mvp of Edit UI: update existing rows

[cldellow]

Build out the MVP of #48:

• [x] know if the page is editable
  • [x] URL must be a row page
  • [x] ?_dux_edit=1 query parameter present (in the future we can define via metadata)
  • [x] user has update-row permission on this table
• [x] render an edit-row template instead of the row template
  • [x] we can re-use much of the row template via jinja magic, see Datasette docs, {% extends "default:row.html" %}
  • [x] it should emit a <form> that wraps all the controls
  • [x] the form's submit event is intercepted and handled by us
  • [x] there is a submit button
  • [x] clicking the submit button tries to send a write API update call
• [x] render_cell should emit an edit control if the control is editable
• [x] implement a StringControl that is just a vanilla text input
• [x] write a function that determines the set of columns that are editable (for tables: all but pkeys; for views: all unaliases columns from base table except pkeys)

[cldellow]

How can we conditionally render an edit page? Ideally, we'd do this at the top level by serving a different jinja template altogether, and only when we detect _dux_edit=1.

I hoped prepare_jinja2_environment would work. But I think it doesn't have the context of the request.

[cldellow]

There is an environment param in the underlying jinja BaseLoader#get_source... does that have something useful, or is that an internal detail?

[cldellow]

It's a global thing, not specific to a given request: https://jinja.palletsprojects.com/en/3.0.x/api/

So, hm. Kinda sucks, maybe we have to hijack the whole row view, which will break customizability.

[cldellow]

We can do something disgusting with a monkey patch on https://github.com/simonw/datasette/blob/1.0a2/datasette/views/row.py#L19 to change the templates it returns to be edit-focused based on the request

[cldellow]

We might want some way to map from a request to a list of editable columns? This would be used when determining if we should show the edit page, when render_cell determines if it should show an edit control, etc.

D'oh, this also reminds me that the version of render_cell that takes a request isn't publicly available yet. Hm.