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.. _contributor-expectations:
Contributor Expectations
########################
Overview
********
The Zephyr project encourages :ref:`contributors <contributor>` to submit
changes as smaller pull requests. Smaller pull requests (PRs) have the following
benefits:
- Reviewed more quickly and reviewed more thoroughly. It's easier for reviewers
to set aside a few minutes to review smaller changes several times than it is
to allocate large blocks of time to review a large PR.
- Less wasted work if reviewers or maintainers reject the direction of the
change.
- Easier to rebase and merge. Smaller PRs are less likely to conflict with other
changes in the tree.
- Easier to revert if the PR breaks functionality.
.. note::
This page does not apply to draft PRs which can have any size, any number of
commits and any combination of smaller PRs for testing and preview purposes.
Draft PRs have no review expectation and PRs created as drafts from the start
do not notify anyone by default.
Defining Smaller PRs
====================
- Smaller PRs should encompass one self-contained logical change.
- When adding a new large feature or API, the PR should address only one part of
the feature. In this case create an :ref:`RFC proposal <rfcs>` to describe the
additional parts of the feature for reviewers.
- PRs should include tests or samples under the following conditions:
- Adding new features or functionality.
- Modifying a feature, especially for API behavior contract changes.
- Fixing a hardware agnostic bug. The test should fail without the bug fixed
and pass with the fix applied.
- PRs must update any documentation affected by a functional code change.
- If introducing a new API, the PR must include an example usage of the API.
This provides context to the reviewer and prevents submitting PRs with unused
APIs.
Multiple Commits on a Single PR
===============================
Contributors are further encouraged to break up PRs into multiple commits. Keep
in mind each commit in the PR must still build cleanly and pass all the CI
tests.
For example, when introducing an extension to an API, contributors can break up
the PR into multiple commits targeting these specific changes:
#. Introduce the new APIs, including shared devicetree bindings
#. Update driver implementation X, with driver specific devicetree bindings
#. Update driver implementation Y
#. Add tests for the new API
#. Add a sample using the API
#. Update the documentation
Large Changes
=============
Large changes to the Zephyr project must submit an :ref:`RFC proposal <rfcs>`
describing the full scope of change and future work. The RFC proposal provides
the required context to reviewers, but allows for smaller, incremental, PRs to
get reviewed and merged into the project. The RFC should also define the minimum
viable implementation.
Changes which require an RFC proposal include:
- Submitting a new feature.
- Submitting a new API.
- :ref:`treewide-changes`.
- Other large changes that can benefit from the RFC proposal process.
Maintainers have the discretion to request that contributors create an RFC for
PRs that are too large or complicated.
PR Requirements
***************
- Each commit in the PR must provide a commit message following the
:ref:`commit-guidelines`.
- All files in the PR must comply with :ref:`Licensing
Requirements<licensing_requirements>`.
- Follow the Zephyr :ref:`coding_style` and :ref:`coding_guidelines`.
- PRs must pass all CI checks. This is a requirement to merge the PR.
Contributors may mark a PR as draft and explicitly request reviewers to
provide early feedback, even with failing CI checks.
- When breaking a PR into multiple commits, each commit must build cleanly. The
CI system does not enforce this policy, so it is the PR author's
responsibility to verify.
- When major new functionality is added, tests for the new functionality shall
be added to the automated test suite. All API functions should have test cases
and there should be tests for the behavior contracts of the API. Maintainers
and reviewers have the discretion to determine if the provided tests are
sufficient. The examples below demonstrate best practices on how to test APIs
effectively.
- :zephyr_file:`Kernel timer tests <tests/kernel/timer/timer_behavior>`
provide around 85% test coverage for the
:zephyr_file:`kernel timer <kernel/timer.c>`, measured by lines of code.
- Emulators for off-chip peripherals are an effective way to test driver
APIs. The :zephyr_file:`fuel gauge tests <tests/drivers/fuel_gauge/sbs_gauge>`
use the :zephyr_file:`smart battery emulator <drivers/sensor/sbs_gauge/emul_sbs_gauge.c>`,
providing test coverage for the
:zephyr_file:`fuel gauge API <include/zephyr/drivers/fuel_gauge.h>`
and the :zephyr_file:`smart battery driver <drivers/fuel_gauge/sbs_gauge/sbs_gauge.c>`.
- Code coverage reports for the Zephyr project are available on `Codecov`_.
- Incompatible changes to APIs must also update the release notes for the
next release detailing the change. APIs marked as experimental are excluded
from this requirement.
- Changes to APIs must increment the API version number according to the API
version rules.
- PRs must also satisfy all :ref:`merge_criteria` before a member of the release
engineering team merges the PR into the zephyr tree.
Maintainers may request that contributors break up a PR into smaller PRs and may
request that they create an :ref:`RFC proposal <rfcs>`.
.. _`Codecov`: https://app.codecov.io/gh/zephyrproject-rtos/zephyr
Workflow Suggestions That Help Reviewers
========================================
- Unless they applied the reviewer's recommendation exactly, authors must not
resolve and hide comments, they must let the initial reviewer do it. The
Zephyr project does not require all comments to be resolved before merge.
Leaving some completed discussions open can sometimes be useful to understand
the greater picture.
- Respond to comments using the "Start Review" and "Add Review" green buttons in
the "Files changed" view. This allows responding to multiple comments and
publishing the responses in bulk. This reduces the number of emails sent to
reviewers.
- As GitHub does not implement |git range-diff|_, try to minimize rebases in the
middle of a review. If a rebase is required, push this as a separate update
with no other changes since the last push of the PR. When pushing a rebase
only, add a comment to the PR indicating which commit is the rebase.
.. |git range-diff| replace:: ``git range-diff``
.. _`git range-diff`: https://git-scm.com/docs/git-range-diff
PR Review Escalation
====================
The Zephyr community is a diverse group of individuals, with different levels of
commitment and priorities. As such, reviewers and maintainers may not get to a
PR right away.
The `Zephyr Dev Meeting`_ performs a triage of PRs missing reviewer approval,
following this process:
#. Identify and update PRs missing an Assignee.
#. Identify PRs without any comments or reviews, ping the PR Assignee to start a
review or assign to a different maintainer.
#. For PRs that have otherwise stalled, the Zephyr Dev Meeting pings the
Assignee and any reviewers that have left comments on the PR.
Contributors may escalate PRs outside of the Zephyr Dev Meeting triage process
as follows:
- After 1 week of inactivity, ping the Assignee or reviewers on the PR by adding
a comment to the PR.
- After 2 weeks of inactivity, post a message on the `#pr-help`_ channel on
Discord linking to the PR.
- After 2 weeks of inactivity, add the `dev-review`_ label to the PR. This
explicitly adds the PR to the agenda for the next `Zephyr Dev Meeting`_
independent of the triage process. Not all contributors have the required
privileges to add labels to PRs, in this case the contributor should request
help on Discord or send an email to the `Zephyr devel mailing list`_.
Note that for new PRs, contributors should generally wait for at least one
Zephyr Dev Meeting before escalating the PR themselves.
.. _Zephyr devel mailing list: https://lists.zephyrproject.org/g/devel
.. _pr_technical_escalation:
PR Technical Escalation
=======================
In cases where a contributor objects to change requests from reviewers, Zephyr
defines the following escalation process for resolving technical disagreements.
- Resolve in the PR among assignee, maintainers and reviewer.
- Assignee to act as moderator if applicable.
- Optionally resolve in the next `Zephyr Dev Meeting`_ or `Architecture Working
Group`_ meeting with more Maintainers and project stakeholders.
- The involved parties and the Assignee to be present when
the (escalated) issue is discussed.
- TSC: Assignees can escalate to the TSC voting members and get a binding
resolution in the TSC by adding the `tsc`_ label on the PR.
- Assignee to ensure the resolution of the escalation is reflected in the PR
review.
.. _#pr-help: https://discord.com/channels/720317445772017664/997527108844798012
.. _dev-review: https://github.com/zephyrproject-rtos/zephyr/labels/dev-review
.. _Zephyr Dev Meeting: https://github.com/zephyrproject-rtos/zephyr/wiki/Zephyr-Committee-and-Working-Group-Meetings#zephyr-dev-meeting
.. _Architecture Project: https://github.com/zephyrproject-rtos/zephyr/projects/18
.. _Architecture Working Group: https://github.com/zephyrproject-rtos/zephyr/wiki/Architecture-Working-Group
.. _tsc: https://github.com/zephyrproject-rtos/zephyr/labels/tsc
Reviewer Expectations
#####################
- Be respectful when commenting on PRs. Refer to the Zephyr `Code of Conduct`_
for more details.
- The Zephyr Project recognizes that reviewers and maintainers have limited
bandwidth. Prioritize review requests in the following order:
#. PRs related to items in the `Zephyr Release Plan`_.
#. PRs that the reviewer has requested blocking changes.
#. PRs assigned to the reviewer as the area maintainer.
#. All other PRs.
- Try to provide feedback on the entire PR in one shot. This provides the
contributor an opportunity to address all comments in the next PR update.
- Partial reviews are permitted, but the reviewer must add a comment indicating
what portion of the PR they reviewed. Examples of useful partial reviews
include:
- Domain specific reviews (e.g. Devicetree).
- Code style changes that impact the readability of the PR.
- Reviewing commits separately when the requested changes cascade into the
later commits.
- Avoid increasing scope of the PR by requesting new features, especially when
there is a corresponding :ref:`RFC <rfcs>` associated with the PR. Instead,
reviewers should add suggestions as a comment to the :ref:`RFC <rfcs>`. This
also encourages more collaboration as it is easier for multiple contributors
to work on a feature once the minimum implementation has merged.
- When using the "Request Changes" option, mark trivial, non-functional,
requests as "Non-blocking" in the comment. Reviewers should approve PRs once
only non-blocking changes remain. The PR author has discretion as to whether
they address all non-blocking comments. PR authors should acknowledge every
review comment in some way, even if it's just with an emoticon.
.. _Code of Conduct: https://github.com/zephyrproject-rtos/zephyr/blob/main/CODE_OF_CONDUCT.md
.. _Zephyr Release Plan: https://github.com/orgs/zephyrproject-rtos/projects/13