorplaceholder
 
     removePlugins:
       - image