Simplified Sliding Sync (#28515)

* Experimental SSS

Working branch to get SSS functional on element-web.

Requires https://github.com/matrix-org/matrix-js-sdk/pull/4400

* Adjust tests to use new behaviour

* Remove well-known proxy URL lookup; always use native

This is actually required for SSS because otherwise it would use
the proxy over native support.

* Linting

* Debug logging

* Control the race condition when swapping between rooms

* Dont' filter by space as synapse doesn't support it

* Remove SS code related to registering lists and managing ranges

- Update the spidering code to spider all the relevant lists.
- Add canonical alias to the required_state to allow room name calcs to work.

Room sort order is busted because we don't yet look at `bump_stamp`.

* User bumpStamp if it is present

* Drop initial room load from 20 per list to 10

* Half the batch size to trickle more quickly

* Prettier

* prettier on tests too

* Remove proxy URL & unused import

* Hopefully fix tests to assert what the behaviour is supposed to be

* Move the singleton to the manager tyo fix import loop

* Very well, code, I will remove you

Why were you there in the first place?

* Strip out more unused stuff

* Fix playwright test

Seems like this lack of order updating unless a room is selected
was just always a bug with both regular and non-sliding sync. I
have no idea how the test passed on develop because it won't run.

* Fix test to do maybe what it was supposed to do... possibly?

* Remove test for old pre-simplified sliding sync behaviour

* Unused import

* Remove sliding sync proxy & test

I was wrong about what this test was asserting, it was suposed
to assert that notification dots aren't shown (because SS didn't
support them somehow I guess) but they are fine in SSS so the test
is just no longer relevant.

* Remove now pointless credentials

* Remove subscription removal as SSS doesn't do that

* Update tests

* add test

* Switch to new labs flag & break if old labs flag is enabled

* Remove unused import & fix test

* Fix other test

* Remove name & description from old labs flag

as they're not displayed anywhere so not useful

* Remove old sliding sync option

by making it not a feature

* Add back unread nindicator test but inverted

and minus the bit about disabling notification which surely would have
defeated the original point anyway?

* Reinstate test for room_subscriptions

...and also make tests actually use sliding sync

* Use UserFriendlyError

* Remove empty constructor

* Remove unrelated changes

* Unused import

* Fix import

* Avoid moving import

---------

Co-authored-by: Kegan Dougal <7190048+kegsay@users.noreply.github.com>

src/settings/Settings.tsx

@@ -198,7 +198,8 @@ export interface Settings {
     "feature_html_topic": IFeature;
     "feature_bridge_state": IFeature;
     "feature_jump_to_date": IFeature;
-    "feature_sliding_sync": IFeature;
+    "feature_sliding_sync": IBaseSetting<boolean>;
+    "feature_simplified_sliding_sync": IFeature;
     "feature_element_call_video_rooms": IFeature;
     "feature_group_calls": IFeature;
     "feature_disable_call_per_sender_encryption": IFeature;
@@ -210,7 +211,6 @@ export interface Settings {
     "feature_ask_to_join": IFeature;
     "feature_notifications": IFeature;
     // These are in the feature namespace but aren't actually features
-    "feature_sliding_sync_proxy_url": IBaseSetting<string>;
     "feature_hidebold": IBaseSetting<boolean>;
 
     "useOnlyCurrentProfiles": IBaseSetting<boolean>;
@@ -539,7 +539,14 @@ export const SETTINGS: Settings = {
             true,
         ),
     },
+    // legacy sliding sync flag: no longer works, will error for anyone who's still using it
     "feature_sliding_sync": {
+        supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG_PRIORITISED,
+        supportedLevelsAreOrdered: true,
+        shouldWarn: true,
+        default: false,
+    },
+    "feature_simplified_sliding_sync": {
         isFeature: true,
         labsGroup: LabGroup.Developer,
         supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG_PRIORITISED,
@@ -550,11 +557,6 @@ export const SETTINGS: Settings = {
         default: false,
         controller: new SlidingSyncController(),
     },
-    "feature_sliding_sync_proxy_url": {
-        // This is not a distinct feature, it is a legacy setting for feature_sliding_sync above
-        supportedLevels: LEVELS_DEVICE_ONLY_SETTINGS_WITH_CONFIG,
-        default: "",
-    },
     "feature_element_call_video_rooms": {
         isFeature: true,
         labsGroup: LabGroup.VoiceAndVideo,

src/settings/controllers/SlidingSyncController.ts

@@ -11,20 +11,19 @@ import SettingController from "./SettingController";
 import PlatformPeg from "../../PlatformPeg";
 import SettingsStore from "../SettingsStore";
 import { _t } from "../../languageHandler";
+import { SlidingSyncManager } from "../../SlidingSyncManager";
 
 export default class SlidingSyncController extends SettingController {
-    public static serverSupportsSlidingSync: boolean;
-
     public async onChange(): Promise<void> {
         PlatformPeg.get()?.reload();
     }
 
     public get settingDisabled(): boolean | string {
         // Cannot be disabled once enabled, user has been warned and must log out and back in.
-        if (SettingsStore.getValue("feature_sliding_sync")) {
+        if (SettingsStore.getValue("feature_simplified_sliding_sync")) {
             return _t("labs|sliding_sync_disabled_notice");
         }
-        if (!SlidingSyncController.serverSupportsSlidingSync) {
+        if (!SlidingSyncManager.serverSupportsSlidingSync) {
             return _t("labs|sliding_sync_server_no_support");
         }