I am trying to create a review of an existing and pushed commit.
It appears that arc's automagic considers only non-pushed commits [^1]. So I need to overwrite that somehow and force it to create a revision from the commit I point it to, no matter whether it is included in any remote branch or not. I find myself unable to do so. The [`arc diff` documentation](https://secure.phabricator.com/book/phabricator/article/arcanist_diff/) does not seem to cover this.
[^1]: I needed to push, to get the change out of the machine where I was writing it originally.
```
$ arc which
REPOSITORY
To identify the repository associated with this working copy, arc followed this process:
Configuration value "repository.callsign" is empty.
Configuration value "project.name" is set to "phabricator"; this project
is associated with the "P" repository.
Found a unique matching repository.
This working copy is associated with the P repository.
COMMIT RANGE
If you run 'arc diff', changes between the commit:
010dcf6afe0c4f4b Allow the LDAP authentication provider to hide its login form
...and the current working copy state will be sent to Differential, because
it is the merge-base of 'origin/feat/ldap-hide-loginform' (the Git upstream
of the current branch) HEAD.
You can see the exact changes that will be sent by running this command:
$ git diff 010dcf6afe0c4f4b..HEAD
These commits will be included in the diff:
(No commits.)
MATCHING REVISIONS
These Differential revisions match the changes in this working copy:
(No revisions match.)
Since there are no revisions in Differential which match this working copy, a
new revision will be created if you run 'arc diff'.
```