Implement `current_date` Function

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As we add more full featured date/time support for DataFusion users need to be able to use the current date to calculate things like "all data in the last 30 days"

Describe the solution you'd like
Support the current_date postgres function https://www.postgresql.org/docs/current/functions-datetime.html#FUNCTIONS-DATETIME-CURRENT

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
This is a feature request we got from an early (internal) user of InfluxDB IOx

I believe this is a good first issue as you can follow the existing implementation of now()

• Physical support: https://github.com/apache/arrow-datafusion/blob/f1322592046a7ea895820286a2ad16d934540d92/datafusion/physical-expr/src/functions.rs#L424-L429) and use the same query_execution_start_time field
• Tests: https://github.com/apache/arrow-datafusion/blob/beeb631d0bb979e9b6826f6cd3eae2d0a24f471e/datafusion/core/tests/sql/timestamp.rs#L417

It would be a good exercise to add a new build in scalar function, physical planing support, and then tests

[comphead]

@alamb please assign the task to me.

And let me know how to regenerate prost.rs locally to reflect latest changes for Scalar types?

[alamb]

Thanks @comphead

@alamb please assign the task to me.

Done

And let me know how to regenerate prost.rs locally to reflect latest changes for Scalar types?

It may be related to #3947 / #3979 . Maybe @avantgardnerio or @tustvold have some ideas or a doc pointer

[avantgardnerio]

@tustvold I see you added instructions for installing protoc... would you mind adding the bash command you use to run it? 🙌

[tustvold]

There is no command, just build the project as normal, the build script does the rest

[comphead]

Hi @tustvold

I have tried to build it first

$ cargo build
Compiling datafusion-proto v13.0.0 (arrow-datafusion/datafusion/proto)
error[E0599]: no variant or associated item named `CurrentDate` found for enum `datafusion::ScalarFunction` in the current scope
    --> datafusion/proto/src/to_proto.rs:1181:57
     |
1181 |             BuiltinScalarFunction::CurrentDate => Self::CurrentDate,
     |                                                         ^^^^^^^^^^^ variant or associated item not found in `datafusion::ScalarFunction`
     |
    ::: datafusion/proto/src/generated/prost.rs:1154:1

If I go to prost.rs I dont see CurrentDate generated. I suppose BuiltinScalarFunction enum is the driver to generate new code?

[tustvold]

Have you updated the protobuf definition in https://github.com/apache/arrow-datafusion/blob/master/datafusion/proto/proto/datafusion.proto ?

[comphead]

Have you updated the protobuf definition in https://github.com/apache/arrow-datafusion/blob/master/datafusion/proto/proto/datafusion.proto ?

Right, sorry, totally forgot about it! :-/