When I run arc mail, where mail is aliased to diff --verbatim, it fails like so:

PHP Fatal error: __clone method called on non-object in /home/csilvers/khan/devtools/arcanist/src/configuration/ArcanistConfiguration.php on line 34

It looks like the error was introduced in b21a175512f9ea949c87. The idx returned 'undefined' (or whatever php does) when the command is an alias. The rest of the system doesn't care, but the newly introduced clone does.

The fix is probably something like:

index = idx($this->buildAllWorkflows(), $command);
return index ? clone(index) : index;