Plugin tweaks: Add jetpack tweaks to always activate the Jetpack blocks

See WordPress/wporg-parent-2021#170

mu-plugins/plugin-tweaks/index.php

@@ -13,4 +13,5 @@
 require_once __DIR__ . '/stream.php';
 require_once __DIR__ . '/incompatible-plugins.php';
 require_once __DIR__ . '/gutenberg.php';
+require_once __DIR__ . '/jetpack.php';
 require_once __DIR__ . '/youtube-shortcode.php';

mu-plugins/plugin-tweaks/jetpack.php

@@ -0,0 +1,26 @@
+<?php
+
+namespace WordPressdotorg\MU_Plugins\Plugin_Tweaks\Jetpack;
+
+defined( 'WPINC' ) || die();
+
+/**
+ * Actions and filters.
+ */
+add_filter( 'jetpack_active_modules', __NAMESPACE__ . '\activate_jetpack_blocks' );
+
+/**
+ * Ensure "blocks" module is active.
+ *
+ * The subscribe block is used in the footer template, so this must be active
+ * for all sites. The filter only fires if Jetpack itself is already active.
+ *
+ * @param string[] $modules Array of active Jetpack modules.
+ * @return string[]
+ */
+function activate_jetpack_blocks( $modules ) {
+	if ( ! in_array( 'blocks', $modules, true ) ) {
+		$modules[] = 'blocks';
+	}
+	return $modules;
+}