**Reason**
AddThis service is shutting down on May 31, 2023.
(This task isn't really actionable until then but I'm creating it now given the current slow rate of people processing extension archivals)
**To-do list**
- This task
-- [X] Add maintainers of that extension as subscribers to this task (if they have no apparent Phabricator account, notify them on-wiki or via email if possible and note it here).
-- [ ] Add Phabricator project <#ProjectX> as a tag for this task, and remove #mediawiki-extensions-other/#other-skins as appropriate.
- On-wiki documentation
-- [ ] Archive documentation on `mediawiki.org` (https://www.mediawiki.org/wiki/Extension:AddThis): replace page contents with `{{Archived extension|last revision id before archiving|task=T335463}}`;
-- [ ] If documentation page was translatable, remove `<translate>`, visit Special:PageTranslation, and click "remove from translation" (if you don't have the translation administrator right, ask a [[ https://www.mediawiki.org/wiki/Special:ListUsers/translationadmin | user who does ]]).
-- [ ] Update Wikidata item (https://www.wikidata.org/wiki/Q21676147) associated with documentation page
--- [ ] add statement `Abandonware (Q281039)` to `instance of (P31)` together with qualifier `start time (P580)` = the YYYY-MM-DD date that you decided to archive extension/skin (generally per edit history)
--- [ ] add qualifier `end time (P582)` = the YYYY-MM-DD (same date as above) to `instance of (P31) = MediaWiki extension (Q6805426)/MediaWiki skin (Q21996535)`
- Phabricator
-- [ ] Mark all Phabricator tasks for the extension/skin either Declined or Invalid. Add a comment pointing to this task when doing so for reference.
-- [ ] Archive Phabricator project <#ProjectX> for the extension/skin.
-- [ ] Edit Phabricator project <#ProjectX> description for the extension/skin with a link to this ticket.
- Translatewiki.net/translations
-- [ ] Remove from `translatewiki.net` ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-extensions.txt | groups/MediaWiki/mediawiki-extensions.txt ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-skins.txt | groups/MediaWiki/mediawiki-skins.txt ]]).
- Configuration/tests/integrations/etc.
-- [ ] Remove tests in [[ https://gerrit.wikimedia.org/g/integration/config | integration/config ]] ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/integration/config/+/master/zuul/layout.yaml | zuul/layout.yaml ]]).
-- [ ] Remove manifest/other references from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/vagrant/+/master | mediawiki/vagrant ]] if they exist.
-- [ ] Remove from https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server).
- Repositories
-- [ ] Empty repository, leaving only the README indicating the repo is archived, and referring to this task by URL.
-- [ ] Remove from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/+/master | mediawiki/extensions ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/skins/+/master | mediawiki/skins ]] (along with in `.gitmodules`).
-- [ ] Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task): (https://gerrit.wikimedia.org/g/mediawiki/extensions/AddThis).
-- [ ] Archive the Diffusion repository for the extension/skin: (rEADT).
-- [ ] Delete the GitHub mirror: (https://github.com/wikimedia/mediawiki-extensions-AddThis).