Blocks: Ensure that metadata registered on the server for core block is preserved on the client (try 2)

packages/blocks/src/api/registration.js

@@ -160,6 +160,23 @@ export const serverSideBlockDefinitions = {};
 // eslint-disable-next-line camelcase
 export function unstable__bootstrapServerSideBlockDefinitions( definitions ) {
 	for ( const blockName of Object.keys( definitions ) ) {
+		// Don't overwrite if already set. It covers the case when metadata
+		// was initialized from the server.
+		if ( serverSideBlockDefinitions[ blockName ] ) {
+			// We still need to polyfill `apiVersion` for WordPress version
+			// lower than 5.7. If it isn't present in the definition shared
+			// from the server, we try to fallback to the definition passed.
+			// @see https://github.com/WordPress/gutenberg/pull/29279
+			if (
+				serverSideBlockDefinitions[ blockName ].apiVersion ===
+					undefined &&
+				definitions[ blockName ].apiVersion
+			) {
+				serverSideBlockDefinitions[ blockName ].apiVersion =
+					definitions[ blockName ].apiVersion;
+			}
+			continue;
+		}
 		serverSideBlockDefinitions[ blockName ] = mapKeys(
 			pickBy( definitions[ blockName ], ( value ) => ! isNil( value ) ),
 			( value, key ) => camelCase( key )

packages/blocks/src/api/test/registration.js

@@ -385,6 +385,43 @@ describe( 'blocks', () => {
 			} );
 		} );
 
+		// This test can be removed once the polyfill for apiVersion gets removed.
+		it( 'should apply apiVersion on the client when not set on the server', () => {
+			const blockName = 'core/test-block-back-compat';
+			unstable__bootstrapServerSideBlockDefinitions( {
+				[ blockName ]: {
+					category: 'widgets',
+				},
+			} );
+			unstable__bootstrapServerSideBlockDefinitions( {
+				[ blockName ]: {
+					apiVersion: 2,
+					category: 'ignored',
+				},
+			} );
+
+			const blockType = {
+				title: 'block title',
+			};
+			registerBlockType( blockName, blockType );
+			expect( getBlockType( blockName ) ).toEqual( {
+				apiVersion: 2,
+				name: blockName,
+				save: expect.any( Function ),
+				title: 'block title',
+				category: 'widgets',
+				icon: {
+					src: blockIcon,
+				},
+				attributes: {},
+				providesContext: {},
+				usesContext: [],
+				keywords: [],
+				supports: {},
+				styles: [],
+			} );
+		} );
+
 		it( 'should validate the icon', () => {
 			const blockType = {
 				save: noop,

packages/e2e-tests/plugins/register-block-type-hooks.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Plugin Name: Gutenberg Test Register Block Type Hooks
+ * Plugin URI: https://github.com/WordPress/gutenberg
+ * Author: Gutenberg Team
+ *
+ * @package gutenberg-test-register-block-type-hooks
+ */
+
+/**
+ * Changes the category for the paragraph block.
+ *
+ * @param array $metadata Array of metadata for registering a block type.
+ *
+ * @return array Filtered metadata for registering a block type.
+ */
+function gutenberg_test_block_type_metadata( $metadata ) {
+	if ( 'core/paragraph' !== $metadata['name'] ) {
+		return $metadata;
+	}
+
+	return array_merge(
+		$metadata,
+		array( 'category' => 'widgets' )
+	);
+}
+
+add_filter( 'block_type_metadata', 'gutenberg_test_block_type_metadata' );

packages/e2e-tests/specs/editor/plugins/register-block-type-hooks.test.js

@@ -0,0 +1,32 @@
+/**
+ * WordPress dependencies
+ */
+import {
+	activatePlugin,
+	createNewPost,
+	deactivatePlugin,
+	openGlobalBlockInserter,
+} from '@wordpress/e2e-test-utils';
+
+describe( 'Register block type hooks', () => {
+	beforeEach( async () => {
+		await activatePlugin( 'gutenberg-test-register-block-type-hooks' );
+		await createNewPost();
+	} );
+
+	afterEach( async () => {
+		await deactivatePlugin( 'gutenberg-test-register-block-type-hooks' );
+	} );
+
+	it( 'has a custom category for Paragraph block', async () => {
+		await openGlobalBlockInserter();
+
+		const widgetsCategory = await page.$(
+			'.block-editor-block-types-list[aria-label="Widgets"]'
+		);
+
+		expect(
+			await widgetsCategory.$( '.editor-block-list-item-paragraph' )
+		).toBeDefined();
+	} );
+} );