Should can_coerce_from promote Utf8 to LargeUtf8?

[gatesn]

Describe the bug

The function can_coerce_from establishes the lossless conversions between data types.

It currently says that LargeUtf8 can be coerced into Utf8. I'm not sure this should be true?

datafusion/datafusion/expr/src/type_coercion/functions.rs

Lines 768 to 769 in 0f584c8

	// Any type can be coerced into strings
	(Utf8 | LargeUtf8, _) => Some(type_into.clone()),

I suppose I could construct a single row that contains more than i32 bytes of string data. But it also seems generally desirable for DataFusion to promote to the large string/binary type?

To Reproduce

No response

Expected behavior

Utf8 promotes into LargeUt8, but not vice versa.

Additional context

No response

[jayzhan211]

You can try TypeSignature::String now if you want to coerce any type to string.

The current logic is which won't coerce Utf8 to LargeUtf8. (LargeUtf8View is currently not supported)

pub fn string_coercion(lhs_type: &DataType, rhs_type: &DataType) -> Option<DataType> {
    use arrow::datatypes::DataType::*;
    match (lhs_type, rhs_type) {
        // If Utf8View is in any side, we coerce to Utf8View.
        (Utf8View, Utf8View | Utf8 | LargeUtf8) | (Utf8 | LargeUtf8, Utf8View) => {
            Some(Utf8View)
        }
        // Then, if LargeUtf8 is in any side, we coerce to LargeUtf8.
        (LargeUtf8, Utf8 | LargeUtf8) | (Utf8, LargeUtf8) => Some(LargeUtf8),
        // Utf8 coerces to Utf8
        (Utf8, Utf8) => Some(Utf8),
        _ => None,
    }
}