Schema: Support anyOf, allOf and oneOf

[ewels]

Description of feature

It's fairly common for parameters to be able to accept one of several input types. For example:

• Either a specific string, or a number (auto or a float number between 0-1)
• An --input flag can support inputs with multiple sample sheet schema

JSON Schema can natively support this kind of thing using anyOf. For example usage, see this ONT workflow schema.

More complex rules can be used with nested allOf and oneOf statements, eg. as done here .

Editing the Nextflow schema manually mostly works - validation within the pipeline uses off-the-shelf JSON schema libraries, so validation passes. However, our custom stack built on top of the Nextflow schema breaks horribly.

It would be good to explicitly support this behaviour. As with all schema extensions, this is across multiple locations:

• nf-core schema build
• nf-core schema lint
• The web schema build UI
• nf-core launch
• The nf-core web launch UI & validation code
• Pipeline template validation code (nextflow run ... )
• Pipeline template help text (nextflow run ... --help)

This is an overview issue and each part of the above should be broken into its own issue / task.