Open up postgres TransactionBuilder::new to pub visibility

[evforde]

Hey folks!

• What do you want to do, and how do you expect Diesel to support you with that?

I'm looking to implement a drop-in replacement for diesel::pg::PgConnection that instruments various methods. The WIP is here. This includes implementing SimpleConnection, Connection, and build_transaction, (which isn't attached to any trait).

• How might this be added to Diesel?

My goal is currently made slightly difficult because TransactionBuilder::new has pub(crate) visibility. In order to re-implement build_transaction() for my drop-in replacement for PgConnection, I'd need to also rewrite the TransactionBuilder. But, it seems TransactionBuilder<C> would work fine with any C: Connection<Backend = Pg, TransactionManager = AnsiTransactionManager> and could be reused in my case - do correct me if I'm wrong here, I'm new 😃

• What are possible alternatives?

Re-implementing TransactionBuilder outside of diesel for my purpose.

• Are there any disadvantages?

Not that I can tell... but correct me if I am missing something.

Thanks for your help, appreciate it!

[weiznich]

I would happily accept a PR exposing this function behind the i-implement-a-third-party-backend-and-opt-into-breaking-changes feature flag. It seems like we just missed exposing it as part of the diesel 2.0 release.

It would be great if you submit a PR that just adds to the function signature

    #[diesel_derives::__diesel_public_if(
        feature = "i-implement-a-third-party-backend-and-opt-into-breaking-changes"
    )]

Otherwise I will try to take care of that in the next weeks before the next minor diesel release.