[Requirement] Param class and common implementations

Executive summary

For auto-generating workflow parameter input widgets, a base class and implementations for common param types are needed

Context and background knowledge

See scipp/ess#152. Have a look at, e.g., https://docs.mantidproject.org/v6.1.0/algorithms/LoadEventNexus-v1.html. The widget and the table of properties in the docs page was generated programmatically. Each line corresponds to a "param" as described here (Mantid calls these "algorithm properties").

Inputs

The param classes will have a number of required and optional inputs. Something like:

Required:

• Name
• Description
• Type
• Required
• Default value

Optional:

• Bounds
• Validators

Methodology

The Param base class (working title) should run things such as validators.

Outputs

Implementations of the Param class must be able to construct a simple widget that can be included in higher-level widgets as part of scipp/ess#152.

Examples of required Param implementations:

• BinEdgeParam (linear/log, start, stop, num, unit, ...)
• Boolean, integer, ...
• Scalar (float) with unit
• Filename/path

Which interfaces are required?

Python module / function

Test cases

Params for ESSsans inputs make a good scenario for prototyping and testing

Comments

• Feature: Generate Python code from param class with set values.

Start by reading scipp/ess#152 and the ESSsans inputs mentioned as a prototype scenario, then compare the Mantid algorithm-property documentation example. No repository file or test entry point is identified in the issue, so locate the Python module and existing widget structure before defining the Param interface. Done means the base class, common implementations, validation behavior, widget construction, and test coverage are agreed and implemented.