enh(db): provide database providers via IDB API

apps/settings/lib/Controller/CheckSetupController.php

@@ -641,7 +641,7 @@ protected function wasEmailTestSuccessful(): bool {
 
 	protected function hasValidTransactionIsolationLevel(): bool {
 		try {
-			if ($this->db->getDatabasePlatform() instanceof SqlitePlatform) {
+			if ($this->connection->getDatabaseProvider() === IDBConnection::PLATFORM_SQLITE) {
 				return true;
 			}
 
@@ -839,7 +839,7 @@ protected function hasBigIntConversionPendingColumns(): array {
 		];
 
 		$schema = new SchemaWrapper($this->db);
-		$isSqlite = $this->db->getDatabasePlatform() instanceof SqlitePlatform;
+		$isSqlite = $this->connection->getDatabaseProvider() === IDBConnection::PLATFORM_SQLITE;
 		$pendingColumns = [];
 
 		foreach ($tables as $tableName => $columns) {

lib/private/DB/ConnectionAdapter.php

@@ -27,6 +27,10 @@
 
 use Doctrine\DBAL\Exception;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
+use Doctrine\DBAL\Platforms\MySQLPlatform;
+use Doctrine\DBAL\Platforms\OraclePlatform;
+use Doctrine\DBAL\Platforms\PostgreSQLPlatform;
+use Doctrine\DBAL\Platforms\SqlitePlatform;
 use Doctrine\DBAL\Schema\Schema;
 use OC\DB\Exceptions\DbalException;
 use OCP\DB\IPreparedStatement;
@@ -242,4 +246,19 @@ public function migrateToSchema(Schema $toSchema): void {
 	public function getInner(): Connection {
 		return $this->inner;
 	}
+
+	public function getDatabaseProvider(): string {
+		$platform = $this->inner->getDatabasePlatform();
+		if ($platform instanceof MySQLPlatform) {
+			return IDBConnection::PLATFORM_MYSQL;
+		} elseif ($platform instanceof OraclePlatform) {
+			return IDBConnection::PLATFORM_ORACLE;
+		} elseif ($platform instanceof PostgreSQLPlatform) {
+			return IDBConnection::PLATFORM_POSTGRES;
+		} elseif ($platform instanceof SqlitePlatform) {
+			return IDBConnection::PLATFORM_SQLITE;
+		} else {
+			throw new \Exception('Database ' . $platform::class . ' not supported');
+		}
+	}
 }

lib/public/IDBConnection.php

@@ -45,6 +45,18 @@
  * @since 6.0.0
  */
 interface IDBConnection {
+	/* @since 28.0.0 */
+	public const PLATFORM_MYSQL = 'mysql';
+
+	/* @since 28.0.0 */
+	public const PLATFORM_ORACLE = 'oracle';
+
+	/* @since 28.0.0 */
+	public const PLATFORM_POSTGRES = 'postgres';
+
+	/* @since 28.0.0 */
+	public const PLATFORM_SQLITE = 'sqlite';
+
 	/**
 	 * Gets the QueryBuilder for the connection.
 	 *
@@ -339,4 +351,12 @@ public function createSchema(): Schema;
 	 * @since 13.0.0
 	 */
 	public function migrateToSchema(Schema $toSchema): void;
+
+	/**
+	 * Returns the database provider name
+	 * @link https://github.com/nextcloud/server/issues/30877
+	 * @since 28.0.0
+	 * @return IDBConnection::PLATFORM_*
+	 */
+	public function getDatabaseProvider(): string;
 }