I had a diff that I was trying to commit. arc which seemed to realize what it was tied to, but arc commit didn't.
The issue turned out to be that not all reviewers had accepted.
I have included full --trace invocations below. There's really nothing there to indicate that a unique working diff was found (but not in the accepted state).
seth@luca:~/update/pjt$ arc which --trace
libphutil loaded from '/home/seth/local/src/arcanist/libphutil/src'.
arcanist loaded from '/home/seth/local/src/arcanist/arcanist/src'.
Config: Reading user configuration file "/home/seth/.arcrc"...
Config: Did not find system configuration at "/etc/arcconfig".
Working Copy: Reading .arcconfig from "/home/seth/update/pjt/.arcconfig".
Working Copy: Path "/home/seth/update/pjt" is part of `svn` working copy "/home/seth/update/pjt".
Working Copy: Project root is at "/home/seth/update/pjt".
Config: Did not find local configuration at "/home/seth/update/pjt/.svn/arc/config".
>>> [0] <conduit> conduit.connect() <bytes = 467>
>>> [1] <http> http://phab.spira:8001/api/conduit.connect
<<< [1] <http> 49,988 us
<<< [0] <conduit> 50,632 us
REPOSITORY
>>> [2] <conduit> repository.query() <bytes = 193>
>>> [3] <http> http://phab.spira:8001/api/repository.query
<<< [3] <http> 45,684 us
<<< [2] <conduit> 46,241 us
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.
>>> [4] <conduit> differential.query() <bytes = 194>
>>> [5] <http> http://phab.spira:8001/api/differential.query
<<< [5] <http> 125,601 us
<<< [4] <conduit> 125,878 us
MATCHING REVISIONS
These Differential revisions match the changes in this working copy:
D2744 pjt - short-circuit for common case
Reason: Matching 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/pjt$ arc commit --trace
libphutil loaded from '/home/seth/local/src/arcanist/libphutil/src'.
arcanist loaded from '/home/seth/local/src/arcanist/arcanist/src'.
Config: Reading user configuration file "/home/seth/.arcrc"...
Config: Did not find system configuration at "/etc/arcconfig".
Working Copy: Reading .arcconfig from "/home/seth/update/pjt/.arcconfig".
Working Copy: Path "/home/seth/update/pjt" is part of `svn` working copy "/home/seth/update/pjt".
Working Copy: Project root is at "/home/seth/update/pjt".
Config: Did not find local configuration at "/home/seth/update/pjt/.svn/arc/config".
>>> [0] <conduit> conduit.connect() <bytes = 468>
>>> [1] <http> http://phab.spira:8001/api/conduit.connect
<<< [1] <http> 53,482 us
<<< [0] <conduit> 53,809 us
>>> [2] <conduit> differential.query() <bytes = 259>
>>> [3] <http> http://phab.spira:8001/api/differential.query
<<< [3] <http> 44,090 us
<<< [2] <conduit> 44,275 us
Usage Exception: Unable to identify the revision in the working copy. Use '--revision <revision_id>' to select a revision.
[2015-08-05 16:07:00] EXCEPTION: (ArcanistUsageException) Unable to identify the revision in the working copy. Use '--revision <revision_id>' to select a revision. at [<arcanist>/src/workflow/ArcanistCommitWorkflow.php:78]
arcanist(head=master, ref.master=7d15b85a1bc0), phutil(head=master, ref.master=92882eb9404d)
#0 ArcanistCommitWorkflow::run() called at [<arcanist>/scripts/arcanist.php:382]
seth@luca:~/update/pjt$