Cannot use temporaries as `query!` arguments when using SQLite

[kangalio]

Many expressions cannot be used as arguments in the query! macro in SQLite mode because it throws a "temporary value dropped while borrowed" error:

sqlx::query!(
    "INSERT INTO todo (task, user_id) VALUES (?, ?)",
    task_description.trim(),
    msg.author.id.0 as i64,
)

error[E0716]: temporary value dropped while borrowed
  --> examples/e15_sqlite_database/src/main.rs:15:5
   |
13 | / sqlx::query!(
14 | |     "INSERT INTO todo (task, user_id) VALUES (?, ?)",
15 | |     task_description.trim(),
   | |     ^^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
16 | |     msg.author.id.0 as i64,
17 | | )
   | |_- temporary value is freed at the end of this statement
18 |   .execute(&self.database)
   |    ------- borrow later used by call

The second argument fails too

error[E0716]: temporary value dropped while borrowed
  --> examples/e15_sqlite_database/src/main.rs:16:5
   |
13 | / sqlx::query!(
14 | |     "INSERT INTO todo (task, user_id) VALUES (?, ?)",
15 | |     task_description.trim(),
16 | |     msg.author.id.0 as i64,
   | |     ^^^^^^^^^^^^^^^^^^^^^^ creates a temporary which is freed while still in use
17 | | )
   | |_- temporary value is freed at the end of this statement
18 |   .execute(&self.database)
   |    ------- borrow later used by call

Equipped with cargo expand and the source code of two bots using SQLx, I found out that the culprit lies in the SqliteArguments struct, which stores arguments to an SQLite query. Other Arguments types (PgArguments, MySqlArguments...) are owned but SqliteArguments has a lifetime and presumably stores references to the arguments instead of owning the arguments.

This is an issue because sqlx::query! expands to something like this:

{
    let arg0 = &(task_description.trim());
    let arg1 = &(msg.author.id.0 as i64);
    let mut query_args = SqliteArguments::new();
    query_args.add(arg0);
    query_args.add(arg1);
    query_args
}

query_args references arg0/arg1 which are destroyed at the end of scope, hence the error.

I don't know how it hard it is to do, but a fix for this would be awesome!

The issue can be worked around by binding the expressions beforehand, although it looks a bit ugly

let (a, b, c, d, e, f) = (
    showcase_msg.id.0 as i64,
    showcase_msg.channel_id.0 as i64,
    ctx.channel_id().0 as i64,
    name.id.0 as i64,
    description.id.0 as i64,
    links.id.0 as i64,
);
sqlx::query!(
    "INSERT INTO showcase (
        output_message,
        output_channel,
        input_channel,
        name_input_message,
        description_input_message,
        links_input_message
    ) VALUES (?, ?, ?, ?, ?, ?)",
    a,
    b,
    c,
    d,
    e,
    f,
)

[abonander]

I believe this is caused by the same thing as #1151

[jannik4]

I just ran into this problem as well and investigated it a bit.
The problem seems to be, as already noted by kangalioo, the lifetime of SqliteArguments.

Unfortunately, I don't think there is a good solution (at least I haven't found one).
As far as I understand it SqliteArguments needs the lifetime so that data like &[u8] can be passed to sqlite without cloning.
Also the macro can't be "fixed" because the block created by the query! ends before the execute call (This can't really be changed, because the macro doesn't "know" about the execute). So all variables will be dropped before the execute call.