PresenceChannel aims to be a generic system for allow the server, and end-users, to track the number and identity of users performing a specific task on the site. For example, it might be used to track who is currently 'replying' to a specific topic, editing a specific wiki post, etc.
A few key pieces of information about the system:
- PresenceChannels are identified by a name of the format `/prefix/blah`, where `prefix` has been configured by some core/plugin implementation, and `blah` can be any string the implementation wants to use.
- Presence is a boolean thing - each user is either present, or not present. If a user has multiple clients 'present' in a channel, they will be deduplicated so that the user is only counted once
- Developers can configure the existence and configuration of channels 'just in time' using a callback. The result of this is cached for 2 minutes.
- Configuration of a channel can specify permissions in a similar way to MessageBus (public boolean, a list of allowed_user_ids, and a list of allowed_group_ids). A channel can also be placed in 'count_only' mode, where the identity of present users is not revealed to end-users.
- The backend implementation uses redis lua scripts, and is designed to scale well. In the future, hard limits may be introduced on the maximum number of users that can be present in a channel.
- Clients can enter/leave at will. If a client has not marked itself 'present' in the last 60 seconds, they will automatically 'leave' the channel. The JS implementation takes care of this regular check-in.
- On the client-side, PresenceChannel instances can be fetched from the `presence` ember service. Each PresenceChannel can be used entered/left/subscribed/unsubscribed, and the service will automatically deduplicate information before interacting with the server.
- When a client joins a PresenceChannel, the JS implementation will automatically make a GET request for the current channel state. To avoid this, the channel state can be serialized into one of your existing endpoints, and then passed to the `subscribe` method on the channel.
- The PresenceChannel JS object is an ember object. The `users` and `count` property can be used directly in ember templates, and in computed properties.
- It is important to make sure that you `unsubscribe()` and `leave()` any PresenceChannel objects after use
An example implementation may look something like this. On the server:
```ruby
register_presence_channel_prefix("site") do |channel|
next nil unless channel == "/site/online"
PresenceChannel::Config.new(public: true)
end
```
And on the client, a component could be implemented like this:
```javascript
import Component from "@ember/component";
import { inject as service } from "@ember/service";
export default Component.extend({
presence: service(),
init() {
this._super(...arguments);
this.set("presenceChannel", this.presence.getChannel("/site/online"));
},
didInsertElement() {
this.presenceChannel.enter();
this.presenceChannel.subscribe();
},
willDestroyElement() {
this.presenceChannel.leave();
this.presenceChannel.unsubscribe();
},
});
```
With this template:
```handlebars
Online: {{presenceChannel.count}}
<ul>
{{#each presenceChannel.users as |user|}}
<li>{{avatar user imageSize="tiny"}} {{user.username}}</li>
{{/each}}
</ul>
```
This bug was introduced by f66007ec83.
In PostJobsEnqueuer we previously did not fire the after_post_create
event and after_topic_create event for private message topics. This was
changed in the above commit in order to publish message bus messages
for topic tracking state updates. Unfortunately this caused the
NotifyMailingListSubscribers job to be enqueued for all posts including
private messages, and admins and the users involved in the PMs got
emailed the contents of the PMs if they had mailing list mode enabled.
Luckily the impact of this was mitigated by a Guardian#can_see? check
for each mailing list mode user in the NotifyMailingListSubscribers job.
We never want to notify mailing list mode subscribers for private messages
so an early return has been added there, plus the logic in PostJobsEnqueuer
has been fixed, and tests have been added to that class where there were
none before.
There are certain design decisions that were made in this commit.
Private messages implements its own version of topic tracking state because there are significant differences between regular and private_message topics. Regular topics have to track categories and tags while private messages do not. It is much easier to design the new topic tracking state if we maintain two different classes, instead of trying to mash this two worlds together.
One MessageBus channel per user and one MessageBus channel per group. This allows each user and each group to have their own channel backlog instead of having one global channel which requires the client to filter away unrelated messages.
This adds a few different things to allow for direct S3 uploads using uppy. **These changes are still not the default.** There are hidden `enable_experimental_image_uploader` and `enable_direct_s3_uploads` settings that must be turned on for any of this code to be used, and even if they are turned on only the User Card Background for the user profile actually uses uppy-image-uploader.
A new `ExternalUploadStub` model and database table is introduced in this pull request. This is used to keep track of uploads that are uploaded to a temporary location in S3 with the direct to S3 code, and they are eventually deleted a) when the direct upload is completed and b) after a certain time period of not being used.
### Starting a direct S3 upload
When an S3 direct upload is initiated with uppy, we first request a presigned PUT URL from the new `generate-presigned-put` endpoint in `UploadsController`. This generates an S3 key in the `temp` folder inside the correct bucket path, along with any metadata from the clientside (e.g. the SHA1 checksum described below). This will also create an `ExternalUploadStub` and store the details of the temp object key and the file being uploaded.
Once the clientside has this URL, uppy will upload the file direct to S3 using the presigned URL. Once the upload is complete we go to the next stage.
### Completing a direct S3 upload
Once the upload to S3 is done we call the new `complete-external-upload` route with the unique identifier of the `ExternalUploadStub` created earlier. Only the user who made the stub can complete the external upload. One of two paths is followed via the `ExternalUploadManager`.
1. If the object in S3 is too large (currently 100mb defined by `ExternalUploadManager::DOWNLOAD_LIMIT`) we do not download and generate the SHA1 for that file. Instead we create the `Upload` record via `UploadCreator` and simply copy it to its final destination on S3 then delete the initial temp file. Several modifications to `UploadCreator` have been made to accommodate this.
2. If the object in S3 is small enough, we download it. When the temporary S3 file is downloaded, we compare the SHA1 checksum generated by the browser with the actual SHA1 checksum of the file generated by ruby. The browser SHA1 checksum is stored on the object in S3 with metadata, and is generated via the `UppyChecksum` plugin. Keep in mind that some browsers will not generate this due to compatibility or other issues.
We then follow the normal `UploadCreator` path with one exception. To cut down on having to re-upload the file again, if there are no changes (such as resizing etc) to the file in `UploadCreator` we follow the same copy + delete temp path that we do for files that are too large.
3. Finally we return the serialized upload record back to the client
There are several errors that could happen that are handled by `UploadsController` as well.
Also in this PR is some refactoring of `displayErrorForUpload` to handle both uppy and jquery file uploader errors.
* FIX: Clear stale status of reloaded reviewables
Navigating away from and back to the reviewables reloaded Reviewable
records, but did not clear the "stale" attribute.
* FEATURE: Show user who last acted on reviewable
When a user acts on a reviewable, all other clients are notified and a
generic "reviewable was resolved by someone" notice was shown instead of
the buttons. There is no need to keep secret the username of the acting
user.
Currently when bulk-awarding a badge that can be granted multiple times, users in the CSV file are granted the badge once no matter how many times they're listed in the file and only if they don't have the badge already.
This PR adds a new option to the Badge Bulk Award feature so that it's possible to grant users a badge even if they already have the badge and as many times as they appear in the CSV file.
This PR fixes a couple of issues related to group SMTP:
1. When running the group SMTP job, we were exiting early if the email was for the OP because of an IMAP race condition. However this causes issues when replying as a new topic for an existing SMTP topic, as the recipient does not get the OP email which can cause threading problems.
2. When sending emails for a new topic spun out like the issue in 1., we are not maintaining the original subject/topic title because that is based on the incoming email record, which we were not doing because the group SMTP email was never sent because of issue 1.
There was an issue with the TopicTimerEnqueuer where any timer
that failed to enqueue_typed_job with an error would prevent
all other pending timers after the one that errored from running.
To mitigate this we just capture the error and log it (so we can
still fix it if needed for bug crushing) and proceed with the
rest of the timer enqueues.
The commit https://github.com/discourse/discourse/pull/13544 highlighted
this issue originally in hosted sites.
<!-- NOTE: All pull requests should have tests (rspec in Ruby, qunit in JavaScript). If your code does not include test coverage, please include an explanation of why it was omitted. -->
Use the `sidekiq_retry_in` code from Jobs::UserEmail in group SMTP. Also we don't need to keep `seconds_to_delay` -- sidekiq uses the default delay calculation if you return 0 or nil from the block. See 3330df0ee3/lib/sidekiq/job_retry.rb (L216-L234) for sidekiq default retry delay logic.
I experimented with extracting this into a concern or a module, but `sidekiq_retry_in` is quite magic and it would not allow me to abstract away into a module that calls some method specificall in the child job class.
I would love to write tests for this, but it does not seem possible (not sure if its because of our test
setup) to write tests that test sidekiq's retry capability, and I am not sure if we should be anyway. Initial addition
to UserEmail did not test this functionality
d224966a0e
Skip group SMTP email (and add log) if:
* topic is deleted
* post is deleted
* smtp has been disabled for the group
Skip without log if:
* enable_smtp site setting is false
* disable_emails site setting is yes
Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>
This PR backtracks a fair bit on this one https://github.com/discourse/discourse/pull/13220/files.
Instead of sending the group SMTP email for each user via `UserNotifications`, we are changing to send only one email with the existing `Jobs::GroupSmtpEmail` job and `GroupSmtpMailer`. We are changing this job and mailer along with `PostAlerter` to make the first topic allowed user the `to_address` for the email and any other `topic_allowed_users` to be the CC address on the email. This is to cut down on emails sent via SMTP, which is subject to daily limits from providers such as Gmail. We log these details in the `EmailLog` table now.
In addition to this, we have changed `PostAlerter` to no longer rely on incoming email email addresses for sending the `GroupSmtpEmail` job. This was unreliable as a user's email could have changed in the meantime. Also it was a little overcomplicated to use the incoming email records -- it is far simpler to reason about to just use topic allowed users.
This also adds a fix to include cc_addresses in the EmailLog.addressed_to_user scope.
* FEATURE: Staff can receive pending user reminders more frequently.
We now express the "pending_users_reminder_delay" in minutes instead of hours so staff can have finer control over the delay.
We need to keep in mind that the reminders could still take up to 20 minutes, even when using a lower value. We send them from a scheduled job.
* Migrate to a new site setting for the reminders delay
ATM it only implements server side of it, as my need is for automation purposes. However it should probably be added in the UI too as it's unexpected to have pinned_until and no bannered_until.
Anonymizing a user changed their email address, destroyed all
associated InvitedUser records, but did not destroy the invites
associated to user's email.
When we call Bookmark.cleanup! we want to make sure that
topic_user.bookmarked is updated for topics linked to the
bookmarks that were deleted. Also when PostDestroyer calls
destroy and recover. We have a job for this already --
SyncTopicUserBookmarked -- so we just utilize that.
Subclasses must call #delete_user_actions inside build_actions to support user deletion. The method adds a delete user bundle, which has a delete and a delete + block option. Every subclass is responsible for implementing these actions.
Notifying about a tag change sometimes resulted in loading a large
number of users in memory just to perform an exclusion. This commit
prefers to do inclusion (i.e. instead of exclude users X, do include
users in groups Y) and does it in SQL to avoid fetching unnecessary
data that is later discarded.
The previous commits removed reviewables leading to a bad user
experience. This commit updates the status, replaces actions with a
message and greys out the reviewable.
Over the years we accrued many spelling mistakes in the code base.
This PR attempts to fix spelling mistakes and typos in all areas of the code that are extremely safe to change
- comments
- test descriptions
- other low risk areas
Email change requests are never deleted no matter if they completed
successfully or not. The abandoned requests have the disadvantage of
showing up as unconfirmed emails in user's preferences page.
Recalculating a ReviewableFlaggedPost's score after rejecting or ignoring it sets the score as 0, which means that we can't find them after reviewing. They don't surpass the minimum priority threshold and are hidden.
Additionally, we only want to use agreed flags when calculating the different priority thresholds.
* FEATURE: add support for like webhooks
Add support for like webhooks. Webhook events only send on user membership
in the defined webhook group filters.
This also fixes group webhook events, as before this was never used, and
the logic was not correct.
This filter hides reviewables with a score lower than the "reviewable_low_priority_threshold" setting. We only use reviewables that already met this threshold to calculate the Medium and High priority filters.
It used to check if an upload record exists, which is wrong because an
invalid upload record exists even if the upload was not created.
The other improvement is a better log message.
Previously watched words ignored topic titles when applying auto tagging rules.
Also copy has been improved to reflect how the system behaves.
The text hints that we are only watching first post now
scopes are incredibly annoying to preload, simply adding :user_emails is not
enough.
Instead of relying on scopes simply iterate through user_emails which is
properly preloaded.
This removes 2 * N+1 when generating user reports.
When posts are moved from one topic to another, the `topic_user.bookmarked` column for all users in the new and the old topic needs to be resynced, for example because a user bookmarks post 12 in topic 1, then it is moved to topic 2, the topic_user record for topic 1 should no longer be bookmarked. A background job has been added to sync the column for a specified topic, or for no topic at all, which does it for all topics like the migration.
Also includes a migration that we have run in the past to fix bad data.
----
This has been addressed in other places in the past:
https://github.com/discourse/discourse/pull/10211https://github.com/discourse/discourse/pull/10188
When bulk inviting, the uploaded CSV file may contain wrong values for
the user fields. This tries to automatically correct them by finding
the most similar option (by ignoring the case).
Admins can use bulk invites to pre-populate user fields. The imported
CSV file must have a header with "email" column (first position) and
names of the user fields (exact match).
Under the hood, the bulk invite will create staged users and populate
the user fields of those.
The user mailing list mode continued to be silently enabled and
UserEmail job checked just that ignoring site setting
disable_mailing_list_mode.
An additional migrate was added to set disable_mailing_list_mode
to false if any users enabled the mailing list mode already.
Currently the process of adding a custom image to badge is quite clunky; you have to upload your image to a topic, and then copy the image URL and pasting it in a text field. Besides being clucky, if the topic or post that contains the image is deleted, the image will be garbage-collected in a few days and the badge will lose the image because the application is not that the image is referenced by a badge.
This commit improves that by adding a proper image uploader widget for badge images.
It was used both when inviting from a topic page and when creating
invites with "Send to topic on first login", while it should be used
only in the former case.
Onebox content may only be resolved during the process_post job. Onebox content could change the content of the excerpt, so we need to make sure the excerpt is updated accordingly.
The urls that we generate for mobile post notifications don't take into
account the subfolder url if a site happens to have one configured. When
this happens when you tap on a new mobile notification it takes you to
a url that doesn't work because it is missing the subfolder portion.
I honestly think this should be handled in the Post model like we do
with the Topic model. `Post.url` should know how to handle subfolder
installs, but that seemed like a very risky change because there are
lots of other places in the codebase where we tack on the base_path and
I didn't want to risk duplicating it.
I also found a small typo in the topics controller spec.
The user interface has been reorganized to show email and link invites
in the same screen. Staff has more control over creating and updating
invites. Bulk invite has also been improved with better explanations.
On the server side, many code paths for email and link invites have
been merged to avoid duplicated logic. The API returns better responses
with more appropriate HTTP status codes.
* FIX: Reduce the time_read threshold to one minute.
Five minutes is too much and could fill the queue with false positives.
* Update spec/jobs/enqueue_suspect_users_spec.rb
Co-authored-by: Arpit Jalan <arpit@techapj.com>
Co-authored-by: Arpit Jalan <arpit@techapj.com>
Completing the discobot tutorial gives you ~3m of reading time, so we set the limit at 5m. Additionally, we use an "OR" clause to cover the case when you just scroll through a single topic.
Original PR was reverted because of broken migration https://github.com/discourse/discourse/pull/12058
I fixed it by adding this line
```
AND topics.id IN(SELECT id FROM topics ORDER BY created_at DESC LIMIT :max_new_topics)
```
This time it is left joining a limited amount of topics. I tested it on few databases and it worked quite smooth
Follow up https://github.com/discourse/discourse/pull/11968
Dismiss all new topics using the same DismissTopicService. In addition, MessageBus receives exact topic ids which should be marked as `seen`.
The bug was mentioned on meta https://meta.discourse.org/t/users-are-seeing-handling-of-unhandled-tag-again/155367
It was related to users who are watching a specific topic. In that case, when the hidden tag was added or removed to the topic they were notified by `NotifyTagChangeJob`.
That job should take hidden tags into consideration. If all changed tags are in a hidden group, it should exclude user not belong to that group.
At the same time, if visible to anyone tag is added or removed users watching topic should be notified.
The 'Discourse SSO' protocol is being rebranded to DiscourseConnect. This should help to reduce confusion when 'SSO' is used in the generic sense.
This commit aims to:
- Rename `sso_` site settings. DiscourseConnect specific ones are prefixed `discourse_connect_`. Generic settings are prefixed `auth_`
- Add (server-side-only) backwards compatibility for the old setting names, with deprecation notices
- Copy `site_settings` database records to the new names
- Rename relevant translation keys
- Update relevant translations
This commit does **not** aim to:
- Rename any Ruby classes or methods. This might be done in a future commit
- Change any URLs. This would break existing integrations
- Make any changes to the protocol. This would break existing integrations
- Change any functionality. Further normalization across DiscourseConnect and other auth methods will be done separately
The risks are:
- There is no backwards compatibility for site settings on the client-side. Accessing auth-related site settings in Javascript is fairly rare, and an error on the client side would not be security-critical.
- If a plugin is monkey-patching parts of the auth process, changes to locale keys could cause broken error messages. This should also be unlikely. The old site setting names remain functional, so security-related overrides will remain working.
A follow-up commit will be made with a post-deploy migration to delete the old `site_settings` rows.
This PR allows entering a float value for topic timers e.g. 0.5 for 30 minutes when entering hours, 0.5 for 12 hours when entering days. This is achieved by adding a new column to store the duration of a topic timer in minutes instead of the ambiguous both hours and days that it could be before.
This PR has ommitted the post migration to delete the duration column in topic timers; it will be done in a subsequent PR to ensure that no data is lost if the UPDATE query to set duration_mintues fails.
I have to keep the old keyword of duration in set_or_create_topic_timer for backwards compat, will remove at a later date after plugins are updated.
This is a try to simplify logic around dismiss new topics to have one solution to work in all places - dismiss all-new, dismiss new in a specific category or even in a specific tag.
* FIX: In FastImage 2.2.2 an error is raised with a `nil` path
Sometimes Discourse.store.path_for would return `nil`, which the job
handled gracefully before, but raises an error with the new version of
the gem.
Note the logic of this job is a bit awkward since it depends on `nil`
being a string, but at least now it's no longer filling logs with
errors.
* Update app/jobs/onceoff/fix_invalid_gravatar_uploads.rb
Co-authored-by: Bianca Nenciu <nbianca@users.noreply.github.com>
Co-authored-by: Bianca Nenciu <nbianca@users.noreply.github.com>
This PR revamps the topic timer UI, using the time shortcut selector from the bookmark modal.
* Fixes an issue where the duration of hours/days after last reply or auto delete replies was not enforced to be > 0
* Fixed an issue where the timer dropdown options were not reloaded correctly if the topic status changes in the background (use `MessageBus` to publish topic state in the open/close timer jobs)
* Moved the duration input and the "based on last post" option from the `future-date-input` component, as it was only used for topic timers. Also moved out the notice that is displayed which was also only relevant for topic timers.
Lots of changes but it's mostly a refactoring.
The interesting part that was fix are the 'load_problem_<model>_ids' methods.
They will now return records with no search data associated so they can be properly indexed for the search.
This "bad" state usually happens after a migration.
This adds a new table UserNotificationSchedules which stores monday-friday start and ends times that each user would like to receive notifications (with a Boolean enabled to remove the use of the schedule). There is then a background job that runs every day and creates do_not_disturb_timings for each user with an enabled notification schedule. The job schedules timings 2 days in advance. The job is designed so that it can be run at any point in time, and it will not create duplicate records.
When a users saves their notification schedule, the schedule processing service will run and schedule do_not_disturb_timings. If the user should be in DND due to their schedule, the user will immediately be put in DND (message bus publishes this state).
The UI for a user's notification schedule is in user -> preferences -> notifications. By default every day is 8am - 5pm when first enabled.
This should make it easier to track down how the incoming email was created, which is one of four locations:
The POP3 poller (which picks up reply via email replies)
The admin email controller #handle_mail (which is where hosted mail is sent)
The IMAP sync tool
The group SMTP mailer, which sends emails when replying to IMAP topics, pre-emptively creating IncomingEmail records to avoid double syncing
Moves the topic timer jobs from being scheduled ahead of time with enqueue_at to a 5 minute scheduled run like bookmark reminders, in a new job called Jobs::EnqueueTopicTimers. Backwards compatibility is maintained by checking if an existing topic timer job is enqueued in sidekiq for the timer, and if it is not running it inside the new job.
The functionality to close/open a topic if it is in the opposite state still remains in the after_save block of TopicTimer, with further commentary, which is used for Open/Close Temporarily.
This also removes the ensure_consistency! functionality of topic timers as it is no longer needed; the new job will always pick up the timers because they are not stored in a fragile state of sidekiq.
This adds a safe default to not process pop3 emails when the pop3 polling option is set up that are > 1 week old. This is to avoid the situation where an older mailbox is used, which causes us to go and process all emails in that mailbox, sending out error emails to the senders of emails which cannot be parsed successfully.
Feature for `Must Approve Users` setup. When a user is rejected, a staff member can optionally set a reason for audit purposes. In addition, feedback email can be sent to the user.
Meta: https://meta.discourse.org/t/account-rejection-email/103112/8
Splits the `ToggleTopicClosed` job into two distinct `OpenTopic` and `CloseTopic` jobs to make the code clearer. The old job cannot be deleted yet because of outstanding sidekiq schedules, so a todo has been added to do so later this year.
Also replaced mentions of `topic_status_update` with `topic_timer` in some files, because the `topic_status_update` model is obsolete and replaced by topic timer.
Added some shortcut methods for checking if a topic is open/whether a user can change an open topic.
* DEV: TopicTrackingState calls should happen in the background
It was observed that calling TopicTrackingState on popular topics could result in a large number of calls to redis, resulting in slow response times when posting replies.
These calls should be moved to a background job.
* DEV: PostUpdateTopicTrackingState should execute on default queue
Fixes a rare race condition causing the `Imap::Sync` class to create an incoming email and associated post/topic, which then kicks off the PostAlerter to notify others in the PM about a reply in the topic, but for the OP which is not necessary (because the person emailing the IMAP inbox already knows about the OP). Basically, we should never be sending the group SMTP email for the first post in a topic.
Also in this PR:
* Custom attribute accessors for the to/from/cc addresses on `IncomingEmail`, to parse them from an array to a joined string so the logic for this is only in one place.
* Store extra detail against the `IncomingEmail` created in `GroupSmtpMailer`
* regex test Mail header Reply-To as string instead of Field, which fixes `warning: deprecated Object#=~ is called on Mail::Field; it always returns nil`
* Add DEBUG_IMAP to log all IMAP logs as warnings for easier debugging
* Changed the Rails logging to `ImapSyncLog` in the `GroupSmtpMailer`
osts from topics with 'auto delete replies timer' with more than
skip_auto_delete_reply_likes likes will no longer be deleted. If 0,
all posts will be deleted.
My initial implementation didn't consider this case. We should skip imported users if the "imported_id" field is present, even if there're other custom fields.
This commit is dedicated to https://twitter.com/FiloSottile/status/1335666583126073354 for reminding me that like timestamps are valuable data.
Likes additionally include the topic_id and post_number of the acted post, to aid in analysis. Flag export does not include the disposition by staff.
When jobs are enqueued inside a transaction, it's possible that they will be executed before the necessary data is available in the database. This commit ensures all jobs are enqueued in an ActiveRecord after_commit hook.
One potential downside here is if the job fails to enqueue, the transaction will no longer be aborted. However, the chance of that happening is reasonably low, and the impact is significantly lower than the current issue where jobs are scheduled before their data is ready.
The `enqueue_jobs` is not correctly post-processing the post since the
post is being created inside a transaction block. This commit explicitly
enqueues the job outside transaction block.
When the linked topic is created we'll not hardcode the topic title and
let onebox work its magic instead so that the title can be updated
automatically.
- IgnoredUser records should all now have an expiring_at value. This commit enforces that in the DB, and fixes any corrupt rows
- Changes to the ignored user list are now handled by the `/u/{username}/notification_level` endpoint. This allows setting expiration dates on the ignore. This commit removes the old logic for saving a list of usernames in the user preferences.
- Many specs were calling `IgnoredUser.create`. This commit changes them to use `Fabricate(:ignored_user)` for consistency
b8c676e7 added the 'forever' option to the UI, and this is correctly stored in the database. However, we had a hard-coded limit of 4 months in the cleanup job. This commit removes the limit, so ignores can last forever.
This commit adds a site setting `auto_close_topics_create_linked_topic`
which when enabled works in conjunction with `auto_close_topics_post_count`
setting and creates a new linked topic for the topic just closed.
The auto-created new topic contains a link for all the previous topics
and the topic titles are appended with `(Part {n})`.
The setting is enabled by default.