Don't crash rebuilding the graph on a wiki with no subjects

RebuildGraphDatabases looked up the numeric id of the subject slot role
before querying for subject pages. On a wiki that has never stored a
Subject, that role was never registered, so the lookup threw
NameTableAccessException and the script aborted.

Guard the lookup and treat a missing slot role as "no subject pages",
mirroring the existing handling in DumpRdf and
DatabaseDeletedSubjectPageIdsLookup. The rebuild now completes and
reports zero pages instead of failing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

maintenance/RebuildGraphDatabases.php

@@ -8,6 +8,7 @@
 use LogicException;
 use Maintenance;
 use MediaWiki\MediaWikiServices;
+use MediaWiki\Storage\NameTableAccessException;
 use MediaWiki\Title\Title;
 use ProfessionalWiki\NeoWiki\Application\PageRefreshOutcome;
 use ProfessionalWiki\NeoWiki\Application\SubjectPageRebuilder;
@@ -145,7 +146,14 @@ private static function skipReason( PageRefreshOutcome $outcome ): string {
 	 */
 	private function getSubjectPageIds(): array {
 		$services = MediaWikiServices::getInstance();
-		$roleId = $services->getSlotRoleStore()->getId( MediaWikiSubjectRepository::SLOT_NAME );
+
+		try {
+			$roleId = $services->getSlotRoleStore()->getId( MediaWikiSubjectRepository::SLOT_NAME );
+		} catch ( NameTableAccessException ) {
+			// No page has ever stored a Subject, so the slot role was never registered. There is
+			// nothing to rebuild; report an empty run instead of crashing.
+			return [];
+		}
 
 		$rows = $this->getReplicaDB()->newSelectQueryBuilder()
 			->select( 'page_id' )

tests/phpunit/Maintenance/RebuildGraphDatabasesTest.php

@@ -37,6 +37,21 @@ protected function tearDown(): void {
 		NeoWikiExtension::resetInstance();
 	}
 
+	public function testRebuildSucceedsOnAWikiThatHasNeverStoredASubject(): void {
+		// A wiki with no Subjects has never registered the 'neo' slot role, so the role-id lookup
+		// throws NameTableAccessException. Forcing that state (empty table + a store without a warmed
+		// cache) proves the rebuild treats it as an empty run instead of crashing.
+		$this->truncateTable( 'slot_roles' );
+		$this->getServiceContainer()->resetServiceForTesting( 'SlotRoleStore' );
+
+		$spy = new SpyGraphDatabasePlugin();
+		$this->registerGraphDatabasePlugins( $spy );
+
+		$this->runRebuild();
+
+		$this->assertSame( [], $spy->savedPages, 'a wiki with no Subjects has nothing to project' );
+	}
+
 	public function testRebuildRemovesADeletedSubjectPageFromTheGraph(): void {
 		$this->createPageWithSubjects( 'Surviving page before', TestSubject::build() );
 		$deleted = $this->createPageWithSubjects( 'Deleted during outage', TestSubject::build() );