llvm/docs/Phabricator.rst - llvm-project - Git at Google

 .. _phabricator-reviews:

 =============================
 Code Reviews with Phabricator
 =============================

 .. contents::
   :local:

 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`_ instance.

 While Phabricator is a useful tool for some, the relevant -commits mailing list
 is the system of record for all LLVM code review. The mailing list should be
 added as a subscriber on all reviews, and Phabricator users should be prepared
 to respond to free-form comments in mail sent to the commits list.

 Sign up
 -------

 To get started with Phabricator, navigate to `https://reviews.llvm.org`_ and
 click the power icon in the top right. You can register with a GitHub account,
 a Google account, or you can create your own profile.

 Make *sure* that the email address registered with Phabricator is subscribed
 to the relevant -commits mailing list. If you are not subscribed to the commit
 list, all mail sent by Phabricator on your behalf will be held for moderation.

 Note that if you use your git 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`_.
 The basic way of creating a revision for the current commit in your local
 repository is to run:

 ::

   arc diff HEAD~


 Sometime you may want to create a draft revision to show the proof of concept
 or for experimental purposes, In that case you can use the `--draft` option. It
 will create a new draft revision. The good part is: it will not send mail to
 llvm-commit mailing list, patch reviewers, and all other subscribers, buildbot
 will also run on every patch update:

 ::

   arc diff --draft HEAD~


 If you later update your commit message, you need to add the `--verbatim`
 option to have `arc` update the description on Phabricator:

 ::

   arc diff --edit --verbatim


 .. _phabricator-request-review-web:

 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 git, but using `arc` on the
 command line (see previous section) is preferred: it adds more metadata to
 Phabricator which are useful for the pre-merge testing system and for
 propagating attribution on commits when someone else has to push it for you.

 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 show HEAD -U999999 > mypatch.patch``
 * ``git diff -U999999 @{u} > mypatch.patch``
 * ``git diff HEAD~1 -U999999 > mypatch.patch``

 Before uploading your patch, please make sure it is formatted properly, as
 described in :ref:`How to Submit a Patch <format patches>`.

 To upload a new patch:

 * Click *Differential*.
 * Click *+ Create Diff*.
 * Paste the text diff or browse to the patch file. Click *Create Diff*.
 * Leave this first Repository field blank. (We'll fill in the Repository
   later, when sending the review.)
 * Leave the drop down on *Create a new Revision...* and click *Continue*.
 * Enter a descriptive title and summary.  The title and summary are usually
   in the form of a :ref:`commit message <commit messages>`.
 * Add reviewers (see below for advice). (If you set the Repository field
   correctly, llvm-commits or cfe-commits will be subscribed automatically;
   otherwise, you will have to manually subscribe them.)
 * In the Repository field, enter "rG LLVM Github Monorepo".
 * Click *Save*.

 To submit an updated patch:

 * Click *Differential*.
 * Click *+ Create Diff*.
 * Paste the updated diff or browse to the updated patch file. Click *Create Diff*.
 * Select the review you want to from the *Attach To* dropdown and click
   *Continue*.
 * Leave the Repository field blank. (We previously filled out the Repository
   for the review request.)
 * Add comments about the changes in the new diff. Click *Save*.

 Choosing reviewers: You typically pick one or two people as initial reviewers.
 This choice is not crucial, because you are merely suggesting and not requiring
 them to participate. Many people will see the email notification on cfe-commits
 or llvm-commits, and if the subject line suggests the patch is something they
 should look at, they will.


 .. _finding-potential-reviewers:

 Finding potential reviewers
 ---------------------------

 Here are a couple of ways to pick the initial reviewer(s):

 * Use ``git blame`` and the commit log to find names of people who have
   recently modified the same area of code that you are modifying.
 * Look in CODE_OWNERS.TXT to see who might be responsible for that area.
 * If you've discussed the change on a dev list, the people who participated
   might be appropriate reviewers.

 Even if you think the code owner is the busiest person in the world, it's still
 okay to put them as a reviewer. Being the code owner means they have accepted
 responsibility for making sure the review happens.

 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.
 When you have added all your comments, scroll to the bottom of the page and
 click the Submit button.

 You can add overall comments in the text box at the bottom of the page.
 When you're done, click the Submit button.

 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.

 .. _pre-merge-testing:

 Pre-merge testing
 -----------------

 The pre-merge tests are a continuous integration (CI) workflow. The workflow
 checks the patches uploaded to Phabricator before a user merges them to the main
 branch - thus the term *pre-merge testing*.

 When a user uploads a patch to Phabricator, Phabricator triggers the checks and
 then displays the results. This way bugs in a patch are contained during the
 code review stage and do not pollute the main branch.

 Our goal with pre-merge testing is to report most true problems while strongly
 minimizing the number of false positive reports.  Our goal is that problems
 reported are always actionable.  If you notice a false positive, please report
 it so that we can identify the cause.

 If you notice issues or have an idea on how to improve pre-merge checks, please
 `create a new issue <https://github.com/google/llvm-premerge-checks/issues/new>`_
 or give a ❤️ to an existing one.

 Requirements
 ^^^^^^^^^^^^

 To get a patch on Phabricator tested, the build server must be able to apply the
 patch to the checked out git repository. Please make sure that either:

 * You set a git hash as ``sourceControlBaseRevision`` in Phabricator which is
   available on the GitHub repository,
 * **or** you define the dependencies of your patch in Phabricator,
 * **or** your patch can be applied to the main branch.

 Only then can the build server apply the patch locally and run the builds and
 tests.

 Accessing build results
 ^^^^^^^^^^^^^^^^^^^^^^^
 Phabricator will automatically trigger a build for every new patch you upload or
 modify. Phabricator shows the build results at the top of the entry. Clicking on
 the links (in the red box) will show more details:

   .. image:: Phabricator_premerge_results.png

 The CI will compile and run tests, run clang-format and clang-tidy on lines
 changed.

 If a unit test failed, this is shown below the build status. You can also expand
 the unit test to see the details:

   .. image:: Phabricator_premerge_unit_tests.png

 Opting Out
 ^^^^^^^^^^

 In case you want to opt-out entirely of pre-merge testing, add yourself to the
 `OPT OUT project <https://reviews.llvm.org/project/view/83/>`_.  If you decide
 to opt-out, please let us know why, so we might be able to improve in the future.

 Operational Details
 ^^^^^^^^^^^^^^^^^^^

 The code responsible for running the pre-merge flow can be found in the `external
 repository <https://github.com/google/llvm-premerge-checks>`_.  For enhancement
 ideas and most bugs, please file an issue on said repository.  For immediate
 operational problems, the point of contact is
 `Mikhail Goncharov <mailto:goncharo@google.com>`_.

 Background on the pre-merge infrastructure can be found in `this 2020 DevMeeting
 talk <https://llvm.org/devmtg/2020-09/slides/Goncharov-Pre-merge_checks.pdf>`_

 Committing a change
 -------------------

 Once a patch has been reviewed and approved on Phabricator it can then be
 committed to trunk. If you do not have commit access, someone has to
 commit the change for you (with attribution). It is sufficient to add
 a comment to the approved review indicating you cannot commit the patch
 yourself. If you have commit access, there are multiple workflows to commit the
 change. Whichever method you follow it is recommended that your commit message
 ends with the line:

 ::

   Differential Revision: <URL>

 where ``<URL>`` is the URL for the code review, starting with
 ``https://reviews.llvm.org/``.

 This allows people reading the version history to see the review for
 context. This also allows Phabricator to detect the commit, close the
 review, and add a link from the review to the commit.

 Note that if you use the Arcanist tool the ``Differential Revision`` line will
 be added automatically. If you don't want to use Arcanist, you can add the
 ``Differential Revision`` line (as the last line) to the commit message
 yourself.

 Using the Arcanist tool can simplify the process of committing reviewed code as
 it will retrieve reviewers, the ``Differential Revision``, etc from the review
 and place it in the commit message. You may also commit an accepted change
 directly using ``git push``, per the section in the :ref:`getting started
 guide <commit_from_git>`.

 Note that if you commit the change without using Arcanist and forget to add the
 ``Differential Revision`` line to your commit message then it is recommended
 that you close the review manually. In the web UI, under "Leap Into Action" put
 the git revision number in the Comment, set the Action to "Close Revision" and
 click Submit.  Note the review must have been Accepted first.

 Committing someone's change from Phabricator
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 On a clean Git repository on an up to date ``main`` branch run the
 following (where ``<Revision>`` is the Phabricator review number):

 ::

   arc patch D<Revision>


 This will create a new branch called ``arcpatch-D<Revision>`` based on the
 current ``main`` and will create a commit corresponding to ``D<Revision>`` with a
 commit message derived from information in the Phabricator review.

 Check you are happy with the commit message and amend it if necessary.
 For example, ensure the 'Author' property of the commit is set to the original author.
 You can use a command to correct the author property if it is incorrect:

 ::

   git commit --amend --author="John Doe <jdoe@llvm.org>"

 Then, make sure the commit is up-to-date, and commit it. This can be done by running
 the following:

 ::

   git pull --rebase https://github.com/llvm/llvm-project.git main
   git show # Ensure the patch looks correct.
   ninja check-$whatever # Rerun the appropriate tests if needed.
   git push https://github.com/llvm/llvm-project.git HEAD:main


 Abandoning a change
 -------------------

 If you decide you should not commit the patch, you should explicitly abandon
 the review so that reviewers don't think it is still open. In the web UI,
 scroll to the bottom of the page where normally you would enter an overall
 comment. In the drop-down Action list, which defaults to "Comment," you should
 select "Abandon Revision" and then enter a comment explaining why. Click the
 Submit button to finish closing the review.

 Status
 ------

 Please let us know whether you like it and what could be improved! We're still
 working on setting up a bug tracker, but you can email klimek-at-google-dot-com
 and chandlerc-at-gmail-dot-com and CC the llvm-dev mailing list with questions
 until then. We also could use help implementing improvements. This sadly is
 really painful and hard because the Phabricator codebase is in PHP and not as
 testable as you might like. However, we've put exactly what we're deploying up
 on an `llvm-reviews GitHub project`_ where folks can hack on it and post pull
 requests. We're looking into what the right long-term hosting for this is, but
 note that it is a derivative of an existing open source project, and so not
 trivially a good fit for an official LLVM project.

 .. _LLVM's Phabricator: https://reviews.llvm.org
 .. _`https://reviews.llvm.org`: https://reviews.llvm.org
 .. _Code Repository Browser: https://reviews.llvm.org/diffusion/
 .. _Arcanist Quick Start: https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/
 .. _Arcanist User Guide: https://secure.phabricator.com/book/phabricator/article/arcanist/
 .. _llvm-reviews GitHub project: https://github.com/r4nt/llvm-reviews/
	.. _phabricator-reviews:

	=============================
	Code Reviews with Phabricator
	=============================

	.. contents::
	:local:

	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`_ instance.

	While Phabricator is a useful tool for some, the relevant -commits mailing list
	is the system of record for all LLVM code review. The mailing list should be
	added as a subscriber on all reviews, and Phabricator users should be prepared
	to respond to free-form comments in mail sent to the commits list.

	Sign up
	-------

	To get started with Phabricator, navigate to `https://reviews.llvm.org`_ and
	click the power icon in the top right. You can register with a GitHub account,
	a Google account, or you can create your own profile.

	Make sure that the email address registered with Phabricator is subscribed
	to the relevant -commits mailing list. If you are not subscribed to the commit
	list, all mail sent by Phabricator on your behalf will be held for moderation.

	Note that if you use your git 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`_.
	The basic way of creating a revision for the current commit in your local
	repository is to run:

	::

	arc diff HEAD~


	Sometime you may want to create a draft revision to show the proof of concept
	or for experimental purposes, In that case you can use the `--draft` option. It
	will create a new draft revision. The good part is: it will not send mail to
	llvm-commit mailing list, patch reviewers, and all other subscribers, buildbot
	will also run on every patch update:

	::

	arc diff --draft HEAD~


	If you later update your commit message, you need to add the `--verbatim`
	option to have `arc` update the description on Phabricator:

	::

	arc diff --edit --verbatim


	.. _phabricator-request-review-web:

	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 git, but using `arc` on the
	command line (see previous section) is preferred: it adds more metadata to
	Phabricator which are useful for the pre-merge testing system and for
	propagating attribution on commits when someone else has to push it for you.

	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 show HEAD -U999999 > mypatch.patch``
	* ``git diff -U999999 @{u} > mypatch.patch``
	* ``git diff HEAD~1 -U999999 > mypatch.patch``

	Before uploading your patch, please make sure it is formatted properly, as
	described in :ref:`How to Submit a Patch <format patches>`.

	To upload a new patch:

	* Click Differential.
	* Click + Create Diff.
	* Paste the text diff or browse to the patch file. Click Create Diff.
	* Leave this first Repository field blank. (We'll fill in the Repository
	later, when sending the review.)
	* Leave the drop down on Create a new Revision... and click Continue.
	* Enter a descriptive title and summary. The title and summary are usually
	in the form of a :ref:`commit message <commit messages>`.
	* Add reviewers (see below for advice). (If you set the Repository field
	correctly, llvm-commits or cfe-commits will be subscribed automatically;
	otherwise, you will have to manually subscribe them.)
	* In the Repository field, enter "rG LLVM Github Monorepo".
	* Click Save.

	To submit an updated patch:

	* Click Differential.
	* Click + Create Diff.
	* Paste the updated diff or browse to the updated patch file. Click Create Diff.
	* Select the review you want to from the Attach To dropdown and click
	Continue.
	* Leave the Repository field blank. (We previously filled out the Repository
	for the review request.)
	* Add comments about the changes in the new diff. Click Save.

	Choosing reviewers: You typically pick one or two people as initial reviewers.
	This choice is not crucial, because you are merely suggesting and not requiring
	them to participate. Many people will see the email notification on cfe-commits
	or llvm-commits, and if the subject line suggests the patch is something they
	should look at, they will.


	.. _finding-potential-reviewers:

	Finding potential reviewers
	---------------------------

	Here are a couple of ways to pick the initial reviewer(s):

	* Use ``git blame`` and the commit log to find names of people who have
	recently modified the same area of code that you are modifying.
	* Look in CODE_OWNERS.TXT to see who might be responsible for that area.
	* If you've discussed the change on a dev list, the people who participated
	might be appropriate reviewers.

	Even if you think the code owner is the busiest person in the world, it's still
	okay to put them as a reviewer. Being the code owner means they have accepted
	responsibility for making sure the review happens.

	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.
	When you have added all your comments, scroll to the bottom of the page and
	click the Submit button.

	You can add overall comments in the text box at the bottom of the page.
	When you're done, click the Submit button.

	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.

	.. _pre-merge-testing:

	Pre-merge testing
	-----------------

	The pre-merge tests are a continuous integration (CI) workflow. The workflow
	checks the patches uploaded to Phabricator before a user merges them to the main
	branch - thus the term pre-merge testing.

	When a user uploads a patch to Phabricator, Phabricator triggers the checks and
	then displays the results. This way bugs in a patch are contained during the
	code review stage and do not pollute the main branch.

	Our goal with pre-merge testing is to report most true problems while strongly
	minimizing the number of false positive reports. Our goal is that problems
	reported are always actionable. If you notice a false positive, please report
	it so that we can identify the cause.

	If you notice issues or have an idea on how to improve pre-merge checks, please
	`create a new issue <https://github.com/google/llvm-premerge-checks/issues/new>`_
	or give a ❤️ to an existing one.

	Requirements
	^^^^^^^^^^^^

	To get a patch on Phabricator tested, the build server must be able to apply the
	patch to the checked out git repository. Please make sure that either:

	* You set a git hash as ``sourceControlBaseRevision`` in Phabricator which is
	available on the GitHub repository,
	* or you define the dependencies of your patch in Phabricator,
	* or your patch can be applied to the main branch.

	Only then can the build server apply the patch locally and run the builds and
	tests.

	Accessing build results
	^^^^^^^^^^^^^^^^^^^^^^^
	Phabricator will automatically trigger a build for every new patch you upload or
	modify. Phabricator shows the build results at the top of the entry. Clicking on
	the links (in the red box) will show more details:

	.. image:: Phabricator_premerge_results.png

	The CI will compile and run tests, run clang-format and clang-tidy on lines
	changed.

	If a unit test failed, this is shown below the build status. You can also expand
	the unit test to see the details:

	.. image:: Phabricator_premerge_unit_tests.png

	Opting Out
	^^^^^^^^^^

	In case you want to opt-out entirely of pre-merge testing, add yourself to the
	`OPT OUT project <https://reviews.llvm.org/project/view/83/>`_. If you decide
	to opt-out, please let us know why, so we might be able to improve in the future.

	Operational Details
	^^^^^^^^^^^^^^^^^^^

	The code responsible for running the pre-merge flow can be found in the `external
	repository <https://github.com/google/llvm-premerge-checks>`_. For enhancement
	ideas and most bugs, please file an issue on said repository. For immediate
	operational problems, the point of contact is
	`Mikhail Goncharov <mailto:goncharo@google.com>`_.

	Background on the pre-merge infrastructure can be found in `this 2020 DevMeeting
	talk <https://llvm.org/devmtg/2020-09/slides/Goncharov-Pre-merge_checks.pdf>`_

	Committing a change
	-------------------

	Once a patch has been reviewed and approved on Phabricator it can then be
	committed to trunk. If you do not have commit access, someone has to
	commit the change for you (with attribution). It is sufficient to add
	a comment to the approved review indicating you cannot commit the patch
	yourself. If you have commit access, there are multiple workflows to commit the
	change. Whichever method you follow it is recommended that your commit message
	ends with the line:

	::

	Differential Revision: <URL>

	where ``<URL>`` is the URL for the code review, starting with
	``https://reviews.llvm.org/``.

	This allows people reading the version history to see the review for
	context. This also allows Phabricator to detect the commit, close the
	review, and add a link from the review to the commit.

	Note that if you use the Arcanist tool the ``Differential Revision`` line will
	be added automatically. If you don't want to use Arcanist, you can add the
	``Differential Revision`` line (as the last line) to the commit message
	yourself.

	Using the Arcanist tool can simplify the process of committing reviewed code as
	it will retrieve reviewers, the ``Differential Revision``, etc from the review
	and place it in the commit message. You may also commit an accepted change
	directly using ``git push``, per the section in the :ref:`getting started
	guide <commit_from_git>`.

	Note that if you commit the change without using Arcanist and forget to add the
	``Differential Revision`` line to your commit message then it is recommended
	that you close the review manually. In the web UI, under "Leap Into Action" put
	the git revision number in the Comment, set the Action to "Close Revision" and
	click Submit. Note the review must have been Accepted first.

	Committing someone's change from Phabricator
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

	On a clean Git repository on an up to date ``main`` branch run the
	following (where ``<Revision>`` is the Phabricator review number):

	::

	arc patch D<Revision>


	This will create a new branch called ``arcpatch-D<Revision>`` based on the
	current ``main`` and will create a commit corresponding to ``D<Revision>`` with a
	commit message derived from information in the Phabricator review.

	Check you are happy with the commit message and amend it if necessary.
	For example, ensure the 'Author' property of the commit is set to the original author.
	You can use a command to correct the author property if it is incorrect:

	::

	git commit --amend --author="John Doe <jdoe@llvm.org>"

	Then, make sure the commit is up-to-date, and commit it. This can be done by running
	the following:

	::

	git pull --rebase https://github.com/llvm/llvm-project.git main
	git show # Ensure the patch looks correct.
	ninja check-$whatever # Rerun the appropriate tests if needed.
	git push https://github.com/llvm/llvm-project.git HEAD:main


	Abandoning a change
	-------------------

	If you decide you should not commit the patch, you should explicitly abandon
	the review so that reviewers don't think it is still open. In the web UI,
	scroll to the bottom of the page where normally you would enter an overall
	comment. In the drop-down Action list, which defaults to "Comment," you should
	select "Abandon Revision" and then enter a comment explaining why. Click the
	Submit button to finish closing the review.

	Status
	------

	Please let us know whether you like it and what could be improved! We're still
	working on setting up a bug tracker, but you can email klimek-at-google-dot-com
	and chandlerc-at-gmail-dot-com and CC the llvm-dev mailing list with questions
	until then. We also could use help implementing improvements. This sadly is
	really painful and hard because the Phabricator codebase is in PHP and not as
	testable as you might like. However, we've put exactly what we're deploying up
	on an `llvm-reviews GitHub project`_ where folks can hack on it and post pull
	requests. We're looking into what the right long-term hosting for this is, but
	note that it is a derivative of an existing open source project, and so not
	trivially a good fit for an official LLVM project.

	.. _LLVM's Phabricator: https://reviews.llvm.org
	.. _`https://reviews.llvm.org`: https://reviews.llvm.org
	.. _Code Repository Browser: https://reviews.llvm.org/diffusion/
	.. _Arcanist Quick Start: https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/
	.. _Arcanist User Guide: https://secure.phabricator.com/book/phabricator/article/arcanist/
	.. _llvm-reviews GitHub project: https://github.com/r4nt/llvm-reviews/