PR #6925 introduced a GUI for connecting non-data (e.g. integer, boolean, color, etc..) workflow input parameter to tool input parameters (the backend for this was originally added in #1306). That ideally was just the beginning of work toward using such values in structured ways in workflows.
This PR extends tool output handling to allow producing of non-data parameters. These can serve as a source for non-data values in workflows the same work workflow input parameters can. To make such values more easy to produce, this PR also introduces Galaxy expression tools - mirroring functionality regularly used in CWL. These small JavaScript-based tools that consume inputs just like a regular Galaxy tool but that produce dictionary of non-data values.
I think these expressions will be maximally useful when paired with format 2 workflows once we allow users to load arbitrary tools (I make the case more in full here https://github.com/galaxyproject/galaxy/pull/7545#issuecomment-473894424), but I outline some potential uses there as well.
Because there is always a checklist in my PR descriptions:
- Tool definition language and plumbing and datatype for expressing expressions as jobs.
- Allow connecting expression tools to parameters in workflows, will delay evaluation of workflow so calculated value
- Example test expression tools for testing and demonstration.
Nicola Soranzo