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.. _phabricator-reviews:
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=============================
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Code Reviews with Phabricator
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=============================
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.. contents::
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:local:
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If you prefer to use a web user interface for code reviews, you can now submit
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your patches for Clang and LLVM at `LLVM's Phabricator`_ instance.
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While Phabricator is a useful tool for some, the relevant -commits mailing list
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is the system of record for all LLVM code review. The mailing list should be
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added as a subscriber on all reviews, and Phabricator users should be prepared
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to respond to free-form comments in mail sent to the commits list.
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Sign up
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-------
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To get started with Phabricator, navigate to `https://reviews.llvm.org`_ and
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click the power icon in the top right. You can register with a GitHub account,
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a Google account, or you can create your own profile.
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Make *sure* that the email address registered with Phabricator is subscribed
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to the relevant -commits mailing list. If you are not subscribed to the commit
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list, all mail sent by Phabricator on your behalf will be held for moderation.
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Note that if you use your git user name as Phabricator user name,
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Phabricator will automatically connect your submits to your Phabricator user in
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the `Code Repository Browser`_.
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Requesting a review via the command line
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----------------------------------------
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Phabricator has a tool called *Arcanist* to upload patches from
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the command line. To get you set up, follow the
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`Arcanist Quick Start`_ instructions.
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You can learn more about how to use arc to interact with
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Phabricator in the `Arcanist User Guide`_.
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.. _phabricator-request-review-web:
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Requesting a review via the web interface
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-----------------------------------------
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The tool to create and review patches in Phabricator is called
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*Differential*.
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Note that you can upload patches created through git.
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To make reviews easier, please always include **as much context as
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possible** with your diff! Don't worry, Phabricator
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will automatically send a diff with a smaller context in the review
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email, but having the full file in the web interface will help the
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reviewer understand your code.
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To get a full diff, use one of the following commands (or just use Arcanist
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to upload your patch):
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* ``git show HEAD -U999999 > mypatch.patch``
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* ``git format-patch -U999999 @{u}``
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Before uploading your patch, please make sure it is formatted properly, as
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described in :ref:`How to Submit a Patch <format patches>`.
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To upload a new patch:
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* Click *Differential*.
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* Click *+ Create Diff*.
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* Paste the text diff or browse to the patch file. Click *Create Diff*.
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* Leave this first Repository field blank. (We'll fill in the Repository
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later, when sending the review.)
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* Leave the drop down on *Create a new Revision...* and click *Continue*.
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* Enter a descriptive title and summary. The title and summary are usually
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in the form of a :ref:`commit message <commit messages>`.
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* Add reviewers (see below for advice). (If you set the Repository field
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correctly, llvm-commits or cfe-commits will be subscribed automatically;
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otherwise, you will have to manually subscribe them.)
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* In the Repository field, enter the name of the project (LLVM, Clang,
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etc.) to which the review should be sent.
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* Click *Save*.
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To submit an updated patch:
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* Click *Differential*.
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* Click *+ Create Diff*.
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* Paste the updated diff or browse to the updated patch file. Click *Create Diff*.
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* Select the review you want to from the *Attach To* dropdown and click
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*Continue*.
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* Leave the Repository field blank. (We previously filled out the Repository
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for the review request.)
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* Add comments about the changes in the new diff. Click *Save*.
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Choosing reviewers: You typically pick one or two people as initial reviewers.
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This choice is not crucial, because you are merely suggesting and not requiring
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them to participate. Many people will see the email notification on cfe-commits
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or llvm-commits, and if the subject line suggests the patch is something they
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should look at, they will.
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.. _finding-potential-reviewers:
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Finding potential reviewers
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---------------------------
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Here are a couple of ways to pick the initial reviewer(s):
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* Use ``git blame`` and the commit log to find names of people who have
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recently modified the same area of code that you are modifying.
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* Look in CODE_OWNERS.TXT to see who might be responsible for that area.
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* If you've discussed the change on a dev list, the people who participated
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might be appropriate reviewers.
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Even if you think the code owner is the busiest person in the world, it's still
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okay to put them as a reviewer. Being the code owner means they have accepted
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responsibility for making sure the review happens.
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Reviewing code with Phabricator
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-------------------------------
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Phabricator allows you to add inline comments as well as overall comments
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to a revision. To add an inline comment, select the lines of code you want
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to comment on by clicking and dragging the line numbers in the diff pane.
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When you have added all your comments, scroll to the bottom of the page and
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click the Submit button.
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You can add overall comments in the text box at the bottom of the page.
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When you're done, click the Submit button.
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Phabricator has many useful features, for example allowing you to select
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diffs between different versions of the patch as it was reviewed in the
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*Revision Update History*. Most features are self descriptive - explore, and
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if you have a question, drop by on #llvm in IRC to get help.
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Note that as e-mail is the system of reference for code reviews, and some
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people prefer it over a web interface, we do not generate automated mail
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when a review changes state, for example by clicking "Accept Revision" in
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the web interface. Thus, please type LGTM into the comment box to accept
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a change from Phabricator.
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Committing a change
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-------------------
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Once a patch has been reviewed and approved on Phabricator it can then be
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committed to trunk. If you do not have commit access, someone has to
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commit the change for you (with attribution). It is sufficient to add
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a comment to the approved review indicating you cannot commit the patch
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yourself. If you have commit access, there are multiple workflows to commit the
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change. Whichever method you follow it is recommended that your commit message
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ends with the line:
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::
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Differential Revision: <URL>
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where ``<URL>`` is the URL for the code review, starting with
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``https://reviews.llvm.org/``.
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This allows people reading the version history to see the review for
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context. This also allows Phabricator to detect the commit, close the
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review, and add a link from the review to the commit.
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Note that if you use the Arcanist tool the ``Differential Revision`` line will
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be added automatically. If you don't want to use Arcanist, you can add the
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``Differential Revision`` line (as the last line) to the commit message
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yourself.
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Using the Arcanist tool can simplify the process of committing reviewed code as
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it will retrieve reviewers, the ``Differential Revision``, etc from the review
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and place it in the commit message. You may also commit an accepted change
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directly using ``git llvm push``, per the section in the :ref:`getting started
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guide <commit_from_git>`.
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Note that if you commit the change without using Arcanist and forget to add the
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``Differential Revision`` line to your commit message then it is recommended
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that you close the review manually. In the web UI, under "Leap Into Action" put
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the git revision number in the Comment, set the Action to "Close Revision" and
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click Submit. Note the review must have been Accepted first.
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Committing someone's change from Phabricator
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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On a clean Git repository on an up to date ``master`` branch run the
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following (where ``<Revision>`` is the Phabricator review number):
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::
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arc patch D<Revision>
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This will create a new branch called ``arcpatch-D<Revision>`` based on the
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current ``master`` and will create a commit corresponding to ``D<Revision>`` with a
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commit message derived from information in the Phabricator review.
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Check you are happy with the commit message and amend it if necessary. Then,
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make sure the commit is up-to-date, and commit it. This can be done by running
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the following:
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::
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git pull --rebase origin master
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git show # Ensure the patch looks correct.
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ninja check-$whatever # Rerun the appropriate tests if needed.
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git llvm push
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Or
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::
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arc land D<Revision>
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Abandoning a change
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-------------------
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If you decide you should not commit the patch, you should explicitly abandon
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the review so that reviewers don't think it is still open. In the web UI,
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scroll to the bottom of the page where normally you would enter an overall
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comment. In the drop-down Action list, which defaults to "Comment," you should
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select "Abandon Revision" and then enter a comment explaining why. Click the
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Submit button to finish closing the review.
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Status
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------
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Please let us know whether you like it and what could be improved! We're still
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working on setting up a bug tracker, but you can email klimek-at-google-dot-com
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and chandlerc-at-gmail-dot-com and CC the llvm-dev mailing list with questions
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until then. We also could use help implementing improvements. This sadly is
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really painful and hard because the Phabricator codebase is in PHP and not as
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testable as you might like. However, we've put exactly what we're deploying up
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on an `llvm-reviews GitHub project`_ where folks can hack on it and post pull
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requests. We're looking into what the right long-term hosting for this is, but
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note that it is a derivative of an existing open source project, and so not
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trivially a good fit for an official LLVM project.
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.. _LLVM's Phabricator: https://reviews.llvm.org
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.. _`https://reviews.llvm.org`: https://reviews.llvm.org
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.. _Code Repository Browser: https://reviews.llvm.org/diffusion/
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.. _Arcanist Quick Start: https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/
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.. _Arcanist User Guide: https://secure.phabricator.com/book/phabricator/article/arcanist/
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.. _llvm-reviews GitHub project: https://github.com/r4nt/llvm-reviews/
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