Layout: avoid resolving global settings for blocks with no layout output

src/wp-includes/block-supports/layout.php

@@ -946,6 +946,7 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
  * @since 6.3.0 Adds compound class to layout wrapper for global spacing styles.
  * @since 6.3.0 Check for layout support via the `layout` key with fallback to `__experimentalLayout`.
  * @since 6.6.0 Removed duplicate container class from layout styles.
+ * @since 7.1.0 Returns early before resolving global settings.
  * @access private
  *
  * @param string $block_content Rendered block content.
@@ -955,13 +956,40 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 function wp_render_layout_support_flag( $block_content, $block ) {
 	static $global_styles = null;
 
-	$block_type               = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
-	$block_supports_layout    = block_has_support( $block_type, 'layout', false ) || block_has_support( $block_type, '__experimentalLayout', false );
-	$style_attr               = $block['attrs']['style'] ?? array();
+	$block_type            = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
+	$block_supports_layout = block_has_support( $block_type, 'layout', false ) || block_has_support( $block_type, '__experimentalLayout', false );
+	$style_attr            = $block['attrs']['style'] ?? array();
+	// If there is any value in style -> layout, the block has a child layout.
+	$child_layout = $style_attr['layout'] ?? null;
+
+	/*
+	 * Responsive child layouts are nested under a style state key such as
+	 * `@mobile`. Which of those keys are active depends on the breakpoints in
+	 * global settings, but whether any of them exist at all does not, so this
+	 * can be answered without resolving settings.
+	 */
+	$has_state_child_layout = false;
+	foreach ( (array) $style_attr as $state_styles ) {
+		if ( is_array( $state_styles ) && ! empty( $state_styles['layout'] ) ) {
+			$has_state_child_layout = true;
+			break;
+		}
+	}
+
+	/*
+	 * Bail out before resolving global settings when the block cannot produce
+	 * layout output. Resolving settings is not read-only: on a cold cache it
+	 * queries the user's `wp_global_styles` post, which fires `the_posts`. A
+	 * callback on that hook that renders blocks would re-enter this filter and,
+	 * without this early return, recurse without a base case.
+	 */
+	if ( ! $block_supports_layout && ! $child_layout && ! $has_state_child_layout ) {
+		return $block_content;
+	}
+
 	$global_settings          = wp_get_global_settings();
 	$viewport_settings        = $global_settings['viewport'] ?? null;
 	$responsive_media_queries = WP_Theme_JSON::get_viewport_media_queries( $viewport_settings );
-	$child_layout             = $style_attr['layout'] ?? null;
 
 	/*
 	 * Collect responsive viewport child layout overrides so that a block with

tests/phpunit/tests/block-supports/layout.php

@@ -1124,4 +1124,77 @@ public function test_layout_support_flag_with_non_string_class_name() {
 			'Layout support should render the expected markup when className is not a string'
 		);
 	}
+
+	/**
+	 * Tests that layout support returns early, without resolving global settings,
+	 * for a block that cannot produce any layout output.
+	 *
+	 * Resolving global settings reads the user's `wp_global_styles` post with a
+	 * `WP_Query`, which fires `the_posts`. A callback on that hook that renders
+	 * blocks re-enters this filter, so the bail-out has to happen before the
+	 * lookup or the recursion has no base case.
+	 *
+	 * @ticket 65741
+	 *
+	 * @covers ::wp_render_layout_support_flag
+	 */
+	public function test_layout_support_flag_returns_early_before_resolving_global_settings() {
+		$user_data_resolutions = 0;
+		add_filter(
+			'wp_theme_json_data_user',
+			static function ( $theme_json ) use ( &$user_data_resolutions ) {
+				++$user_data_resolutions;
+				return $theme_json;
+			}
+		);
+
+		// A block with no layout support and no child layout, as produced by
+		// parsing content that has no block delimiters.
+		$block_content = '<p>Not a block.</p>';
+		$block         = array(
+			'blockName' => null,
+			'attrs'     => array(),
+		);
+
+		$this->reset_global_settings();
+
+		$this->assertSame(
+			$block_content,
+			wp_render_layout_support_flag( $block_content, $block ),
+			'Block content should be returned unchanged when the block has no layout support.'
+		);
+		$this->assertSame(
+			0,
+			$user_data_resolutions,
+			'Global settings should not be resolved for a block that cannot produce layout output.'
+		);
+
+		// A block that does support layout still resolves global settings, which
+		// confirms the assertion above is not passing because of a warm cache.
+		$this->reset_global_settings();
+
+		wp_render_layout_support_flag(
+			'<div class="wp-block-group"></div>',
+			array(
+				'blockName' => 'core/group',
+				'attrs'     => array( 'layout' => array( 'type' => 'constrained' ) ),
+			)
+		);
+
+		$this->assertGreaterThan(
+			0,
+			$user_data_resolutions,
+			'Global settings should still be resolved for a block that supports layout.'
+		);
+	}
+
+	/**
+	 * Drops both layers of global settings caching: the resolver's static
+	 * properties and the array cached by wp_get_global_settings().
+	 */
+	private function reset_global_settings() {
+		WP_Theme_JSON_Resolver::clean_cached_data();
+		wp_cache_delete( 'wp_get_global_settings_custom', 'theme_json' );
+		wp_cache_delete( 'wp_get_global_settings_theme', 'theme_json' );
+	}
 }