`mach artifact install` requires the `pushhead` revlog extension, which is provided by a Firefox-specific hg extension. We don't do a great job documenting this, and we don't help a user who's not configured get configured. This ticket tracks doing better.

rnewman saw this. mhammoud provides the following screencap of the error in #mobile: http://i.imgur.com/Jt8OXhm.png

To fix this, we need to handle errors around https://dxr.mozilla.org/mozilla-central/source/python/mozbuild/mozbuild/artifacts.py#193. We might consider running `hg` once just to test the extensions are available; or we might just try to parse this particular error out and link to documentation.

Review commit: https://reviewboard.mozilla.org/r/29841/diff/#index_header See other reviews: https://reviewboard.mozilla.org/r/29841/

Comment on attachment 8704971 [details] MozReview Request: Bug 1234912 - Check for |mozext| after |mach artifact install| hg failure. r?gps https://reviewboard.mozilla.org/r/29841/#review26773 ::: python/mozbuild/mozbuild/artifacts.py:415 (Diff revision 1) > + raise Exception('Could not find candidate pushheads. Enable the "mozext" hg extension.') Can you make this message actionable? Provide a URL to instructions or just print the instructions inline.

https://hg.mozilla.org/integration/fx-team/rev/98623463f9b9e879767add7103fa10dbd470fb50 Bug 1234912 - Check for mozext and pushlog entries after |mach artifact install| hg failure. r=gps