From 60e4ca71dde99fc1b79504c8696908c00eacd04a Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Tue, 7 Jul 2020 16:44:55 +0200
Subject: [PATCH 1/7] Table headingRows attribute change triggers downcasting
 of the whole table.

---
 .../src/commands/removerowcommand.js          |  10 +-
 .../src/converters/downcast.js                | 100 ------------------
 packages/ckeditor5-table/src/tableediting.js  |  28 ++++-
 packages/ckeditor5-table/src/tableutils.js    |  16 +--
 .../tests/converters/downcast.js              |  30 ------
 5 files changed, 31 insertions(+), 153 deletions(-)

diff --git a/packages/ckeditor5-table/src/commands/removerowcommand.js b/packages/ckeditor5-table/src/commands/removerowcommand.js
index 7df37cdc74d..2bed009af8e 100644
--- a/packages/ckeditor5-table/src/commands/removerowcommand.js
+++ b/packages/ckeditor5-table/src/commands/removerowcommand.js
@@ -60,20 +60,14 @@ export default class RemoveRowCommand extends Command {
 
 		const columnIndexToFocus = this.editor.plugins.get( 'TableUtils' ).getCellLocation( firstCell ).column;
 
-		// Use single batch to modify table in steps but in one undo step.
-		const batch = model.createBatch();
-
-		model.enqueueChange( batch, () => {
+		model.change( writer => {
 			const rowsToRemove = removedRowIndexes.last - removedRowIndexes.first + 1;
 
 			this.editor.plugins.get( 'TableUtils' ).removeRows( table, {
 				at: removedRowIndexes.first,
-				rows: rowsToRemove,
-				batch
+				rows: rowsToRemove
 			} );
-		} );
 
-		model.enqueueChange( batch, writer => {
 			const cellToFocus = getCellToFocus( table, removedRowIndexes.first, columnIndexToFocus );
 
 			writer.setSelection( writer.createPositionAt( cellToFocus, 0 ) );
diff --git a/packages/ckeditor5-table/src/converters/downcast.js b/packages/ckeditor5-table/src/converters/downcast.js
index f5339aaa5cd..ffdf6e83a5e 100644
--- a/packages/ckeditor5-table/src/converters/downcast.js
+++ b/packages/ckeditor5-table/src/converters/downcast.js
@@ -173,79 +173,6 @@ export function downcastInsertCell() {
 	} );
 }
 
-/**
- * Conversion helper that acts on heading row table attribute change.
- *
- * This converter will:
- *
- * * Rename `<td>` to `<th>` elements or vice versa depending on headings.
- * * Create `<thead>` or `<tbody>` elements if needed.
- * * Remove empty `<thead>` or `<tbody>` if needed.
- *
- * @returns {Function} Conversion helper.
- */
-export function downcastTableHeadingRowsChange() {
-	return dispatcher => dispatcher.on( 'attribute:headingRows:table', ( evt, data, conversionApi ) => {
-		const table = data.item;
-
-		if ( !conversionApi.consumable.consume( data.item, evt.name ) ) {
-			return;
-		}
-
-		const figureElement = conversionApi.mapper.toViewElement( table );
-		const viewTable = getViewTable( figureElement );
-
-		const oldRows = data.attributeOldValue;
-		const newRows = data.attributeNewValue;
-
-		// The head section has grown so move rows from <tbody> to <thead>.
-		if ( newRows > oldRows ) {
-			// Filter out only those rows that are in wrong section.
-			const rowsToMove = Array.from( table.getChildren() ).filter( ( { index } ) => isBetween( index, oldRows - 1, newRows ) );
-
-			const viewTableHead = getOrCreateTableSection( 'thead', viewTable, conversionApi );
-			moveViewRowsToTableSection( rowsToMove, viewTableHead, conversionApi, 'end' );
-
-			// Rename all table cells from moved rows to 'th' as they lands in <thead>.
-			for ( const tableRow of rowsToMove ) {
-				for ( const tableCell of tableRow.getChildren() ) {
-					renameViewTableCell( tableCell, 'th', conversionApi );
-				}
-			}
-		}
-		// The head section has shrunk so move rows from <thead> to <tbody>.
-		else {
-			// Filter out only those rows that are in wrong section.
-			const rowsToMove = Array.from( table.getChildren() )
-				.filter( ( { index } ) => isBetween( index, newRows - 1, oldRows ) )
-				.reverse(); // The rows will be moved from <thead> to <tbody> in reverse order at the beginning of a <tbody>.
-
-			const viewTableBody = getOrCreateTableSection( 'tbody', viewTable, conversionApi );
-			moveViewRowsToTableSection( rowsToMove, viewTableBody, conversionApi, 0 );
-
-			// Check if cells moved from <thead> to <tbody> requires renaming to <td> as this depends on current heading columns attribute.
-			const tableWalker = new TableWalker( table, { startRow: newRows ? newRows - 1 : newRows, endRow: oldRows - 1 } );
-
-			const tableAttributes = {
-				headingRows: table.getAttribute( 'headingRows' ) || 0,
-				headingColumns: table.getAttribute( 'headingColumns' ) || 0
-			};
-
-			for ( const tableSlot of tableWalker ) {
-				renameViewTableCellIfRequired( tableSlot, tableAttributes, conversionApi );
-			}
-		}
-
-		// Cleanup: Ensure that thead & tbody sections are removed if left empty after moving rows. See #6437, #6391.
-		removeTableSectionIfEmpty( 'thead', viewTable, conversionApi );
-		removeTableSectionIfEmpty( 'tbody', viewTable, conversionApi );
-
-		function isBetween( index, lower, upper ) {
-			return index > lower && index < upper;
-		}
-	} );
-}
-
 /**
  * Conversion helper that acts on heading column table attribute change.
  *
@@ -333,11 +260,6 @@ function renameViewTableCell( tableCell, desiredCellElementName, conversionApi )
 	const viewWriter = conversionApi.writer;
 	const viewCell = conversionApi.mapper.toViewElement( tableCell );
 
-	// View cell might be not yet converted - skip it as it will be properly created by cell converter later on.
-	if ( !viewCell ) {
-		return;
-	}
-
 	const editable = viewWriter.createEditableElement( desiredCellElementName, viewCell.getAttributes() );
 	const renamedCell = toWidgetEditable( editable, viewWriter );
 
@@ -545,28 +467,6 @@ function removeTableSectionIfEmpty( sectionName, tableElement, conversionApi ) {
 	}
 }
 
-// Moves view table rows associated with passed model rows to the provided table section element.
-//
-// **Note**: This method will skip not converted table rows.
-//
-// @param {Array.<module:engine/model/element~Element>} rowsToMove
-// @param {module:engine/view/element~Element} viewTableSection
-// @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi
-// @param {Number|'end'|'before'|'after'} offset Offset or one of the flags.
-function moveViewRowsToTableSection( rowsToMove, viewTableSection, conversionApi, offset ) {
-	for ( const tableRow of rowsToMove ) {
-		const viewTableRow = conversionApi.mapper.toViewElement( tableRow );
-
-		// View table row might be not yet converted - skip it as it will be properly created by cell converter later on.
-		if ( viewTableRow ) {
-			conversionApi.writer.move(
-				conversionApi.writer.createRangeOn( viewTableRow ),
-				conversionApi.writer.createPositionAt( viewTableSection, offset )
-			);
-		}
-	}
-}
-
 // Finds a '<table>' element inside the `<figure>` widget.
 //
 // @param {module:engine/view/element~Element} viewFigure
diff --git a/packages/ckeditor5-table/src/tableediting.js b/packages/ckeditor5-table/src/tableediting.js
index bdaf9fcda70..4fa0e0ed89b 100644
--- a/packages/ckeditor5-table/src/tableediting.js
+++ b/packages/ckeditor5-table/src/tableediting.js
@@ -15,8 +15,7 @@ import {
 	downcastInsertRow,
 	downcastInsertTable,
 	downcastRemoveRow,
-	downcastTableHeadingColumnsChange,
-	downcastTableHeadingRowsChange
+	downcastTableHeadingColumnsChange
 } from './converters/downcast';
 
 import InsertTableCommand from './commands/inserttablecommand';
@@ -113,9 +112,11 @@ export default class TableEditing extends Plugin {
 		conversion.attributeToAttribute( { model: 'colspan', view: 'colspan' } );
 		conversion.attributeToAttribute( { model: 'rowspan', view: 'rowspan' } );
 
-		// Table heading rows and columns conversion.
+		// Table heading columns conversion (change of heading rows requires reconversion of the whole table).
 		conversion.for( 'editingDowncast' ).add( downcastTableHeadingColumnsChange() );
-		conversion.for( 'editingDowncast' ).add( downcastTableHeadingRowsChange() );
+
+		// Table heading rows change requires reconversion of the whole table.
+		this.listenTo( model, 'applyOperation', headingRowsAttributeChangeHandler( model ) );
 
 		// Define all the commands.
 		editor.commands.add( 'insertTable', new InsertTableCommand( editor ) );
@@ -155,3 +156,22 @@ export default class TableEditing extends Plugin {
 		return [ TableUtils ];
 	}
 }
+
+// Model#applyOperation handler for headingRows attribute changes.
+function headingRowsAttributeChangeHandler( model ) {
+	return ( event, [ operation ] ) => {
+		if ( !operation.isDocumentOperation ) {
+			return;
+		}
+
+		if ( operation.type != 'addAttribute' && operation.type != 'removeAttribute' && operation.type != 'changeAttribute' ) {
+			return;
+		}
+
+		const element = operation.range.getContainedElement();
+
+		if ( element && element.is( 'table' ) && operation.key == 'headingRows' ) {
+			model.document.differ.refreshItem( element );
+		}
+	};
+}
diff --git a/packages/ckeditor5-table/src/tableutils.js b/packages/ckeditor5-table/src/tableutils.js
index 47a8b2d1c48..86413b72b8c 100644
--- a/packages/ckeditor5-table/src/tableutils.js
+++ b/packages/ckeditor5-table/src/tableutils.js
@@ -136,7 +136,7 @@ export default class TableUtils extends Plugin {
 
 			// Inserting rows inside heading section requires to update `headingRows` attribute as the heading section will grow.
 			if ( headingRows > insertAt ) {
-				writer.setAttribute( 'headingRows', headingRows + rowsToInsert, table );
+				updateNumericAttribute( 'headingRows', headingRows + rowsToInsert, table, writer, 0 );
 			}
 
 			// Inserting at the end or at the beginning of a table doesn't require to calculate anything special.
@@ -309,9 +309,8 @@ export default class TableUtils extends Plugin {
 		const rowsToRemove = options.rows || 1;
 		const first = options.at;
 		const last = first + rowsToRemove - 1;
-		const batch = options.batch || 'default';
 
-		model.enqueueChange( batch, writer => {
+		model.change( writer => {
 			// Removing rows from the table require that most calculations to be done prior to changing table structure.
 			// Preparations must be done in the same enqueueChange callback to use the current table structure.
 
@@ -341,7 +340,7 @@ export default class TableUtils extends Plugin {
 			removeEmptyColumns( table, this );
 
 			// 2e. Adjust heading rows if removed rows were in a heading section.
-			updateHeadingRows( table, first, last, model, batch );
+			updateHeadingRows( table, first, last, model );
 		} );
 	}
 
@@ -776,13 +775,8 @@ function adjustHeadingColumns( table, removedColumnIndexes, writer ) {
 }
 
 // Calculates a new heading rows value for removing rows from heading section.
-function updateHeadingRows( table, first, last, model, batch ) {
-	// Must be done after the changes in table structure (removing rows).
-	// Otherwise the downcast converter for headingRows attribute will fail.
-	// See https://github.com/ckeditor/ckeditor5/issues/6391.
-	//
-	// Must be completely wrapped in enqueueChange to get the current table state (after applying other enqueued changes).
-	model.enqueueChange( batch, writer => {
+function updateHeadingRows( table, first, last, model ) {
+	model.change( writer => {
 		const headingRows = table.getAttribute( 'headingRows' ) || 0;
 
 		if ( first < headingRows ) {
diff --git a/packages/ckeditor5-table/tests/converters/downcast.js b/packages/ckeditor5-table/tests/converters/downcast.js
index e138160f42b..db5d41d6afa 100644
--- a/packages/ckeditor5-table/tests/converters/downcast.js
+++ b/packages/ckeditor5-table/tests/converters/downcast.js
@@ -941,36 +941,6 @@ describe( 'downcast converters', () => {
 				], { headingRows: 2, asWidget: true } ) );
 			} );
 
-			it( 'should be possible to overwrite', () => {
-				editor.conversion.attributeToAttribute( {
-					model: 'headingRows',
-					view: 'headingRows',
-					converterPriority: 'high'
-				} );
-				setModelData( model, modelTable( [ [ '00' ] ] ) );
-
-				const table = root.getChild( 0 );
-
-				model.change( writer => {
-					writer.setAttribute( 'headingRows', 1, table );
-				} );
-
-				assertEqualMarkup( getViewData( view, { withoutSelection: true } ),
-					'<figure class="ck-widget ck-widget_with-selection-handle table" contenteditable="false" headingRows="1">' +
-						'<div class="ck ck-widget__selection-handle"></div>' +
-						'<table>' +
-							'<tbody>' +
-								'<tr>' +
-									'<td class="ck-editor__editable ck-editor__nested-editable" contenteditable="true">' +
-										'<span style="display:inline-block">00</span>' +
-									'</td>' +
-								'</tr>' +
-							'</tbody>' +
-						'</table>' +
-					'</figure>'
-				);
-			} );
-
 			it( 'should work with adding table rows at the beginning of a table', () => {
 				setModelData( model, modelTable( [
 					[ '00', '01' ],

From e7492641bad8c9476cff8bdbbab33bbf0aeacf0a Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Tue, 7 Jul 2020 16:54:23 +0200
Subject: [PATCH 2/7] Added test for #7454 issue.

---
 packages/ckeditor5-table/tests/tableutils.js | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/packages/ckeditor5-table/tests/tableutils.js b/packages/ckeditor5-table/tests/tableutils.js
index ef6d498c9a0..cba404dacd1 100644
--- a/packages/ckeditor5-table/tests/tableutils.js
+++ b/packages/ckeditor5-table/tests/tableutils.js
@@ -959,6 +959,21 @@ describe( 'TableUtils', () => {
 				], { headingRows: 1 } ) );
 			} );
 
+			it( 'should change heading rows if removing a heading row (and cell below is row-spanned)', () => {
+				setData( model, modelTable( [
+					[ '00', '01' ],
+					[ '10', { contents: '11', rowspan: 2 } ],
+					[ '20' ]
+				], { headingRows: 1 } ) );
+
+				tableUtils.removeRows( root.getChild( 0 ), { at: 0 } );
+
+				assertEqualMarkup( getData( model, { withoutSelection: true } ), modelTable( [
+					[ '10', { contents: '11', rowspan: 2 } ],
+					[ '20' ]
+				] ) );
+			} );
+
 			it( 'should decrease rowspan of table cells from previous rows', () => {
 				// +----+----+----+----+----+
 				// | 00 | 01 | 02 | 03 | 04 |

From 66ebfe46ff30baccb6933dc2666460750e1f1f81 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Tue, 7 Jul 2020 17:53:23 +0200
Subject: [PATCH 3/7] Fixed removing empty rows and columns when multiple rows
 and columns should be removed.

---
 .../src/commands/mergecellcommand.js          |  2 +-
 .../src/commands/mergecellscommand.js         |  2 +-
 .../ckeditor5-table/src/tableclipboard.js     |  6 +--
 packages/ckeditor5-table/src/tableutils.js    | 18 +++++--
 .../ckeditor5-table/src/utils/structure.js    | 36 ++++++++------
 .../tests/commands/mergecellscommand.js       | 47 +++++++++++++++++++
 6 files changed, 85 insertions(+), 26 deletions(-)

diff --git a/packages/ckeditor5-table/src/commands/mergecellcommand.js b/packages/ckeditor5-table/src/commands/mergecellcommand.js
index 7a59f9af2ab..dbd90871f85 100644
--- a/packages/ckeditor5-table/src/commands/mergecellcommand.js
+++ b/packages/ckeditor5-table/src/commands/mergecellcommand.js
@@ -109,7 +109,7 @@ export default class MergeCellCommand extends Command {
 			const table = findAncestor( 'table', removedTableCellRow );
 
 			// Remove empty rows and columns after merging.
-			removeEmptyRowsColumns( table, tableUtils, writer.batch );
+			removeEmptyRowsColumns( table, tableUtils );
 		} );
 	}
 
diff --git a/packages/ckeditor5-table/src/commands/mergecellscommand.js b/packages/ckeditor5-table/src/commands/mergecellscommand.js
index f737e58d94b..3f278c34894 100644
--- a/packages/ckeditor5-table/src/commands/mergecellscommand.js
+++ b/packages/ckeditor5-table/src/commands/mergecellscommand.js
@@ -60,7 +60,7 @@ export default class MergeCellsCommand extends Command {
 			const table = findAncestor( 'table', firstTableCell );
 
 			// Remove rows and columns that become empty (have no anchored cells).
-			removeEmptyRowsColumns( table, tableUtils, writer.batch );
+			removeEmptyRowsColumns( table, tableUtils );
 
 			writer.setSelection( firstTableCell, 'in' );
 		} );
diff --git a/packages/ckeditor5-table/src/tableclipboard.js b/packages/ckeditor5-table/src/tableclipboard.js
index 84ff5e5b65e..7bfe8a84b0c 100644
--- a/packages/ckeditor5-table/src/tableclipboard.js
+++ b/packages/ckeditor5-table/src/tableclipboard.js
@@ -205,7 +205,7 @@ function prepareTableForPasting( selectedTableCells, pastedDimensions, writer, t
 		selection.lastRow += pastedDimensions.height - 1;
 		selection.lastColumn += pastedDimensions.width - 1;
 
-		expandTableSize( selectedTable, selection.lastRow + 1, selection.lastColumn + 1, writer, tableUtils );
+		expandTableSize( selectedTable, selection.lastRow + 1, selection.lastColumn + 1, tableUtils );
 	}
 
 	// In case of expanding selection we do not reset the selection so in this case we will always try to fix selection
@@ -320,13 +320,12 @@ function replaceSelectedCellsWithPasted( pastedTable, pastedDimensions, selected
 }
 
 // Expand table (in place) to expected size.
-function expandTableSize( table, expectedHeight, expectedWidth, writer, tableUtils ) {
+function expandTableSize( table, expectedHeight, expectedWidth, tableUtils ) {
 	const tableWidth = tableUtils.getColumns( table );
 	const tableHeight = tableUtils.getRows( table );
 
 	if ( expectedWidth > tableWidth ) {
 		tableUtils.insertColumns( table, {
-			batch: writer.batch,
 			at: tableWidth,
 			columns: expectedWidth - tableWidth
 		} );
@@ -334,7 +333,6 @@ function expandTableSize( table, expectedHeight, expectedWidth, writer, tableUti
 
 	if ( expectedHeight > tableHeight ) {
 		tableUtils.insertRows( table, {
-			batch: writer.batch,
 			at: tableHeight,
 			rows: expectedHeight - tableHeight
 		} );
diff --git a/packages/ckeditor5-table/src/tableutils.js b/packages/ckeditor5-table/src/tableutils.js
index 86413b72b8c..fba6e2558e8 100644
--- a/packages/ckeditor5-table/src/tableutils.js
+++ b/packages/ckeditor5-table/src/tableutils.js
@@ -336,11 +336,15 @@ export default class TableUtils extends Plugin {
 				updateNumericAttribute( 'rowspan', rowspan, cell, writer );
 			}
 
-			// 2d. Remove empty columns (without anchored cells) if there are any.
-			removeEmptyColumns( table, this );
-
-			// 2e. Adjust heading rows if removed rows were in a heading section.
+			// 2d. Adjust heading rows if removed rows were in a heading section.
 			updateHeadingRows( table, first, last, model );
+
+			// 2e. Remove empty columns (without anchored cells) if there are any.
+			if ( !removeEmptyColumns( table, this ) ) {
+				// If there wasn't any empty columns then we still need to check if this wasn't called
+				// because of cleaning empty rows and we only removed one of them.
+				removeEmptyRows( table, this );
+			}
 		} );
 	}
 
@@ -395,7 +399,11 @@ export default class TableUtils extends Plugin {
 			}
 
 			// Remove empty rows that could appear after removing columns.
-			removeEmptyRows( table, this, writer.batch );
+			if ( !removeEmptyRows( table, this ) ) {
+				// If there wasn't any empty rows then we still need to check if this wasn't called
+				// because of cleaning empty columns and we only removed one of them.
+				removeEmptyColumns( table, this );
+			}
 		} );
 	}
 
diff --git a/packages/ckeditor5-table/src/utils/structure.js b/packages/ckeditor5-table/src/utils/structure.js
index 41fc71a496c..b8bb6f4023d 100644
--- a/packages/ckeditor5-table/src/utils/structure.js
+++ b/packages/ckeditor5-table/src/utils/structure.js
@@ -342,13 +342,17 @@ export function removeEmptyColumns( table, tableUtils ) {
 		return cellsCount ? result : [ ...result, column ];
 	}, [] );
 
-	// @if CK_DEBUG_TABLE // emptyColumns.length > 0 && console.log( `Removing empty columns: ${ emptyColumns.join( ', ' ) }.` );
+	if ( emptyColumns.length > 0 ) {
+		// Remove only last empty column because it will recurrently trigger removing empty rows.
+		const emptyColumn = emptyColumns[ emptyColumns.length - 1 ];
 
-	emptyColumns.reverse().forEach( column => {
-		tableUtils.removeColumns( table, { at: column } );
-	} );
+		// @if CK_DEBUG_TABLE // console.log( `Removing empty column: ${ emptyColumn }.` );
+		tableUtils.removeColumns( table, { at: emptyColumn } );
 
-	return emptyColumns.length > 0;
+		return true;
+	}
+
+	return false;
 }
 
 /**
@@ -380,10 +384,9 @@ export function removeEmptyColumns( table, tableUtils ) {
  * @protected
  * @param {module:engine/model/element~Element} table
  * @param {module:table/tableutils~TableUtils} tableUtils
- * @param {module:engine/model/batch~Batch|null} [batch] Batch that should be used for removing empty rows.
  * @returns {Boolean} True if removed some rows.
  */
-export function removeEmptyRows( table, tableUtils, batch ) {
+export function removeEmptyRows( table, tableUtils ) {
 	const emptyRows = [];
 
 	for ( let rowIndex = 0; rowIndex < table.childCount; rowIndex++ ) {
@@ -394,13 +397,17 @@ export function removeEmptyRows( table, tableUtils, batch ) {
 		}
 	}
 
-	// @if CK_DEBUG_TABLE // emptyRows.length > 0 && console.log( `Removing empty rows: ${ emptyRows.join( ', ' ) }.` );
+	if ( emptyRows.length > 0 ) {
+		// Remove only last empty row because it will recurrently trigger removing empty columns.
+		const emptyRow = emptyRows[ emptyRows.length - 1 ];
 
-	emptyRows.reverse().forEach( row => {
-		tableUtils.removeRows( table, { at: row, batch } );
-	} );
+		// @if CK_DEBUG_TABLE // console.log( `Removing empty row: ${ emptyRow }.` );
+		tableUtils.removeRows( table, { at: emptyRow } );
+
+		return true;
+	}
 
-	return emptyRows.length > 0;
+	return false;
 }
 
 /**
@@ -428,14 +435,13 @@ export function removeEmptyRows( table, tableUtils, batch ) {
  * @protected
  * @param {module:engine/model/element~Element} table
  * @param {module:table/tableutils~TableUtils} tableUtils
- * @param {module:engine/model/batch~Batch|null} [batch] Batch that should be used for removing empty rows.
  */
-export function removeEmptyRowsColumns( table, tableUtils, batch ) {
+export function removeEmptyRowsColumns( table, tableUtils ) {
 	const removedColumns = removeEmptyColumns( table, tableUtils );
 
 	// If there was some columns removed then cleaning empty rows was already triggered.
 	if ( !removedColumns ) {
-		removeEmptyRows( table, tableUtils, batch );
+		removeEmptyRows( table, tableUtils );
 	}
 }
 
diff --git a/packages/ckeditor5-table/tests/commands/mergecellscommand.js b/packages/ckeditor5-table/tests/commands/mergecellscommand.js
index 272e3b5b585..1ef468844ab 100644
--- a/packages/ckeditor5-table/tests/commands/mergecellscommand.js
+++ b/packages/ckeditor5-table/tests/commands/mergecellscommand.js
@@ -706,6 +706,53 @@ describe( 'MergeCellsCommand', () => {
 					]
 				] ) );
 			} );
+
+			it( 'should remove all empty rows and columns', () => {
+				setData( model, modelTable( [
+					[ '00', '01', '02' ],
+					[ '10', '11', '12' ],
+					[ '20', '21', '22' ]
+				] ) );
+
+				tableSelection.setCellSelection(
+					root.getNodeByPath( [ 0, 0, 0 ] ),
+					root.getNodeByPath( [ 0, 2, 2 ] )
+				);
+
+				command.execute();
+
+				assertEqualMarkup( getData( model ), modelTable( [
+					[
+						'<paragraph>[00</paragraph><paragraph>01</paragraph><paragraph>02</paragraph>' +
+						'<paragraph>10</paragraph><paragraph>11</paragraph><paragraph>12</paragraph>' +
+						'<paragraph>20</paragraph><paragraph>21</paragraph><paragraph>22]</paragraph>'
+					]
+				] ) );
+			} );
+
+			it( 'should remove all empty rows and columns (asymmetrical case)', () => {
+				setData( model, modelTable( [
+					[ '00', '01', { contents: '02', rowspan: 3 } ],
+					[ '10', '11' ],
+					[ '20', '21' ]
+				] ) );
+
+				tableSelection.setCellSelection(
+					root.getNodeByPath( [ 0, 0, 0 ] ),
+					root.getNodeByPath( [ 0, 2, 1 ] )
+				);
+
+				command.execute();
+
+				assertEqualMarkup( getData( model ), modelTable( [
+					[
+						'<paragraph>[00</paragraph><paragraph>01</paragraph>' +
+						'<paragraph>10</paragraph><paragraph>11</paragraph>' +
+						'<paragraph>20</paragraph><paragraph>21]</paragraph>',
+						'02'
+					]
+				] ) );
+			} );
 		} );
 	} );
 

From 2eb2a1114bf6cd80c5cdb5e9eee024bcd4ae5b0b Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Wed, 8 Jul 2020 10:40:36 +0200
Subject: [PATCH 4/7] Removed redundant model.change block.

---
 packages/ckeditor5-table/src/tableutils.js | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/packages/ckeditor5-table/src/tableutils.js b/packages/ckeditor5-table/src/tableutils.js
index fba6e2558e8..5a9202d8cc4 100644
--- a/packages/ckeditor5-table/src/tableutils.js
+++ b/packages/ckeditor5-table/src/tableutils.js
@@ -337,7 +337,7 @@ export default class TableUtils extends Plugin {
 			}
 
 			// 2d. Adjust heading rows if removed rows were in a heading section.
-			updateHeadingRows( table, first, last, model );
+			updateHeadingRows( table, first, last, writer );
 
 			// 2e. Remove empty columns (without anchored cells) if there are any.
 			if ( !removeEmptyColumns( table, this ) ) {
@@ -783,16 +783,14 @@ function adjustHeadingColumns( table, removedColumnIndexes, writer ) {
 }
 
 // Calculates a new heading rows value for removing rows from heading section.
-function updateHeadingRows( table, first, last, model ) {
-	model.change( writer => {
-		const headingRows = table.getAttribute( 'headingRows' ) || 0;
+function updateHeadingRows( table, first, last, writer ) {
+	const headingRows = table.getAttribute( 'headingRows' ) || 0;
 
-		if ( first < headingRows ) {
-			const newRows = last < headingRows ? headingRows - ( last - first + 1 ) : first;
+	if ( first < headingRows ) {
+		const newRows = last < headingRows ? headingRows - ( last - first + 1 ) : first;
 
-			updateNumericAttribute( 'headingRows', newRows, table, writer, 0 );
-		}
-	} );
+		updateNumericAttribute( 'headingRows', newRows, table, writer, 0 );
+	}
 }
 
 // Finds cells that will be:

From 17a7242fb920269116c5f7e56470ac66b0481bd4 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Wed, 8 Jul 2020 12:15:35 +0200
Subject: [PATCH 5/7] Added test for handling headingRows attribute in undo.

---
 .../tests/converters/downcast.js              | 35 +++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-table/tests/converters/downcast.js b/packages/ckeditor5-table/tests/converters/downcast.js
index db5d41d6afa..0243a76076b 100644
--- a/packages/ckeditor5-table/tests/converters/downcast.js
+++ b/packages/ckeditor5-table/tests/converters/downcast.js
@@ -5,6 +5,7 @@
 
 import VirtualTestEditor from '@ckeditor/ckeditor5-core/tests/_utils/virtualtesteditor';
 import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
+import UndoEditing from '@ckeditor/ckeditor5-undo/src/undoediting';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import { getData as getViewData } from '@ckeditor/ckeditor5-engine/src/dev-utils/view';
 import { setData as setModelData } from '@ckeditor/ckeditor5-engine/src/dev-utils/model';
@@ -19,7 +20,7 @@ describe( 'downcast converters', () => {
 	testUtils.createSinonSandbox();
 
 	beforeEach( async () => {
-		editor = await VirtualTestEditor.create( { plugins: [ Paragraph, TableEditing ] } );
+		editor = await VirtualTestEditor.create( { plugins: [ Paragraph, TableEditing, UndoEditing ] } );
 
 		model = editor.model;
 		root = model.document.getRoot( 'main' );
@@ -840,8 +841,10 @@ describe( 'downcast converters', () => {
 		} );
 	} );
 
-	describe( 'downcastTableHeadingRowsChange()', () => {
+	describe( 'downcastTableHeadingRowsChange', () => {
 		// The heading rows change downcast conversion is not executed in data pipeline.
+		// Note that headingRows table attribute triggers whole table downcast.
+
 		describe( 'editing pipeline', () => {
 			it( 'should work for adding heading rows', () => {
 				setModelData( model, modelTable( [
@@ -1017,6 +1020,34 @@ describe( 'downcast converters', () => {
 					'</figure>'
 				);
 			} );
+
+			it( 'should properly integrate with undo', () => {
+				setModelData( model, modelTable( [
+					[ '00', '01' ],
+					[ '10', '11' ],
+					[ '20', '21' ]
+				], { headingRows: 1 } ) );
+
+				const table = root.getChild( 0 );
+
+				model.change( writer => {
+					writer.setAttribute( 'headingRows', 2, table );
+				} );
+
+				assertEqualMarkup( getViewData( view, { withoutSelection: true } ), viewTable( [
+					[ '00', '01' ],
+					[ '10', '11' ],
+					[ '20', '21' ]
+				], { headingRows: 2, asWidget: true } ) );
+
+				editor.execute( 'undo' );
+
+				assertEqualMarkup( getViewData( view, { withoutSelection: true } ), viewTable( [
+					[ '00', '01' ],
+					[ '10', '11' ],
+					[ '20', '21' ]
+				], { headingRows: 1, asWidget: true } ) );
+			} );
 		} );
 	} );
 

From 70b5134324f8682c15dd90140bfa7081b087b000 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Wed, 8 Jul 2020 14:13:07 +0200
Subject: [PATCH 6/7] Added table post-fixer that marks table to refresh on
 headingRows attribute change.

---
 .../table-heading-rows-refresh-post-fixer.js  | 53 +++++++++++++++++++
 packages/ckeditor5-table/src/tableediting.js  | 24 +--------
 2 files changed, 55 insertions(+), 22 deletions(-)
 create mode 100644 packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js

diff --git a/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js b/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js
new file mode 100644
index 00000000000..77be279de6d
--- /dev/null
+++ b/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js
@@ -0,0 +1,53 @@
+/**
+ * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
+ */
+
+/**
+ * @module table/converters/table-heading-rows-refresh-post-fixer
+ */
+
+/**
+ * Injects a table post-fixer into the model which marks the table in the differ to have it re-rendered.
+ *
+ * Table heading rows are represented in model just by `headingRows` attribute but in the view it's rendered as separate
+ * sections of the table (`thead`, `tbody`) so any change of that attribute would trigger a lot changes in view.
+ *
+ * When table `headingRows` attribute changes, entire table is re-rendered.
+ *
+ * @param {module:engine/model/model~Model} model
+ */
+export default function injectTableHeadingRowsRefreshPostFixer( model ) {
+	model.document.registerPostFixer( () => tableHeadingRowsRefreshPostFixer( model ) );
+}
+
+function tableHeadingRowsRefreshPostFixer( model ) {
+	const differ = model.document.differ;
+
+	// Stores tables to be refreshed so the table will be refreshed once for multiple changes.
+	const tablesToRefresh = new Set();
+
+	for ( const change of differ.getChanges() ) {
+		if ( change.type != 'attribute' ) {
+			continue;
+		}
+
+		const element = change.range.start.nodeAfter;
+
+		if ( element && element.is( 'table' ) && change.attributeKey == 'headingRows' ) {
+			tablesToRefresh.add( element );
+		}
+	}
+
+	if ( tablesToRefresh.size ) {
+		// @if CK_DEBUG_TABLE // console.log( `Post-fixing table: refreshing heading rows (${ tablesToRefresh.size }).` );
+
+		for ( const table of tablesToRefresh.values() ) {
+			differ.refreshItem( table );
+		}
+
+		return true;
+	}
+
+	return false;
+}
diff --git a/packages/ckeditor5-table/src/tableediting.js b/packages/ckeditor5-table/src/tableediting.js
index 4fa0e0ed89b..f46c8e27d36 100644
--- a/packages/ckeditor5-table/src/tableediting.js
+++ b/packages/ckeditor5-table/src/tableediting.js
@@ -35,6 +35,7 @@ import TableUtils from '../src/tableutils';
 import injectTableLayoutPostFixer from './converters/table-layout-post-fixer';
 import injectTableCellParagraphPostFixer from './converters/table-cell-paragraph-post-fixer';
 import injectTableCellRefreshPostFixer from './converters/table-cell-refresh-post-fixer';
+import injectTableHeadingRowsRefreshPostFixer from './converters/table-heading-rows-refresh-post-fixer';
 
 import '../theme/tableediting.css';
 
@@ -115,9 +116,6 @@ export default class TableEditing extends Plugin {
 		// Table heading columns conversion (change of heading rows requires reconversion of the whole table).
 		conversion.for( 'editingDowncast' ).add( downcastTableHeadingColumnsChange() );
 
-		// Table heading rows change requires reconversion of the whole table.
-		this.listenTo( model, 'applyOperation', headingRowsAttributeChangeHandler( model ) );
-
 		// Define all the commands.
 		editor.commands.add( 'insertTable', new InsertTableCommand( editor ) );
 		editor.commands.add( 'insertTableRowAbove', new InsertRowCommand( editor, { order: 'above' } ) );
@@ -144,6 +142,7 @@ export default class TableEditing extends Plugin {
 		editor.commands.add( 'selectTableRow', new SelectRowCommand( editor ) );
 		editor.commands.add( 'selectTableColumn', new SelectColumnCommand( editor ) );
 
+		injectTableHeadingRowsRefreshPostFixer( model );
 		injectTableLayoutPostFixer( model );
 		injectTableCellRefreshPostFixer( model );
 		injectTableCellParagraphPostFixer( model );
@@ -156,22 +155,3 @@ export default class TableEditing extends Plugin {
 		return [ TableUtils ];
 	}
 }
-
-// Model#applyOperation handler for headingRows attribute changes.
-function headingRowsAttributeChangeHandler( model ) {
-	return ( event, [ operation ] ) => {
-		if ( !operation.isDocumentOperation ) {
-			return;
-		}
-
-		if ( operation.type != 'addAttribute' && operation.type != 'removeAttribute' && operation.type != 'changeAttribute' ) {
-			return;
-		}
-
-		const element = operation.range.getContainedElement();
-
-		if ( element && element.is( 'table' ) && operation.key == 'headingRows' ) {
-			model.document.differ.refreshItem( element );
-		}
-	};
-}

From 13c9fd8122cea943656849cecbdf7ff93a09e422 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20Go=C5=82aszewski?= <jodator@jodator.net>
Date: Fri, 10 Jul 2020 10:09:45 +0200
Subject: [PATCH 7/7] Update injectTableHeadingRowsRefreshPostFixer()
 documentation.

---
 .../converters/table-heading-rows-refresh-post-fixer.js    | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js b/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js
index 77be279de6d..b1f0b6bc8d6 100644
--- a/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js
+++ b/packages/ckeditor5-table/src/converters/table-heading-rows-refresh-post-fixer.js
@@ -10,10 +10,11 @@
 /**
  * Injects a table post-fixer into the model which marks the table in the differ to have it re-rendered.
  *
- * Table heading rows are represented in model just by `headingRows` attribute but in the view it's rendered as separate
- * sections of the table (`thead`, `tbody`) so any change of that attribute would trigger a lot changes in view.
+ * Table heading rows are represented in the model by a `headingRows` attribute. However, in the view, it's represented as separate
+ * sections of the table (`<thead>` or `<tbody>`) and changing `headingRows` attribute requires moving table rows between two sections.
+ * This causes problems with structural changes in a table (like adding and removing rows) thus atomic converters cannot be used.
  *
- * When table `headingRows` attribute changes, entire table is re-rendered.
+ * When table `headingRows` attribute changes, the entire table is re-rendered.
  *
  * @param {module:engine/model/model~Model} model
  */