Merge pull request #9742 from ckeditor/i/5797

Fix (engine): Updated `downcastwriter` to allow setting up attribute element's priority to 0. Closes #5797.

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

@@ -583,7 +583,7 @@ export function createViewElementFromHighlightDescriptor( writer, descriptor ) {
 		viewElement._addClass( descriptor.classes );
 	}
 
-	if ( descriptor.priority ) {
+	if ( typeof descriptor.priority === 'number' ) {
 		viewElement._priority = descriptor.priority;
 	}
 

packages/ckeditor5-engine/src/view/downcastwriter.js

@@ -191,7 +191,7 @@ export default class DowncastWriter {
 	createAttributeElement( name, attributes, options = {} ) {
 		const attributeElement = new AttributeElement( this.document, name, attributes );
 
-		if ( options.priority ) {
+		if ( typeof options.priority === 'number' ) {
 			attributeElement._priority = options.priority;
 		}
 

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

@@ -3513,6 +3513,15 @@ describe( 'downcast converters', () => {
 			expect( element.priority ).to.equal( 7 );
 			expect( element.hasClass( 'foo-class' ) ).to.be.true;
 		} );
+
+		it( 'should pass priority 0', () => {
+			const descriptor = {
+				priority: 0
+			};
+			const element = createViewElementFromHighlightDescriptor( viewWriter, descriptor );
+
+			expect( element.priority ).to.equal( 0 );
+		} );
 	} );
 } );
 

packages/ckeditor5-engine/tests/view/downcastwriter/writer.js

@@ -122,6 +122,12 @@ describe( 'DowncastWriter', () => {
 			expect( element.id ).to.equal( 'bar' );
 			assertElementAttributes( element, attributes );
 		} );
+
+		it( 'should pass priority 0', () => {
+			const element = writer.createAttributeElement( 'foo', attributes, { priority: 0 } );
+
+			expect( element.priority ).to.equal( 0 );
+		} );
 	} );
 
 	describe( 'createContainerElement()', () => {