fix(mysql): Close prepared statement if persistence is disabled

[larsschumacher]

This pull request fixes an issue that prepared statements are not closed if persistence or statement cache are disabled.

How to reproduce this issue

use sqlx::{Connection, MySqlConnection, Row};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let url = std::env::var("DATABASE_URL")?;
    let mut connection = MySqlConnection::connect(&url).await?;

    for i in 0..10 {
        let _ = sqlx::query("SELECT ? AS val")
            .bind(i)
            .persistent(false)
            .fetch_one(&mut connection)
            .await?;
    }

    let rows = sqlx::query(
        r#"
        SELECT 
              psi.STATEMENT_ID
            , psi.SQL_TEXT
        FROM performance_schema.threads AS t
        INNER JOIN performance_schema.prepared_statements_instances AS psi
            ON psi.OWNER_THREAD_ID = t.THREAD_ID 
        WHERE t.processlist_id = CONNECTION_ID()
        "#,
    )
    .fetch_all(&mut connection)
    .await?;

    for row in rows {
        let id: u64 = row.try_get("STATEMENT_ID")?;
        let sql: String = row.try_get("SQL_TEXT")?;

        println!("ID: {id}; SQL: {sql}");
    }

    Ok(())
}

Output:

ID: 1; SQL: SELECT ? AS val
ID: 3; SQL: SELECT ? AS val
ID: 5; SQL: SELECT ? AS val
ID: 7; SQL: SELECT ? AS val
ID: 9; SQL: SELECT ? AS val
ID: 11; SQL: SELECT ? AS val
ID: 13; SQL: SELECT ? AS val
ID: 15; SQL: SELECT ? AS val
ID: 17; SQL: SELECT ? AS val
ID: 19; SQL: SELECT ? AS val
ID: 21; SQL: SELECT
              psi.STATEMENT_ID
            , psi.SQL_TEXT
        FROM performance_schema.threads AS t
        INNER JOIN performance_schema.prepared_statements_instances AS psi
            ON psi.OWNER_THREAD_ID = t.THREAD_ID
        WHERE t.processlist_id = CONNECTION_ID()

I only expect the last statement in the output.

Info

SQLx version: 0.7.3
Database server: MySQL 8.0.33

[sticnarf]

Hi @abonander, is there a release plan in the near future? It'll be good to get a released sqlx version with the issue fixed. Thanks.