@epriestley I have seen you working on Mercurial stuff. Can you take a look at my findings above?

Ok, I think the problem is here: https://github.com/phacility/phabricator/blob/master/src/applications/diffusion/controller/DiffusionServeController.php#L816

I've managed to find the root of the problem, I think. Here is the actual error message that arises somwhere deep in Phabricator and then gets cut turning into non-informative ** unknown exception encountered, please report by visiting:

I still having this problem. @rafaelrabeloit, had you chance to fix or work-around this?

In T5726#88706, @epriestley wrote:

One concern about this is that this information is policy-bypassing.

This is pretty sad that this bug is still open. I haven't found a way to use Phabricator with recent Mercurial, so I'm sticking on 4.0.1 ATM.

After fiddling with some more upgrades, I started to get

Just faced that problem on my micro hosting. I've updated some software and then started to get the same error as OP when cloning/pulling/pushing mercurial repos. Here is the list of software, that got updated back then: https://paste.kde.org/pqelvuhjf