seth@luca:~/update/p3$ arc which
REPOSITORY
To identify the repository associated with this working copy, arc followed this process:

    Configuration value "repository.callsign" is set to "M".

    Found a unique matching repository.

This working copy is associated with the M repository.

[2015-01-27 15:49:49] ERROR 8: Undefined index: sourcePath at [/home/seth/local/src/arcanist/arcanist/src/repository/api/ArcanistSubversionAPI.php:662]
  #0 ArcanistSubversionAPI::loadWorkingCopyDifferentialRevisions(ConduitClient, array) called at [<arcanist>/src/workflow/ArcanistWhichWorkflow.php:177]
  #1 ArcanistWhichWorkflow::run() called at [<arcanist>/scripts/arcanist.php:364]
MATCHING REVISIONS
These Differential revisions match the changes in this working copy:

    D264 p3 - Fix uninitialized return code when aborting
        Reason: Matching arcanist project name and working copy directory path.

Since exactly one revision in Differential matches this working copy, it will
be updated if you run 'arc diff'.

seth@luca:~/update/p3$