No-op wiring to get ref "extends" into Parsoid

This doesn't change behavior yet, it's pure wiring to make the
attribute available to Parsoid logic.

Bug: T378567
Change-Id: I6182b601f6fee66a9c32d5006d0a36150eb47e7f

src/Parsoid/RefGroupItem.php

@@ -27,6 +27,7 @@ class RefGroupItem {
 	public string $dir = '';
 	public string $group = '';
 	public int $groupIndex = 1;
+	public ?string $extendsRef = null;
 	public int $index = 0;
 	public string $key;
 	public string $id;

src/Parsoid/References.php

@@ -163,6 +163,7 @@ class References extends ExtensionTagHandler {
 		$refName = $refDmw->attrs->name ?? '';
 		$followName = $refDmw->attrs->follow ?? '';
 		$refDir = strtolower( $refDmw->attrs->dir ?? '' );
+		$extendsRef = $refDmw->attrs->extends ?? null;
 
 		// Add ref-index linkback
 		$linkBack = $doc->createElement( 'sup' );
@@ -285,7 +286,7 @@ class References extends ExtensionTagHandler {
 			// Even worse would be if it tried to redefine itself!
 
 			if ( !$ref ) {
-				$ref = $refsData->add( $extApi, $groupName, $refName, $refDir );
+				$ref = $refsData->add( $extApi, $groupName, $refName, $extendsRef, $refDir );
 			}
 
 			// Handle linkbacks

src/Parsoid/ReferencesData.php

@@ -68,7 +68,7 @@ class ReferencesData {
 	}
 
 	public function add(
-		ParsoidExtensionAPI $extApi, string $groupName, string $refName, string $refDir
+		ParsoidExtensionAPI $extApi, string $groupName, string $refName, ?string $extendsRef, string $refDir
 	): RefGroupItem {
 		$group = $this->getRefGroup( $groupName, true );
 		$hasRefName = $refName !== '';
@@ -93,6 +93,9 @@ class ReferencesData {
 		$ref->dir = $refDir;
 		$ref->group = $group->name;
 		$ref->groupIndex = count( $group->refs ) + 1;
+		if ( $extendsRef ) {
+			$ref->extendsRef = $extendsRef;
+		}
 		$ref->index = $n;
 		$ref->key = $refIdBase;
 		$ref->id = $hasRefName ? $refIdBase . '-0' : $refIdBase;

tests/phpunit/unit/Parsoid/ReferencesDataTest.php

@@ -56,6 +56,7 @@ class ReferencesDataTest extends MediaWikiUnitTestCase {
 			$this->createNoOpMock( ParsoidExtensionAPI::class ),
 			Cite::DEFAULT_GROUP,
 			'',
+			null,
 			''
 		);
 
@@ -76,6 +77,7 @@ class ReferencesDataTest extends MediaWikiUnitTestCase {
 			$this->createNoOpMock( ParsoidExtensionAPI::class ),
 			'note',
 			'wales',
+			'main',
 			'rtl'
 		);
 
@@ -85,6 +87,7 @@ class ReferencesDataTest extends MediaWikiUnitTestCase {
 		$expected->key = 'cite_ref-wales_1';
 		$expected->id = 'cite_ref-wales_1-0';
 		$expected->name = 'wales';
+		$expected->extendsRef = 'main';
 		$expected->target = 'cite_note-wales-1';
 		$this->assertEquals( $expected, $ref );