[Wikitech-ambassadors] Replacing Tidy on Wikimedia wikis, second wave

Subramanya Sastry ssastry at wikimedia.org

Mon Jan 22 19:46:58 UTC 2018

TL;DR
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On January 31, 2018, on ru.wp, sv.wp, fi.wp and he.wp, we are going to
turn off Tidy and switch to the Remex HTML5 parsing library.
Besides those, another 200+ wikis will also be switched away from Tidy
on that day. You can find the list of such wikis at T184656 [1].
Do any of you belong to or know someone active in these communities?
While we've also announced this on Tech News, based on our previous
experience, since we don't anticipate the change to be ground-breaking
for these communities, we think that "spamming" the village pumps
may be not so effective and so we'd appreciate your help in assuring
these wikis that they can contact us @ mw:Help_talk:Extension:Linter [2]
if needed, and that there's plenty of documentation to help with
Linter fixes at mw:Help:Extension:Linter [3].
Thanks!
Background
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In July 2017, we announced [4] our intention to replace Tidy with a
HTML5-based solution on the Wikimedia cluster by the end of June 2018
at the latest. Please refer to that original posting for specifics of
the project and why we are replacing Tidy.
Status of Tidy replacement
--------------------------
Over the last 3 months, we have now replaced Tidy with RemexHTML
on mediawiki, testwiki, nowiki, fawiki, itwiki, dewiki and 170 other
small wikis. [5]
We have approached ruwiki, svwiki, fiwiki, hewiki for replacement this
month based on remaining linter errors and progress those wikis have
been making. We expect to approach other medium and large wikis for
replacement next month.
In addition, for any wiki that has < 10 linter errors in any
high-priority category, we will be replacing Tidy with RemexHTML.
T184656 [1] has the list of wikis that will see this change (this list
includes wikis that have already had Tidy replaced in December).
To be clear, if we notice problems (or if the wiki requests it), we will
revert the change after identifying the source of the problem. If you
notice any incorrect rendering, you can use ?action=parsermigration-edit
to identify if the switch from Tidy actually caused it.
Status of linter fixes
----------------------
We have been publishing weekly stats [6] of changes to linter counts
which shows how wikis have been progressing with making linter fixes.
Based on what we've observed, of the 38 largest wikis, besides the one
that have Tidy replaced already or will get it replaced this month, most
other wikis seem to be making progress, albeit at different rates.
idwiki, viwiki, jawiki, and rowiki haven't seen a lot of activity yet.
Results from pixel diff tests
-----------------------------
We have also been doing weekly test runs to calculate pixel diffs on
about 70K pages which we have sampled from over 50 wikis. To do this,
we generate a screenshot of a page with Tidy and one with RemexHTML,
and compare the renderings while ignoring vertical whitespace shifts.
We generate a numeric score for the diff that tries to be reflective
of the magnitude of differences we are seeing.
Thanks to fixes to pages and our testing infrastructure to more
accurately detect differences, between July 2017 and January 2018,
the percentage of pages that rendered with only vertical whitespace
shifts increased from 91.9% to 94.6%. Similarly, the percentage of
pages that rendered with pixel perfect accuracy went up from
63.2% to 68.3%. For technical reasons related to the testing setup
that I will skip here, 100% for either metric is not achievable.
Summary
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Overall, at the end of January, about 400 of Wikimedia's wikis will
have replaced Tidy.  This includes 7 of the largest wikis.
Linter fixes are also happening on lots of wikis, but some large wikis
could pick up the pace.
We still expect to replace Tidy on all wikis by end of June 2018,
and your cooperation and help with fixing pages identified by the
Linter tool is greatly appreciated.
Subbu,
Manager and Technical Lead,
Parsing Team @ the WMF.
1. https://phabricator.wikimedia.org/T184656
2. https://www.mediawiki.org/wiki/Help_talk:Extension:Linter
3. https://www.mediawiki.org/wiki/Help:Extension:Linter
4. https://www.mediawiki.org/wiki/Talk:Parsing/Replacing_Tidy/FAQ
5. https://phabricator.wikimedia.org/T175706
6. https://www.mediawiki.org/wiki/Parsing/Replacing_Tidy/Linter/Stats
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Erica Litrenta