TableIterator doesn't like single-column tuples

[ccleve]

#[pg_extern]
fn single_column() -> TableIterator<'static, (name!(foo_col, String) /* name!(bar_col, String) */,)>
{
    let mut out = vec![];
    let foo = "foo".to_owned();
    let bar = "bar".to_owned();
    out.push((foo /*bar*/,));
    TableIterator::new(out.into_iter())
}

# select * from single_column();
ERROR:  return type must be a row type

Uncomment the reference to bar in two places and it works fine.

The workaround is to use SetOfIterator for single-column tables.

Rust also has a weird syntax issue that tripped me up for an hour. TableIterator needs a tuple type, but if you do something like this: out.push((foo)), the parentheses get ignored. You need the trailing comma: out.push((foo,)). This is a Rust thing, not a pgx thing, but a bit of documentation on it in https://github.com/tcdi/pgx/blob/master/pgx-examples/srf/src/lib.rs might save others some time.

[eeeebbbbrrrr]

Is the ask here that we improve the docs or somehow teach TableIterator about single-element tuples? The former is easy, the latter seems pretty low-priority from our end.

[ccleve]

Either. Docs are good enough.

[eeeebbbbrrrr]

This was fixed in PR #1164