[MM-35925] Follow thread when posting in one, even if previously unfollowed (#17926)

app/post.go

@@ -353,6 +353,16 @@ func (a *App) CreatePost(c *request.Context, post *model.Post, channel *model.Ch
 	// to be done when we send the post over the websocket in handlePostEvents
 	rpost = a.PreparePostForClient(rpost, true, false)
 
+	// Make sure poster is following the thread
+	if *a.Config().ServiceSettings.ThreadAutoFollow && rpost.RootId != "" {
+		_, err := a.Srv().Store.Thread().MaintainMembership(user.Id, rpost.RootId, store.ThreadMembershipOpts{
+			Following: true,
+		})
+		if err != nil {
+			mlog.Warn("Failed to update thread membership", mlog.Err(err))
+		}
+	}
+
 	if err := a.handlePostEvents(c, rpost, user, channel, triggerWebhooks, parentPostList, setOnline); err != nil {
 		mlog.Warn("Failed to handle post events", mlog.Err(err))
 	}

app/post_test.go

@@ -20,6 +20,7 @@ import (
 	"github.com/mattermost/mattermost-server/v5/services/imageproxy"
 	"github.com/mattermost/mattermost-server/v5/services/searchengine/mocks"
 	"github.com/mattermost/mattermost-server/v5/shared/mlog"
+	"github.com/mattermost/mattermost-server/v5/store"
 	"github.com/mattermost/mattermost-server/v5/store/storetest"
 	storemocks "github.com/mattermost/mattermost-server/v5/store/storetest/mocks"
 	"github.com/mattermost/mattermost-server/v5/testlib"
@@ -2258,3 +2259,45 @@ func TestSharedChannelSyncForPostActions(t *testing.T) {
 		assert.Equal(t, channel.Id, remoteClusterService.channelNotifications[2])
 	})
 }
+
+func TestAutofollowOnPostingAfterUnfollow(t *testing.T) {
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+	os.Setenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS", "true")
+	defer os.Unsetenv("MM_FEATUREFLAGS_COLLAPSEDTHREADS")
+
+	th.App.UpdateConfig(func(cfg *model.Config) {
+		*cfg.ServiceSettings.ThreadAutoFollow = true
+		*cfg.ServiceSettings.CollapsedThreads = model.COLLAPSED_THREADS_DEFAULT_ON
+	})
+
+	channel := th.BasicChannel
+	user := th.BasicUser
+	user2 := th.BasicUser2
+	appErr := th.App.JoinChannel(th.Context, channel, user.Id)
+	require.Nil(t, appErr)
+	appErr = th.App.JoinChannel(th.Context, channel, user2.Id)
+	require.Nil(t, appErr)
+	p1, err := th.App.CreatePost(th.Context, &model.Post{UserId: user.Id, ChannelId: channel.Id, Message: "Hi @" + user2.Username}, channel, false, false)
+	require.Nil(t, err)
+	_, err = th.App.CreatePost(th.Context, &model.Post{RootId: p1.Id, UserId: user2.Id, ChannelId: channel.Id, Message: "Hola"}, channel, false, false)
+	require.Nil(t, err)
+	_, err = th.App.CreatePost(th.Context, &model.Post{RootId: p1.Id, UserId: user.Id, ChannelId: channel.Id, Message: "reply"}, channel, false, false)
+	require.Nil(t, err)
+
+	// unfollow thread
+	m, nErr := th.App.Srv().Store.Thread().MaintainMembership(user.Id, p1.Id, store.ThreadMembershipOpts{
+		Following: false,
+	})
+	require.NoError(t, nErr)
+	require.False(t, m.Following)
+
+	_, err = th.App.CreatePost(th.Context, &model.Post{RootId: p1.Id, UserId: user.Id, ChannelId: channel.Id, Message: "another reply"}, channel, false, false)
+	require.Nil(t, err)
+
+	// User should be following thread after posting in it, even after previously
+	// unfollowing it, if ThreadAutoFollow is true
+	m, err = th.App.GetThreadMembershipForUser(user.Id, p1.Id)
+	require.Nil(t, err)
+	require.True(t, m.Following)
+}