Use case

After #221 and #244, we still can't support flattened structs such as:

#[derive(Row, Serialize)]
struct Metadata {
    foo: String,
    bar: String,
}

#[derive(Row, Serialize)]
struct MyRow {
    #[serde(flatten)]
    metadata: Metadata,
    data: String,
}

while inserting data to a table like this:

CREATE TABLE test (
  foo  String,
  bar  String,
  data String
)

Currently, with enabled validation, it will complain about number of fields (2 in struct vs 3 in the db), cause currently it will derive only [ "metadata", "data" ], and not [ "foo", "bar", "data" ] as it should have been.

Describe the solution you'd like

To solve this, derive macro needs adjustments to support recursive resolution.

Additional context

See #99, #101 for more details.