Require certain parameters, show UI if they are missing

[simonw]

Atom feed entries have some required content.

• atom:id
• atom:title
• atom:updated
• atom:content (unless you link to content instead)

We need to know which query columns should correspond to each of these fields.

We can accept these as ?_atom_id=xxx&_atom_updated=yyy and so-on - but what do we do if those parameters are missing?

Some of them we can guess (based on naming conventions, primary keys or Datasette's existing label detection mechanism and metadata.json configuration) - but what do we do if we can't guess them?

I'm going to fall back to returning an HTML page (with a invalid parameters 400 HTTP status code) that helps the user select the missing parameters.

[simonw]

WIP on this: c0e3bd9

[simonw]

I'm not going to do this. I like the configuration-by-SQL-query mechanism better.