Respect and fix understanding of legacy options

Fixes https://github.com/vector-im/riot-web/issues/14372

We read/use the options in multiple places, and those places were not in sync. Now when algorithms change and on initial load, both will come to the same conclusions about how to order & sort the rooms.

src/settings/Settings.js

@@ -478,13 +478,13 @@ export const SETTINGS = {
             deny: [],
         },
     },
-    // TODO: Remove setting: https://github.com/vector-im/riot-web/issues/14231
+    // TODO: Remove setting: https://github.com/vector-im/riot-web/issues/14373
     "RoomList.orderAlphabetically": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td("Order rooms by name"),
         default: false,
     },
-    // TODO: Remove setting: https://github.com/vector-im/riot-web/issues/14231
+    // TODO: Remove setting: https://github.com/vector-im/riot-web/issues/14373
     "RoomList.orderByImportance": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td("Show rooms with unread notifications first"),

src/stores/room-list/RoomListStore2.ts

@@ -31,6 +31,7 @@ import RoomViewStore from "../RoomViewStore";
 import { Algorithm, LIST_UPDATED_EVENT } from "./algorithms/Algorithm";
 import { EffectiveMembership, getEffectiveMembership } from "./membership";
 import { ListLayout } from "./ListLayout";
+import { isNullOrUndefined } from "matrix-js-sdk/src/utils";
 
 interface IState {
     tagsEnabled?: boolean;
@@ -321,6 +322,28 @@ export class RoomListStore2 extends AsyncStore<ActionPayload> {
         return <SortAlgorithm>localStorage.getItem(`mx_tagSort_${tagId}`);
     }
 
+    // logic must match calculateListOrder
+    private calculateTagSorting(tagId: TagID): SortAlgorithm {
+        const defaultSort = SortAlgorithm.Alphabetic;
+        const settingAlphabetical = SettingsStore.getValue("RoomList.orderAlphabetically", null, true);
+        const definedSort = this.getTagSorting(tagId);
+        const storedSort = this.getStoredTagSorting(tagId);
+
+        // We use the following order to determine which of the 4 flags to use:
+        // Stored > Settings > Defined > Default
+
+        let tagSort = defaultSort;
+        if (storedSort) {
+            tagSort = storedSort;
+        } else if (!isNullOrUndefined(settingAlphabetical)) {
+            tagSort = settingAlphabetical ? SortAlgorithm.Alphabetic : SortAlgorithm.Recent;
+        } else if (definedSort) {
+            tagSort = definedSort;
+        } // else default (already set)
+
+        return tagSort;
+    }
+
     public async setListOrder(tagId: TagID, order: ListAlgorithm) {
         await this.algorithm.setListOrdering(tagId, order);
         // TODO: Per-account? https://github.com/vector-im/riot-web/issues/14114
@@ -337,19 +360,35 @@ export class RoomListStore2 extends AsyncStore<ActionPayload> {
         return <ListAlgorithm>localStorage.getItem(`mx_listOrder_${tagId}`);
     }
 
-    private async updateAlgorithmInstances() {
-        const defaultSort = SortAlgorithm.Alphabetic;
+    // logic must match calculateTagSorting
+    private calculateListOrder(tagId: TagID): ListAlgorithm {
         const defaultOrder = ListAlgorithm.Natural;
+        const settingImportance = SettingsStore.getValue("RoomList.orderByImportance", null, true);
+        const definedOrder = this.getListOrder(tagId);
+        const storedOrder = this.getStoredListOrder(tagId);
 
+        // We use the following order to determine which of the 4 flags to use:
+        // Stored > Settings > Defined > Default
+
+        let listOrder = defaultOrder;
+        if (storedOrder) {
+            listOrder = storedOrder;
+        } else if (!isNullOrUndefined(settingImportance)) {
+            listOrder = settingImportance ? ListAlgorithm.Importance : ListAlgorithm.Natural;
+        } else if (definedOrder) {
+            listOrder = definedOrder;
+        } // else default (already set)
+
+        return listOrder;
+    }
+
+    private async updateAlgorithmInstances() {
         for (const tag of Object.keys(this.orderedLists)) {
             const definedSort = this.getTagSorting(tag);
             const definedOrder = this.getListOrder(tag);
 
-            const storedSort = this.getStoredTagSorting(tag);
-            const storedOrder = this.getStoredListOrder(tag);
-
-            const tagSort = storedSort ? storedSort : (definedSort ? definedSort : defaultSort);
-            const listOrder = storedOrder ? storedOrder : (definedOrder ? definedOrder : defaultOrder);
+            const tagSort = this.calculateTagSorting(tag);
+            const listOrder = this.calculateListOrder(tag);
 
             if (tagSort !== definedSort) {
                 await this.setTagSorting(tag, tagSort);
@@ -378,8 +417,8 @@ export class RoomListStore2 extends AsyncStore<ActionPayload> {
         const sorts: ITagSortingMap = {};
         const orders: IListOrderingMap = {};
         for (const tagId of OrderedDefaultTagIDs) {
-            sorts[tagId] = this.getStoredTagSorting(tagId) || SortAlgorithm.Alphabetic;
-            orders[tagId] = this.getStoredListOrder(tagId) || ListAlgorithm.Natural;
+            sorts[tagId] = this.calculateTagSorting(tagId);
+            orders[tagId] = this.calculateListOrder(tagId);
         }
 
         if (this.state.tagsEnabled) {

src/stores/room-list/algorithms/Algorithm.ts

@@ -109,6 +109,7 @@ export class Algorithm extends EventEmitter {
     }
 
     public getTagSorting(tagId: TagID): SortAlgorithm {
+        if (!this.sortAlgorithms) return null;
         return this.sortAlgorithms[tagId];
     }
 
@@ -125,6 +126,7 @@ export class Algorithm extends EventEmitter {
     }
 
     public getListOrdering(tagId: TagID): ListAlgorithm {
+        if (!this.listAlgorithms) return null;
         return this.listAlgorithms[tagId];
     }