Info to potentially link to: https://www.mediawiki.org/wiki/Reading/Web/PDF_Functionality

Docs to update (e.g. add {{TNT|historical}} or {{TNT|obsolete}}:
https://wikitech.wikimedia.org/wiki/OCG
https://www.mediawiki.org/wiki/Offline_content_generator
https://www.mediawiki.org/wiki/Offline_content_generator/Bundle_format
https://www.mediawiki.org/wiki/Offline_content_generator/status
https://www.mediawiki.org/wiki/Offline_content_generator/print-on-demand_service
https://www.mediawiki.org/wiki/Offline_content_generator/Architecture
https://www.mediawiki.org/wiki/Offline_content_generator/metabook.json
https://www.mediawiki.org/wiki/Wikimedia_Services#Services_owned_by_other_teams
https://www.mediawiki.org/wiki/Reading/Web/Projects#Offline_Content_Generation_and_Printing
https://www.mediawiki.org/wiki/Extension:Collection
https://www.mediawiki.org/wiki/Extension:Collection/OfflineContentGenerator

As already announced in Tech News, OfflineContentGenerator (OCG) will not be used anymore after October 1st, 2017 on Wikimedia sites. OCG will be replaced by Electron. You can read more on mediawiki.org.

@Aklapper with regards to bugs - the plan is to go through them and see if they exist in the new service (and transfer them over).
If helpful I think you can archive the OCG project. They should all be tagged with Proton (and if not should be).

In T161312#3832142, @Jdlrobson wrote:

If helpful I think you can archive the OCG project. They should all be tagged with Proton (and if not should be).

@Jdlrobson: 117 open tasks in OCG* projects but not in Proton: https://phabricator.wikimedia.org/maniphest/query/zn_UULSWfKEb/#R
I don't want to make things on the Proton workboard more messy than needed so I won't mass-tag them (but if you explicitly want me to, I will, of course!).

@ovasileva would be most appropriate to help with deciding what to do here ^

@ovasileva: Any opinions / feedback on how to proceed here?

@Aklapper - we're currently identifying next steps on OCG tasks/book creation. We're planning on making an announcement this week after which we'll be ready to begin clearing these out - most of them will likely be closed.

One year later, to allow average humans to understand the situation around PDFs, I'm simply going to drop my notes here (Partially quoting Tgr from T172488). Someone feel free to correct me.

• Currently, Proton is a HTML to PDF renderer service that uses a headless Chromium process remote-controlled by Puppeteer.
• Currently, Tasks about the PDF rendering functionality go to PDF-Rendering.
• Currently, Collection is only used for "Create a book", not "Download as PDF" (and doesn't offer any actual rendering, just passes data to PediaPress).
  • Currently, it's unclear to me which project handles the actual rendering after choosing to "Create a book".
• Legacy: ElectronPdfRenderer (tracked under Electron-PDFs) is being undeployed as of 2019. See T226675 and T210651.
• Legacy: OCG-General, OCG-PDFRenderer, OfflineContentGenerator are deprecated. OCG was turned off in 2017 (the feature-parity task T150871 is still open). OCG still has many open tasks to clean up.

In T161312#5345340, @Aklapper wrote:

• Currently, Tasks about the PDF rendering functionality go to PDF-Rendering.

Note that, with PDFs being generated by a headless browser, PDF issues might be caused anywhere between Proton, the configuration (fonts etc.) of the machine running Proton, the MediaWiki print CSS, and the HTML generated by various extensions. The first is tracked under Proton, the last two under PDF-Rendering (and machine config under both, I guess).

Currently, it's unclear to me which project handles the actual rendering after choosing to "Create a book".

There is no option to render books as PDF, you can only buy them as physical books. AIUI PediaPress plans to provide PDFs eventually, via the mwlib library they maintain (which has its own issue tracker on Github).
Alternatively you can save the book definition as a wiki page and use the volunteer-maintained MediaWiki2LaTeX service to maintain it. The bug tracker for that is Dirk's talk page, I think.

Legacy: ElectronPdfRenderer (tracked under Electron-PDFs) is being undeployed as of 2019.

ElectronPdfRenderer is a MediaWiki extension that displays the "Download as PDF" link, which goes to a special page (Special:ElectronPdf - see T224985 about that) , where you can set some basic parameters, and then it will give you a download link, which used to be a link to the Electron service (which the browser could directly download from). Electron is being (has been, for the most part) undeployed; ElectronPdfRenderer now links to Proton. (It's really the same link, the actual routing is done by RESTBase. This allowed us to run Electron and Proton in parallel for a testing period.) The name is pretty confusing, but allegedly, renaming extensions is hard.

Big thanks to Tgr for taking the time to explain the stack! I edited the project descriptions of Proton, PDF-Rendering and Electron-PDFs accordingly.

In T161312#3850230, @Jdlrobson wrote:

@ovasileva would be most appropriate to help with deciding what to do here ^

@ovasileva: Excluding tasks with { PDF-Rendering | Proton | Electron-PDFs }, there are 87 open OCG tickets: https://phabricator.wikimedia.org/maniphest/query/0vc8hUlNgNuX/#R . The question is what to do with them. Mass-ask reporters to check if still an issue on Wikimedia sites / close if no reply?
Happy to help clean up, but need input. A quick "Nobody cares anymore about OCG tasks, go ahead." could be an answer, for example.
(Note to myself: A bunch of Collection tasks might also welcome triage.)