Brought back previously reverted changes to elementToStructure() throwing when invoked for an element that allows $text""

packages/ckeditor5-engine/src/conversion/downcasthelpers.js

@@ -21,7 +21,6 @@ import ConversionHelpers from './conversionhelpers';
 import { cloneDeep } from 'lodash-es';
 import CKEditorError from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
 import toArray from '@ckeditor/ckeditor5-utils/src/toarray';
-import { logWarning } from '@ckeditor/ckeditor5-utils';
 
 /**
  * Downcast conversion helper functions.
@@ -1042,9 +1041,6 @@ export function insertElement( elementCreator, consumer = defaultConsumer ) {
 			return;
 		}
 
-		// Check if only one element has been created.
-		validateChildren( viewElement );
-
 		// Consume an element insertion and all present attributes that are specified as a reconversion triggers.
 		consumer( data.item, conversionApi.consumable );
 
@@ -1703,6 +1699,48 @@ function downcastElementToStructure( config ) {
 	config.model.children = true;
 
 	return dispatcher => {
+		if ( dispatcher._conversionApi.schema.checkChild( config.model.name, '$text' ) ) {
+			/**
+			 * This error occurs when a {@link module:engine/model/element~Element model element} is downcasted
+			 * via {@link module:engine/conversion/downcasthelpers~DowncastHelpers#elementToStructure} helper but the element was
+			 * allowed to host `$text` by the {@link module:engine/model/schema~Schema model schema}.
+			 *
+			 * For instance, this may be the result of `myElement` allowing the content of
+			 * {@glink framework/guides/deep-dive/schema#generic-items `$block`} in its schema definition:
+			 *
+			 *		// Element definition in schema.
+			 *		schema.register( 'myElement', {
+			 *			allowContentOf: '$block',
+			 *
+			 *			// ...
+			 *		} );
+			 *
+			 *		// ...
+			 *
+			 *		// Conversion of myElement with the use of elementToStructure().
+			 *		editor.conversion.for( 'downcast' ).elementToStructure( {
+			 *			model: 'myElement',
+			 *			view: ( modelElement, { writer } ) => {
+			 *				// ...
+			 *			}
+			 *		} );
+			 *
+			 * In such case, {@link module:engine/conversion/downcasthelpers~DowncastHelpers#elementToElement `elementToElement()`} helper
+			 * can be used instead to get around this problem:
+			 *
+			 *		editor.conversion.for( 'downcast' ).elementToElement( {
+			 *			model: 'myElement',
+			 *			view: ( modelElement, { writer } ) => {
+			 *				// ...
+			 *			}
+			 *		} );
+			 *
+			 * @error conversion-element-to-structure-disallowed-text
+			 * @param {String} elementName The name of the element the structure is to be created for.
+			 */
+			throw new CKEditorError( 'conversion-element-to-structure-disallowed-text', dispatcher, { elementName: config.model.name } );
+		}
+
 		dispatcher.on(
 			'insert:' + config.model.name,
 			insertStructure( config.view, createConsumer( config.model ) ),
@@ -2121,31 +2159,6 @@ function createConsumer( model ) {
 	};
 }
 
-// Check if given element children list contains only UI elements and warns otherwise.
-//
-// @param {module:engine/view/element~Element} viewElement.
-function validateChildren( viewElement ) {
-	const children = Array.from( viewElement.getChildren() );
-	const hasNonUiChildren = children.some( element => !element.is( 'uiElement' ) );
-
-	if ( hasNonUiChildren ) {
-		/**
-		 * Only one container element without any children elements other than
-		 * {@link module:engine/view/uielement~UIElement `UIElement`}s should be created in
-		 * {@link module:engine/conversion/downcasthelpers~DowncastHelpers#elementToElement} function.
-		 *
-		 * Please make sure you don't create more than one element in
-		 * {@link module:engine/conversion/downcasthelpers~DowncastHelpers#elementToElement} and if you need
-		 * to create multiple elements use {@link module:engine/conversion/downcasthelpers~DowncastHelpers#elementToStructure}
-		 * instead.
-		 *
-		 * @error conversion-element-to-element-created-multiple-elements
-		 * @param {module:engine/model/element~Element} viewElement
-		 */
-		logWarning( 'conversion-element-to-element-created-multiple-elements', { viewElement } );
-	}
-}
-
 // Creates a function that create view slots.
 //
 // @param {module:engine/model/element~Element} element

packages/ckeditor5-engine/tests/conversion/downcasthelpers.js

@@ -808,7 +808,7 @@ describe( 'DowncastHelpers', () => {
 		} );
 
 		describe( 'with multiple child elements', () => {
-			it( 'warns if multiple child elements are created', () => {
+			it( 'does not warn if multiple child elements are created', () => {
 				let viewElement;
 
 				testUtils.sinon.stub( console, 'warn' );
@@ -828,12 +828,7 @@ describe( 'DowncastHelpers', () => {
 					writer.insertElement( 'multiItemBox', null, modelRoot, 0 );
 				} );
 
-				sinon.assert.calledOnce( console.warn );
-				sinon.assert.calledWithExactly( console.warn,
-					sinon.match( /^conversion-element-to-element-created-multiple-elements/ ),
-					{ viewElement },
-					sinon.match.string // Link to the documentation
-				);
+				sinon.assert.notCalled( console.warn );
 			} );
 
 			it( 'does not warn if multiple child UI elements are created', () => {
@@ -2301,6 +2296,25 @@ describe( 'DowncastHelpers', () => {
 				} );
 			}, /^conversion-slot-filter-incomplete/, controller.downcastDispatcher );
 		} );
+
+		// https://github.com/ckeditor/ckeditor5/issues/11163
+		it( 'should throw an exception when invoked for a model element that allows $text', () => {
+			model.schema.register( 'myElement', {
+				allowIn: '$root',
+
+				// This makes it accept $text.
+				allowContentOf: '$block'
+			} );
+
+			expectToThrowCKEditorError( () => {
+				downcastHelpers.elementToStructure( {
+					model: 'myElement',
+					view: ( modelElement, { writer } ) => {
+						return writer.createContainerElement( 'div' );
+					}
+				} );
+			}, /^conversion-element-to-structure-disallowed-text/, controller.downcastDispatcher, { elementName: 'myElement' } );
+		} );
 	} );
 
 	describe( 'attributeToElement()', () => {

packages/ckeditor5-widget/tests/widget-events.js

@@ -72,7 +72,7 @@ describe( 'Widget - Events', () => {
 
 		function defineSchema( editor ) {
 			editor.model.schema.register( 'simpleWidgetElement', {
-				inheritAllFrom: '$block',
+				allowIn: '$root',
 				isObject: true
 			} );
 		}

packages/ckeditor5-widget/tests/widget.js

@@ -96,13 +96,12 @@ describe( 'Widget', () => {
 					.elementToElement( { model: 'imageBlock', view: 'img' } )
 					.elementToElement( { model: 'blockQuote', view: 'blockquote' } )
 					.elementToElement( { model: 'div', view: 'div' } )
-					.elementToStructure( {
+					.elementToElement( {
 						model: 'widget',
 						view: ( modelItem, { writer } ) => {
 							const b = writer.createAttributeElement( 'b' );
 							const div = writer.createContainerElement( 'div' );
 							writer.insert( writer.createPositionAt( div, 0 ), b );
-							writer.insert( writer.createPositionAt( div, 0 ), writer.createSlot() );
 
 							return toWidget( div, writer, { label: 'element label' } );
 						}

packages/ckeditor5-widget/tests/widgetresize.js

@@ -693,7 +693,7 @@ describe( 'WidgetResize', () => {
 		} );
 
 		editor.conversion.for( 'downcast' )
-			.elementToStructure( {
+			.elementToElement( {
 				model: 'widget',
 				view: ( modelItem, { writer } ) => {
 					const parentDiv = writer.createContainerElement( 'div' );

packages/ckeditor5-widget/tests/widgettypearound/widgettypearound.js

@@ -1872,14 +1872,13 @@ describe( 'WidgetTypeAround', () => {
 		} );
 
 		editor.conversion.for( 'downcast' )
-			.elementToStructure( {
+			.elementToElement( {
 				model: 'blockWidget',
 				view: ( modelItem, { writer } ) => {
 					const container = writer.createContainerElement( 'div' );
 					const viewText = writer.createText( 'block-widget' );
 
 					writer.insert( writer.createPositionAt( container, 0 ), viewText );
-					writer.insert( writer.createPositionAt( container, 0 ), writer.createSlot() );
 
 					return toWidget( container, writer, {
 						label: 'block widget'