Step 1. Create a revision on git branch example_branch
Step 2. Checkout master, make a change to example_file.php; git push.
Step 3. Checkout example_branch, make a conflicting change to example_file.php
Step 4. arc land. The command will fail, and upon restoring local branch, all your hard work on example_file.php will be gone.
This is a bug in ArcanistGitLandEngine:restoreLocalState., $api->execxLocal('reset --hard %s --', $this->localCommit);
One way to fix this is add $api->execxLocal('stash'); and $api->execxLocal('stash pop'); before and after that command, respectively.