get_metadata() plugin hook should support async await_me_maybe pattern

[simonw]

https://docs.datasette.io/en/1.0a13/plugin_hooks.html#get-metadata-datasette-key-database-table currently says:

Refs:

• Plugin hook for dynamic metadata #1384

We can fix that with await_me_maybe() which wasn't a pattern we were using back when that hook was added.

[simonw]

Here's where it's called:

datasette/datasette/app.py

Lines 649 to 695 in 8f9509f

	def metadata(self, key=None, database=None, table=None, fallback=True):
	"""
	Looks up metadata, cascading backwards from specified level.
	Returns None if metadata value is not found.
	"""
	assert not (
	database is None and table is not None
	), "Cannot call metadata() with table= specified but not database="
	metadata = {}
	for hook_dbs in pm.hook.get_metadata(
	datasette=self, key=key, database=database, table=table
	):
	metadata = self._metadata_recursive_update(metadata, hook_dbs)
	# security precaution!! don't allow anything in the local config
	# to be overwritten. this is a temporary measure, not sure if this
	# is a good idea long term or maybe if it should just be a concern
	# of the plugin's implemtnation
	metadata = self._metadata_recursive_update(metadata, self._metadata_local)
	databases = metadata.get("databases") or {}
	search_list = []
	if database is not None:
	search_list.append(databases.get(database) or {})
	if table is not None:
	table_metadata = ((databases.get(database) or {}).get("tables") or {}).get(
	table
	) or {}
	search_list.insert(0, table_metadata)
	search_list.append(metadata)
	if not fallback:
	# No fallback allowed, so just use the first one in the list
	search_list = search_list[:1]
	if key is not None:
	for item in search_list:
	if key in item:
	return item[key]
	return None
	else:
	# Return the merged list
	m = {}
	for item in search_list:
	m.update(item)
	return m

[simonw]

And here's that `_metadata_recursive_update() method:

datasette/datasette/app.py

Lines 638 to 647 in 8f9509f

	def _metadata_recursive_update(self, orig, updated):
	if not isinstance(orig, dict) or not isinstance(updated, dict):
	return orig
	for key, upd_value in updated.items():
	if isinstance(upd_value, dict) and isinstance(orig.get(key), dict):
	orig[key] = self._metadata_recursive_update(orig[key], upd_value)
	else:
	orig[key] = upd_value
	return orig