better api for passing parameters to *_raw methods

[vemoo]

This enables passing iterators of &dyn ToSql or T: ToSql as the params argument to *_raw methods.

Adds the a helper trait BorrowToSql that is only implemented for both &dyn ToSql and T: ToSql. This trait shouldn't be implemented by users.

Maybe there's a better name for the trait, I chose it because I works as Borrow<dyn ToSql> if that was possible.

Fixes #683

[Stargateur]

this make impossible to use query_raw with mixed slice type.

On a second though maybe not but query_raw API is strange I need to send a concrete implementation and then the function transform it to dyn ToSql I don't really see the point.

[Stargateur]

no I confirm this make the api way more limited to use

here a small example of what I try:

let params: &[&(dyn ToSql)] = &[&last_one, &(MAX as i64)];
client
    .query_raw(&statement, params)
    .await
    .context(PostgreSQLError)?

I explicitly add the type cause that wasn't compiling, now here the error:

error[E0277]: the size for values of type `dyn ToSql` cannot be known at compilation time
  --> src\accounts.rs:69:36
   |
69 |             .query_raw(&statement, params.iter())
   |                                    ^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn ToSql`
   = note: required because of the requirements on the impl of `ToSql` for `&dyn ToSql`
   = note: 1 redundant requirements hidden
   = note: required because of the requirements on the impl of `ToSql` for `&&dyn ToSql`
   = note: required because of the requirements on the impl of `BorrowToSql` for `&&dyn ToSql`

[Stargateur]

in the end I need to not use query_raw or implement a small enum that wrap my two type that will be them converted to dynamic dispatch... we finally do a static dynamic dispatch !

[Stargateur]

is there any actual test that prove this can be used with &dyn ToSql ?

[Stargateur]

seem this is what is needed:

let params: [&dyn ToSql; 2] = [&last_one, &(MAX as i64)];
client
    .query_raw(&statement, params)
    .await
    .context(PostgreSQLError)?

my real problem seem to be unrelated to this, nevermind I need to dig more.

[Stargateur]

still doesn't work I run into Sync issue and I'm unable to create a MCVE

[Stargateur]

I end up copied

rust-postgres/tokio-postgres/src/lib.rs

Line 248 in ff7d88f

fn slice_iter<'a>(

and it's work. I have literally zero clue why.