register_output_renderer can_render mechanism

[simonw]

I would like is the ability for renderers to opt-in / opt-out of being displayed as options on the page.

https://www.niche-museums.com/browse/museums for example shows a atom link because the datasette-atom plugin is installed... but clicking it will give you a 400 error because the correct columns are not present.

Here's the code that passes a list of renderers to the template:

datasette/datasette/views/base.py

Lines 411 to 423 in 2d099ad

	renderers = {
	key: path_with_format(request, key, {**url_labels_extra})
	for key in self.ds.renderers.keys()
	}
	url_csv_args = {"_size": "max", **url_labels_extra}
	url_csv = path_with_format(request, "csv", url_csv_args)
	url_csv_path = url_csv.split("?")[0]
	context = {
	**data,
	**extras,
	**{
	"renderers": renderers,
	"url_csv": url_csv,

A renderer is currently defined as a two-key dictionary:

@hookimpl
def register_output_renderer(datasette):
    return {
        'extension': 'test',
        'callback': render_test
    }

I can add a third key, "should_suggest" which is a function that returns True or False for a given query. If that key is missing it is assumed to return True.

One catch: what arguments should be passed to the should_suggest(...) function?

UPDATE: now calling it can_render instead.

Originally posted by @simonw in #581 (comment)

[simonw]

This can_render callback should take the same arguments as the redesigned render (previously called callback): #581 (comment)

• datasette - a Datasette instance
• columns - the list of columns
• rows - the list of rows (each one a SQLite Row object)
• sql - the SQL query being executed
• query_name - the name of the canned query, if this is one
• database - the database name
• table - the table or view name
• request - the request object (to be documented in Documentation for the "request" object #706)
• view_name - the name of the view

[simonw]

I'm going to rename callback to render but continue supporting callback until Datasette 1.0.

[simonw]

Can I come up with a better name than should_suggest?

It's a check that sees if the current query is supported by the renderer plugin. Some options:

• can_render
• supports_query
• is_supported

I like can_render.

[simonw]

This should be optionally awaitable, as in #776