Setting up Arcanist for Mozilla development on Windows
2 min read

Setting up Arcanist for Mozilla development on Windows

Note: Since I first published this, Mozilla have created a Windows specific guide to address this same topic. I encourage people to use Mozilla's guide -- my original guide was intended to provide a stop gap while waiting for something like the above.

Mozilla is rolling out Phabricator as part of our tooling. However, at the time of writing I was unable to find a straight forward setup to get the Phabricator tooling playing nice on Windows with MozillaBuild.

Right now there are a couple of separate threads around how to interact with Phabricator on Windows:

However, I have stuff waiting for me on Phabricator that I'd like to interact with now, so let's get a work around in place! I started with the Arcanist windows steps, but have adapted them to a MozillaBuild specific environment.


Arcanist requires PHP. Grab a build from here. The docs for Arcanist indicate the type of build doesn't really matter, but I opted for a thread safe one because that seems like a nice thing to have.

I installed PHP outside of my MozillaBuild directory, but you can put it anywhere. For the sake of example, my install is in C:\Patches\Php\php-7.2.6-Win32-VC15-x64.

We need to enable the curl extension: in the PHP install dir copy php.ini-development to php.ini and uncomment (by removing the ;) the extension=curl line.

Finally, enable PHP to find its extension by uncommenting the extension_dir = "ext" line. The Arcanist instructions suggest setting a fully qualified path, but I found a relative path worked fine.


Create somewhere to store Arcanist and libphutil. Note, these need to be located in the same directory for arc to work.

$ mkdir somewhere/
$ cd somewhere/
somewhere/ $ git clone
somewhere/ $ git clone

For me this is C:\Patches\phacility\.

Wire everything into MozillaBuild

Since I want arc to be usable in MozillaBuild until this work around is no longer required, we're going to modify start up settings. We can do this by changing ...mozilla-build/msys/etc/profile.d/ and adding to the PATH already being constructed. In my case I've added that paths mentioned earlier, but with MSYS syntax: /c/Patches/Php/php-7.2.6-Win32-VC15-x64:/c/Patches/phacility/arcanist/bin:.

Now arc should run inside newly started MozillaBuild shells.


We still need credentials in order to use arc with mozilla-central. For this to work we need a Phabricator account, see here for that. After that's done, in order to get your credentials run arc install-certificate, navigate to the page as instructed and copy your API key back to the command line.

Other problems

There was an issue with the evolve Mercurial extension the would cuase Unknown Mercurial log field 'instability'!. This should now be fixed in Arcanist. See this bug for more info.

Finally, I had some issues with arc diff based on my Mercurial config. Updating my extensions and running a ./mach bootsrap seemed to help.

Ready to go

Hopefully everything is ready to go at this point. I found working through the Mozilla docs for how to use arc after setup helpful. If have any comments, please let me know either via email or on IRC.