[MM-37933] Channel preference to auto-follow all threads in the channel (#21430)

* Add auto-follow feature --------- Co-authored-by: Mattermod <mattermod@users.noreply.github.com> Co-authored-by: Mattermost Build <build@mattermost.com>
2023-05-05 12:09:00 +05:30
--- a/server/channels/app/channel.go
+++ b/server/channels/app/channel.go
@@ -1354,6 +1354,10 @@ func (a *App) UpdateChannelMemberNotifyProps(c request.CTX, data map[string]stri
 		filteredProps[model.IgnoreChannelMentionsNotifyProp] = ignoreChannelMentions
 	}

+	if channelAutoFollowThreads, exists := data[model.ChannelAutoFollowThreads]; exists {
+		filteredProps[model.ChannelAutoFollowThreads] = channelAutoFollowThreads
+	}
+
 	member, err := a.Srv().Store().Channel().UpdateMemberNotifyProps(channelID, userID, filteredProps)
 	if err != nil {
 		var appErr *model.AppError
--- a/server/channels/app/notification.go
+++ b/server/channels/app/notification.go
@@ -101,13 +101,15 @@ func (a *App) SendNotifications(c request.CTX, post *model.Post, team *model.Tea
 	}
 	channelMemberNotifyPropsMap := result.Data.(map[string]model.StringMap)

-	followers := make(model.StringArray, 0)
+	followers := make(model.StringSet, 0)
 	if tchan != nil {
 		result = <-tchan
 		if result.NErr != nil {
 			return nil, result.NErr
 		}
-		followers = result.Data.([]string)
+		for _, v := range result.Data.([]string) {
+			followers.Add(v)
+		}
 	}

 	groups := make(map[string]*model.Group)
@@ -235,6 +237,14 @@ func (a *App) SendNotifications(c request.CTX, post *model.Post, team *model.Tea
 			threadParticipants[id] = true
 		}

+		if channel.Type != model.ChannelTypeDirect {
+			for id, propsMap := range channelMemberNotifyPropsMap {
+				if ok := followers.Has(id); !ok && propsMap[model.ChannelAutoFollowThreads] == model.ChannelAutoFollowThreadsOn {
+					threadParticipants[id] = true
+				}
+			}
+		}
+
 		// sema is a counting semaphore to throttle the number of concurrent DB requests.
 		// A concurrency of 8 should be sufficient.
 		// We don't want to set a higher limit which can bring down the DB.
@@ -286,8 +296,8 @@ func (a *App) SendNotifications(c request.CTX, post *model.Post, team *model.Tea

 				followersMutex.Lock()
 				// add new followers to existing followers
-				if threadMembership.Following && !followers.Contains(userID) {
-					followers = append(followers, userID)
+				if ok := followers.Has(userID); !ok && threadMembership.Following {
+					followers.Add(userID)
 					newParticipants[userID] = true
 				}
 				followersMutex.Unlock()
@@ -330,7 +340,7 @@ func (a *App) SendNotifications(c request.CTX, post *model.Post, team *model.Tea

 	notificationsForCRT := &CRTNotifiers{}
 	if isCRTAllowed && post.RootId != "" {
-		for _, uid := range followers {
+		for uid := range followers {
 			profile := profileMap[uid]
 			if profile == nil || !a.IsCRTEnabledForUser(c, uid) {
 				continue
@@ -578,7 +588,7 @@ func (a *App) SendNotifications(c request.CTX, post *model.Post, team *model.Tea

 	// If this is a reply in a thread, notify participants
 	if isCRTAllowed && post.RootId != "" {
-		for _, uid := range followers {
+		for uid := range followers {
 			// A user following a thread but had left the channel won't get a notification
 			// https://mattermost.atlassian.net/browse/MM-36769
 			if profileMap[uid] == nil {
--- a/server/channels/app/notification_test.go
+++ b/server/channels/app/notification_test.go
@@ -10,6 +10,7 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"

+	"github.com/mattermost/mattermost-server/server/v8/channels/store"
 	"github.com/mattermost/mattermost-server/server/v8/channels/utils"
 	"github.com/mattermost/mattermost-server/server/v8/model"
 	"github.com/mattermost/mattermost-server/server/v8/platform/shared/i18n"
@@ -2819,3 +2820,66 @@ func TestReplyPostNotificationsWithCRT(t *testing.T) {
 		assert.Nil(t, membership)
 	})
 }
+
+func TestChannelAutoFollowThreads(t *testing.T) {
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+
+	u1 := th.BasicUser
+	u2 := th.BasicUser2
+	u3 := th.CreateUser()
+	th.LinkUserToTeam(u3, th.BasicTeam)
+	c1 := th.BasicChannel
+	th.AddUserToChannel(u2, c1)
+	th.AddUserToChannel(u3, c1)
+
+	// Set auto-follow for user 2
+	member, appErr := th.App.UpdateChannelMemberNotifyProps(th.Context, map[string]string{model.ChannelAutoFollowThreads: model.ChannelAutoFollowThreadsOn}, c1.Id, u2.Id)
+	require.Nil(t, appErr)
+	require.Equal(t, model.ChannelAutoFollowThreadsOn, member.NotifyProps[model.ChannelAutoFollowThreads])
+
+	rootPost := &model.Post{
+		ChannelId: c1.Id,
+		Message:   "root post by user3",
+		UserId:    u3.Id,
+	}
+	rpost, appErr := th.App.CreatePost(th.Context, rootPost, c1, false, true)
+	require.Nil(t, appErr)
+
+	replyPost1 := &model.Post{
+		ChannelId: c1.Id,
+		Message:   "reply post by user1",
+		UserId:    u1.Id,
+		RootId:    rpost.Id,
+	}
+	_, appErr = th.App.CreatePost(th.Context, replyPost1, c1, false, true)
+	require.Nil(t, appErr)
+
+	// user-2 starts auto-following thread
+	threadMembership, appErr := th.App.GetThreadMembershipForUser(u2.Id, rpost.Id)
+	require.Nil(t, appErr)
+	require.NotNil(t, threadMembership)
+	assert.True(t, threadMembership.Following)
+
+	// Set "following" to false
+	_, err := th.App.Srv().Store().Thread().MaintainMembership(u2.Id, rpost.Id, store.ThreadMembershipOpts{
+		Following:       false,
+		UpdateFollowing: true,
+	})
+	require.NoError(t, err)
+
+	replyPost2 := &model.Post{
+		ChannelId: c1.Id,
+		Message:   "reply post 2 by user1",
+		UserId:    u1.Id,
+		RootId:    rpost.Id,
+	}
+	_, appErr = th.App.CreatePost(th.Context, replyPost2, c1, false, true)
+	require.Nil(t, appErr)
+
+	// Do NOT start auto-following thread, once "un-followed"
+	threadMembership, appErr = th.App.GetThreadMembershipForUser(u2.Id, rpost.Id)
+	require.Nil(t, appErr)
+	require.NotNil(t, threadMembership)
+	assert.False(t, threadMembership.Following)
+}
--- a/server/i18n/en.json
+++ b/server/i18n/en.json
@@ -8459,6 +8459,10 @@
    "id": "model.channel.is_valid.update_at.app_error",
    "translation": "Update at must be a valid time."
  },
+  {
+    "id": "model.channel_member.is_valid.channel_auto_follow_threads_value.app_error",
+    "translation": "Invalid channel-auto-follow-threads value."
+  },
  {
    "id": "model.channel_member.is_valid.channel_id.app_error",
    "translation": "Invalid channel id."
--- a/server/model/channel_member.go
+++ b/server/model/channel_member.go
@@ -19,6 +19,9 @@ const (
 	IgnoreChannelMentionsOff        = "off"
 	IgnoreChannelMentionsOn         = "on"
 	IgnoreChannelMentionsNotifyProp = "ignore_channel_mentions"
+	ChannelAutoFollowThreadsOff     = "off"
+	ChannelAutoFollowThreadsOn      = "on"
+	ChannelAutoFollowThreads        = "channel_auto_follow_threads"
 )

 type ChannelUnread struct {
@@ -172,6 +175,12 @@ func (o *ChannelMember) IsValid() *AppError {
 		}
 	}

+	if channelAutoFollowThreads, ok := o.NotifyProps[ChannelAutoFollowThreads]; ok {
+		if len(channelAutoFollowThreads) > 3 || !IsChannelAutoFollowThreadsValid(channelAutoFollowThreads) {
+			return NewAppError("ChannelMember.IsValid", "model.channel_member.is_valid.channel_auto_follow_threads_value.app_error", nil, "channel_auto_follow_threads="+channelAutoFollowThreads, http.StatusBadRequest)
+		}
+	}
+
 	if len(o.Roles) > UserRolesMaxLength {
 		return NewAppError("ChannelMember.IsValid", "model.channel_member.is_valid.roles_limit.app_error",
 			map[string]any{"Limit": UserRolesMaxLength}, "", http.StatusBadRequest)
@@ -223,6 +232,10 @@ func IsIgnoreChannelMentionsValid(ignoreChannelMentions string) bool {
 	return ignoreChannelMentions == IgnoreChannelMentionsOn || ignoreChannelMentions == IgnoreChannelMentionsOff || ignoreChannelMentions == IgnoreChannelMentionsDefault
 }

+func IsChannelAutoFollowThreadsValid(channelAutoFollowThreads string) bool {
+	return channelAutoFollowThreads == ChannelAutoFollowThreadsOn || channelAutoFollowThreads == ChannelAutoFollowThreadsOff
+}
+
 func GetDefaultChannelNotifyProps() StringMap {
 	return StringMap{
 		DesktopNotifyProp:               ChannelNotifyDefault,
@@ -230,5 +243,6 @@ func GetDefaultChannelNotifyProps() StringMap {
 		PushNotifyProp:                  ChannelNotifyDefault,
 		EmailNotifyProp:                 ChannelNotifyDefault,
 		IgnoreChannelMentionsNotifyProp: IgnoreChannelMentionsDefault,
+		ChannelAutoFollowThreads:        ChannelAutoFollowThreadsOff,
 	}
 }
--- a/server/model/utils.go
+++ b/server/model/utils.go
@@ -41,8 +41,26 @@ const (
 var ErrMaxPropSizeExceeded = fmt.Errorf("max prop size of %d exceeded", maxPropSizeBytes)

 type StringInterface map[string]any
+type StringSet map[string]struct{}
 type StringArray []string

+func (ss StringSet) Has(val string) bool {
+	_, ok := ss[val]
+	return ok
+}
+
+func (ss StringSet) Add(val string) {
+	ss[val] = struct{}{}
+}
+
+func (ss StringSet) Val() []string {
+	keys := make([]string, 0, len(ss))
+	for k := range ss {
+		keys = append(keys, k)
+	}
+	return keys
+}
+
 func (sa StringArray) Remove(input string) StringArray {
 	for index := range sa {
 		if sa[index] == input {
--- a/webapp/channels/src/components/admin_console/team_channel_settings/channel/details/channel_members/snapshots/channel_members.test.tsx.snap
+++ b/webapp/channels/src/components/admin_console/team_channel_settings/channel/details/channel_members/snapshots/channel_members.test.tsx.snap
@@ -124,6 +124,7 @@ exports[`admin_console/team_channel_settings/channel/ChannelMembers should match
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -145,6 +146,7 @@ exports[`admin_console/team_channel_settings/channel/ChannelMembers should match
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -166,6 +168,7 @@ exports[`admin_console/team_channel_settings/channel/ChannelMembers should match
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
--- a/webapp/channels/src/components/admin_console/team_channel_settings/group/group_users/snapshots/users_to_remove_role.test.tsx.snap
+++ b/webapp/channels/src/components/admin_console/team_channel_settings/group/group_users/snapshots/users_to_remove_role.test.tsx.snap
@@ -95,6 +95,7 @@ exports[`components/admin_console/team_channel_settings/group/UsersToRemoveRole
      "msg_count": 0,
      "msg_count_root": 0,
      "notify_props": Object {
+        "channel_auto_follow_threads": "off",
        "desktop": "default",
        "email": "default",
        "ignore_channel_mentions": "default",
@@ -186,6 +187,7 @@ exports[`components/admin_console/team_channel_settings/group/UsersToRemoveRole
      "msg_count": 0,
      "msg_count_root": 0,
      "notify_props": Object {
+        "channel_auto_follow_threads": "off",
        "desktop": "default",
        "email": "default",
        "ignore_channel_mentions": "default",
@@ -277,6 +279,7 @@ exports[`components/admin_console/team_channel_settings/group/UsersToRemoveRole
      "msg_count": 0,
      "msg_count_root": 0,
      "notify_props": Object {
+        "channel_auto_follow_threads": "off",
        "desktop": "default",
        "email": "default",
        "ignore_channel_mentions": "default",
--- a/webapp/channels/src/components/channel_header/snapshots/channel_header.test.tsx.snap
+++ b/webapp/channels/src/components/channel_header/snapshots/channel_header.test.tsx.snap
@@ -284,6 +284,7 @@ exports[`components/ChannelHeader should match snapshot with last active display
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -589,6 +590,7 @@ exports[`components/ChannelHeader should match snapshot with no last active disp
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -893,6 +895,7 @@ exports[`components/ChannelHeader should render active channel files 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -1196,6 +1199,7 @@ exports[`components/ChannelHeader should render active flagged posts 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -1499,6 +1503,7 @@ exports[`components/ChannelHeader should render active mentions posts 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -1802,6 +1807,7 @@ exports[`components/ChannelHeader should render active pinned posts 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -2074,6 +2080,7 @@ exports[`components/ChannelHeader should render archived view 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -2409,6 +2416,7 @@ exports[`components/ChannelHeader should render correct menu when muted 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -2712,6 +2720,7 @@ exports[`components/ChannelHeader should render not active channel files 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -3036,6 +3045,7 @@ exports[`components/ChannelHeader should render properly when custom status is e
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -3381,6 +3391,7 @@ exports[`components/ChannelHeader should render properly when custom status is s
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -3685,6 +3696,7 @@ exports[`components/ChannelHeader should render properly when empty 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -3988,6 +4000,7 @@ exports[`components/ChannelHeader should render properly when populated 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -4310,6 +4323,7 @@ exports[`components/ChannelHeader should render properly when populated with cha
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -4626,6 +4640,7 @@ exports[`components/ChannelHeader should render shared view 1`] = `
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
@@ -4938,6 +4953,7 @@ exports[`components/ChannelHeader should render the pinned icon with the pinned
          "msg_count": 0,
          "msg_count_root": 0,
          "notify_props": Object {
+            "channel_auto_follow_threads": "off",
            "desktop": "default",
            "email": "default",
            "ignore_channel_mentions": "default",
--- a/webapp/channels/src/components/channel_notifications_modal/snapshots/channel_notifications_modal.test.tsx.snap
+++ b/webapp/channels/src/components/channel_notifications_modal/snapshots/channel_notifications_modal.test.tsx.snap
@@ -121,6 +121,20 @@ exports[`components/channel_notifications_modal/ChannelNotificationsModal should
              serverError={null}
            />
          </div>
+          <div
+            className="divider-light"
+          />
+          <NotificationSection
+            channelAutoFollowThreads="off"
+            expand={false}
+            ignoreChannelMentions="off"
+            memberNotificationLevel="all"
+            onChange={[Function]}
+            onSubmit={[Function]}
+            onUpdateSection={[Function]}
+            section="channelAutoFollowThreads"
+            serverError={null}
+          />
          <div
            className="divider-dark"
          />
--- a/webapp/channels/src/components/channel_notifications_modal/channel_notifications_modal.test.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/channel_notifications_modal.test.tsx
@@ -4,7 +4,7 @@
 import React, {ComponentProps} from 'react';
 import {shallow} from 'enzyme';

-import {IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
+import {ChannelAutoFollowThreads, IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
 import {TestHelper} from 'utils/test_helper';

 import ChannelNotificationsModal from 'components/channel_notifications_modal/channel_notifications_modal';
@@ -25,6 +25,7 @@ describe('components/channel_notifications_modal/ChannelNotificationsModal', ()
                mark_unread: NotificationLevels.ALL,
                push: NotificationLevels.DEFAULT,
                ignore_channel_mentions: IgnoreChannelMentions.DEFAULT,
+                channel_auto_follow_threads: ChannelAutoFollowThreads.OFF,
                desktop_threads: NotificationLevels.ALL,
                push_threads: NotificationLevels.DEFAULT,
            },
@@ -62,6 +63,7 @@ describe('components/channel_notifications_modal/ChannelNotificationsModal', ()
        expect(wrapper.state('markUnreadNotifyLevel')).toEqual(NotificationLevels.ALL);
        expect(wrapper.state('pushNotifyLevel')).toEqual(NotificationLevels.DEFAULT);
        expect(wrapper.state('ignoreChannelMentions')).toEqual(IgnoreChannelMentions.OFF);
+        expect(wrapper.state('channelAutoFollowThreads')).toEqual(ChannelAutoFollowThreads.OFF);
    });

    test('should provide correct default when currentUser channel notify props is true', () => {
@@ -207,7 +209,7 @@ describe('components/channel_notifications_modal/ChannelNotificationsModal', ()

        expect(wrapper.state('desktopNotifyLevel')).toEqual(NotificationLevels.NONE);

-        wrapper.instance().updateSection('');
+        wrapper.instance().updateSection(NotificationSections.NONE);

        expect(wrapper.state('desktopNotifyLevel')).toEqual(baseProps.channelMember?.notify_props.desktop);
    });
@@ -348,6 +350,7 @@ describe('components/channel_notifications_modal/ChannelNotificationsModal', ()
        expect(wrapper.state('markUnreadNotifyLevel')).toEqual(NotificationLevels.MENTION);
        expect(wrapper.state('pushNotifyLevel')).toEqual(NotificationLevels.ALL);
        expect(wrapper.state('ignoreChannelMentions')).toEqual(IgnoreChannelMentions.ON);
+        expect(wrapper.state('channelAutoFollowThreads')).toEqual(ChannelAutoFollowThreads.OFF);

        wrapper.instance().resetStateFromNotifyProps(currentUserNotifyProps, {...channelMemberNotifyProps, desktop: NotificationLevels.ALL});
        expect(wrapper.state('desktopNotifyLevel')).toEqual(NotificationLevels.ALL);
--- a/webapp/channels/src/components/channel_notifications_modal/channel_notifications_modal.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/channel_notifications_modal.tsx
@@ -8,7 +8,7 @@ import {FormattedMessage} from 'react-intl';

 import {isChannelMuted} from 'mattermost-redux/utils/channel_utils';

-import {IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
+import {ChannelAutoFollowThreads, IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';

 import NotificationSection from 'components/channel_notifications_modal/components/notification_section.jsx';

@@ -47,6 +47,7 @@ type State = {
    pushNotifyLevel: ChannelNotifyProps['push'];
    pushThreadsNotifyLevel: UserNotifyProps['push_threads'];
    ignoreChannelMentions: ChannelNotifyProps['ignore_channel_mentions'];
+    channelAutoFollowThreads: ChannelNotifyProps['channel_auto_follow_threads'];
 };

 export default class ChannelNotificationsModal extends React.PureComponent<Props, State> {
@@ -95,6 +96,7 @@ export default class ChannelNotificationsModal extends React.PureComponent<Props
            pushNotifyLevel: channelMemberNotifyProps?.push || NotificationLevels.DEFAULT,
            pushThreadsNotifyLevel: channelMemberNotifyProps?.push_threads || NotificationLevels.ALL,
            ignoreChannelMentions,
+            channelAutoFollowThreads: channelMemberNotifyProps?.channel_auto_follow_threads || ChannelAutoFollowThreads.OFF,
        };
    }

@@ -190,7 +192,7 @@ export default class ChannelNotificationsModal extends React.PureComponent<Props
        const {ignoreChannelMentions} = this.state;

        if (channelNotifyProps?.ignore_channel_mentions === ignoreChannelMentions) {
-            this.updateSection('');
+            this.updateSection(NotificationSections.NONE);
            return;
        }

@@ -198,6 +200,21 @@ export default class ChannelNotificationsModal extends React.PureComponent<Props
        this.handleUpdateChannelNotifyProps(props);
    };

+    handleUpdateChannelAutoFollowThreads = (channelAutoFollowThreads: ChannelNotifyProps['channel_auto_follow_threads']) => this.setState({channelAutoFollowThreads});
+
+    handleSubmitChannelAutoFollowThreads = () => {
+        const channelNotifyProps = this.props.channelMember && this.props.channelMember.notify_props;
+        const {channelAutoFollowThreads} = this.state;
+
+        if (channelNotifyProps?.channel_auto_follow_threads === channelAutoFollowThreads) {
+            this.updateSection(NotificationSections.NONE);
+            return;
+        }
+
+        const props = {channel_auto_follow_threads: channelAutoFollowThreads};
+        this.handleUpdateChannelNotifyProps(props);
+    };
+
    render() {
        const {
            activeSection,
@@ -207,6 +224,7 @@ export default class ChannelNotificationsModal extends React.PureComponent<Props
            pushNotifyLevel,
            pushThreadsNotifyLevel,
            ignoreChannelMentions,
+            channelAutoFollowThreads,
            serverError,
        } = this.state;

@@ -301,6 +319,18 @@ export default class ChannelNotificationsModal extends React.PureComponent<Props
                                    }
                                </div>
                                }
+                                <div className='divider-light'/>
+                                <NotificationSection
+                                    section={NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS}
+                                    expand={activeSection === NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS}
+                                    memberNotificationLevel={markUnreadNotifyLevel}
+                                    ignoreChannelMentions={ignoreChannelMentions}
+                                    channelAutoFollowThreads={channelAutoFollowThreads}
+                                    onChange={this.handleUpdateChannelAutoFollowThreads}
+                                    onSubmit={this.handleSubmitChannelAutoFollowThreads}
+                                    onUpdateSection={this.updateSection}
+                                    serverError={serverError}
+                                />
                                <div className='divider-dark'/>
                            </div>
                        </div>
--- a/webapp/channels/src/components/channel_notifications_modal/components/collapse_view.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/collapse_view.tsx
@@ -10,13 +10,14 @@ import SectionTitle from './section_title';

 type Props = {
    ignoreChannelMentions?: string;
+    channelAutoFollowThreads?: string;
    onExpandSection: (section: string) => void;
    globalNotifyLevel?: string;
    memberNotifyLevel: string;
    section: string;
 }

-export default function CollapseView({onExpandSection, globalNotifyLevel, memberNotifyLevel, section, ignoreChannelMentions}: Props) {
+export default function CollapseView({onExpandSection, globalNotifyLevel, memberNotifyLevel, section, ignoreChannelMentions, channelAutoFollowThreads}: Props) {
    return (
        <SettingItemMin
            title={<SectionTitle section={section}/>}
@@ -24,6 +25,7 @@ export default function CollapseView({onExpandSection, globalNotifyLevel, member
                <Describe
                    section={section}
                    ignoreChannelMentions={ignoreChannelMentions}
+                    channelAutoFollowThreads={channelAutoFollowThreads}
                    memberNotifyLevel={memberNotifyLevel}
                    globalNotifyLevel={globalNotifyLevel}
                    isCollapsed={true}
--- a/webapp/channels/src/components/channel_notifications_modal/components/describe.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/describe.tsx
@@ -4,18 +4,19 @@
 import React from 'react';
 import {FormattedMessage} from 'react-intl';

-import {IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
+import {ChannelAutoFollowThreads, IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
 import {t} from 'utils/i18n';

 type Props = {
    globalNotifyLevel?: string;
    ignoreChannelMentions?: string;
+    channelAutoFollowThreads?: string;
    memberNotifyLevel: string;
    section: string;
    isCollapsed?: boolean;
 }

-export default function Describe({section, isCollapsed, memberNotifyLevel, globalNotifyLevel, ignoreChannelMentions}: Props) {
+export default function Describe({section, isCollapsed, memberNotifyLevel, globalNotifyLevel, ignoreChannelMentions, channelAutoFollowThreads}: Props) {
    if (memberNotifyLevel === NotificationLevels.DEFAULT && globalNotifyLevel) {
        t('channel_notifications.levels.default');
        t('channel_notifications.levels.all');
@@ -70,6 +71,26 @@ export default function Describe({section, isCollapsed, memberNotifyLevel, globa
                defaultMessage='Off'
            />
        );
+    } else if (
+        section === NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS &&
+        channelAutoFollowThreads === ChannelAutoFollowThreads.ON
+    ) {
+        return (
+            <FormattedMessage
+                id='channel_notifications.channelAutoFollowThreads.on.title'
+                defaultMessage='On'
+            />
+        );
+    } else if (
+        section === NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS &&
+        channelAutoFollowThreads === ChannelAutoFollowThreads.OFF
+    ) {
+        return (
+            <FormattedMessage
+                id='channel_notifications.channelAutoFollowThreads.off.title'
+                defaultMessage='Off'
+            />
+        );
    } else if (memberNotifyLevel === NotificationLevels.MENTION) {
        return (
            <FormattedMessage
--- a/webapp/channels/src/components/channel_notifications_modal/components/expand_view.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/expand_view.tsx
@@ -7,7 +7,7 @@ import {useSelector} from 'react-redux';

 import {isCollapsedThreadsEnabled} from 'mattermost-redux/selectors/entities/preferences';

-import {IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';
+import {ChannelAutoFollowThreads, IgnoreChannelMentions, NotificationLevels, NotificationSections} from 'utils/constants';

 import SettingItemMax from 'components/setting_item_max';

@@ -17,6 +17,7 @@ import SectionTitle from './section_title';

 type Props = {
    ignoreChannelMentions?: string;
+    channelAutoFollowThreads?: string;
    onChange: (e: ChangeEvent<HTMLInputElement>) => void;
    onChangeThreads?: (e: ChangeEvent<HTMLInputElement>) => void;
    onCollapseSection: (section: string) => void;
@@ -39,6 +40,7 @@ export default function ExpandView({
    serverError,
    onCollapseSection,
    ignoreChannelMentions,
+    channelAutoFollowThreads,
 }: Props) {
    const isCRTEnabled = useSelector(isCollapsedThreadsEnabled);

@@ -153,6 +155,46 @@ export default function ExpandView({
                    </div>
                </fieldset>
            }
+            {section === NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS &&
+                <fieldset>
+                    <div className='radio'>
+                        <label>
+                            <input
+                                id='channelAutoFollowThreadsOn'
+                                name='channelAutoFollowThreads'
+                                type='radio'
+                                value={ChannelAutoFollowThreads.ON}
+                                checked={channelAutoFollowThreads === ChannelAutoFollowThreads.ON}
+                                onChange={onChange}
+                            />
+                            <Describe
+                                section={section}
+                                channelAutoFollowThreads={ChannelAutoFollowThreads.ON}
+                                memberNotifyLevel={memberNotifyLevel}
+                                globalNotifyLevel={globalNotifyLevel}
+                            />
+                        </label>
+                    </div>
+                    <div className='radio'>
+                        <label>
+                            <input
+                                id='channelAutoFollowThreadsOff'
+                                name='channelAutoFollowThreads'
+                                type='radio'
+                                value={ChannelAutoFollowThreads.OFF}
+                                checked={channelAutoFollowThreads === ChannelAutoFollowThreads.OFF}
+                                onChange={onChange}
+                            />
+                            <Describe
+                                section={section}
+                                channelAutoFollowThreads={ChannelAutoFollowThreads.OFF}
+                                memberNotifyLevel={memberNotifyLevel}
+                                globalNotifyLevel={globalNotifyLevel}
+                            />
+                        </label>
+                    </div>
+                </fieldset>
+            }
            {section === NotificationSections.MARK_UNREAD &&
            <fieldset>
                <div className='radio'>
--- a/webapp/channels/src/components/channel_notifications_modal/components/extra_info.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/extra_info.tsx
@@ -48,6 +48,15 @@ export default function ExtraInfo({section}: Props) {
                />
            </span>
        );
+    case NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS:
+        return (
+            <span>
+                <FormattedMessage
+                    id='channel_notifications.channelAutoFollowThreads.help'
+                    defaultMessage='When enabled, you will auto-follow all new threads created in this channel unless you unfollow a thread explicitly.'
+                />
+            </span>
+        );
    default:
        return null;
    }
--- a/webapp/channels/src/components/channel_notifications_modal/components/notification_section.jsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/notification_section.jsx
@@ -37,6 +37,11 @@ export default class NotificationSection extends React.PureComponent {
         */
        ignoreChannelMentions: PropTypes.string,

+        /**
+         * Auto-follow all new threads in this channel
+         */
+        channelAutoFollowThreads: PropTypes.string,
+
        /**
         * User's global notification level
         */
@@ -93,6 +98,7 @@ export default class NotificationSection extends React.PureComponent {
            memberNotificationLevel,
            memberThreadsNotificationLevel,
            ignoreChannelMentions,
+            channelAutoFollowThreads,
            onSubmit,
            section,
            serverError,
@@ -106,6 +112,7 @@ export default class NotificationSection extends React.PureComponent {
                    memberThreadsNotifyLevel={memberThreadsNotificationLevel}
                    globalNotifyLevel={globalNotificationLevel}
                    ignoreChannelMentions={ignoreChannelMentions}
+                    channelAutoFollowThreads={channelAutoFollowThreads}
                    onChange={this.handleOnChange}
                    onChangeThreads={this.handleOnChangeThreads}
                    onSubmit={onSubmit}
@@ -122,6 +129,7 @@ export default class NotificationSection extends React.PureComponent {
                memberNotifyLevel={memberNotificationLevel}
                globalNotifyLevel={globalNotificationLevel}
                ignoreChannelMentions={ignoreChannelMentions}
+                channelAutoFollowThreads={channelAutoFollowThreads}
            />
        );
    }
--- a/webapp/channels/src/components/channel_notifications_modal/components/section_title.tsx
+++ b/webapp/channels/src/components/channel_notifications_modal/components/section_title.tsx
@@ -39,6 +39,13 @@ export default function SectionTitle({section}: Props) {
                defaultMessage='Ignore mentions for @channel, @here and @all'
            />
        );
+    } else if (section === NotificationSections.CHANNEL_AUTO_FOLLOW_THREADS) {
+        return (
+            <FormattedMessage
+                id='channel_notifications.channelAutoFollowThreads'
+                defaultMessage='Auto-follow all new threads in this channel'
+            />
+        );
    }

    return null;
--- a/webapp/channels/src/i18n/en.json
+++ b/webapp/channels/src/i18n/en.json
@@ -2978,6 +2978,10 @@
  "channel_modal.type.public.description": "Anyone can join",
  "channel_modal.type.public.title": "Public Channel",
  "channel_notifications.allActivity": "For all activity",
+  "channel_notifications.channelAutoFollowThreads": "Auto-follow all new threads in this channel",
+  "channel_notifications.channelAutoFollowThreads.help": "When enabled, you will auto-follow all new threads created in this channel unless you unfollow a thread explicitly.",
+  "channel_notifications.channelAutoFollowThreads.off.title": "Off",
+  "channel_notifications.channelAutoFollowThreads.on.title": "On",
  "channel_notifications.globalDefault": "Global default ({notifyLevel})",
  "channel_notifications.ignoreChannelMentions": "Ignore mentions for @channel, @here and @all",
  "channel_notifications.ignoreChannelMentions.help": "When enabled, @channel, @here and @all will not trigger mentions or mention notifications in this channel.",
--- a/webapp/channels/src/packages/mattermost-redux/test/test_helper.ts
+++ b/webapp/channels/src/packages/mattermost-redux/test/test_helper.ts
@@ -453,6 +453,7 @@ class TestHelper {
            mark_unread: 'mention',
            push: 'default',
            ignore_channel_mentions: 'default',
+            channel_auto_follow_threads: 'off',
            ...override,
        };
    };
--- a/webapp/channels/src/utils/constants.tsx
+++ b/webapp/channels/src/utils/constants.tsx
@@ -1009,8 +1009,14 @@ export const IgnoreChannelMentions = {
    DEFAULT: 'default',
 } as const;

+export const ChannelAutoFollowThreads = {
+    ON: 'on',
+    OFF: 'off',
+} as const;
+
 export const NotificationSections = {
    IGNORE_CHANNEL_MENTIONS: 'ignoreChannelMentions',
+    CHANNEL_AUTO_FOLLOW_THREADS: 'channelAutoFollowThreads',
    MARK_UNREAD: 'markUnread',
    DESKTOP: 'desktop',
    PUSH: 'push',
--- a/webapp/channels/src/utils/test_helper.ts
+++ b/webapp/channels/src/utils/test_helper.ts
@@ -155,6 +155,7 @@ export class TestHelper {
            mark_unread: 'all',
            push: 'default',
            ignore_channel_mentions: 'default',
+            channel_auto_follow_threads: 'off',
        };
        const notifyProps = Object.assign({}, defaultNotifyProps, overrideNotifyProps);

--- a/webapp/platform/types/src/channels.ts
+++ b/webapp/platform/types/src/channels.ts
@@ -25,6 +25,7 @@ export type ChannelNotifyProps = {
    mark_unread: 'all' | 'mention';
    push: 'default' | 'all' | 'mention' | 'none';
    ignore_channel_mentions: 'default' | 'off' | 'on';
+    channel_auto_follow_threads: 'off' | 'on';
 };

 export type Channel = {