Substrait: Handle inner map fields in schema renaming

[cht42]

Which issue does this PR close?

• Closes Substrait: Handle inner map fields in schema renaming #15868.

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[gabotechs]

Thanks for this fix! would it be possible to add a test that replicates the issue on main and shows that this PR solves it?

[gabotechs]

Thanks for the tests! I think it might be worth to expand a bit on them, as they are only testing the new functionality partially. For example, I could replace the code committed in datafusion/substrait/src/logical_plan/consumer.rs with just the following:

        ...
        DataType::Map(inner, _) => match inner.data_type() {
            DataType::Struct(key_and_value) if key_and_value.len() == 2 => {
                *name_idx += 1;
                Ok(field.clone())
            }
            _ => substrait_err!("Map fields must contain a Struct with exactly 2 fields"),
        },
        ...

And make the test green, even though the code is wrong.

Maybe @Blizzara or @westonpace can give a bit more insights about how to better test this.

[cht42]

updated with unit tests

[Blizzara]

make keys also a struct?

[cht42]

done

[Blizzara]

Thanks! (I work with @cht42 )