Code Reviews with Phabricator

If you prefer to use a web user interface for code reviews, you can now submit your patches for Clang and LLVM at LLVM’s Phabricator.

Sign up

There are two options to get an account on Phabricator. You can sign up immediately with one of the supported OAuth account types if you’re comfortable with OAuth, but you can also email to request an account to be created manually without using OAuth. We’re working to get support in Phabricator to directly create new accounts, but currently this is a manual process.

Note that if you use your Subversion user name as Phabricator user name, Phabricator will automatically connect your submits to your Phabricator user in the Code Repository Browser.

Requesting a review via the command line

Phabricator has a tool called Arcanist to upload patches from the command line. To get you set up, follow the Arcanist Quick Start instructions.

You can learn more about how to use arc to interact with Phabricator in the Arcanist User Guide.

Requesting a review via the web interface

The tool to create and review patches in Phabricator is called Differential.

Note that you can upload patches created through various diff tools, including git and svn. To make reviews easier, please always include as much context as possible with your diff! Don’t worry, Phabricator will automatically send a diff with a smaller context in the review email, but having the full file in the web interface will help the reviewer understand your code.

To get a full diff, use one of the following commands (or just use Arcanist to upload your patch):

  • git diff -U999999 other-branch
  • svn diff --diff-cmd=diff -x -U999999

To upload a new patch:

  • Click Differential.
  • Click Create Diff.
  • Paste the text diff or upload the patch file. Note that TODO
  • Leave the drop down on Create a new Revision... and click Continue.
  • Enter a descriptive title and summary; add reviewers and mailing lists that you want to be included in the review. If your patch is for LLVM, cc llvm-commits; if your patch is for Clang, cc cfe-commits.
  • Click Save.

To submit an updated patch:

  • Click Differential.
  • Click Create Diff.
  • Paste the updated diff.
  • Select the review you want to from the Attach To dropdown and click Continue.
  • Click Save.

Reviewing code with Phabricator

Phabricator allows you to add inline comments as well as overall comments to a revision. To add an inline comment, select the lines of code you want to comment on by clicking and dragging the line numbers in the diff pane.

You can add overall comments or submit your comments at the bottom of the page.

Phabricator has many useful features, for example allowing you to select diffs between different versions of the patch as it was reviewed in the Revision Update History. Most features are self descriptive - explore, and if you have a question, drop by on #llvm in IRC to get help.

Note that as e-mail is the system of reference for code reviews, and some people prefer it over a web interface, we do not generate automated mail when a review changes state, for example by clicking “Accept Revision” in the web interface. Thus, please type LGTM into the comment box to accept a change from Phabricator.


Currently, we’re testing Phabricator for use with Clang/LLVM. Please let us know whether you like it and what could be improved!