Adding new Date/Time operations (-, date_add, date_diff, date_part)

[radeusgd]

Pull Request Description

• Adds Column.date_diff for computing date/time difference as integer multiply of some unit.
• Adds Column.date_add for shifting date/time by a unit.
• Adds Column.date_part for extracting various parts of the date/time value as integer.
• Adds widgets for the 3 methods above whose content depends on the column value type.
• Adds shorthands: Column.hour, Column.minute and Column.second to extract these date parts.
• Extends Time_Period with support for milli-, micro- and nano- seconds; and adapts functions taking Time_Period to support these wherever possible.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.

[GregoryTravis]

Could we have a more restrictive type than Any | Nothing? Such as Row_Number_Metadata | Date_Period_Metadata? Or do you think there will be too many?

[radeusgd]

We could probably.

I'm not sure if this gives us much benefit - since the 'right' type depends on the particular kind anyway, this will not be checking much. We definitely want stronger typing in the new IR, but with this one which is rather dynamic, I'd stick to it I think.

Ideally we should have one parent 'class' or interface for the metadata, but due to lack of inheritance/interfaces we cannot have it. The sum type could work, but I'm afraid it could become long - ideally we should define an alias in the file with metadata and only reference the alias here - but type aliases are not supported yet.

[radeusgd]

Widgets depending on the type:

If the Date_Period/Time_Period is invalid for a given type, an error is reported:

[radeusgd]

I wasn't sure what to display if the input column type is invalid (i.e. Integer not date/time).
Ideally, we want an error there, but IIRC we cannot easily trigger it from the widget - and the function will not error until all non-default arguments are provided.

So what I did is I 'sneak' the error message into the widget:

After all arguments are provided, the error appears on the node as well:

I'm however not sure if this is the right approach. It seems good to notify the user of the error as soon as possible, but that seems a bit abusing the architecture - the widget is probably not the right place to display errors/warnings.

However, I definitely did not want to display an empty selector there - that would be even worse.

As a viable alternative, I think we can just display all available options (i.e. the same as for Date_Time) when the type is invalid - so the user can choose whatever and then possibly fix the type.

Which one of these two you think is better?

1. Display all possible choices when type is wrong.
2. Display the error message like shown on screenshots.

[jdunkerley]

Looks good - minor comment but great to have this in.