Iframe: always enable for block themes, in core too (#66800)

Co-authored-by: ellatrix <ellatrix@git.wordpress.org>
Co-authored-by: jsnajdr <jsnajdr@git.wordpress.org>

packages/edit-post/src/components/layout/use-should-iframe.js

@@ -11,39 +11,27 @@ import { store as blockEditorStore } from '@wordpress/block-editor';
  */
 import { unlock } from '../../lock-unlock';
 
-const isGutenbergPlugin = globalThis.IS_GUTENBERG_PLUGIN ? true : false;
-
 export function useShouldIframe() {
-	const {
-		isBlockBasedTheme,
-		hasV3BlocksOnly,
-		isEditingTemplateOrPattern,
-		isZoomOutMode,
-		deviceType,
-	} = useSelect( ( select ) => {
+	return useSelect( ( select ) => {
 		const { getEditorSettings, getCurrentPostType, getDeviceType } =
 			select( editorStore );
-		const { isZoomOut } = unlock( select( blockEditorStore ) );
-		const { getBlockTypes } = select( blocksStore );
-		const editorSettings = getEditorSettings();
-		return {
-			isBlockBasedTheme: editorSettings.__unstableIsBlockBasedTheme,
-			hasV3BlocksOnly: getBlockTypes().every( ( type ) => {
-				return type.apiVersion >= 3;
-			} ),
-			isEditingTemplateOrPattern: [ 'wp_template', 'wp_block' ].includes(
-				getCurrentPostType()
-			),
-			isZoomOutMode: isZoomOut(),
-			deviceType: getDeviceType(),
-		};
+		return (
+			// If the theme is block based, we ALWAYS use the iframe for
+			// consistency across the post and site editor. The iframe was
+			// introduced long before the sited editor and block themes, so
+			// these themes are expecting it.
+			getEditorSettings().__unstableIsBlockBasedTheme ||
+			// For classic themes, we also still want to iframe all the special
+			// editor features and modes such as device previews, zoom out, and
+			// template/pattern editing.
+			getDeviceType() !== 'Desktop' ||
+			[ 'wp_template', 'wp_block' ].includes( getCurrentPostType() ) ||
+			unlock( select( blockEditorStore ) ).isZoomOut() ||
+			// Finally, still iframe the editor for classic themes if all blocks
+			// are v3 (which means they are marked as iframe-compatible).
+			select( blocksStore )
+				.getBlockTypes()
+				.every( ( type ) => type.apiVersion >= 3 )
+		);
 	}, [] );
-
-	return (
-		hasV3BlocksOnly ||
-		( isGutenbergPlugin && isBlockBasedTheme ) ||
-		isEditingTemplateOrPattern ||
-		isZoomOutMode ||
-		[ 'Tablet', 'Mobile' ].includes( deviceType )
-	);
 }