Fixed: List postfixers should check if attribute is allowed od elemen…

…t before removing it.

src/converters.js

@@ -602,13 +602,15 @@ export function modelChangePostFixer( model, writer ) {
 				// In case of renamed element.
 				const item = entry.position.nodeAfter;
 
-				if ( item.hasAttribute( 'indent' ) ) {
+				// Only remove 'indent' attribute from items that doesn't allow such attribute. #103
+				if ( item.hasAttribute( 'indent' ) && !model.schema.checkAttribute( item, 'indent' ) ) {
 					writer.removeAttribute( 'indent', item );
 
 					applied = true;
 				}
 
-				if ( item.hasAttribute( 'type' ) ) {
+				// Only remove 'type' attribute from items that doesn't allow such attribute. #103
+				if ( item.hasAttribute( 'type' ) && !model.schema.checkAttribute( item, 'type' ) ) {
 					writer.removeAttribute( 'type', item );
 
 					applied = true;

tests/listediting.js

@@ -45,6 +45,13 @@ describe( 'ListEditing', () => {
 				view = editor.editing.view;
 				viewDoc = view.document;
 				viewRoot = viewDoc.getRoot();
+
+				model.schema.register( 'foo', {
+					allowWhere: '$block',
+					allowAttributes: [ 'indent', 'type' ],
+					isBlock: true,
+					isObject: true
+				} );
 			} );
 	} );
 
@@ -3279,6 +3286,22 @@ describe( 'ListEditing', () => {
 
 				expect( getModelData( model, { withoutSelection: true } ) ).to.equal( expectedModel );
 			} );
+
+			it( 'should not remove attributes from elements that allows that attributes', () => {
+				const modelBefore =
+					'<listItem indent="0" type="bulleted">a</listItem>' +
+					'<listItem indent="1" type="bulleted">b</listItem>' +
+					'<foo indent="baz" type="bar"></foo>';
+
+				const expectedModel =
+					'<listItem indent="0" type="bulleted">a</listItem>' +
+					'<listItem indent="1" type="bulleted">b</listItem>' +
+					'<foo indent="baz" type="bar"></foo>';
+
+				setModelData( model, modelBefore );
+
+				expect( getModelData( model, { withoutSelection: true } ) ).to.equal( expectedModel );
+			} );
 		} );
 	} );