## tl;dr

- Regressions should be [reverted first](../infra/Landing-Changes-With-Autosubmit.md) and questions asked later. Bringing the tree to green is higher priority.
- A breaking change is one that breaks the tests in the flutter/tests repo, and those need a migration guide.
- Expect that a new patch will be reviewed within two weeks, unless it is fixing a P0 bug in which case it should be reviewed the same day. If it has not been reviewed in that timeframe, reach out on [Chat](Chat.md). Remember that reviewers are human beings with additional professional and personal responsibilities.
- Contributors without write access are limited to **2 concurrent open pull requests** per repository (draft PRs are exempt). Focus on merging or closing existing PRs before opening new ones.

## Introduction

This page covers how to land a PR and other aspects of writing code for
Flutter other than the actual writing of the code. For guidance on
designing APIs, documenting, and formatting your code, see the
[Style guide for Flutter repo](Style-guide-for-Flutter-repo.md) document.

Across the document we use the word "tree" to mean "the health state of flutter/flutter repository". Tree status is shown:

- On our [build dashboard](https://flutter-dashboard.appspot.com/)
- On every PR (referred to as "Tree Status")
  - A failing "tree-status" check on a PR indicates a problem with the main branch,
    not the PR itself. The check will pass once tree maintainers resolve the issue; no action is needed within the PR.
- In the [tree-status](https://discord.com/channels/608014603317936148/613398423093116959) Discord channel

## Overview

The general process for submitting code to a Flutter repository is as follows:

1. Fork the repository on GitHub (see the
   [contributing guide](https://github.com/flutter/flutter/blob/main/CONTRIBUTING.md)
   for advice on doing this and in general setting up your development environment).

2. If there is not already an issue covering the work you are interested in doing,
   then file a new bug to describe the issue you are addressing. Having an issue means
   that if we have to revert the PR, we can reopen the issue and not lose track of the
   fact that the work didn't fully land. Similarly if someone works on a PR then stops
   before it can land, having an issue means we have somewhere to point to the code when
   we close the PR without landing it, so other people can take it over.

3. Discuss your design on the issue. See [Design Documents](Design-Documents.md) for advice.
   For larger architectural proposals or breaking changes, follow the [Flutter RFC process](https://github.com/flutter/rfc) (see [RFC 000.0002](https://github.com/flutter/rfc/blob/main/rfc/000.0002-flutter-rfc-review-process.md)).
   You may wish to discuss the topic on our [Chat](Chat.md) channels. The more buy-in you get from the rest of the
   team (especially the relevant leads), the easier the rest of the process will be.
   You can put the label "proposal" on your issue to indicate that you have a design
   up for discussion in the issue.

4. If the work you are doing affects our privacy surface, such as modifying how
   we collect analytics, crash logs, or the like, then please reach out to a Googler
   to discuss your changes (you'll want to start an RFC or design doc to
   solicit feedback, see [Design Documents](Design-Documents.md)),
   who will be happy to loop in one of our engineers who explicitly focus on privacy issues
   so that they're able to give feedback on the work you plan to do.

5. Create a branch off of `main` (or if the repository has not yet switched to
   having a `main` branch, from `master`) on your GitHub fork of the repository, and implement
   your change. Make sure it is tested (see the next section for details).

   You must follow the guidelines described in the [Style guide for Flutter repo](Style-guide-for-Flutter-repo.md).
   Files must not have trailing spaces.
   For the engine repository, C, C++, and Objective-C code should be formatted with
   `clang-format` before submission (use `buildtools/<OS>/clang/bin/clang-format
   --style=file -i`).

6. Submit this branch as a PR to the relevant Flutter repository.
   _(See also: [Signing commits](./Signing-commits.md))_

   To ensure maintainers can provide timely and high-quality feedback, contributors without write access are limited to **2 concurrent open pull requests** per public Flutter repository.
   * **Draft PRs are exempt**: Work-in-progress draft PRs do not count toward your limit.
   * **Focus on Quality**: Once you reach the limit, please focus on merging or closing your existing PRs before opening new ones.

   All submissions to Google Open Source projects need to follow
   [Google’s Contributor License Agreement (CLA)](https://cla.developers.google.com/),
   in which contributors agree that their contribution is an original work of authorship.
   This doesn’t prohibit the use of coding assistance tools, but what’s submitted does
   need to be a contributor’s original creation.

7. Get your code reviewed (see below). If you are a team member, request review
   from the relevant expert(s) for the areas you touched. Otherwise, wait for
   [reviewers to be assigned](#who).

8. Make sure your PR passes all the pre-commit tests. Consider running some of the
   post-commit tests locally (see the
   [devicelab](https://github.com/flutter/flutter/blob/main/dev/devicelab/README.md)
   directory). If any tests break, especially the `customer_testing` tests, please
   see the breaking change policy section below for details on how to proceed.

   The `luci-flutter` test isn't checking your PR, it's letting you know
   whether the tree itself is passing the tests right now (including post-
   commit tests).

   **If the trees or dashboards are showing any regressions, only fixes
   that improve the situation are allowed to go in.**

   Two pre-commit tests are special, as failures are not caused by the PR's code and cannot be fixed directly within the PR.
   - The "tree-status" test is a status indicator for the stability of the main branch.
     It will pass once the issues blocking the tree are resolved.
   - The "Google Testing" tests run internally at Google and are not publicly accessible.
     If these fail, a Google employee (for example, the PR reviewer) should be contacted
     to check the internal tests and recommend a solution.

9. Once everything is green and you have an LGTM from the owners of the code you are affecting (or someone to whom they
   have delegated), and an LGTM from any other contributor who left comments, add the "autosubmit" label if you're in the flutter-hackers github group. A bot will land the patch when it feels like it. If you're not in the flutter-hackers group a reviewer will add the label for you.

10. Watch the post-commit tests on the [dashboard](https://dashboard.flutter.dev/#/build) to make sure everything passes. If anything
   goes wrong, revert your patch and study the problem. You should aim to be the one to revert your patch. You will be racing everyone
   else on the team who will also be trying to revert your patch. (See below for guidance on reverting PRs.)

_See also: [What should I work on?](What-should-I-work-on.md)_

## Tests

Every change in the flutter/flutter and flutter/packages repos
must be tested; consider using the code coverage tools to check that all your
new code is covered by tests (see [Test coverage for package:flutter](./testing/Test-coverage-for-package-flutter.md)).

There is an automatic exception for PRs that:

* only remove code (no modified or added lines) to remove a feature or remove dead code.
   * **removing code to fix a bug still needs a test**, the exemption does not apply
* only affect comments (including documentation).
* only affect code inside the `.github` directory or `.ci.yaml` config files.
* only affect `.md` files.
* are generated by automated bots (rollers).

If a reviewer says a PR should have a test, then it needs a test regardless of the exemptions above.

Feel free to update the bot's logic to catch more cases that should be
automatically exempt ([in the cocoon repo](https://github.com/flutter/cocoon/blob/main/app_dart/lib/src/request_handlers/github/webhook_subscription.dart)).

> [!NOTE]
> PRs adding data-driven fixes require tests that fall under the test_fixes
> directory, but are _not_ yet recognized by the bot as being tested.

The following kinds of PRs are *not* automatically exempt and require an exemption even if the answer may be obvious:

* refactors with no semantic change (e.g. null safety migrations)
* configuration changes in the aforementioned repos
* changes to analysis (fixing lints, turning on lints)
* changes to test infrastructure
* manual dependency rolls
* fixes to existing tests
* cosmetic fixes to unpublished example apps.

**In the repositories listed above, a bot will comment on your PR if you need an explicit exemption.**

> [!IMPORTANT]
> If the PR is in a repository that is not listed above, meaning is not
> supported by the bot, then it is _still_ a responsibility of the pull request
> reviewer to make sure that tests have been added to support the code change.

### Test Exemptions

A `@test-exemption-reviewer` member on [Discord](Chat.md) can exempt a PR by
commenting `test-exempt: <reason>`.

The reviewer of the PR (_not_ the test exemption reviewer) should first:

1. ensure that the PR meets the criteria for exemption
1. LGTM the PR before requesting the exemption, _or_ clarify why an LGTM was
   not given.

Exemption reviewers are a **small volunteer group** - _all_ reviewers should
feel empowered to ask for tests.

## Using git

Assuming your environment has been configured according to the instructions in
[Setting up the Engine development environment](../../docs/engine/contributing/Setting-up-the-Engine-development-environment.md),
[Setting up the Framework development environment](Setting-up-the-Framework-development-environment.md), or
[Setting up the Packages development environment](../ecosystem/contributing/Setting-up-the-Packages-development-environment.md),
follow these steps to start working on a patch:

 * `git fetch upstream`
 * `git checkout upstream/main -b name_of_your_branch`
 * `flutter update-packages`
 * Hack away.
 * `git commit -a -m "<your informative commit message>"`
 * `git push origin name_of_your_branch`

GitHub provides you with a link for submitting the pull request in the message output by `git push`.

Because `git pull` will often miss tags that are used to define the release of the flutter tool, it is recommended to use `git fetch` typically to avoid version mismatches when running `flutter update-packages`.

Use `git fetch upstream; git rebase upstream/main; git push origin your_branch_name` to update your PRs, rather than using merge, because that way our tooling will recognize your PR as being up to date. (Otherwise it'll try testing against the tests at the time you originally branched.) Also, **be wary of force pushing to your PR branch** if you are dealing with golden image tests; see [gold troubleshooting instructions](./testing/Writing-a-golden-file-test-for-package-flutter.md#troubleshooting).

Please make sure all your patches have detailed commit messages explaining what the problem was and
what the solution is. (Avoid GitHub @-mentions in commit messages. GitHub turns this into a notification
for the person any time someone rebases your commit on their own fork. On a project of this size, that's
rather disruptive. If you need to @-mention someone, do it as a separate comment on the PR.)

You must complete the
[Contributor License Agreement](https://cla.developers.google.com/clas).
You can do this online, and it only takes a minute.


## Getting a code review

Every PR must be code-reviewed before check-in, including things like
rolling a dependency. Getting a review means that a regular Flutter
contributor (someone with commit access; see [contributor access](Contributor-access.md) for details) has "approved" the PR in the
GitHub UI. We call this "getting an LGTM" ("looks good to me").

If you are not yourself someone with commit access, then a second person
with commit access must also review and approve your PR. This ensures that
two people with commit access (trusted contributors) agree on every commit.

### Why

Code review serves many critical purposes. There's the obvious
purpose: catching errors. Even the most experienced engineers
frequently make errors that are caught by code review. But there are
also many other benefits of code reviews:

 * It spreads knowledge among the team. Since every line of code will
   have been read by two people, it's more likely that once you move
   on, someone else will understand the code.

 * It keeps you honest. Knowing that someone will be reading your
   code, you are less tempted to cut corners and more motivated to
   write code you are proud of.

 * It exposes you to different modes of thinking. Your code reviewer
   has probably not thought about the problem in the same way you
   have, and so may have a fresh perspective and may find you a better
   way to solve the problem.

We recommend you consider
[these suggestions](https://testing.googleblog.com/2017/06/code-health-too-many-comments-on-your.html)
for addressing code review comments on your PR.

### When

If you're working on a big patch, don't hesitate to get reviews early,
before you're ready to check code in. Also, don't hesitate to ask for
multiple people to review your code, and don't hesitate to provide unsolicited
comments on other people's PRs (although approvals in the GitHub UI
should be reserved for those with contributor access). The more
reviews the better.

If nobody reviews your PR within two weeks, you can ask for
a review via our [Chat](Chat.md) channels. Start by asking in #hackers,
saying what your patch does and providing a link.

### Who

PRs are assigned reviewers weekly. The precise process varies by team but tends to be combined with issue [triage](../triage/README.md).

Code should be reviewed by the owner (tech lead) of the area(s) of the codebase that you are changing,
or someone to whom they have delegated that authority.
If anyone else leaves comments, please also wait for their approval (LGTM) before landing code.

If nobody has reviewed your code after two weeks, then reach out on our [Chat](Chat.md) channels.
The `#hackers-new` channel is a good place to ask for help if you're a new contributor.

### How

Code review status is managed via GitHub's approval system. PRs should
not be merged unless one or more contributors with commit access (at
least one of which should be very familiar with the code in question)
have approved the PR in the GitHub UI.

Reviewers should carefully read the code and make sure they understand
it. A reviewer should check the code for both high level concerns,
such as whether the approach is reasonable and whether the code's structure makes sense, as well as
lower-level issues like how readable the code is and adherence to the
[Flutter style guide](Style-guide-for-Flutter-repo.md).
Use [these best practices](https://mtlynch.io/human-code-reviews-1/)
when reviewing code and providing comments.

As a reviewer, you are the last line of defense.

0. Did the author sign the CLA? If not, ask them to do so and don't look at the code.
1. Take a step back. What problem is the PR trying to solve? Is it a real problem?
2. What other solutions could we consider? What could we do to make this even better?
3. Is it the best API? See our [philosophy](Style-guide-for-Flutter-repo.md#philosophy) section. Look for state duplication, synchronous slow work, complecting, global state, overly-specific APIs, API cliffs and API oceans, API design in a vacuum (without a customer). If these terms don't make sense, read the style guide again. :-)
4. Is it the best implementation? Again, see our [style guide](Style-guide-for-Flutter-repo.md#coding-patterns-and-catching-bugs-early), in particular its section on good coding patterns. Are there hacks? Are we taking on more technical debt? Think of ways in which the code could break.
5. Is it testable? Is it tested? **All code must be tested.** Are there asserts? Encourage liberal use of assertions.
6. Look for mistakes in indenting the code and other trivial formatting problems.
7. Is new code licensed correctly?
8. Is the documentation thorough and useful? Look for useless documentation, empty prose, and breadcrumbs. See the [documentation section](Style-guide-for-Flutter-repo.md#documentation-dartdocs-javadocs-etc) of our style guide for what that means.
9. Check for good grammar in API docs and comments. Check that identifiers are named according to our conventions.

Once you are satisfied with the contribution, and _only_ once you are satisfied,
use the GitHub "Approval" mechanism (an "LGTM" comment is not sufficient).
If you feel like you are being worn down, hand the review to someone else. Consider
our [conflict resolution](https://github.com/flutter/flutter/blob/main/CODE_OF_CONDUCT.md#conflict-resolution)
policy if you feel like you are being forced to agree to something you don't like.

Reviewers should not give an LGTM unless the patch has tests that verify
all the affected code, or unless a test would make no sense. If you
review a patch, you are sharing the responsibility for the patch with
its author. You should only give an LGTM if you would feel confident
answering questions about the code.

In general, reviewers should favor approving a PR once it is in a state where it definitely improves the overall code health of the system being worked on, even if the PR isn't perfect. Reviewers should also provide positive feedback throughout the process, to offset the impact of the stream of critiques that is code review.

Reviewers should always feel free to leave comments expressing that something could be better, but if it's not very important, prefix it with something like "Shouldn't block this PR but: " to let the author know that it's just a point of polish that they could choose to ignore in the current PR (these should be documented in TODO comments with a tracking issue).

If you are not a regular Flutter contributor (someone with commit access),
we very much welcome your reviews on code contributions in the form of comments
on the code, but please refrain from approving or LGTM'ing changes, as it
confuses PR authors, who may think your approval is authoritative and merge
the PR prematurely.

When commenting on a PR, keep in mind the following mantra:

* Be polite and grateful. Graceful professionalism.
* Explain what is happening. Explain why it is happening.
* Provide next steps. Set expectations.

It's better to close a PR than to leave it in limbo.

_See also:_
* _[How to review a Flutter PR](https://docs.google.com/presentation/d/1apKVLEAEqxINby49JhLWSLI-CMH0nxCcnrf90nW4cts/edit?usp=sharing)_
* _[AI guidelines for reviewers](#reviewer-guidelines)_

### What (to do when the patch is abandoned)

Sometimes the contributor is unable to finish the work of landing the patch. In that case, if the PR has promise, we may close it but mention it on the relevant issue so that other interested parties can pick it up. Such issues are given the label [`has partial patch`](https://github.com/flutter/flutter/labels/has%20partial%20patch).

## AI contribution guidelines

PRs prepared using AI tools must follow these requirements:

1. You must review all AI-generated code before opening a (non-draft) PR, and before requesting
   re-review of any updates to the PR.
   * You are responsible for ensuring that code you submit meets the Flutter project’s standards.
   * Unmodified AI output generally does not meet those standards.
2. You must understand and be able to discuss the code in the PR.
   * Non-trivial PRs require discussion and iteration during review. If you do not understand the
     code, you cannot meaningfully respond to review feedback.
   * In our experience, simply feeding review feedback into an AI agent and uncritically reposting
     its output will not lead to a constructive review.
3. You must verify the accuracy of any AI-generated text you include in the PR description or
   review discussion comments.
   * If an AI provides you incorrect information, it is just hallucinating; if you choose to paste
     that text into GitHub, you are misrepresenting your PR to your reviewer.
   * In particular, do not tell a reviewer that you have addressed their feedback just because
     AI output says so. It is your responsibility to make sure that review feedback has actually
     been addressed.

### Reviewer guidelines

Because the Flutter team’s time is limited, and the capacity for people outside the team to generate
plausible-looking code is unlimited, be mindful as a reviewer about what code you choose to review.
Consider immediately closing PRs that have any of the following red flags:

* The PR description has entirely replaced our template with AI-generated output, and the PR is
  missing at least one obvious checklist item (tests, issue link, etc.).
  * If the contributor did not follow our process from the outset, they are unlikely to
    understand what is expected of them during review.
* The PR description does not match the changes.
  * If the contributor did not review both the changes and the description enough to notice this,
    they have not followed the AI contribution policy.
* The PR contains irrelevant AI-generated files, such as agent planning .md files.
  * If the contributor did not review the changes enough to notice and remove these files, they
    have not followed the AI contribution policy.

As always when closing a PR, explain why and provide next steps.

As a guiding principle, if at any point in the process you feel that you are getting unfiltered
or minimally filtered AI output as code and/or comment responses, ask yourself:
* If this PR weren’t here, would I choose to spend my time fixing this issue?
* Would I choose to fix it using an AI agent that took hours or days to respond to every prompt?

Unless the answer to both questions is yes, the review is not a good use of your time.

This applies even if you are multiple rounds into the review: if the contributor closed the PR,
would you take it over using an extremely high-latency agent? Beware the sunk cost fallacy.

### Philosophy

A common question in discussions around AI policies for open source projects is: “Why have an
AI policy at all? Why does it matter how the code was created; shouldn’t the code speak for itself?”

In general, we agree, which is why our policy focuses on behaviors rather than tools. The behaviors
that led to the creation of this policy are problematic regardless of whether they are AI-generated
or human-generated. However, it is useful to highlight these policies in the context of AI because
we have seen that these behaviors are orders of magnitude more common when AI is involved. For example:
* Submitting a PR containing hundreds of lines of code that the contributor doesn't understand is
  always a problem. This was rare before the widespread use of AI agents, but is more common with
  AI-assisted development.
* Having several rounds of exchanges where a reviewer asks for a change, and the contributor says
  that they have made that change but haven't, is always a waste of reviewer time. It’s very rare
  for a contributor to deliberately and obviously lie to a reviewer, but unfortunately common
  for contributors to uncritically repeat AI agent hallucinations.
* PRs that ignore our process have always been problematic, because standardizing the PR process
  is an important part of how we keep our review load manageable. However, a contributor who has
  spent hours or days on a PR is much more likely to take some time to learn and follow our process
  to avoid having that effort be wasted than someone who spent a few minutes generating the PR.

## Landing a patch

Once you have submitted your patch and received your LGTM, if you do not have commit access to
the repository yet, then wait for one of the project maintainers to submit it for you.

If you do have access, add the "autosubmit" label. A bot will land the PR for you.

## Tree breakage (regressions in functionality)

If a check-in has caused a regression on the main branch (sometimes "master") for any of the flutter repositories,
revert (roll back) the check-in (even if it isn't yours). Do not attempt to forward-fix post-submit test failures.

There is no shame in making mistakes! Reverts happen all the time and are a normal part of engineering.

To revert a PR, just add the `revert` label to it. _For more details, see [Landing Changes With Autosubmit](../infra/Landing-Changes-With-Autosubmit.md)._


### Avoid "Revert "Revert "Revert "Revert "Fix foo"""" commit messages

Please limit yourself to one "Revert" per commit message, otherwise we won't
have any idea what is actually landing. Is it putting us back to where we were before?
Is it adding new code? Is it a controversial new feature that actually caused
a regression before but is now fixed (we hope)?

Only use "Revert" if you are actually returning us to a known-good state.

Also avoid using "Reland" in the commit message.
When you later revert the revert, just land the PR afresh with the original commit message,
possibly updated with the information since collected, and include a link
to the original PR and to the revert PR so that people can follow the breadcrumbs later.


## Regressions in performance

After each check-in, please monitor the [performance dashboards](https://flutter-dashboard.appspot.com/).

If you see a regression (any of the charts increasing after your commit), please
follow these steps:

* Comment on the PR acknowledging the regression.
* If the regression is expected and is a desirable trade-off (e.g. disk size
increased slightly in exchange for a significant improvement in speed), then
rebaseline the relevant benchmarks (log in, then click the magnifying glass
at the top right of each chart, then click the button to auto rebaseline and
commit).
* If the regression is not expected, and may be a problem in your PR, revert
your PR and investigate.
* If the regression is not expected, and is quite severe, revert your PR and
investigate.
* If the regression is not expected, and is not severe, and is definitely not
a problem in your PR (e.g. you changed a comment and the analyzer performance
got worse, or you deleted a README and the rasterizer slowed down), then file
a bug, labeled with the "regression", "performance", `P0` labels, and either
investigate or delegate to someone to investigate. The investigation should be
considered a high priority. It is your responsibility to make sure that the
cause is understood within a few days.

Performance regressions are not a problem so long as they are promptly dealt with.
Therefore, Flutter considers all unexpected performance regressions to be `P0` until
we have it under control (e.g. we know what caused it and either have a fix under
way or have determined it is an acceptable trade-off).

### Performance regressions caused by auto-roller commits

Although reverting a normal commit that caused performance regressions is the default
behavior, reverting an [auto-roller](../infra/Autorollers.md)
(e.g., an engine-roller commit like https://github.com/flutter/flutter/commit/fdcb57b69eff2162e9aead6dec0f8058788e7608)
commit could cause some complications:

1. The auto-roller commit usually include multiple commits of the source repo (e.g., skia-roller
commit includes multiple commits of https://github.com/google/skia). This can be applied
recursively as some rollers might include a commit from another roller.
Therefore, a roller commit could actually include a ton of leaf-level commits, which makes it
really hard to triage which leaf commit actually caused the regression.

2. The auto-roller will try to roll again as soon as possible that will reland any changes reverted
by a Flutter commit revert. So in order to keep the revert effective, one has to either
(1) pause the auto-roller, or (2) revert the leaf commit in the source repo.

3. If the auto-roller is paused for a long time (say 1 day), the source repo will accumulate many
commits. That makes the next roll very hard to manage: it's difficult to triage a build failure
or a new performance regression caused by the next roll, since that roll will include all the commits
in the paused period.

Therefore, reverting a roller commit or pausing the auto-roller is
*NOT* the default action if it causes a performance regression.
The default action should be to file an issue with labels "performance", "regression", and `P0`
immediately, and start investigating which leaf-commit caused the regression. Once the leaf-commit
is identified, check if it's an expected trade-off. If so, remove the `P0` label and try to see
if there's any way to mitigate the regression. If not, revert the leaf commit in the source repo
and let the auto-roller apply that revert. Once the revert is rolled into Flutter, close the issue.

## Handling interdependent/multi-repo changes

If you're working on a feature that requires changes in both the [framework](https://github.com/flutter/flutter) and [engine](https://github.com/flutter/flutter) repos, you'll need to make 2 separate PRs. In such situation CI on the framework PR may fail because it depends on engine code that is not (yet) on engine repo's main branch. In such situation, you need to land the changes in the engine first, wait for them to roll into the framework's main branch, and then rebase your framework PR.

## Handling breaking changes

In general, we want to avoid making changes to Flutter, our plugins, or our packages, that force developers using Flutter to change their code in order to upgrade to new versions of Flutter. See [our compatibility policy](https://docs.flutter.dev/resources/compatibility).

Sometimes, however, doing this is necessary for the greater good. We want our APIs to be
intuitive; if being backwards-compatible requires making an API into something that we would
never have designed that way unless forced to by circumstances, then we should instead break
the API and make it good.

The process for making breaking changes is as follows:

### 1. Determine if your change is a breaking change

Implement the change you wish to see and run the existing tests against your new code (without having changed the tests first). Changes that break (i.e. require changes to) one or more of the contributed tests are considered "breaking changes".

The "contributed tests" are:

* Those in the [`customer_testing`](https://github.com/flutter/tests) shard on `flutter/flutter` PRs.
* Additional test suites that we have been allowed to run but that are not public. (Notably, Google allows us to run several tens of thousands of [proprietary tests](../infra/Understanding-Google-Testing.md) on each commit.)

There are no exemptions to this policy, because these tests run in our CI and breaking them will close the tree.

In cases where these tests pass but we can nonetheless imagine reasonable scenarios where developers would be affected negatively, by courtesy, once the change has landed, engineers are encouraged to announce the changes by sending an e-mail to [flutter-announce@](https://groups.google.com/g/flutter-announce), a message to the `#announcements` channel on our [Chat](Chat.md), and tagging the relevant issues with the [**c: API break** label](https://github.com/flutter/flutter/labels/c%3A%20API%20break) (such that they will be included in our release notes). However, we do not consider these breaking changes. (One reason to do this would be if we see our own tests being significantly affected, even if no contributed test actually fails.)

### 2. Evaluate the breaking change

If your change counts as a breaking change, seriously consider whether it is truly necessary and beneficial. Per the [RFC Threshold](https://github.com/flutter/rfc/blob/main/rfc/000.0002-flutter-rfc-review-process.md#when-to-write-an-rfc-the-threshold), breaking changes require a full design doc (RFC) in the [flutter/rfc](https://github.com/flutter/rfc) repository before coding the change. The RFC is categorized under the primary subsystem being changed (e.g. `130` for widgets, `210` for graphics; see [RFC 000.0001](https://github.com/flutter/rfc/blob/main/rfc/000.0001-flutter-architecture-and-reference-taxonomy.md) for taxonomy). Also review our guidance in [Design Documents](Design-Documents.md), discuss it with your code reviewer, and raise it in [Chat](Chat.md).

### 3. Prepare your change.

If you decide your change is valuable enough to deploy, adjust your PR so that it introduces the new functionality, API, behavior change, etc, in an opt-in fashion, thus avoiding the immediate breakage.

_For example, rather than replacing a widget with another, introduce the new widget and discourage use of the old one. Rather than changing the order in which a certain argument is processed, provide a flag that selects which order the arguments will be processed in._

When changing the semantics of an API with a temporary opt-in, a three-phase change is needed (adding the new API and opt-in, then removing the old API, then removing the opt-in.)

If possible, avoid four-phase deprecations (adding a new API with a temporary name and deprecating an old API, removing the old API, changing the new API to the old name and deprecating the temporary name, and finally removing the temporary name), because they involve a lot of churn and will irritate our developers.

Stage your change and the documentation for your change. Typically this will be two or more PRs, plus PRs to fix the tests that were broken (see step 1), as well as writing a migration guide as a PR to the Website repository.

If possible, include flutter fixes to aid users in migration. Whether or not the change is supported by flutter fix should be included in the migration guide. To learn about authoring fixes, see [Data driven Fixes](Data-driven-Fixes.md).

**Use our [breaking change migration guide template](https://github.com/flutter/website/blob/main/sites/docs/src/content/release/breaking-changes/template.md)** (follow all the instructions in the comments) to create the migration guide that describes the change. Do not land the migration guide at this time. You will need to update it before you land it in the last step.

### 4. Land your change.

Once you are ready, have received feedback, iterated on your design and your migration guide, land your initial change and start migrating clients. *Do not yet land the migration guide.* Once all the clients are migrated, land your final change. (You may have several iterations here if you have a multiphase roll-out.)

During this process, each individual PR does not break any tests, so it should not block any autorollers.


### 5. Document the change, including clear documentation for migrating code, with samples, and clear rationales for each change

Once everything has landed:

* update your migration guide based on your experience migrating everyone,
* update the timeline on the guide, and push it to [the flutter.dev Web site](https://docs.flutter.dev/release/breaking-changes) (don't forget to update the [index](https://github.com/flutter/website/blob/main/sites/docs/src/content/release/breaking-changes/index.md) of that directory as well),
* e-mail a copy to [flutter-announce@](https://groups.google.com/g/flutter-announce),
* notify the `#announcements` channel on our [Chat](Chat.md), and
* add the [**c: API break** label](https://github.com/flutter/flutter/labels/c%3A%20API%20break) to the relevant issues, so they get listed in the upcoming Release notes.

### Deprecations

Old APIs can be marked as deprecated as part of this process. Deprecation is not a way to avoid making a breaking change; you should consider deprecating an API to be equivalent to removing it, as some of our customers (and we ourselves) consider using a deprecated API to be anathema (triggering a build failure).

The syntax for deprecations must match the following pattern:

```dart
@Deprecated(
  'Call prepareFrame followed by owner.requestVisualUpdate() instead. '
  'This will enable an improvement to performance in a future version of Flutter. '
  'This feature was deprecated after v2.9.0-0.1.pre.'
)
```

In other words:

```dart
@Deprecated(
  '[description of how to migrate] '
  '[brief motivation for why we are breaking the API] '
  'This feature was deprecated after v[beta version at time of deprecation].'
)
```

Using this standard form ensures that we can write a script to detect all deprecated APIs and remove them. We have a test that verifies that this syntax is followed.

To determine the latest beta version, see <https://docs.flutter.dev/install/archive>.

When adding a deprecation notice to the framework, a flutter fix should be included with your change. This helps users migrate to the new API as easily as possible. To learn more about authoring fixes, see [Data driven Fixes](Data-driven-Fixes.md). If a fix cannot be written for the new API, please file an issue in https://github.com/dart-lang/sdk and link to it in your change.

When deprecating features, be aware that *you* will not by default be informed when the Flutter code itself uses the deprecated feature (there is a `deprecated_member_use_from_same_package: ignore` line in the root `analysis_options.yaml` file). To find places where the old feature is used, rename its declaration and see where the compiler complains. (You can't just comment out the "ignore" in the `analysis_options.yaml` file because it's hiding hundreds of other warnings...)

Removing deprecated APIs from the framework are not currently planned. In the past, deprecations were removed after a set
amount of time. This is not currently in practice. If and when we do resume removing deprecated APIs, it will be announced
across several channels like the [flutter-announce group](https://groups.google.com/g/flutter-announce), and the
[Discord](../contributing/Chat.md).

## Skipped Tests

Tests can be skipped using the `skip` parameter of `test()`, `group()` and `testWidgets()`. However, they  should be kept to a minimum and only done for the following two reasons.

The first is if there is a test that is flaky, we can mark is as *temporarily* skipped to keep the tree green while a fix for it is developed. For these types of skips you need to file a tracking issue so we can ensure there is follow up to remove the skip. This tracking issue should be tagged with the `skip-test` label. Then in a comment on the same line as the parameter, include a link to this issue:

```dart
  skip: true, // https://github.com/flutter/flutter/issues/XXXXX
```

The other reason to use the skip parameter is to mark a test that by design doesn't make sense to test under a specific condition. An example would be a test that only tests a feature available on a specific platform or environment. For these cases, include a comment on the same line as the skip parameter with the text `[intended]` and a short description of why the skip is needed:

```dart
  skip: isBrowser, // [intended] There are no default transitions to test on the web.
```

If the analyzer script sees a skip without a comment containing either an issue link or an `[intended]` tag, it will report and error and fail the check.