Template Part: Add fallback to the current theme when not provided

packages/block-library/src/navigation/use-template-part-area-label.js

@@ -45,14 +45,16 @@ export default function useTemplatePartAreaLabel( clientId ) {
 					'core/editor'
 				).__experimentalGetDefaultTemplatePartAreas();
 			/* eslint-enable @wordpress/data-no-store-string-literals */
-			const { getEditedEntityRecord } = select( coreStore );
+			const { getCurrentTheme, getEditedEntityRecord } =
+				select( coreStore );
 
 			for ( const templatePartClientId of parentTemplatePartClientIds ) {
 				const templatePartBlock = getBlock( templatePartClientId );
 
 				// The 'area' usually isn't stored on the block, but instead
 				// on the entity.
-				const { theme, slug } = templatePartBlock.attributes;
+				const { theme = getCurrentTheme()?.stylesheet, slug } =
+					templatePartBlock.attributes;
 				const templatePartEntityId = createTemplatePartId(
 					theme,
 					slug

packages/block-library/src/pattern/edit.js

@@ -20,7 +20,8 @@ const PatternEdit = ( { attributes, clientId } ) => {
 	);
 
 	const currentThemeStylesheet = useSelect(
-		( select ) => select( coreStore ).getCurrentTheme()?.stylesheet
+		( select ) => select( coreStore ).getCurrentTheme()?.stylesheet,
+		[]
 	);
 
 	const { replaceBlocks, __unstableMarkNextChangeAsNotPersistent } =

packages/block-library/src/template-part/edit/index.js

@@ -35,7 +35,11 @@ export default function TemplatePartEdit( {
 	setAttributes,
 	clientId,
 } ) {
-	const { slug, theme, tagName, layout = {} } = attributes;
+	const currentTheme = useSelect(
+		( select ) => select( coreStore ).getCurrentTheme()?.stylesheet,
+		[]
+	);
+	const { slug, theme = currentTheme, tagName, layout = {} } = attributes;
 	const templatePartId = createTemplatePartId( theme, slug );
 	const hasAlreadyRendered = useHasRecursion( templatePartId );
 	const [ isTemplatePartSelectionOpen, setIsTemplatePartSelectionOpen ] =

packages/block-library/src/template-part/index.js

@@ -32,10 +32,11 @@ export const settings = {
 			return;
 		}
 
-		const entity = select( coreDataStore ).getEntityRecord(
+		const { getCurrentTheme, getEntityRecord } = select( coreDataStore );
+		const entity = getEntityRecord(
 			'postType',
 			'wp_template_part',
-			theme + '//' + slug
+			( theme || getCurrentTheme()?.stylesheet ) + '//' + slug
 		);
 		if ( ! entity ) {
 			return;

packages/block-library/src/template-part/variations.js

@@ -35,10 +35,12 @@ export function enhanceTemplatePartVariations( settings, name ) {
 			// Find a matching variation from the created template part
 			// by checking the entity's `area` property.
 			if ( ! slug ) return false;
-			const entity = select( coreDataStore ).getEntityRecord(
+			const { getCurrentTheme, getEntityRecord } =
+				select( coreDataStore );
+			const entity = getEntityRecord(
 				'postType',
 				'wp_template_part',
-				`${ theme }//${ slug }`
+				`${ theme || getCurrentTheme()?.stylesheet }//${ slug }`
 			);
 
 			if ( entity?.slug ) {

packages/edit-site/src/hooks/template-part-edit.js

@@ -24,11 +24,13 @@ function EditTemplatePartMenuItem( { attributes } ) {
 	const { params } = useLocation();
 	const templatePart = useSelect(
 		( select ) => {
-			return select( coreStore ).getEntityRecord(
+			const { getCurrentTheme, getEntityRecord } = select( coreStore );
+
+			return getEntityRecord(
 				'postType',
 				TEMPLATE_PART_POST_TYPE,
 				// Ideally this should be an official public API.
-				`${ theme }//${ slug }`
+				`${ theme || getCurrentTheme()?.stylesheet }//${ slug }`
 			);
 		},
 		[ theme, slug ]