One of our engineers just tried to submit a diff with lint errors, but it just hung. When arc diff runs arc --recon diff --no-diff --ansi (ArcanistDiffWorkflow.php:443-ish), it just hangs rather than returning. If I add --no-lint it goes through fine.
I've isolated it to $lint_workflow->run(); on ~ArcanistDiffWorkflow.php:1240 - it never makes it to the switch on the next line. As best I can tell, it has started hanging if there's a prompt for an autofix patch. I tried throwing a $argv = '--never-apply-patches into ArcanistDiffWorkflow's runLint() function and it appears to fix the issue, but that seems like the wrong way to fix the problem. I also didn't see a recent change that looks like it would have introduced the error, but it's admittedly been a while since I did arc upgrade.