Add database extension to LocalSettings.php.

Bug: T226857
Change-Id: Ifbcc8db4f96895fef76bdd747f3411536b9e6894

includes/installer/Installer.php

@@ -1862,4 +1862,18 @@ abstract class Installer {
 		set_time_limit( 0 );
 		Wikimedia\restoreWarnings();
 	}
+
+	/**
+	 * Return the name of the extension selected to provide the database or null
+	 * if the database is provided by core.
+	 *
+	 * @return string|null
+	 */
+	public function getUsedExtensionName() : ?string {
+		if ( empty( $this->settings['wgDBtype'] ) ) {
+			return null;
+		}
+		return $this->installerDbSupport
+			->getExtensionNameForDatabase( $this->settings['wgDBtype'] );
+	}
 }

includes/installer/Services/InstallerDBSupport.php

@@ -67,19 +67,19 @@ class InstallerDBSupport {
 			'installer' => MysqlInstaller::class,
 			'updater' => MysqlUpdater::class,
 			'driver' => DatabaseMysqli::class,
-			'extension' => 'core'
+			'extension' => null
 		],
 		'postgres' => [
 			'installer' => PostgresInstaller::class,
 			'updater' => PostgresUpdater::class,
 			'driver' => DatabasePostgres::class,
-			'extension' => 'core'
+			'extension' => null
 		],
 		'sqlite' => [
 			'installer' => SqliteInstaller::class,
 			'updater' => SqliteUpdater::class,
 			'driver' => DatabaseSqlite::class,
-			'extension' => 'core'
+			'extension' => null
 		]
 	];
 
@@ -296,7 +296,7 @@ class InstallerDBSupport {
 	 */
 	public function getExtensionNameForDatabase(
 		string $database
-	): string {
+	): ?string {
 		if ( !isset( $this->databaseInfo[strtolower( $database )] ) ) {
 			throw new InvalidArgumentException( __METHOD__ .
 				" no registered database found for type '$database'" );

includes/installer/WebInstallerOptions.php

@@ -545,6 +545,10 @@ class WebInstallerOptions extends WebInstallerPage {
 				$extsToInstall[] = $ext;
 			}
 		}
+		$dbext = $this->parent->getUsedExtensionName();
+		if ( $dbext ) {
+			$extsToInstall[] = $dbext;
+		}
 		$this->parent->setVar( '_Extensions', $extsToInstall );
 
 		if ( $this->getVar( '_MainCacheType' ) == 'memcached' ) {