PLATFORM-9121 | Do not swallow DB errors in Cargo query

Cargo currently swallows all exceptions thrown while it is running
queries, mainly because it may throw MWExceptions as validation errors
which should be formatted nicely without breaking the rest of the page.
However, the queries themselves may fail due to transient database
issues, and Cargo wraps the resulting DBError exceptions as well without
much ado. The effect is that these errors never get logged (so we don't
even know how often this happens), and the error gets cached in parser
cache and on the CDN, forcing people to check for and periodically purge
pages with such errors.

Instead, detect and rethrow errors coming from MediaWiki's DBAL so that
we can track them in our logs, and so that they do not get cached.

includes/CargoLuaLibrary.php

@@ -48,6 +48,8 @@ public function cargoQuery( $tables, $fields, $args ): array {
 			$query = CargoSQLQuery::newFromValues( $tables, $fields, $where, $join,
 				$groupBy, $having, $orderBy, $limit, $offset );
 			$rows = $query->run();
+		} catch ( \Wikimedia\Rdbms\DBError $e ) {
+			throw $e;
 		} catch ( Exception $e ) {
 			// Allow for error handling within Lua.
 			throw new Scribunto_LuaError( $e->getMessage() );

includes/parserfunctions/CargoQuery.php

@@ -114,6 +114,8 @@ public static function run( $parser ) {
 				);
 				$queryResultsJustForResultsTitle = $sqlQueryJustForResultsTitle->run();
 			}
+		} catch ( \Wikimedia\Rdbms\DBError $e ) {
+			throw $e;
 		} catch ( Exception $e ) {
 			return CargoUtils::formatError( $e->getMessage() );
 		}