Including admin, consent, key, synapse, and media. All REST servlets
(the synapse.rest module) now require typed method definitions.

Also enables Mypy for related tests.

In `MatrixFederationHttpClient._send_request()`, we make a HTTP request
using an `Agent`, wrap that request in a timeout and await the resulting
`Deferred`. On its own, the `Agent` performing the HTTP request
correctly stashes and restores the logging context while waiting.
The addition of the timeout introduces a path where the logging context
is not restored when execution resumes.

To address this, we wrap the timeout `Deferred` in a
`make_deferred_yieldable()` to stash the logging context and restore it
on completion of the `await`. However this is not sufficient, since by
the time we construct the timeout `Deferred`, the `Agent` has already
stashed and cleared the logging context when using
`make_deferred_yieldable()` to produce its `Deferred` for the request.

Hence, we wrap the `Agent` request in a `run_in_background()` to "fork"
and preserve the logging context so that we can stash and restore it
when `await`ing the timeout `Deferred`.

This approach is similar to the one used with `defer.gatherResults`.

Note that the code is still not fully correct. When a timeout occurs,
the request remains running in the background (existing behavior which
is nothing to do with the new call to `run_in_background`) and may
re-start the logging context after it has finished.

Synapse 1.43.0rc1 (2021-09-14)

This release drops support for the deprecated, unstable API for [MSC2858](https://github.com/matrix-org/matrix-doc/blob/master/proposals/2858-Multiple-SSO-Identity-Providers.md#unstable-prefix), as well as the undocumented `experimental.msc2858_enabled` config option. Client authors should update their clients to use the stable API, available since Synapse 1.30.

Features
--------

- Allow room creators to send historical events specified by [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) in existing room versions. ([\#10566](https://github.com/matrix-org/synapse/issues/10566))
- Add config option to use non-default manhole password and keys. ([\#10643](https://github.com/matrix-org/synapse/issues/10643))
- Skip final GC at shutdown to improve restart performance. ([\#10712](https://github.com/matrix-org/synapse/issues/10712))
- Allow configuration of the oEmbed URLs used for URL previews. ([\#10714](https://github.com/matrix-org/synapse/issues/10714), [\#10759](https://github.com/matrix-org/synapse/issues/10759))
- Prefer [room version 9](https://github.com/matrix-org/matrix-doc/pull/3375) for restricted rooms per the [room version capabilities](https://github.com/matrix-org/matrix-doc/pull/3244) API. ([\#10772](https://github.com/matrix-org/synapse/issues/10772))

Bugfixes
--------

- Fix a long-standing bug where room avatars were not included in email notifications. ([\#10658](https://github.com/matrix-org/synapse/issues/10658))
- Fix a bug where the ordering algorithm was skipping the `origin_server_ts` step in the spaces summary resulting in unstable room orderings. ([\#10730](https://github.com/matrix-org/synapse/issues/10730))
- Fix edge case when persisting events into a room where there are multiple events we previously hadn't calculated auth chains for (and hadn't marked as needing to be calculated). ([\#10743](https://github.com/matrix-org/synapse/issues/10743))
- Fix a bug which prevented calls to `/createRoom` that included the `room_alias_name` parameter from being handled by worker processes. ([\#10757](https://github.com/matrix-org/synapse/issues/10757))
- Fix a bug which prevented user registration via SSO to require consent tracking for SSO mapping providers that don't prompt for Matrix ID selection. Contributed by @AndrewFerr. ([\#10733](https://github.com/matrix-org/synapse/issues/10733))
- Only return the stripped state events for the `m.space.child` events in a room for the spaces summary from [MSC2946](https://github.com/matrix-org/matrix-doc/pull/2946). ([\#10760](https://github.com/matrix-org/synapse/issues/10760))
- Properly handle room upgrades of spaces. ([\#10774](https://github.com/matrix-org/synapse/issues/10774))
- Fix a bug which generated invalid homeserver config when the `frontend_proxy` worker type was passed to the Synapse Worker-based Complement image. ([\#10783](https://github.com/matrix-org/synapse/issues/10783))

Improved Documentation
----------------------

- Minor fix to the `media_repository` developer documentation. Contributed by @cuttingedge1109. ([\#10556](https://github.com/matrix-org/synapse/issues/10556))
- Update the documentation to note that the `/spaces` and `/hierarchy` endpoints can be routed to workers. ([\#10648](https://github.com/matrix-org/synapse/issues/10648))
- Clarify admin API documentation on undoing room deletions. ([\#10735](https://github.com/matrix-org/synapse/issues/10735))
- Split up the modules documentation and add examples for module developers. ([\#10758](https://github.com/matrix-org/synapse/issues/10758))
- Correct 2 typographical errors in the [Log Contexts documentation](https://matrix-org.github.io/synapse/latest/log_contexts.html). ([\#10795](https://github.com/matrix-org/synapse/issues/10795))
- Fix a wording mistake in the sample configuration. Contributed by @bramvdnheuvel:nltrix.net. ([\#10804](https://github.com/matrix-org/synapse/issues/10804))

Deprecations and Removals
-------------------------

- Remove the [unstable MSC2858 API](https://github.com/matrix-org/matrix-doc/blob/master/proposals/2858-Multiple-SSO-Identity-Providers.md#unstable-prefix), including the undocumented `experimental.msc2858_enabled` config option. The unstable API has been deprecated since Synapse 1.35. Client authors should update their clients to use the stable API introduced in Synapse 1.30 if they have not already done so. ([\#10693](https://github.com/matrix-org/synapse/issues/10693))

Internal Changes
----------------

- Add OpenTracing logging to help debug stuck messages (as described by issue [#9424](https://github.com/matrix-org/synapse/issues/9424)). ([\#10704](https://github.com/matrix-org/synapse/issues/10704))
- Add type annotations to the `synapse.util` package. ([\#10601](https://github.com/matrix-org/synapse/issues/10601))
- Ensure `rooms.creator` field is always populated for easy lookup in [MSC2716](https://github.com/matrix-org/matrix-doc/pull/2716) usage later. ([\#10697](https://github.com/matrix-org/synapse/issues/10697))
- Add missing type hints to REST servlets. ([\#10707](https://github.com/matrix-org/synapse/issues/10707), [\#10728](https://github.com/matrix-org/synapse/issues/10728), [\#10736](https://github.com/matrix-org/synapse/issues/10736))
- Do not include rooms with unknown room versions in the spaces summary results. ([\#10727](https://github.com/matrix-org/synapse/issues/10727))
- Additional error checking for the `preset` field when creating a room. ([\#10738](https://github.com/matrix-org/synapse/issues/10738))
- Clean up some of the federation event authentication code for clarity. ([\#10744](https://github.com/matrix-org/synapse/issues/10744), [\#10745](https://github.com/matrix-org/synapse/issues/10745), [\#10746](https://github.com/matrix-org/synapse/issues/10746), [\#10771](https://github.com/matrix-org/synapse/issues/10771), [\#10773](https://github.com/matrix-org/synapse/issues/10773), [\#10781](https://github.com/matrix-org/synapse/issues/10781))
- Add an index to `presence_stream` to hopefully speed up startups a little. ([\#10748](https://github.com/matrix-org/synapse/issues/10748))
- Refactor event size checking code to simplify searching the codebase for the origins of certain error strings that are occasionally emitted. ([\#10750](https://github.com/matrix-org/synapse/issues/10750))
- Move tests relating to rooms having encryption out of the user directory tests. ([\#10752](https://github.com/matrix-org/synapse/issues/10752))
- Use `attrs` internally for the URL preview code & update documentation. ([\#10753](https://github.com/matrix-org/synapse/issues/10753))
- Minor speed ups when joining large rooms over federation. ([\#10754](https://github.com/matrix-org/synapse/issues/10754), [\#10755](https://github.com/matrix-org/synapse/issues/10755), [\#10756](https://github.com/matrix-org/synapse/issues/10756), [\#10780](https://github.com/matrix-org/synapse/issues/10780), [\#10784](https://github.com/matrix-org/synapse/issues/10784))
- Add a constant for `m.federate`. ([\#10775](https://github.com/matrix-org/synapse/issues/10775))
- Add a script to update the Debian changelog in a Docker container for systems that are not Debian-based. ([\#10778](https://github.com/matrix-org/synapse/issues/10778))
- Change the format of authenticated users in logs when a user is being puppeted by and admin user. ([\#10779](https://github.com/matrix-org/synapse/issues/10779))
- Remove fixed and flakey tests from the Sytest blacklist. ([\#10788](https://github.com/matrix-org/synapse/issues/10788))
- Improve internal details of the user directory code. ([\#10789](https://github.com/matrix-org/synapse/issues/10789))
- Use direct references to config flags. ([\#10798](https://github.com/matrix-org/synapse/issues/10798))
- Ensure the Rust reporter passes type checking with jaeger-client 4.7's type annotations. ([\#10799](https://github.com/matrix-org/synapse/issues/10799))

This is mostly an internal change, but improves type hints in the
media code.

I had one of these error messages yesterday and assumed it was an
invalid auth token (because that was an HTTP query parameter in the
test) I was working on. In fact, it was an invalid next batch token for
syncing.

Instead of proxying through the magic getter of the RootConfig
object. This should be more performant (and is more explicit).

This fixes mypy errors with jaeger-client >= 4.7.0 and should be a no-op
for versions before that.

By copying the `room_type` field of the create event and
migrating any non-empty `m.space.child` events to the
new room that is created.

No functional changes here. This came out as I was working to tackle #5677 

We want to blacklist only known, consistent failures. We should deflake tests rather than ignoring them.

Fixes #10732: consent flow skipped during SSO user registration if username is left at default

Signed-off-by: Andrew Ferrazzutti <fair@miscworks.net>

We've already batched up the events previously, and assume in other
places in the events.py file that we have. Removing this makes it easier
to adjust the batch sizes in one place.

Signed-off-by: Sean Quah <seanq@element.io>

Hint to clients via the room capabilities API (MSC3244) that
room version 9 should be preferred for creating a room with
restricted join rules (instead of room version 8).

This is only called in two places, and the code seems much clearer without it.

* Split up the documentation in several files rather than one huge one
* Add examples for each callback category
* Other niceties like fixing https://github.com/matrix-org/synapse/issues/10632
* Add titles to callbacks so they're easier to find in the navigation panels and link to

When releasing 1.42.0 with @Azrenbeth and talking with @clokep yesterday I realised doing the dch incantations related to releasing Synapse wasn't trivial on eg a macOS system, so this is a script to run in a Debian container to make things a bit easier.

Also refactors some of the registration of endpoints on workers.

Outlier events don't ever have push actions associated with them, so we
can skip some expensive queries during event persistence.

This used to be a comma and got accidentally changed to a period in #9654, but a pipe character is more easier to parse visually.

This adds the format to the request arguments / URL to
ensure that JSON data is returned (which is all that
Synapse supports).

This also adds additional error checking / filtering to the
configuration file to ignore XML-only providers.

I think I have finally teased apart the codepaths which handle outliers, and those that handle non-outliers. 
Let's add some assertions to demonstrate my newfound knowledge.

If we're persisting an event E which has auth_events A1, A2, then we ought to make sure that we correctly auth
and persist A1 and A2, before we blindly accept E.

This PR does part of that - it persists the auth events first - but it does not fully solve the problem, because we
still don't check that the auth events weren't rejected.