Transactor.transact catches every Throwable, including OOM and StackOverflow

[haskiindahouse]

Transactor.transact wraps the user's body in try ... catch case t =>, which matches every Throwable — including fatal ones like OutOfMemoryError, StackOverflowError, and other VirtualMachineErrors. On a fatal error the code then attempts con.rollback() on a connection whose state is, by definition, undefined. That call can hang, mask the original error, or raise a secondary error that gets only added as suppressed.

Reproducer (illustrative — same control flow without a real DB):

//> using scala 3.8.3

import scala.util.control.NonFatal

@main def run(): Unit =
  // Magnum's pattern: catches everything
  def magnumStyle[T](f: => T): T =
    try f
    catch case t =>
      // would call con.rollback() here on a corrupted connection
      println(s"caught fatal: ${t.getClass.getSimpleName}")
      throw t

  try magnumStyle(throw new StackOverflowError("simulated"))
  catch case _: StackOverflowError => ()

Source:

magnum/magnum/src/main/scala/com/augustnagro/magnum/Transactor.scala

Lines 27 to 35 in 2801364

	try
	val res = f(using DbTx(con, sqlLogger))
	con.commit()
	res
	catch
	case t =>
	try con.rollback()
	catch { case t2 => t.addSuppressed(t2) }
	throw t

try
  val res = f(using DbTx(con, sqlLogger))
  con.commit()
  res
catch
  case t =>
    try con.rollback()
    catch { case t2 => t.addSuppressed(t2) }
    throw t

The standard Scala convention is case NonFatal(t) =>, which lets VirtualMachineError, ThreadDeath, LinkageError, etc. propagate without trying to do recovery on a JVM that may already be doomed. In a transactor specifically this matters because con.rollback() on OutOfMemoryError can itself try to allocate, which then deadlocks or compounds the failure.

Suggested fix:

catch
  case NonFatal(t) =>
    try con.rollback()
    catch { case NonFatal(t2) => t.addSuppressed(t2) }
    throw t

Happy to PR.

[haskiindahouse]

sorry — the broad case t => is intentional, you touched this exact block in #126 and kept the wide arm. style preference filed as logic-error on my part, my bad. closing 🙏