HTML API: Pin virtual closer ordering before a same-name opener.

A new A opener immediately after the foreign subtree closes is the one
input where the adjusted-current-node guard and the same-name next-event
lookahead must cooperate: the removed outer A's virtual closer must fire
before the new same-name element opens as a sibling. Add a regression
test walking every A visit, and document the identity invariant that the
next-event lookahead recovers in the queueing guard.

Author: sirreal

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

@@ -914,6 +914,13 @@ private function queue_virtual_closer_after_non_lifo_removal(): bool {
 			return false;
 		}
 
+		/*
+		 * The depth and node-name checks above cannot distinguish the removed
+		 * element from a same-named element at the same depth; identity is
+		 * recovered here. If a queued POP closes a different element with the
+		 * same name, that element owns the current breadcrumb and the virtual
+		 * closer must wait for it.
+		 */
 		$next_event = reset( $this->element_queue );
 		if (
 			false !== $next_event &&

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

@@ -649,6 +649,51 @@ public function test_visits_outer_anchor_virtual_closer_after_mathml_text_integr
 		);
 	}
 
+	/**
+	 * Ensures that the removed outer A element's virtual closer is visited
+	 * before a new same-name opener immediately following the subtree.
+	 *
+	 * This is the one input where the adjusted-current-node guard and the
+	 * same-name next-event lookahead in the virtual-closer queueing must
+	 * cooperate: the new A opener shares the removed element's tag name, but
+	 * the virtual closer must still fire first so the new element opens as a
+	 * sibling, not a child.
+	 *
+	 * @ticket 61576
+	 *
+	 * @covers WP_HTML_Processor::get_breadcrumbs
+	 * @covers WP_HTML_Processor::is_tag_closer
+	 */
+	public function test_visits_outer_anchor_virtual_closer_before_same_name_opener() {
+		$processor = WP_HTML_Processor::create_fragment( '<a><math><mi>x<a>y</a></mi></math><a>z' );
+
+		$visits = array();
+		while ( $processor->next_tag(
+			array(
+				'tag_name'    => 'A',
+				'tag_closers' => 'visit',
+			)
+		) ) {
+			$visits[] = array(
+				$processor->is_tag_closer() ? 'closer' : 'opener',
+				$processor->get_breadcrumbs(),
+			);
+		}
+
+		$this->assertSame(
+			array(
+				array( 'opener', array( 'HTML', 'BODY', 'A' ) ),
+				array( 'opener', array( 'HTML', 'BODY', 'A', 'MATH', 'MI', 'A' ) ),
+				array( 'closer', array( 'HTML', 'BODY', 'A', 'MATH', 'MI' ) ),
+				array( 'closer', array( 'HTML', 'BODY' ) ),
+				array( 'opener', array( 'HTML', 'BODY', 'A' ) ),
+				array( 'closer', array( 'HTML', 'BODY' ) ),
+			),
+			$visits,
+			'Expected the removed outer A virtual closer to be visited before the new same-name A opener.'
+		);
+	}
+
 	/**
 	 * Ensures that an outer A element removed from the stack of open elements
 	 * remains visitable as a virtual closer when the fragment ends inside its