Introducing list.multiBlock config option

packages/ckeditor5-engine/src/view/renderer.ts

@@ -357,7 +357,7 @@ export default class Renderer extends ObservableMixin() {
 		//
 		// Converting live list to an array to make the list static.
 		const actualDomChildren = Array.from(
-			this.domConverter.mapViewToDom( viewElement )!.childNodes
+			domElement.childNodes
 		);
 		const expectedDomChildren = Array.from(
 			this.domConverter.viewChildrenToDom( viewElement, { withChildren: false } )

packages/ckeditor5-html-support/src/integrations/documentlist.ts

@@ -89,9 +89,7 @@ export default class DocumentListElementSupport extends Plugin {
 
 			const allowAttributes = viewElements.map( element => getHtmlAttributeName( element ) );
 
-			schema.extend( '$block', { allowAttributes } );
-			schema.extend( '$blockObject', { allowAttributes } );
-			schema.extend( '$container', { allowAttributes } );
+			schema.extend( '$listItem', { allowAttributes } );
 
 			conversion.for( 'upcast' ).add( dispatcher => {
 				dispatcher.on<UpcastElementEvent>(

packages/ckeditor5-list/src/documentlist/converters.ts

@@ -269,7 +269,7 @@ export function reconvertItemsOnDataChange(
 			return true;
 		}
 
-		if ( !item.is( 'element', 'paragraph' ) ) {
+		if ( !item.is( 'element', 'paragraph' ) && !item.is( 'element', 'listItem' ) ) {
 			return false;
 		}
 

packages/ckeditor5-list/src/documentlist/documentlistcommand.ts

@@ -19,7 +19,8 @@ import {
 	ListItemUid,
 	sortBlocks,
 	getSelectedBlockObject,
-	isListItemBlock
+	isListItemBlock,
+	canBecomeSimpleListItem
 } from './utils/model';
 
 /**
@@ -75,7 +76,7 @@ export default class DocumentListCommand extends Command {
 		const selectedBlockObject = getSelectedBlockObject( model );
 
 		const blocks = Array.from( document.selection.getSelectedBlocks() )
-			.filter( block => model.schema.checkAttribute( block, 'listType' ) );
+			.filter( block => model.schema.checkAttribute( block, 'listType' ) || canBecomeSimpleListItem( block, model.schema ) );
 
 		// Whether we are turning off some items.
 		const turnOff = options.forceValue !== undefined ? !options.forceValue : this.value;
@@ -92,7 +93,7 @@ export default class DocumentListCommand extends Command {
 					changedBlocks.push( ...splitListItemBefore( itemBlocks[ 1 ], writer ) );
 				}
 
-				// Convert list blocks to plain blocks.
+				// Strip list attributes.
 				changedBlocks.push( ...removeListAttributes( blocks, writer ) );
 
 				// Outdent items following the selected list item.
@@ -117,6 +118,11 @@ export default class DocumentListCommand extends Command {
 				for ( const block of blocks ) {
 					// Promote the given block to the list item.
 					if ( !block.hasAttribute( 'listType' ) ) {
+						// Rename block to a simple list item if this option is enabled.
+						if ( !block.is( 'element', 'listItem' ) && canBecomeSimpleListItem( block, model.schema ) ) {
+							writer.rename( block, 'listItem' );
+						}
+
 						writer.setAttributes( {
 							listIndent: 0,
 							listItemId: ListItemUid.next(),
@@ -194,7 +200,7 @@ export default class DocumentListCommand extends Command {
 		}
 
 		for ( const block of blocks ) {
-			if ( schema.checkAttribute( block, 'listType' ) ) {
+			if ( schema.checkAttribute( block, 'listType' ) || canBecomeSimpleListItem( block, schema ) ) {
 				return true;
 			}
 		}

packages/ckeditor5-list/src/documentlist/documentlistediting.ts

@@ -9,6 +9,7 @@
 
 import {
 	Plugin,
+	type Editor,
 	type MultiCommand
 } from 'ckeditor5/src/core';
 
@@ -108,12 +109,22 @@ export default class DocumentListEditing extends Plugin {
 		return [ Enter, Delete, DocumentListUtils ] as const;
 	}
 
+	/**
+	 * @inheritDoc
+	 */
+	constructor( editor: Editor ) {
+		super( editor );
+
+		editor.config.define( 'list.multiBlock', true );
+	}
+
 	/**
 	 * @inheritDoc
 	 */
 	public init(): void {
 		const editor = this.editor;
 		const model = editor.model;
+		const multiBlock = editor.config.get( 'list.multiBlock' );
 
 		if ( editor.plugins.has( 'ListEditing' ) ) {
 			/**
@@ -125,9 +136,18 @@ export default class DocumentListEditing extends Plugin {
 			throw new CKEditorError( 'document-list-feature-conflict', this, { conflictPlugin: 'ListEditing' } );
 		}
 
-		model.schema.extend( '$container', { allowAttributes: LIST_BASE_ATTRIBUTES } );
-		model.schema.extend( '$block', { allowAttributes: LIST_BASE_ATTRIBUTES } );
-		model.schema.extend( '$blockObject', { allowAttributes: LIST_BASE_ATTRIBUTES } );
+		model.schema.register( '$listItem', { allowAttributes: LIST_BASE_ATTRIBUTES } );
+
+		if ( multiBlock ) {
+			model.schema.extend( '$container', { allowAttributesOf: '$listItem' } );
+			model.schema.extend( '$block', { allowAttributesOf: '$listItem' } );
+			model.schema.extend( '$blockObject', { allowAttributesOf: '$listItem' } );
+		} else {
+			model.schema.register( 'listItem', {
+				inheritAllFrom: '$block',
+				allowAttributesOf: '$listItem'
+			} );
+		}
 
 		for ( const attribute of LIST_BASE_ATTRIBUTES ) {
 			model.schema.setAttributeProperties( attribute, {
@@ -142,12 +162,14 @@ export default class DocumentListEditing extends Plugin {
 		editor.commands.add( 'indentList', new DocumentListIndentCommand( editor, 'forward' ) );
 		editor.commands.add( 'outdentList', new DocumentListIndentCommand( editor, 'backward' ) );
 
-		editor.commands.add( 'mergeListItemBackward', new DocumentListMergeCommand( editor, 'backward' ) );
-		editor.commands.add( 'mergeListItemForward', new DocumentListMergeCommand( editor, 'forward' ) );
-
 		editor.commands.add( 'splitListItemBefore', new DocumentListSplitCommand( editor, 'before' ) );
 		editor.commands.add( 'splitListItemAfter', new DocumentListSplitCommand( editor, 'after' ) );
 
+		if ( multiBlock ) {
+			editor.commands.add( 'mergeListItemBackward', new DocumentListMergeCommand( editor, 'backward' ) );
+			editor.commands.add( 'mergeListItemForward', new DocumentListMergeCommand( editor, 'forward' ) );
+		}
+
 		this._setupDeleteIntegration();
 		this._setupEnterIntegration();
 		this._setupTabIntegration();
@@ -208,8 +230,8 @@ export default class DocumentListEditing extends Plugin {
 	 */
 	private _setupDeleteIntegration() {
 		const editor = this.editor;
-		const mergeBackwardCommand: DocumentListMergeCommand = editor.commands.get( 'mergeListItemBackward' )!;
-		const mergeForwardCommand: DocumentListMergeCommand = editor.commands.get( 'mergeListItemForward' )!;
+		const mergeBackwardCommand: DocumentListMergeCommand | undefined = editor.commands.get( 'mergeListItemBackward' );
+		const mergeForwardCommand: DocumentListMergeCommand | undefined = editor.commands.get( 'mergeListItemForward' );
 
 		this.listenTo<ViewDocumentDeleteEvent>( editor.editing.view.document, 'delete', ( evt, data ) => {
 			const selection = editor.model.document.selection;
@@ -248,7 +270,7 @@ export default class DocumentListEditing extends Plugin {
 					}
 					// Merge block with previous one (on the block level or on the content level).
 					else {
-						if ( !mergeBackwardCommand.isEnabled ) {
+						if ( !mergeBackwardCommand || !mergeBackwardCommand.isEnabled ) {
 							return;
 						}
 
@@ -267,7 +289,7 @@ export default class DocumentListEditing extends Plugin {
 						return;
 					}
 
-					if ( !mergeForwardCommand.isEnabled ) {
+					if ( !mergeForwardCommand || !mergeForwardCommand.isEnabled ) {
 						return;
 					}
 
@@ -390,13 +412,18 @@ export default class DocumentListEditing extends Plugin {
 		const editor = this.editor;
 		const model = editor.model;
 		const attributeNames = this.getListAttributeNames();
+		const multiBlock = editor.config.get( 'list.multiBlock' );
+		const elementName = multiBlock ? 'paragraph' : 'listItem';
 
 		editor.conversion.for( 'upcast' )
-			// Convert <li> to a generic paragraph so the content of <li> is always inside a block.
+			// Convert <li> to a generic paragraph (or listItem element) so the content of <li> is always inside a block.
 			// Setting the listType attribute to let other features (to-do list) know that this is part of a list item.
+			// This is also important to properly handle simple lists so that paragraphs inside a list item won't break the list item.
+			// <li>  <-- converted to listItem
+			//   <p></p> <-- should be also converted to listItem, so it won't split and replace the listItem generated from the above li.
 			.elementToElement( {
 				view: 'li',
-				model: ( viewElement, { writer } ) => writer.createElement( 'paragraph', { listType: '' } )
+				model: ( viewElement, { writer } ) => writer.createElement( elementName, { listType: '' } )
 			} )
 			// Convert paragraph to the list block (without list type defined yet).
 			// This is important to properly handle bogus paragraph and to-do lists.
@@ -407,7 +434,7 @@ export default class DocumentListEditing extends Plugin {
 				view: 'p',
 				model: ( viewElement, { writer } ) => {
 					if ( viewElement.parent && viewElement.parent.is( 'element', 'li' ) ) {
-						return writer.createElement( 'paragraph', { listType: '' } );
+						return writer.createElement( elementName, { listType: '' } );
 					}
 
 					return null;
@@ -420,9 +447,17 @@ export default class DocumentListEditing extends Plugin {
 				dispatcher.on<UpcastElementEvent>( 'element:ol', listUpcastCleanList(), { priority: 'high' } );
 			} );
 
+		if ( !multiBlock ) {
+			editor.conversion.for( 'downcast' )
+				.elementToElement( {
+					model: 'listItem',
+					view: 'p'
+				} );
+		}
+
 		editor.conversion.for( 'editingDowncast' )
 			.elementToElement( {
-				model: 'paragraph',
+				model: elementName,
 				view: bogusParagraphCreator( attributeNames ),
 				converterPriority: 'high'
 			} )
@@ -435,7 +470,7 @@ export default class DocumentListEditing extends Plugin {
 
 		editor.conversion.for( 'dataDowncast' )
 			.elementToElement( {
-				model: 'paragraph',
+				model: elementName,
 				view: bogusParagraphCreator( attributeNames, { dataPipeline: true } ),
 				converterPriority: 'high'
 			} )
@@ -649,6 +684,7 @@ function modelChangePostFixer(
 ) {
 	const changes = model.document.differ.getChanges();
 	const itemToListHead = new Map<ListElement, ListElement>();
+	const multiBlock = documentListEditing.editor.config.get( 'list.multiBlock' );
 
 	let applied = false;
 
@@ -693,6 +729,19 @@ function modelChangePostFixer(
 				findAndAddListHeadToMap( entry.range.start.getShiftedBy( 1 ), itemToListHead );
 			}
 		}
+
+		// Make sure that there is no left over listItem element without attributes or a block with list attributes that is not a listItem.
+		if ( !multiBlock && entry.type == 'attribute' && LIST_BASE_ATTRIBUTES.includes( entry.attributeKey ) ) {
+			const element = entry.range.start.nodeAfter!;
+
+			if ( entry.attributeNewValue === null && element && element.is( 'element', 'listItem' ) ) {
+				writer.rename( element, 'paragraph' );
+				applied = true;
+			} else if ( entry.attributeOldValue === null && element && element.is( 'element' ) && element.name != 'listItem' ) {
+				writer.rename( element, 'listItem' );
+				applied = true;
+			}
+		}
 	}
 
 	// Make sure that IDs are not shared by split list.

packages/ckeditor5-list/src/documentlist/documentlistmergecommand.ts

@@ -106,7 +106,7 @@ export default class DocumentListMergeCommand extends Command {
 				// Check if the element after it was in the same list item and adjust it if needed.
 				const nextSibling = lastElementAfterDelete.nextSibling;
 
-				changedBlocks.push( lastElementAfterDelete as any );
+				changedBlocks.push( lastElementAfterDelete as Element );
 
 				if ( nextSibling && nextSibling !== lastElement && nextSibling.getAttribute( 'listItemId' ) == lastElementId ) {
 					changedBlocks.push( ...mergeListItemBefore( nextSibling, lastElementAfterDelete, writer ) );

packages/ckeditor5-list/src/documentlist/utils/model.ts

@@ -393,6 +393,14 @@ export function removeListAttributes(
 ): Array<Element> {
 	blocks = toArray( blocks );
 
+	// Convert simple list items to plain paragraphs.
+	for ( const block of blocks ) {
+		if ( block.is( 'element', 'listItem' ) ) {
+			writer.rename( block, 'paragraph' );
+		}
+	}
+
+	// Remove list attributes.
 	for ( const block of blocks ) {
 		for ( const attributeKey of block.getAttributeKeys() ) {
 			if ( attributeKey.startsWith( 'list' ) ) {
@@ -546,7 +554,21 @@ export function getSelectedBlockObject( model: Model ): Element | null {
 	return null;
 }
 
-// Merges a given block to the given parent block if parent is a list item and there is no more blocks in the same item.
+/**
+ * Checks whether the given block can be replaced by a listItem.
+ *
+ * Note that this is possible only when multiBlock = false option is set in feature config.
+ *
+ * @param block A block to be tested.
+ * @param schema The schema of the document.
+ */
+export function canBecomeSimpleListItem( block: Element, schema: Schema ): boolean {
+	return schema.checkChild( block.parent as Element, 'listItem' ) && schema.checkChild( block, '$text' ) && !schema.isObject( block );
+}
+
+/**
+ * Merges a given block to the given parent block if parent is a list item and there is no more blocks in the same item.
+ */
 function mergeListItemIfNotLast(
 	block: ListElement,
 	parentBlock: ListElement,

packages/ckeditor5-list/src/documentlist/utils/postfixers.ts

@@ -135,6 +135,17 @@ export function fixListItemIds(
 
 		seenIds.add( listItemId );
 
+		// Make sure that all items in a simple list have unique IDs.
+		if ( node.is( 'element', 'listItem' ) ) {
+			if ( node.getAttribute( 'listItemId' ) != listItemId ) {
+				writer.setAttribute( 'listItemId', listItemId, node );
+
+				applied = true;
+			}
+
+			continue;
+		}
+
 		for ( const block of getListItemBlocks( node, { direction: 'forward' } ) ) {
 			visited.add( block );
 

packages/ckeditor5-list/src/documentlistproperties/documentlistpropertiesediting.ts

@@ -68,12 +68,10 @@ export default class DocumentListPropertiesEditing extends Plugin {
 	constructor( editor: Editor ) {
 		super( editor );
 
-		editor.config.define( 'list', {
-			properties: {
-				styles: true,
-				startIndex: false,
-				reversed: false
-			}
+		editor.config.define( 'list.properties', {
+			styles: true,
+			startIndex: false,
+			reversed: false
 		} );
 	}
 
@@ -91,9 +89,7 @@ export default class DocumentListPropertiesEditing extends Plugin {
 		for ( const strategy of strategies ) {
 			strategy.addCommand( editor );
 
-			model.schema.extend( '$container', { allowAttributes: strategy.attributeName } );
-			model.schema.extend( '$block', { allowAttributes: strategy.attributeName } );
-			model.schema.extend( '$blockObject', { allowAttributes: strategy.attributeName } );
+			model.schema.extend( '$listItem', { allowAttributes: strategy.attributeName } );
 
 			// Register downcast strategy.
 			documentListEditing.registerDowncastStrategy( {

packages/ckeditor5-list/src/listconfig.ts

@@ -33,6 +33,13 @@ export interface ListConfig {
 	 * Read more in {@link module:list/listconfig~ListPropertiesConfig}.
 	 */
 	properties?: ListPropertiesConfig;
+
+	/**
+	 * Allows multiple blocks in single list item.
+	 *
+	 * @default true
+	 */
+	multiBlock?: boolean;
 }
 
 /**