Block Hooks: Respect "multiple": false

src/wp-includes/blocks.php

@@ -1056,9 +1056,64 @@ function apply_block_hooks_to_content( $content, $context, $callback = 'insert_h
 		$after_block_visitor  = make_after_block_visitor( $hooked_blocks, $context, $callback );
 	}
 
-	$blocks = parse_blocks( $content );
+	$block_allows_multiple_instances = array();
+	/*
+	 * Remove hooked blocks from `$hooked_block_types` if they have `multiple` set to false and
+	 * are already present in `$content`.
+	 */
+	foreach ( $hooked_blocks as &$relative_positions ) {
+		foreach ( $relative_positions as &$hooked_block_types ) {
+			foreach ( $hooked_block_types as &$hooked_block_type ) {
+				$hooked_block_type_definition =
+					WP_Block_Type_Registry::get_instance()->get_registered( $hooked_block_type );
+				if ( block_has_support( $hooked_block_type_definition, 'multiple', true ) ) {
+					$block_allows_multiple_instances[ $hooked_block_type ] = true;
+				} elseif ( has_block( $hooked_block_type, $content ) ) {
+					unset( $hooked_block_type );
+					if ( empty( $hooked_block_types ) ) {
+						unset( $hooked_block_types );
+					}
+					if ( empty( $relative_positions ) ) {
+						unset( $relative_positions );
+					}
+				}
+			}
+		}
+	}
 
-	return traverse_and_serialize_blocks( $blocks, $before_block_visitor, $after_block_visitor );
+	/*
+	 * We also need to cover the case where there the hooked block is not present in
+	 * `$content` at first and we're allowed to insert it once -- but not again.
+	 */
+	$suppress_single_instance_blocks = static function ( $hooked_block_types, $relative_position, $anchor_block_name ) use ( &$block_allows_multiple_instances, $content ) {
+		foreach ( $hooked_block_types as $index => $hooked_block_type ) {
+			if ( ! isset( $block_allows_multiple_instances[ $hooked_block_type ] ) ) {
+				$hooked_block_type_definition =
+					WP_Block_Type_Registry::get_instance()->get_registered( $hooked_block_type );
+
+				$block_allows_multiple_instances[ $hooked_block_type ] =
+					block_has_support( $hooked_block_type_definition, 'multiple', true );
+
+				if ( ! $block_allows_multiple_instances[ $hooked_block_type ] && has_block( $hooked_block_type, $content ) ) {
+					unset( $hooked_block_types[ $index ] );
+				}
+			} elseif ( ! $block_allows_multiple_instances[ $hooked_block_type ] ) {
+				// An instance of the hooked block was previously encountered, and its `multiple` support is false.
+				unset( $hooked_block_types[ $index ] );
+			}
+		}
+
+		return $hooked_block_types;
+	};
+	add_filter( 'hooked_block_types', $suppress_single_instance_blocks, PHP_INT_MAX, 3 );
+	$content = traverse_and_serialize_blocks(
+		parse_blocks( $content ),
+		$before_block_visitor,
+		$after_block_visitor
+	);
+	remove_filter( 'hooked_block_types', $suppress_single_instance_blocks, PHP_INT_MAX );
+
+	return $content;
 }
 
 /**

tests/phpunit/tests/blocks/applyBlockHooksToContent.php

@@ -27,6 +27,27 @@ public static function wpSetUpBeforeClass() {
 				),
 			)
 		);
+
+		register_block_type(
+			'tests/hooked-block-with-multiple-false',
+			array(
+				'block_hooks' => array(
+					'tests/other-anchor-block' => 'after',
+				),
+				'supports'    => array(
+					'multiple' => false,
+				),
+			)
+		);
+
+		register_block_type(
+			'tests/dynamically-hooked-block-with-multiple-false',
+			array(
+				'supports' => array(
+					'multiple' => false,
+				),
+			)
+		);
 	}
 
 	/**
@@ -38,6 +59,8 @@ public static function wpTearDownAfterClass() {
 		$registry = WP_Block_Type_Registry::get_instance();
 
 		$registry->unregister( 'tests/hooked-block' );
+		$registry->unregister( 'tests/hooked-block-with-multiple-false' );
+		$registry->unregister( 'tests/dynamically-hooked-block-with-multiple-false' );
 	}
 
 	/**
@@ -67,4 +90,82 @@ public function test_apply_block_hooks_to_content_inserts_hooked_block() {
 			$actual
 		);
 	}
+
+	/**
+	 * @ticket 61902
+	 */
+	public function test_apply_block_hooks_to_content_respect_multiple_false() {
+		$context          = new WP_Block_Template();
+		$context->content = '<!-- wp:tests/hooked-block-with-multiple-false /--><!-- wp:tests/other-anchor-block /-->';
+
+		$actual = apply_block_hooks_to_content( $context->content, $context, 'insert_hooked_blocks' );
+		$this->assertSame(
+			'<!-- wp:tests/hooked-block-with-multiple-false /--><!-- wp:tests/other-anchor-block /-->',
+			$actual
+		);
+	}
+
+	/**
+	 * @ticket 61902
+	 */
+	public function test_apply_block_hooks_to_content_respect_multiple_false_after_inserting_once() {
+		$context          = new WP_Block_Template();
+		$context->content = '<!-- wp:tests/other-anchor-block /--><!-- wp:tests/other-block /--><!-- wp:tests/other-anchor-block /-->';
+
+		$actual = apply_block_hooks_to_content( $context->content, $context, 'insert_hooked_blocks' );
+		$this->assertSame(
+			'<!-- wp:tests/other-anchor-block /--><!-- wp:tests/hooked-block-with-multiple-false /--><!-- wp:tests/other-block /--><!-- wp:tests/other-anchor-block /-->',
+			$actual
+		);
+	}
+
+	/**
+	 * @ticket 61902
+	 */
+	public function test_apply_block_hooks_to_content_respect_multiple_false_with_filter() {
+		$filter = function ( $hooked_block_types, $relative_position, $anchor_block_type ) {
+			if ( 'tests/yet-another-anchor-block' === $anchor_block_type && 'after' === $relative_position ) {
+				$hooked_block_types[] = 'tests/dynamically-hooked-block-with-multiple-false';
+			}
+
+			return $hooked_block_types;
+		};
+
+		$context          = new WP_Block_Template();
+		$context->content = '<!-- wp:tests/dynamically-hooked-block-with-multiple-false /--><!-- wp:tests/yet-another-anchor-block /-->';
+
+		add_filter( 'hooked_block_types', $filter, 10, 3 );
+		$actual = apply_block_hooks_to_content( $context->content, $context, 'insert_hooked_blocks' );
+		remove_filter( 'hooked_block_types', $filter, 10 );
+
+		$this->assertSame(
+			'<!-- wp:tests/dynamically-hooked-block-with-multiple-false /--><!-- wp:tests/yet-another-anchor-block /-->',
+			$actual
+		);
+	}
+
+	/**
+	 * @ticket 61902
+	 */
+	public function test_apply_block_hooks_to_content_respect_multiple_false_after_inserting_once_with_filter() {
+		$filter = function ( $hooked_block_types, $relative_position, $anchor_block_type ) {
+			if ( 'tests/yet-another-anchor-block' === $anchor_block_type && 'after' === $relative_position ) {
+				$hooked_block_types[] = 'tests/dynamically-hooked-block-with-multiple-false';
+			}
+
+			return $hooked_block_types;
+		};
+
+		$context          = new WP_Block_Template();
+		$context->content = '<!-- wp:tests/yet-another-anchor-block /--><!-- wp:tests/other-block /--><!-- wp:tests/yet-another-anchor-block /-->';
+
+		add_filter( 'hooked_block_types', $filter, 10, 3 );
+		$actual = apply_block_hooks_to_content( $context->content, $context, 'insert_hooked_blocks' );
+		remove_filter( 'hooked_block_types', $filter, 10 );
+
+		$this->assertSame(
+			'<!-- wp:tests/yet-another-anchor-block /--><!-- wp:tests/dynamically-hooked-block-with-multiple-false /--><!-- wp:tests/other-block /--><!-- wp:tests/yet-another-anchor-block /-->',
+			$actual
+		);
+	}
 }