On commit detail page it's possible to view file in external editor via "View Options > View in Editor" button. Problem is that path that Phabricator provides to the editor comes directly from repository and doesn't have any information on where this file is located locally on user machine.
For example in the SVN repository file is located at `/projects/project_name/some_file.php`, but the `project_name` has been checked out at `/Volumes/web/project_name` and the path to the editor should be `/Volumes/web/project_name/some_file.php` instead.
I'm not sure how this could even work in Phabricator because nobody has 1-to-1 mapping between working copy (svn)/repository (git/hg) location and file path stored in commit on Phabricator side.