The ResourceLoader-code that existed for printable and handheld parmeters looked unused, but I was wrong. It is used in the following way:

• Sidebar links to "Printable view" (example: index.php?title…&printable=yes)
• OutputPage arbirtrarily forwards printable parameter to ResourceLoader for use in any of its embedded load.php URLs.
• There is nothing in ResourceLoader or ResourceLoaderContext that reads or varies its logic by this in any way. Hence my assumption that it is only a Skin-level thing.
• But behold, when ResourceLoader::makeModuleResponse is concatenating the result of various modules in the main styles-only request, there is a call to OutputPage::transformCssMedia which gets its hands on the internal RL state (after reading and processing of LESS/CSS, but before concatenating), and changes any top-level media block (those defined in Resources.php/skin.json) for "print" to "" so that it applies on screen, and discards any top-level block for "only screen".
  • It does this based on reading out wgRequest directly, thus bypassing ResourceLoaderContext, but relying on wgRequest working inside a load.php request, kind of.

Pratically speaking, this means:

• mediawiki.toc.styles is loaded in a way where its screen.less is removed and print.css unwrapped in its stead.
• mediawiki.page.gallery.styles is loaded with its print.css unwrapped.
• ResourceLoaderSkinModule loads legacy-print unwrapped and omits most of its other stuff.

That's pretty much it. It does potentially have other random impact depending on how extensions have written their styles. I imagine they generally don't have print.css as a separate extension.json entry with "print" as media key though, so I assume the above is the 99% that matters.

What are the blockers for deprecating this in 1.35?
This is causing some real problems in the desktop improvements project - the new Vector breaks in this mode (see T253842) and we currently don't have plans to fix that.

Change 610323 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/core@master] Deprecate printableversion=yes

https://gerrit.wikimedia.org/r/610323

I propose adding a banner like so:

and changing the sidebar link as part of the 1.35 release.

As we update Vector we have no interest in fixing the following:

Given this is a performance recommendation, I think now is the time to deprecate this.

@ovasileva super sorry for the late sprint entry but given my recent analysis of the print mode in T253842, I think it's essential we set the intention that this is not supported and aim for a deprecation in for 1.35 (which is cut on 14 July 2020 at 02:00 UTC.)

In T167956#6291623, @Jdlrobson wrote:

@ovasileva super sorry for the late sprint entry but given my recent analysis of the print mode in T253842, I think it's essential we set the intention that this is not supported and aim for a deprecation in for 1.35 (which is cut on 14 July 2020 at 02:00 UTC.)

That sounds good, but let me discuss it with Szymon as well - will get back to you later today

@Jdlrobson - does this mean that the link would still exist but it would just trigger the browser print (i.e. all we're removing is the page like https://en.wikipedia.org/w/index.php?title=1937_Fox_vault_fire&printable=yes)

In T167956#6293378, @ovasileva wrote:

@Jdlrobson - does this mean that the link would still exist but it would just trigger the browser print (i.e. all we're removing is the page like https://en.wikipedia.org/w/index.php?title=1937_Fox_vault_fire&printable=yes)

The link would exist yes and point to browser print. If there is no JavaScript it will be hidden. The page would also exist but have a banner saying it is no longer supported.

In T167956#6293378, @ovasileva wrote:

@Jdlrobson - does this mean that the link would still exist but it would just trigger the browser print (i.e. all we're removing is the page like https://en.wikipedia.org/w/index.php?title=1937_Fox_vault_fire&printable=yes)

Note that the "Printable version" link already triggers the browser print in production today.

The printable=yet URL comes in when e.g. we're in Grade C mode, or when one chooses to share the link or open it in a new tab. Those capabilities would no longer be supported.

Blocked on review from @Krinkle. I will backport when that's done.

Change 613171 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/core@REL1_35] Deprecate printableversion=yes

https://gerrit.wikimedia.org/r/613171

Change 610323 merged by jenkins-bot:
[mediawiki/core@master] Deprecate printableversion=yes

https://gerrit.wikimedia.org/r/610323

Change 613171 merged by jenkins-bot:
[mediawiki/core@REL1_35] Deprecate printableversion=yes

https://gerrit.wikimedia.org/r/613171

@Jdlrobson, I tried a few Grade C browsers. I could not get the "Printable version" link to appear even with Javascript enabled. Is this as expected? Here is IE 9

Yep expected! If there's no link showing that's good

The bits of this that need to be done by 1.35 are now done (and merged into REL1_35), right? In that case, maybe let's drop the tag saying this is a blocker for 1.35 for the rest of the work?

Made a new task for the actual removal since we're doing some QA right now. T259141

Thanks!

Test Result - Beta

Status: ✅ PASS
Environment: beta
OS: macOS Catalina
Browser: Chrome
Device: MBP
Emulated Device: NA
Test Artifact(s):

QA steps

✅ AC1: The printable=yes URL comes in when e.g. we're in Grade C mode. The page would also exist but have a banner saying it is no longer supported.
Here is IE 9

I linked mw:Help:Printing to this ticket. It was already mentioned that this feature was deprecated but there was an info like "It appears a warning box".