Stabilize extensible profiles

[Half-Shot]

Description:

https://spec.matrix.org/unstable/client-server-api/#profiles is now merged into the spec, so the experimental features flag can be dropped and the stable endpoints implemented.

[clokep]

Does this encompass more work than what was done in #18635?

[anoadragon453]

Fairly sure this is already done. We left some of the unstable markers in place to aid client transition, i.e.

synapse/synapse/rest/client/capabilities.py

Lines 106 to 110 in 3671bdb

	# For transition from unstable to stable identifiers.
	if self.config.experimental.msc4133_enabled:
	response["capabilities"]["uk.tcpip.msc4133.profile_fields"] = response[
	"capabilities"
	]["m.profile_fields"]

Please re-open if there's more to it.

[Half-Shot]

Hang on, I'm confused. If the MSC was merged and the spec has landed then does self.config.experimental.msc4133_enabled still need to exist and, critically, default to False?

I suppose my initial title was wrong, I mean to say can we stop marking it as experimental now?

[Half-Shot]

Ah, I think I might be confusing myself. self.config.experimental.msc4133_enabled defaulting to False doesn't disable the profile API extensions? Then perhaps my client is confused.

EDIT: Ah, this is the same problem we've seen before where experimental features become stable but because of the lag with Synapse declaring support for a version of the spec, you can end up in a situation where clients won't pick up the API post-stabilisation (unless you turn on the unstable feature to bring back the old endpoints). Bleh.