[MM-60603] Don't follow threads when marking them as read on focus (#28263)

* [MM-60603] Don't follow threads when marking them as read on focus

* Fix tests

* Fix lint

* Fix the original bug in the API call

server/channels/api4/user.go

@@ -3344,6 +3344,14 @@ func setUnreadThreadByPostId(c *Context, w http.ResponseWriter, r *http.Request)
 		return
 	}
 
+	// We want to make sure the thread is followed when marking as unread
+	// https://mattermost.atlassian.net/browse/MM-36430
+	err := c.App.UpdateThreadFollowForUser(c.Params.UserId, c.Params.TeamId, c.Params.ThreadId, true)
+	if err != nil {
+		c.Err = err
+		return
+	}
+
 	thread, err := c.App.UpdateThreadReadForUserByPost(c.AppContext, c.AppContext.Session().Id, c.Params.UserId, c.Params.TeamId, c.Params.ThreadId, c.Params.PostId)
 	if err != nil {
 		c.Err = err

server/channels/api4/user_test.go

@@ -6855,29 +6855,6 @@ func TestThreadSocketEvents(t *testing.T) {
 		require.Truef(t, caught, "User should have received %s event", model.WebsocketEventThreadUpdated)
 	})
 
-	resp, err = th.Client.UpdateThreadFollowForUser(context.Background(), th.BasicUser.Id, th.BasicTeam.Id, rpost.Id, false)
-	require.NoError(t, err)
-	CheckOKStatus(t, resp)
-
-	t.Run("Listed for follow event", func(t *testing.T) {
-		var caught bool
-		func() {
-			for {
-				select {
-				case ev := <-userWSClient.EventChannel:
-					if ev.EventType() == model.WebsocketEventThreadFollowChanged {
-						caught = true
-						require.Equal(t, ev.GetData()["state"], false)
-						require.Equal(t, ev.GetData()["reply_count"], float64(1))
-					}
-				case <-time.After(2 * time.Second):
-					return
-				}
-			}
-		}()
-		require.Truef(t, caught, "User should have received %s event", model.WebsocketEventThreadFollowChanged)
-	})
-
 	_, resp, err = th.Client.UpdateThreadReadForUser(context.Background(), th.BasicUser.Id, th.BasicTeam.Id, rpost.Id, replyPost.CreateAt+1)
 	require.NoError(t, err)
 	CheckOKStatus(t, resp)
@@ -6907,6 +6884,31 @@ func TestThreadSocketEvents(t *testing.T) {
 		require.Truef(t, caught, "User should have received %s event", model.WebsocketEventThreadReadChanged)
 	})
 
+	resp, err = th.Client.UpdateThreadFollowForUser(context.Background(), th.BasicUser.Id, th.BasicTeam.Id, rpost.Id, false)
+	require.NoError(t, err)
+	CheckOKStatus(t, resp)
+
+	t.Run("Listed for follow event", func(t *testing.T) {
+		var caught bool
+		func() {
+			for {
+				select {
+				case ev := <-userWSClient.EventChannel:
+					if ev.EventType() == model.WebsocketEventThreadFollowChanged {
+						caught = true
+						require.Equal(t, ev.GetData()["state"], false)
+						require.Equal(t, ev.GetData()["reply_count"], float64(1))
+					}
+				case <-time.After(2 * time.Second):
+					return
+				}
+			}
+		}()
+		require.Truef(t, caught, "User should have received %s event", model.WebsocketEventThreadFollowChanged)
+	})
+
+	_, err = th.Client.UpdateThreadFollowForUser(context.Background(), th.BasicUser.Id, th.BasicTeam.Id, rpost.Id, true)
+	require.NoError(t, err)
 	_, resp, err = th.Client.SetThreadUnreadByPostId(context.Background(), th.BasicUser.Id, th.BasicTeam.Id, rpost.Id, rpost.Id)
 	require.NoError(t, err)
 	CheckOKStatus(t, resp)