api: Add "followed" user-topic state, as synonym of "unmuted"

In all the places we currently consult the user's visibility policy
for a topic, treating "followed" as "unmuted" will give it the most
accurate behavior from among what we currently implement.

In particular this makes it so that when the stream is muted, the
topic will correctly be treated as not muted.

There's still more we could do to fully implement this feature:
notably, surface in the UI what the current state is, and give the
option to set a topic to followed.  But this is an important start.

Fixes: zulip#5769

src/action-sheets/__tests__/action-sheet-test.js

@@ -12,6 +12,7 @@ import {
 import { makeUnreadState } from '../../unread/__tests__/unread-testlib';
 import { makeMuteState } from '../../mute/__tests__/mute-testlib';
 import { Role } from '../../api/permissionsTypes';
+import { UserTopicVisibilityPolicy } from '../../api/modelTypes';
 
 const buttonTitles = buttons => buttons.map(button => button.title);
 
@@ -92,6 +93,11 @@ describe('constructTopicActionButtons', () => {
     expect(titles({ ...eg.plusBackgroundData, mute })).toContain('Mute topic');
   });
 
+  test('show muteTopic on followed topic', () => {
+    const mute = makeMuteState([[eg.stream, topic, UserTopicVisibilityPolicy.Followed]]);
+    expect(titles({ ...eg.plusBackgroundData, mute })).toContain('Mute topic');
+  });
+
   test('show resolveTopic', () => {
     expect(titles({ ...eg.plusBackgroundData })).toContain('Resolve topic');
   });

src/action-sheets/index.js

@@ -664,6 +664,7 @@ export const constructTopicActionButtons = (args: {|
         break;
       case UserTopicVisibilityPolicy.None:
       case UserTopicVisibilityPolicy.Unmuted:
+      case UserTopicVisibilityPolicy.Followed:
         buttons.push(muteTopic);
         break;
     }
@@ -677,6 +678,7 @@ export const constructTopicActionButtons = (args: {|
           buttons.push(unmuteTopicInMutedStream);
           break;
         case UserTopicVisibilityPolicy.Unmuted:
+        case UserTopicVisibilityPolicy.Followed:
           buttons.push(muteTopic);
           break;
       }

src/api/modelTypes.js

@@ -644,6 +644,10 @@ export enum UserTopicVisibilityPolicy {
   None = 0,
   Muted = 1,
   Unmuted = 2,
+  // Not in the API docs yet.  But it is, uh, in the server implementation:
+  //   https://github.com/zulip/zulip/blob/2ec8273c6/zerver/models.py#L2794-L2797
+  // TODO(server): delete this comment once documented
+  Followed = 3,
 }
 
 /**

src/mute/__tests__/muteModel-test.js

@@ -45,6 +45,13 @@ describe('getters', () => {
         UserTopicVisibilityPolicy.Unmuted,
       );
     });
+
+    test('with topic followed', () => {
+      check(
+        makeMuteState([[eg.stream, 'topic', UserTopicVisibilityPolicy.Followed]]),
+        UserTopicVisibilityPolicy.Followed,
+      );
+    });
   });
 
   describe('isTopicVisibleInStream', () => {
@@ -67,6 +74,10 @@ describe('getters', () => {
     test('with topic unmuted', () => {
       check(makeMuteState([[eg.stream, 'topic', UserTopicVisibilityPolicy.Unmuted]]), true);
     });
+
+    test('with topic followed', () => {
+      check(makeMuteState([[eg.stream, 'topic', UserTopicVisibilityPolicy.Followed]]), true);
+    });
   });
 
   describe('isTopicVisible', () => {
@@ -90,6 +101,10 @@ describe('getters', () => {
       check(false, UserTopicVisibilityPolicy.Unmuted, true);
     });
 
+    test('stream unmuted, topic-policy Followed', () => {
+      check(false, UserTopicVisibilityPolicy.Followed, true);
+    });
+
     test('stream muted, topic-policy None', () => {
       check(true, UserTopicVisibilityPolicy.None, false);
     });
@@ -101,6 +116,10 @@ describe('getters', () => {
     test('stream muted, topic-policy Unmuted', () => {
       check(true, UserTopicVisibilityPolicy.Unmuted, true);
     });
+
+    test('stream muted, topic-policy Followed', () => {
+      check(true, UserTopicVisibilityPolicy.Followed, true);
+    });
   });
 });
 

src/mute/muteModel.js

@@ -62,6 +62,7 @@ export function isTopicVisibleInStream(streamId: number, topic: string, mute: Mu
     case UserTopicVisibilityPolicy.Muted:
       return false;
     case UserTopicVisibilityPolicy.Unmuted:
+    case UserTopicVisibilityPolicy.Followed:
       return true;
   }
 }
@@ -89,6 +90,7 @@ export function isTopicVisible(
     case UserTopicVisibilityPolicy.Muted:
       return false;
     case UserTopicVisibilityPolicy.Unmuted:
+    case UserTopicVisibilityPolicy.Followed:
       return true;
   }
 }