HTML API: Implement active format reconstruction

src/wp-includes/html-api/class-wp-html-active-formatting-elements.php

@@ -43,6 +43,22 @@ class WP_HTML_Active_Formatting_Elements {
 	 */
 	private $stack = array();
 
+	/**
+	 * Returns the node at the given index in the list of active formatting elements.
+	 *
+	 * Do not use this method; it is meant to be used only by the HTML Processor.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @access private
+	 *
+	 * @param int $index Number of nodes from the top node to return.
+	 * @return WP_HTML_Token|null Node at the given index in the stack, if one exists, otherwise null.
+	 */
+	public function at( $index ) {
+		return $this->stack[ $index ];
+	}
+
 	/**
 	 * Reports if a specific node is in the stack of active formatting elements.
 	 *
@@ -86,6 +102,16 @@ public function current_node() {
 		return $current_node ? $current_node : null;
 	}
 
+	/**
+	 * Inserts a marker at the end of the list of active formatting elements.
+	 *
+	 * @since 6.7.0
+	 */
+	public function insert_marker() {
+		$marker = new WP_HTML_Token( null, 'marker', false );
+		$this->push( $marker );
+	}
+
 	/**
 	 * Pushes a node onto the stack of active formatting elements.
 	 *

src/wp-includes/html-api/class-wp-html-processor.php

@@ -2832,15 +2832,19 @@ private function generate_implied_end_tags_thoroughly() {
 	 * @return bool Whether any formatting elements needed to be reconstructed.
 	 */
 	private function reconstruct_active_formatting_elements() {
+		$count = $this->state->active_formatting_elements->count();
+
 		/*
 		 * > If there are no entries in the list of active formatting elements, then there is nothing
 		 * > to reconstruct; stop this algorithm.
 		 */
-		if ( 0 === $this->state->active_formatting_elements->count() ) {
+		if ( 0 === $count ) {
 			return false;
 		}
 
-		$last_entry = $this->state->active_formatting_elements->current_node();
+		// Start at the last node in the list of active formatting elements.
+		$currently_at = $count - 1;
+		$last_entry   = $this->state->active_formatting_elements->at( $currently_at );
 		if (
 
 			/*
@@ -2859,8 +2863,39 @@ private function reconstruct_active_formatting_elements() {
 			return false;
 		}
 
-		$this->last_error = self::ERROR_UNSUPPORTED;
-		throw new WP_HTML_Unsupported_Exception( 'Cannot reconstruct active formatting elements when advancing and rewinding is required.' );
+		$entry = $last_entry;
+
+		while ( $currently_at >= 0 ) {
+			if ( 0 === $currently_at ) {
+				goto create;
+			}
+			$entry = $this->state->active_formatting_elements->at( --$currently_at );
+
+			/*
+			 * > If entry is neither a marker nor an element that is also in the stack of open elements,
+			 * > go to the step labeled rewind.
+			 */
+			if ( 'marker' === $entry->node_name || $this->state->stack_of_open_elements->contains_node( $entry ) ) {
+				break;
+			}
+		}
+
+		advance:
+		$entry = $this->state->active_formatting_elements->at( ++$currently_at );
+
+		create:
+		$this->insert_html_element( $entry );
+
+		/*
+		 * > Replace the entry for entry in the list with an entry for new element.
+		 * This doesn't need to happen here since no DOM is being created.
+		 */
+
+		if ( $count - 1 !== $currently_at ) {
+			goto advance;
+		}
+
+		return true;
 	}
 
 	/**

tests/phpunit/tests/html-api/wpHtmlProcessor.php

@@ -112,18 +112,23 @@ public function test_clear_to_navigate_after_seeking() {
 	}
 
 	/**
-	 * Ensures that support is added for reconstructing active formatting elements
-	 * before the HTML Processor handles situations with unclosed formats requiring it.
+	 * Ensures that support is added for reconstructing active formatting elements.
 	 *
 	 * @ticket 58517
 	 *
 	 * @covers WP_HTML_Processor::reconstruct_active_formatting_elements
 	 */
-	public function test_fails_to_reconstruct_formatting_elements() {
-		$processor = WP_HTML_Processor::create_fragment( '<p><em>One<p><em>Two<p><em>Three<p><em>Four' );
+	public function test_reconstructs_formatting_elements() {
+		$processor = WP_HTML_Processor::create_fragment( '<p><em>One<p><em><span>Two<p><em>Three<p><em>Four' );
 
 		$this->assertTrue( $processor->next_tag( 'EM' ), 'Could not find first EM.' );
-		$this->assertFalse( $processor->next_tag( 'EM' ), 'Should have aborted before finding second EM as it required reconstructing the first EM.' );
+		$this->assertSame( array( 'HTML', 'BODY', 'P', 'EM' ), $processor->get_breadcrumbs(), 'Found incorrect breadcrumbs for first EM.' );
+		$this->assertTrue( $processor->next_tag( 'SPAN' ), 'Could not find test span.' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'P', 'EM', 'EM', 'SPAN' ),
+			$processor->get_breadcrumbs(),
+			'Found incorrect breadcrumbs for test SPAN; should have created two EMs.'
+		);
 	}
 
 	/**

tests/phpunit/tests/html-api/wpHtmlProcessorBreadcrumbs.php

@@ -219,45 +219,55 @@ public static function data_unsupported_elements() {
 	}
 
 	/**
-	 * @ticket 58517
-	 *
-	 * @dataProvider data_unsupported_markup
+	 * Ensures that formats inside unclosed A elements are reconstructed.
 	 *
-	 * @param string $html HTML containing unsupported markup.
+	 * @ticket 61576
 	 */
-	public function test_fails_when_encountering_unsupported_markup( $html, $description ) {
-		$processor = WP_HTML_Processor::create_fragment( $html );
-
-		while ( $processor->next_token() && null === $processor->get_attribute( 'supported' ) ) {
-			continue;
-		}
+	public function test_reconstructs_formatting_from_unclosed_a_elements() {
+		$processor = WP_HTML_Processor::create_fragment( '<a><strong>Click <a><big>Here</big></a></strong></a>' );
 
-		$this->assertNull(
-			$processor->get_last_error(),
-			'Bailed on unsupported input before finding supported checkpoint: check test code.'
+		$processor->next_tag( 'STRONG' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'A', 'STRONG' ),
+			$processor->get_breadcrumbs(),
+			'Failed to construct starting breadcrumbs properly.'
 		);
 
-		$this->assertTrue( $processor->get_attribute( 'supported' ), 'Did not find required supported element.' );
-		$processor->next_token();
-		$this->assertNotNull( $processor->get_last_error(), "Didn't properly reject unsupported markup: {$description}" );
+		$processor->next_tag( 'BIG' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'STRONG', 'A', 'BIG' ),
+			$processor->get_breadcrumbs(),
+			'Failed to reconstruct the active formatting elements after an unclosed A element.'
+		);
 	}
 
 	/**
-	 * Data provider.
+	 * Ensures that unclosed A elements are reconstructed.
 	 *
-	 * @return array[]
+	 * @ticket 61576
 	 */
-	public static function data_unsupported_markup() {
-		return array(
-			'A with formatting following unclosed A' => array(
-				'<a><strong>Click <span supported><a unsupported><big>Here</big></a></strong></a>',
-				'Unclosed formatting requires complicated reconstruction.',
-			),
+	public function test_reconstructs_unclosed_a_elements() {
+		$processor = WP_HTML_Processor::create_fragment( '<a><div><a></div></a>' );
 
-			'A after unclosed A inside DIV'          => array(
-				'<a><div supported><a unsupported></div></a>',
-				'A is a formatting element, which requires more complicated reconstruction.',
-			),
+		$processor->next_tag( 'DIV' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'DIV' ),
+			$processor->get_breadcrumbs(),
+			'Failed to construct breadcrumbs properly - the DIV should have closed the A element.'
+		);
+
+		// When the DIV re-opens, it reconstructs an unclosed A, then the A in the text is a second A.
+		$processor->next_tag( 'A' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'DIV', 'A' ),
+			'Failed to create proper breadcrumbs for recreated A element.'
+		);
+
+		// This is the one that's second in the raw text.
+		$processor->next_tag( 'A' );
+		$this->assertSame(
+			array( 'HTML', 'BODY', 'DIV', 'A' ),
+			'Failed to create proper breadcrumbs for explicit A element - this A should have closed the reconstructed A.'
 		);
 	}