fix: hide sqlx_postgres::any

[Zarathustra2]

Currently you can call begin() on a postgres transaction without causing an error.

This causes errors such as:

    let url = "postgres://dario@localhost/sqlx".parse().unwrap();
    let opts: PgConnectOptions = ConnectOptions::from_url(&url).unwrap();

    let pool = PgPoolOptions::new()
        .max_connections(10)
        .connect_with(opts)
        .await
        .expect("PgPool");

    sqlx::query("drop table if exists sqlx_issue").execute(&pool).await.unwrap();
    sqlx::query("create table sqlx_issue (name varchar(255))").execute(&pool).await.unwrap();
    sqlx::query("insert into sqlx_issue (name) values ('issue')").execute(&pool).await.unwrap();

    {
        let mut trans: Transaction<'static, Postgres> = pool.begin().await.unwrap();
        // Call begin again()
        trans.begin().await.unwrap();

        sqlx::query("delete from sqlx_issue").execute(&mut *trans).await.unwrap();
        trans.commit().await.unwrap();
    }
        

    let row = sqlx::query("select name from sqlx_issue").fetch_optional(&pool).await.unwrap();
    // This will fail because we started the transaction twice. 
    // Calling commit does not actually commit the transaction because we rewrapped the inner transaction.
    // As a result the delete query had never been committed. 
    assert!(row.is_none());

[abonander]

Nesting of transactions is intentional. Once inside a transaction, begin() creates a savepoint and dropping the transaction (which happens immediately) queues a ROLLBACK TO SAVEPOINT statement to be executed the next time the connection is used.

Something else is going on here.

[Zarathustra2]

@abonander I see. I can take another look and try to debug it + fix it.

I assume the nested transactions does not get committed but rollbacked. Let me take a look again

[Zarathustra2]

Okay, I found the issue:

use sqlx::{postgres::{PgConnectOptions, PgPoolOptions}, ConnectOptions, PgPool, Postgres, Row, Transaction};

// Comment out `use sqlx::Acquire` and comment in `sqlx::postgres::any::AnyConnectionBackend`
// and the transaction will not be committed.
//
// use sqlx::postgres::any::AnyConnectionBackend;
use sqlx::Acquire;

#[tokio::main]
async fn main() {

    let url = "postgres://dario@localhost/sqlx".parse().unwrap();
    let opts: PgConnectOptions = ConnectOptions::from_url(&url).unwrap();

    let pool = PgPoolOptions::new()
        .max_connections(10)
        .connect_with(opts)
        .await
        .expect("PgPool");


    sqlx::query("drop table if exists sqlx_issue").execute(&pool).await.unwrap();
    sqlx::query("create table sqlx_issue (name varchar(255))").execute(&pool).await.unwrap();
    sqlx::query("insert into sqlx_issue (name) values ('issue')").execute(&pool).await.unwrap();

    let row = sqlx::query("select name from sqlx_issue").fetch_optional(&pool).await.unwrap();
    println!("{:?}", row.unwrap().get::<String, _>(0));

    {
        let mut trans = pool.begin().await.unwrap();
        // Call begin again()
        trans.begin().await.unwrap();
        trans.begin().await.unwrap();
        trans.begin().await.unwrap();

        sqlx::query("delete from sqlx_issue").execute(&mut *trans).await.unwrap();
        trans.commit().await.unwrap();
    }
        

    let row = sqlx::query("select name from sqlx_issue").fetch_optional(&pool).await.unwrap();
    // Succeeds with `use sqlx::Acquire`. Fails with `use sqlx::postgres::any::AnyConnectionBackend`
    assert!(row.is_none());
}

[dependencies]
tokio = { version = "1.34.0", features = ["full"] }
sqlx = { version = "0.7.4", features = [ "runtime-tokio", "tls-native-tls", "postgres", "rust_decimal", "chrono", "uuid", "migrate", "macros" ] }

A wrong use can break the nested transactions it seems.

[abonander]

That's why. AnyConnectionBackend is not an end-user trait, it doesn't use the Transaction RAII guard. Your IDE probably suggested it as an import.

The any module of sqlx-postgres is public but it should be #[doc(hidden)]: https://github.com/launchbadge/sqlx/blob/main/sqlx-postgres/src/lib.rs#L29

It needs to be accessible from the sqlx facade crate which is why it can't just be private. Still, marking it hidden should mean an IDE won't recommend importing anything from it.

[Zarathustra2]

Ah that makes sense. Thanks for the explanation. I have added that as well as a comment.

Thanks for the help!