Preserve existing errors when using transaction

[endertunc]

Fixes #issue_number

Problem

I would like to be able to run ZIO effects without losing existing information on error channel.

For example;

enum AppError {
  case UserNotFound(message: String) extends AppErrorScala3
  case InvalidCredentials(message: String) extends AppErrorScala3
}

val login: ZIO[Connection, SQLException | InvalidCredentials | UserNotFound, User] = for {
  maybeUser <- userRepository.findByEmail(email)
  user <- ZIO.getOrFailWith[UserNotFound, User](UserNotFound(s"User with given email [$email] is not found"))(
    maybeUser
  )
  result <- hasherService.check(plainTextPassword, user.hashedPassword)
  _      <- ZIO.fail[InvalidCredentials](InvalidCredentials("Invalid Credentials")).unless(result)
} yield user

// Given above code, if we were to run "login" effect in transaction we will lose existing errors.
val transactionResult: ZIO[Connection, Throwable, User] = ctx.underlying.transaction(login)

// I would like to be able to run "login" effect in transaction and still keep existing errors.
// This PR allows you to do the following
val transactionResult: ZIO[Connection, SQLException | InvalidCredentials | UserNotFound, User] = ctx.underlying.transaction(login)

// In case of missing SQLException in error channel, it should added to error channel along with the existing ones
val zioThatCanFailWithString = ZIO[Connection, String, User] = ???
val zioThatCanFailWithStringTransaction: ZIO[Connection, String | SQLException, User] = ctx.underlying.transaction(zioThatCanFailWithString)

Solution

I changed ZioJdbcUnderlyingContext.transaction

// from
def transaction[R <: Connection, A](f: ZIO[R, Throwable, A]): ZIO[R, Throwable, A]
// to
def transaction[R <: Connection, E, A](f: ZIO[R, E, A]): ZIO[R, E | SQLException, A]

Also updated QuillZioExtPlain.onDataSource and QuillZioExtPlain.implicitDS so that can be run on ZIO[Connection, E, T] rather than ZIO[Connection, Throwable, T]

Notes

I only updated ZioJdbcUnderlyingContext.transaction as part of the initial PoC/Draft. If we are happy with the approach, we need to apply the same approach to ZioJdbcContext.transaction as well.

Checklist

• Unit test all changes - TODO
• Update README.md if applicable TODO
• Add [WIP] to the pull request title if it's work in progress
• Squash commits that aren't meaningful changes

@getquill/maintainers

[deusaquilus]

This looks good. Could you please change ZioJdbcContext.transaction as well?

[endertunc]

Hi @deusaquilus thanks for taking a look. Yes, I will take a look at this again this weekend and implement the remaining pieces. I will ping you again once it's ready to review.

[endertunc]

Hi @deusaquilus I think this should be ready to review. Let me know if you have any feedback! :)

[endertunc]

I wrote the tests in this style (something must compile) because the only thing that changed is the types. Let me know if you have any suggestions!

[endertunc]

Hi @deusaquilus, did you have chance to look at the changes? Let me know if there is anything I can improve/change.