Function 'struct' may change the data type of input parameters

[yukkit]

When I construct the structure through the function struct, my original data type is changed. I don't know if this is a bug or an expected design, but I think a better way is to retain the original type

To Reproduce

CREATE TABLE values(
    c0 INT,
    c1 String,
    c2 String
) AS VALUES
  (1, 'a', 'a'),
  (2, 'b', 'b'),
  (3, 'c', 'c');

explain verbose select struct(c0, c1, c2) from VALUES;

+------------------------------------------------------------+----------------------------------------------------------------------------------------------------------+
| plan_type                                                  | plan                                                                                                     |
+------------------------------------------------------------+----------------------------------------------------------------------------------------------------------+
| initial_logical_plan                                       | Projection: struct(values.c0, values.c1, values.c2)                                                      |
|                                                            |   TableScan: values                                                                                      |
| logical_plan after inline_table_scan                       | SAME TEXT AS ABOVE                                                                                       |
| logical_plan after type_coercion                           | Projection: struct(CAST(values.c0 AS Utf8), values.c1, values.c2)                                        |
|                                                            |   TableScan: values                                                                                      |
| logical_plan after count_wildcard_rule                     | SAME TEXT AS ABOVE                                                                                       |
| analyzed_logical_plan                                      | SAME TEXT AS ABOVE  

I see AnalyzerRule type_coercion cast values.c0 to values.c0 AS Utf8.

I also have some questions, why struct only supports the following types? @Ted-Jiang My idea is that struct can support any type. Is it possible to use TypeSignature::VariadicAny type of function signature?

/// Currently supported types by the struct function.
pub static SUPPORTED_STRUCT_TYPES: &[DataType] = &[
    DataType::Boolean,
    DataType::UInt8,
    DataType::UInt16,
    DataType::UInt32,
    DataType::UInt64,
    DataType::Int8,
    DataType::Int16,
    DataType::Int32,
    DataType::Int64,
    DataType::Float32,
    DataType::Float64,
    DataType::Utf8,
    DataType::LargeUtf8,
];

[alamb]

I also looked at the implementation in

https://github.com/apache/arrow-datafusion/blob/3df895597d8c2073081fd9d990048c7aefb3b62e/datafusion/physical-expr/src/struct_expressions.rs#L32-L63

I agree there is no reason to restrict the types supported as field types.