MM-38445: Set isFollowing to false only when explicitly unfollowed (#18740)

Summary
Set post.IsFollowing to false only if the post is explicitly unfollowed. Otherwise leave it as nil.

Ticket Link
https://mattermost.atlassian.net/browse/MM-38445

store/sqlstore/post_store.go

@@ -528,7 +528,7 @@ func (s *SqlPostStore) getPostWithCollapsedThreads(id, userID string, extended b
 		"COALESCE(Threads.ReplyCount, 0) as ThreadReplyCount",
 		"COALESCE(Threads.LastReplyAt, 0) as LastReplyAt",
 		"COALESCE(Threads.Participants, '[]') as ThreadParticipants",
-		"COALESCE(ThreadMemberships.Following, false) as IsFollowing",
+		"ThreadMemberships.Following as IsFollowing",
 	)
 	var post postWithExtra
 
@@ -879,7 +879,7 @@ func (s *SqlPostStore) getPostsCollapsedThreads(options model.GetPostsOptions) (
 		"COALESCE(Threads.ReplyCount, 0) as ThreadReplyCount",
 		"COALESCE(Threads.LastReplyAt, 0) as LastReplyAt",
 		"COALESCE(Threads.Participants, '[]') as ThreadParticipants",
-		"COALESCE(ThreadMemberships.Following, false) as IsFollowing",
+		"ThreadMemberships.Following as IsFollowing",
 	)
 	var posts []*postWithExtra
 	offset := options.PerPage * options.Page
@@ -965,7 +965,7 @@ func (s *SqlPostStore) getPostsSinceCollapsedThreads(options model.GetPostsSince
 		"COALESCE(Threads.ReplyCount, 0) as ThreadReplyCount",
 		"COALESCE(Threads.LastReplyAt, 0) as LastReplyAt",
 		"COALESCE(Threads.Participants, '[]') as ThreadParticipants",
-		"COALESCE(ThreadMemberships.Following, false) as IsFollowing",
+		"ThreadMemberships.Following as IsFollowing",
 	)
 	var posts []*postWithExtra
 
@@ -1181,7 +1181,7 @@ func (s *SqlPostStore) getPostsAround(before bool, options model.GetPostsOptions
 			"COALESCE(Threads.ReplyCount, 0) as ThreadReplyCount",
 			"COALESCE(Threads.LastReplyAt, 0) as LastReplyAt",
 			"COALESCE(Threads.Participants, '[]') as ThreadParticipants",
-			"COALESCE(ThreadMemberships.Following, false) as IsFollowing",
+			"ThreadMemberships.Following as IsFollowing",
 		)
 	}
 	query := s.getQueryBuilder().Select(columns...)

store/storetest/post_store.go

@@ -502,26 +502,64 @@ func testPostStoreGet(t *testing.T, ss store.Store) {
 }
 
 func testPostStoreGetForThread(t *testing.T, ss store.Store) {
-	o1 := &model.Post{ChannelId: model.NewId(), UserId: model.NewId(), Message: NewTestId()}
+	t.Run("Post thread is followed", func(t *testing.T) {
-	o1, err := ss.Post().Save(o1)
+		o1 := &model.Post{ChannelId: model.NewId(), UserId: model.NewId(), Message: NewTestId()}
-	require.NoError(t, err)
+		o1, err := ss.Post().Save(o1)
-	_, err = ss.Post().Save(&model.Post{ChannelId: o1.ChannelId, UserId: model.NewId(), Message: NewTestId(), RootId: o1.Id})
+		require.NoError(t, err)
-	require.NoError(t, err)
+		_, err = ss.Post().Save(&model.Post{ChannelId: o1.ChannelId, UserId: model.NewId(), Message: NewTestId(), RootId: o1.Id})
+		require.NoError(t, err)
 
-	threadMembership := &model.ThreadMembership{
+		threadMembership := &model.ThreadMembership{
-		PostId:         o1.Id,
+			PostId:         o1.Id,
-		UserId:         o1.UserId,
+			UserId:         o1.UserId,
-		Following:      true,
+			Following:      true,
-		LastViewed:     0,
+			LastViewed:     0,
-		LastUpdated:    0,
+			LastUpdated:    0,
-		UnreadMentions: 0,
+			UnreadMentions: 0,
-	}
+		}
-	_, err = ss.Thread().SaveMembership(threadMembership)
+		_, err = ss.Thread().SaveMembership(threadMembership)
-	require.NoError(t, err)
+		require.NoError(t, err)
-	r1, err := ss.Post().Get(context.Background(), o1.Id, false, true, false, o1.UserId)
+		r1, err := ss.Post().Get(context.Background(), o1.Id, false, true, false, o1.UserId)
-	require.NoError(t, err)
+		require.NoError(t, err)
-	require.Equal(t, r1.Posts[o1.Id].CreateAt, o1.CreateAt, "invalid returned post")
+		require.Equal(t, r1.Posts[o1.Id].CreateAt, o1.CreateAt, "invalid returned post")
-	require.True(t, *r1.Posts[o1.Id].IsFollowing)
+		require.True(t, *r1.Posts[o1.Id].IsFollowing)
+	})
+
+	t.Run("Post thread is explicitly not followed", func(t *testing.T) {
+		o1 := &model.Post{ChannelId: model.NewId(), UserId: model.NewId(), Message: NewTestId()}
+		o1, err := ss.Post().Save(o1)
+		require.NoError(t, err)
+		_, err = ss.Post().Save(&model.Post{ChannelId: o1.ChannelId, UserId: model.NewId(), Message: NewTestId(), RootId: o1.Id})
+		require.NoError(t, err)
+
+		threadMembership := &model.ThreadMembership{
+			PostId:         o1.Id,
+			UserId:         o1.UserId,
+			Following:      false,
+			LastViewed:     0,
+			LastUpdated:    0,
+			UnreadMentions: 0,
+		}
+		_, err = ss.Thread().SaveMembership(threadMembership)
+		require.NoError(t, err)
+		r1, err := ss.Post().Get(context.Background(), o1.Id, false, true, false, o1.UserId)
+		require.NoError(t, err)
+		require.Equal(t, r1.Posts[o1.Id].CreateAt, o1.CreateAt, "invalid returned post")
+		require.False(t, *r1.Posts[o1.Id].IsFollowing)
+	})
+
+	t.Run("Post threadmembership does not exist", func(t *testing.T) {
+		o1 := &model.Post{ChannelId: model.NewId(), UserId: model.NewId(), Message: NewTestId()}
+		o1, err := ss.Post().Save(o1)
+		require.NoError(t, err)
+		_, err = ss.Post().Save(&model.Post{ChannelId: o1.ChannelId, UserId: model.NewId(), Message: NewTestId(), RootId: o1.Id})
+		require.NoError(t, err)
+
+		r1, err := ss.Post().Get(context.Background(), o1.Id, false, true, false, o1.UserId)
+		require.NoError(t, err)
+		require.Equal(t, r1.Posts[o1.Id].CreateAt, o1.CreateAt, "invalid returned post")
+		require.Nil(t, r1.Posts[o1.Id].IsFollowing)
+	})
 }
 
 func testPostStoreGetSingle(t *testing.T, ss store.Store) {