accountsReducer: Make REALM_ADD store feature level in Redux.

Firstly, we add zulipFeatureLevel in Account type. We
had to tweak `loginSuccess()` and `realmAdd()` methods
in accountsReducer to include `zulipFeatureLevel` in
their return values too.

Then, we store the feature level in Redux on REALM_ADD.

Part of #4049.

Author: hashirsarwar

src/__tests__/lib/exampleData.js

@@ -123,6 +123,7 @@ export const makeAccount = (
     email?: string,
     realm?: string,
     apiKey?: string,
+    zulipFeatureLevel?: number | null,
     zulipVersion?: ZulipVersion | null,
     ackedPushToken?: string | null,
   } = {},
@@ -132,13 +133,15 @@ export const makeAccount = (
     email = user.email,
     realm: realmInner = realm,
     apiKey = randString() + randString(),
+    zulipFeatureLevel: zulipFeatureLevelInner = zulipFeatureLevel,
     zulipVersion: zulipVersionInner = zulipVersion,
     ackedPushToken = null,
   } = args;
   return deepFreeze({
     realm: realmInner,
     email,
     apiKey,
+    zulipFeatureLevel: zulipFeatureLevelInner,
     zulipVersion: zulipVersionInner,
     ackedPushToken,
   });

src/account/__tests__/accountsReducer-test.js

@@ -171,6 +171,7 @@ describe('accountsReducer', () => {
         email: '[email protected]',
         realm: 'https://new.realm.org',
         zulipVersion: null,
+        zulipFeatureLevel: null,
       });
 
       const action = deepFreeze({

src/account/accountsReducer.js

@@ -21,6 +21,7 @@ const realmAdd = (state, action) => {
   if (accountIndex !== -1) {
     const newAccount = {
       ...state[accountIndex],
+      zulipFeatureLevel: action.zulipFeatureLevel,
       zulipVersion: action.zulipVersion,
     };
     return [newAccount, ...state.slice(0, accountIndex), ...state.slice(accountIndex + 1)];
@@ -32,6 +33,7 @@ const realmAdd = (state, action) => {
       apiKey: '',
       email: '',
       ackedPushToken: null,
+      zulipFeatureLevel: action.zulipFeatureLevel,
       zulipVersion: action.zulipVersion,
     },
     ...state,
@@ -65,7 +67,10 @@ const loginSuccess = (state, action) => {
   const { realm, email, apiKey } = action;
   const accountIndex = findAccount(state, { realm, email });
   if (accountIndex === -1) {
-    return [{ realm, email, apiKey, ackedPushToken: null, zulipVersion: null }, ...state];
+    return [
+      { realm, email, apiKey, ackedPushToken: null, zulipVersion: null, zulipFeatureLevel: null },
+      ...state,
+    ];
   }
   return [
     { ...state[accountIndex], email, apiKey, ackedPushToken: null },

src/types.js

@@ -95,6 +95,16 @@ export type Account = {|
    */
   zulipVersion: ZulipVersion | null,
 
+  /**
+   * An integer indicating what features are available on the server.
+   *
+   * The feature level increases monotonically; a value of N means the
+   * server supports all API features introduced before feature level N.
+   * This is designed to provide a simple way for mobile apps to decide
+   * whether the server supports a given feature or API change.
+   */
+  zulipFeatureLevel: number | null,
+
   /**
    * The last device token value the server has definitely heard from us.
    *