Implement FromStr for DataType / Parse DataType description

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As part of implementing apache/datafusion#5016 in DataFusion I needed some way to convert from a string passed in by the user to a DataType.

Since we already had a function arrow_typeof that provides a useful human readable type name by calling DataType::to_string() I wanted the opposite: A way to take the output of DataType::to_string() and make a DataType

Describe the solution you'd like

I think having FromStr implementation that matches the https://docs.rs/arrow/34.0.0/arrow/datatypes/enum.DataType.html#impl-Display-for-DataType implementation for DataType would be very nice.

Example usage:

let data_type = DataType:Int32;

// use (existing) Display impl to get a string representaiton
let data_type_string = data_type.to_string();
assert_eq!(data_type_string, "Int32");

// use proposed FromStr impl to get the DataType back
let parsed_datatype: DataType = data_type_string.parse()?
assert_eq!(parsed_datatype, DataType::Int32);

Describe alternatives you've considered
@tustvold pointed out that there is already a way to encode data types in String for the IPC format https://arrow.apache.org/docs/format/CDataInterface.html#data-type-description-format-strings

While this format is (designed to be) easy to parse by computers, I don't think it is easy to parse by Humans (quick quiz, what type does tdD represent?)

Additional context
See apache/datafusion#5166 (comment)

We can probably lift the implementation from apache/datafusion#5166 into Arrow-rs

The implementation in apache/datafusion#5166 currently does not cover:

• Parsing Timezones in Timestamp types (@waitingkuo expressed interest in this)
• Parsing Struct, Union, Map or List types (though it does handle Dictionary)

[alamb]

I think this is a good first issue because the code and tests already exists, so this ticket would be a matter of porting the code, and adjusting the interface

[Weijun-H]

This is nice extention. I want to take this ticket.

[Weijun-H]

Should we also keep the part like,Int32, Int64 in arrow-rs?

[tustvold]

Should we also keep the part like,Int32, Int64 in arrow-rs?

I'm not sure I follow what you mean, but it should be able to parse the output of DataType: Display

[Weijun-H]

Should we also keep the part like,Int32, Int64 in arrow-rs?

I'm not sure I follow what you mean, but it should be able to parse the output of DataType: Display

Sorry for the ambiguity. I mean, should we migrate parts that have been completed in arrow-datafusion to arrow-rs?

[alamb]

Sorry for the ambiguity. I mean, should we migrate parts that have been completed in arrow-datafusion to arrow-rs?

that would be my suggestion

[alamb]

Maybe we can port the implementation in arrow-datafusion first and then add support for Timezones and struct types as follow on PRs

[opensourcegeek]

If this issue is still open, can I take a stab at it please?

[alamb]

Yes please @opensourcegeek -- I think this would be a fairly straightforward addition (port code, add some docs and tests)