Block editor: Hotfix performance regression (#41309)

* Block editor: Hotfix performance regression

* Regenerate files

* Fix path

* Bail when running a local dev build of Gutenberg

* Simplify file path

* Add Gutenberg stubs

* Update Jetpack Phan config with Gutenberg stubs

* Load Gutenberg stubs

* Rename function and update docblock

* Don't hotfix if blocks module is not active

* Fix version in docblock

* Revert changes in the Jetpack plugin

* Remove Jetpack changelog

* Revert Phan changes for the Jetpack plugin

* Move hotfix to jetpack-mu-wpcom

* Revert automated linter changes

* Fix Phan errors

* Remove Phan suppression

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/13051029268

Upstream-Ref: Automattic/jetpack@40d66c6

CHANGELOG.md

@@ -27,6 +27,7 @@ This is an alpha version! The changes listed here are not final.
 - Adds verify email task to newsletter goal launchpad
 - Admin Bar: Point the Edit Site menu item to /site-editor.php
 - Always loads Odyssey Stats widget regardless of wpcom_admin_interface
+- Block editor: Hotfix performance regression
 - Changed the experiment cache key so that users get assigned once the experiment starts.
 - Code: Use function-style exit() and die() with a default status code of 0.
 - Coming Soon: Add more checks to the ETK version comparison.

src/features/starter-page-templates/class-starter-page-templates.php

@@ -433,7 +433,7 @@ public function add_default_editor_styles_for_classic_themes( $editor_settings,
 			return $editor_settings;
 		}
 
-		$default_editor_styles_file = gutenberg_dir_path() . 'build/block-editor/default-editor-styles.css'; // @phan-suppress-current-line PhanUndeclaredFunction
+		$default_editor_styles_file = gutenberg_dir_path() . 'build/block-editor/default-editor-styles.css';
 		if ( ! file_exists( $default_editor_styles_file ) ) {
 			return $editor_settings;
 		}

src/features/wpcom-hotfixes/wpcom-hotfixes.php

@@ -50,3 +50,39 @@ function ( $content ) {
 		1
 	);
 }
+
+/**
+ * Overrides the `wp-block-editor` script with a hotfix to prevent a performance issue present in
+ * Gutenberg v19.0, v20.0, and v20.1 (see https://github.com/WordPress/gutenberg/issues/68875).
+ *
+ * Our custom script has been generated by applying the fix introduced in Gutenberg v20.2
+ * (see https://github.com/WordPress/gutenberg/pull/68898) in a local Gutenberg environment and
+ * running `npm run build` to extract the fixed `wp-block-editor` script.
+ *
+ * @param WP_Scripts $scripts WP_Scripts instance.
+ */
+function wpcom_fix_performance_issue_block_editor_v19_9_v20_0_v20_1( $scripts ) {
+	if ( ! defined( 'GUTENBERG_VERSION' ) ) {
+		return;
+	}
+
+	if ( ! in_array( GUTENBERG_VERSION, array( '19.9.0', '20.0.0', '20.1.0' ), true ) ) {
+		return;
+	}
+
+	$path         = gutenberg_dir_path() . 'build/block-editor/index.min.js';
+	$handle       = 'wp-block-editor';
+	$asset_file   = substr( $path, 0, - ( strlen( '.js' ) ) ) . '.asset.php';
+	$asset        = file_exists( $asset_file ) ? require $asset_file : null;
+	$dependencies = $asset['dependencies'] ?? array();
+	$version      = $asset['version'] ?? GUTENBERG_VERSION;
+	gutenberg_override_script(
+		$scripts,
+		$handle,
+		plugins_url( 'wp-block-editor-' . GUTENBERG_VERSION . '-hotfix.min.js', __FILE__ ),
+		$dependencies,
+		$version,
+		true
+	);
+}
+add_action( 'wp_default_scripts', 'wpcom_fix_performance_issue_block_editor_v19_9_v20_0_v20_1', 11 );