The package needs to be installed (sudo apt-get install hhvm-tidy) and tidy.so needs to be added to hhvm.dynamic_extensions in the config file. This is a really new config change. Before we always shelled out for running tidy.

The package is installed and configured via the puppet ::hhvm class:

integration-slave1009:~$ apt-cache policy hhvm-tidy
hhvm-tidy:
  Installed: 0.1-3
  Candidate: 0.1-3
  Version table:
 *** 0.1-3 0
       1001 http://apt.wikimedia.org/wikimedia/ trusty-wikimedia/main amd64 Packages
        100 /var/lib/dpkg/status
     0.1-1 0
       1001 http://apt.wikimedia.org/wikimedia/ trusty-wikimedia/universe amd64 Packages

$ grep dynamic_extensions /etc/hhvm/php.ini 
hhvm.dynamic_extensions[fss.so] = fss.so
hhvm.dynamic_extensions[luasandbox.so] = luasandbox.so
hhvm.dynamic_extensions[tidy.so] = tidy.so
hhvm.dynamic_extensions[wikidiff2.so] = wikidiff2.so
$

Maybe it is not loaded properly.

There's a bug in MWTidy I think. It's checking for the tidy class, but since the HHVM implementation does not provide that class and instead provides the procedural interface as explained in the if ( wfIsHHVM() ) block starting around line 260.

Change 178872 had a related patch set uploaded (by BryanDavis):
hhvm: Check for tidy function instead of class

https://gerrit.wikimedia.org/r/178872

Patch-For-Review

Change 178872 merged by jenkins-bot:
hhvm: Check for tidy function instead of class

https://gerrit.wikimedia.org/r/178872

HtmlFormatterTest.php and TidyTest.php both pass locally for me on my mw-vagrant instance now. They seem to still be failing in Jenkins however. Is the tidy.so version there possibly out of date? I have hhvm-tidy 0.1-3 installed locally.

In T78166#838359, @bd808 wrote:

HtmlFormatterTest.php and TidyTest.php both pass locally for me on my mw-vagrant instance now. They seem to still be failing in Jenkins however. Is the tidy.so version there possibly out of date? I have hhvm-tidy 0.1-3 installed locally.

@hashar's apt-cache policy hhvm-tidy output in T78166#837937 seems to match. The failed test I'm looking at is https://integration.wikimedia.org/ci/job/mediawiki-core-regression-hhvm-master/2908/#showFailuresLink which ran on integration-slave1006 but it has the same apt-cache policy hhvm-tidy output and shows tidy.so in /etc/hhvm/php.ini as well.

The first time the tests fails is https://integration.wikimedia.org/ci/job/mediawiki-core-regression-hhvm-master/2902/testReport/ at noon. Around that time I got a puppet change to ensure hhvm package is the latest and that instance had: 2014-12-10 11:07:25 upgrade hhvm:amd64 3.3.0+dfsg1-1+wm4 3.3.0+dfsg1-1+wm5

I noticed a change in mediawiki/core which "Simplify MWTidy" https://gerrit.wikimedia.org/r/#/c/176862/ I rebuild it and got the same failure.

But taking the commit before and rebuilding it pass TidyTest::testTidyWrapping.testTidyWrapping:
https://integration.wikimedia.org/ci/job/mediawiki-core-regression-hhvm-master/2913/testReport/

Though HtmlFormatterTest::testTransform.testTransform fails with:

HtmlFormatterTest::testTransform with data set #0 ('<img src="/foo/bar.jpg" alt="Blah"/>', '', array('<img src="/foo/bar.jpg" alt="Blah">'), Closure$HtmlFormatterTest::getHtmlData;976590306)
MWException: MWTidy::clean: error text return from HHVM tidy is not supported

:(