CONTRIBUTING.md - third_party/github/bazelbuild/rules_python - Git at Google

 # How to contribute

 We'd love to accept your patches and contributions to this project. There are
 just a few small guidelines you need to follow.

 ## Contributor License Agreement

 First, the most important step: signing the Contributor License Agreement. We
 cannot look at any of your code unless one is signed.

 Contributions to this project must be accompanied by a Contributor License
 Agreement. You (or your employer) retain the copyright to your contribution,
 this simply gives us permission to use and redistribute your contributions as
 part of the project. Head over to <https://cla.developers.google.com/> to see
 your current agreements on file or to sign a new one.

 You generally only need to submit a CLA once, so if you've already submitted one
 (even if it was for a different project), you probably don't need to do it
 again.

 ## Getting started

 Before we can work on the code, we need to get a copy of it and setup some
 local environment and tools.

 First, fork the code to your user and clone your fork. This gives you a private
 playground where you can do any edits you'd like. For this guide, we'll use
 the [GitHub `gh` tool](https://github.com/cli/cli)
 ([Linux install](https://github.com/cli/cli/blob/trunk/docs/install_linux.md)).
 (More advanced users may prefer the GitHub UI and raw `git` commands).

 ```shell
 gh repo fork bazelbuild/rules_python --clone --remote
 ```

 Next, make sure you have a new enough version of Python installed that supports the
 various code formatters and other devtools. For a quick start,
 [install pyenv](https://github.com/pyenv/pyenv-installer) and
 at least Python 3.9.15:

 ```shell
 curl https://pyenv.run | bash
 pyenv install 3.9.15
 pyenv shell 3.9.15
 ```

 ## Development workflow

 It's suggested that you create what is called a "feature/topic branch" in your
 fork when you begin working on code you want to eventually send or code review.

 ```
 git checkout main # Start our branch from the latest code
 git checkout -b my-feature # Create and switch to our feature branch
 git push origin my-feature # Cause the branch to be created in your fork.
 ```

 From here, you then edit code and commit to your local branch. If you want to
 save your work to github, you use `git push` to do so:

 ```
 git push origin my-feature
 ```

 Once the code is in your github repo, you can then turn it into a Pull Request
 to the actual rules_python project and begin the code review process.

 ## Developer guide

 For more more details, guidance, and tips for working with the code base,
 see [DEVELOPING.md](DEVELOPING.md)

 ## Formatting

 Starlark files should be formatted by
 [buildifier](https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md).
 Otherwise the Buildkite CI will fail with formatting/linting violations.
 We suggest using a pre-commit hook to automate this.
 First [install pre-commit](https://pre-commit.com/#installation),
 then run

 ```shell
 pre-commit install
 ```

 ### Running buildifer manually

 You can also run buildifier manually. To do this,
 [install buildifier](https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md),
 and run the following command:

 ```shell
 $ buildifier --lint=fix --warnings=native-py -warnings=all WORKSPACE
 ```

 Replace the argument "WORKSPACE" with the file that you are linting.

 ## Code reviews

 All submissions, including submissions by project members, require review. We
 use GitHub pull requests for this purpose. Consult [GitHub Help] for more
 information on using pull requests.

 [GitHub Help]: https://help.github.com/articles/about-pull-requests/

 ### Commit messages

 Commit messages (upon merging) and PR messages should follow the [Conventional
 Commits](https://www.conventionalcommits.org/) style:

 ```
 type(scope)!: <summary>

 <body>

 BREAKING CHANGE: <summary>
 ```

 Where `(scope)` is optional, and `!` is only required if there is a breaking change.
 If a breaking change is introduced, then `BREAKING CHANGE:` is required; see
 the [Breaking Changes](#breaking-changes) section for how to introduce breaking
 changes.

 User visible changes, such as features, fixes, or notable refactors, should
 be documneted in CHANGELOG.md and their respective API doc. See [Documenting
 changes] for how to do so.

 Common `type`s:

 * `build:` means it affects the building or development workflow.
 * `docs:` means only documentation is being added, updated, or fixed.
 * `feat:` means a user-visible feature is being added. See [Documenting version
   changes] for how to documenAdd `{versionadded}`
   to appropriate docs.
 * `fix:` means a user-visible behavior is being fixed. If the fix is changing
   behavior of a function, add `{versionchanged}` to appropriate docs, as necessary.
 * `refactor:` means some sort of code cleanup that doesn't change user-visible
   behavior. Add `{versionchanged}` to appropriate docs, as necessary.
 * `revert:` means a prior change is being reverted in some way.
 * `test:` means only tests are being added.

 For the full details of types, see
 [Conventional Commits](https://www.conventionalcommits.org/).

 ### Documenting changes

 Changes are documented in two places: CHANGELOG.md and API docs.

 CHANGELOG.md contains a brief, human friendly, description. This text is
 intended for easy skimming so that, when people upgrade, they can quickly get a
 sense of what's relevant to them.

 API documentation are the doc strings for functions, fields, attributes, etc.
 When user-visible or notable behavior is added, changed, or removed, the
 `{versionadded}`, `{versionchanged}` or `{versionremoved}` directives should be
 used to note the change. When specifying the version, use the values
 `VERSION_NEXT_FEATURE` or `VERSION_NEXT_PATCH` to indicate what sort of
 version increase the change requires.

 These directives use Sphinx MyST syntax, e.g.

 ```
 :::{versionadded} VERSION_NEXT_FEATURE
 The `allow_new_thing` arg was added.
 :::

 :::{versionchanged} VERSION_NEXT_PATCH
 Large numbers no longer consume exponential memory.
 :::

 :::{versionremoved} VERSION_NEXT_FEATURE
 The `legacy_foo` arg was removed
 :::
 ```

 ## Generated files

 Some checked-in files are generated and need to be updated when a new PR is
 merged:

 * **requirements lock files**: These are usually generated by a
   `compile_pip_requirements` update target, which is usually in the same directory.
   e.g. `bazel run //docs:requirements.update`

 ## Binary artifacts

 Checking in binary artifacts is not allowed. This is because they are extremely
 problematic to verify and ensure they're safe

 Examples include, but aren't limited to: prebuilt binaries, shared libraries,
 zip files, or wheels.


 (breaking-changes)=
 ## Breaking Changes

 Breaking changes are generally permitted, but we follow a 3-step process for
 introducing them. The intent behind this process is to balance the difficulty of
 version upgrades for users, maintaining multiple code paths, and being able to
 introduce modern functionality.

 The general process is:

 1. In version `N`, introduce the new behavior, but it must be disabled by
    default. Users can opt into the new functionality when they upgrade to
    version `N`, which lets them try it and verify functionality.
 2. In version `N+1`, the new behavior can be enabled by default. Users can
    opt out if necessary, but doing so causes a warning to be issued.
 3. In version `N+2`, the new behavior is always enabled and cannot be opted out
    of. The API for the control mechanism can be removed in this release.

 Note that the `+1` and `+2` releases are just examples; the steps are not
 required to happen in immediately subsequent releases.

 Once The first major version is released, the process will be:
 1. In `N.M.0` we introduce the new behaviour, but it is disabled by a feature flag.
 2. In `N.M+1.0` we may choose the behaviour to become the default if it is not too
    disruptive.
 3. In `N+1.0.0` we get rid of the old behaviour.

 ### How to control breaking changes

 The details of the control mechanism will depend on the situation. Below is
 a summary of some different options.

 * Environment variables are best for repository rule behavior. Environment
   variables can be propagated to rules and macros using the generated
   `@rules_python_internal//:config.bzl` file.
 * Attributes are applicable to macros and regular rules, especially when the
   behavior is likely to vary on a per-target basis.
 * [User defined build settings](https://bazel.build/extending/config#user-defined-build-settings)
   (aka custom build flags) are applicable for rules when the behavior change
   generally wouldn't vary on a per-target basis. They also have the benefit that
   an entire code base can have them easily enabled by a bazel command line flag.
 * Allowlists allow a project to centrally control if something is
   enabled/disabled. Under the hood, they are basically a specialized custom
   build flag.

 Note that attributes and flags can seamlessly interoperate by having the default
 controlled by a flag, and an attribute can override the flag setting. This
 allows a project to enable the new behavior by default while they work to fix
 problematic cases to prepare for the next upgrade.

 ### What is considered a breaking change?

 Precisely defining what constitutes a breaking change is hard because it's
 easy for _someone, somewhere_ to depend on _some_ observable behavior, despite
 our best efforts to thoroughly document what is or isn't supported and hiding
 any internal details.

 In general, something is considered a breaking change when it changes the
 direct behavior of a supported public API. Simply being able to observe a
 behavior change doesn't necessarily mean it's a breaking change.

 Long standing undocumented behavior is a large grey area and really depends on
 how load-bearing it has become and what sort of reasonable expectation of
 behavior there is.

 Here's some examples of what would or wouldn't be considered a breaking change.

 Breaking changes:
   * Renaming an function argument for public functions.
   * Enforcing stricter validation than was previously required when there's a
     sensible reason users would run afoul of it.
   * Changing the name of a public rule.

 Not breaking changes:
   * Upgrading dependencies
   * Changing internal details, such as renaming an internal file.
   * Changing a rule to a macro.

 ## FAQ

 ### Installation errors when during `git commit`

 If you did `pre-commit install`, various tools are run when you do `git commit`.
 This might show as an error such as:

 ```
 [INFO] Installing environment for https://github.com/psf/black.
 [INFO] Once installed this environment will be reused.
 [INFO] This may take a few minutes...
 An unexpected error has occurred: CalledProcessError: command: ...
 ```

 To fix, you'll need to figure out what command is failing and why. Because these
 are tools that run locally, its likely you'll need to fix something with your
 environment or the installation of the tools. For Python tools (e.g. black or
 isort), you can try using a different Python version in your shell by using
 tools such as [pyenv](https://github.com/pyenv/pyenv).
	# How to contribute

	We'd love to accept your patches and contributions to this project. There are
	just a few small guidelines you need to follow.

	## Contributor License Agreement

	First, the most important step: signing the Contributor License Agreement. We
	cannot look at any of your code unless one is signed.

	Contributions to this project must be accompanied by a Contributor License
	Agreement. You (or your employer) retain the copyright to your contribution,
	this simply gives us permission to use and redistribute your contributions as
	part of the project. Head over to <https://cla.developers.google.com/> to see
	your current agreements on file or to sign a new one.

	You generally only need to submit a CLA once, so if you've already submitted one
	(even if it was for a different project), you probably don't need to do it
	again.

	## Getting started

	Before we can work on the code, we need to get a copy of it and setup some
	local environment and tools.

	First, fork the code to your user and clone your fork. This gives you a private
	playground where you can do any edits you'd like. For this guide, we'll use
	the [GitHub `gh` tool](https://github.com/cli/cli)
	([Linux install](https://github.com/cli/cli/blob/trunk/docs/install_linux.md)).
	(More advanced users may prefer the GitHub UI and raw `git` commands).

	```shell
	gh repo fork bazelbuild/rules_python --clone --remote
	```

	Next, make sure you have a new enough version of Python installed that supports the
	various code formatters and other devtools. For a quick start,
	[install pyenv](https://github.com/pyenv/pyenv-installer) and
	at least Python 3.9.15:

	```shell
	curl https://pyenv.run \| bash
	pyenv install 3.9.15
	pyenv shell 3.9.15
	```

	## Development workflow

	It's suggested that you create what is called a "feature/topic branch" in your
	fork when you begin working on code you want to eventually send or code review.

	```
	git checkout main # Start our branch from the latest code
	git checkout -b my-feature # Create and switch to our feature branch
	git push origin my-feature # Cause the branch to be created in your fork.
	```

	From here, you then edit code and commit to your local branch. If you want to
	save your work to github, you use `git push` to do so:

	```
	git push origin my-feature
	```

	Once the code is in your github repo, you can then turn it into a Pull Request
	to the actual rules_python project and begin the code review process.

	## Developer guide

	For more more details, guidance, and tips for working with the code base,
	see [DEVELOPING.md](DEVELOPING.md)

	## Formatting

	Starlark files should be formatted by
	[buildifier](https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md).
	Otherwise the Buildkite CI will fail with formatting/linting violations.
	We suggest using a pre-commit hook to automate this.
	First [install pre-commit](https://pre-commit.com/#installation),
	then run

	```shell
	pre-commit install
	```

	### Running buildifer manually

	You can also run buildifier manually. To do this,
	[install buildifier](https://github.com/bazelbuild/buildtools/blob/master/buildifier/README.md),
	and run the following command:

	```shell
	$ buildifier --lint=fix --warnings=native-py -warnings=all WORKSPACE
	```

	Replace the argument "WORKSPACE" with the file that you are linting.

	## Code reviews

	All submissions, including submissions by project members, require review. We
	use GitHub pull requests for this purpose. Consult [GitHub Help] for more
	information on using pull requests.

	[GitHub Help]: https://help.github.com/articles/about-pull-requests/

	### Commit messages

	Commit messages (upon merging) and PR messages should follow the [Conventional
	Commits](https://www.conventionalcommits.org/) style:

	```
	type(scope)!: <summary>

	<body>

	BREAKING CHANGE: <summary>
	```

	Where `(scope)` is optional, and `!` is only required if there is a breaking change.
	If a breaking change is introduced, then `BREAKING CHANGE:` is required; see
	the [Breaking Changes](#breaking-changes) section for how to introduce breaking
	changes.

	User visible changes, such as features, fixes, or notable refactors, should
	be documneted in CHANGELOG.md and their respective API doc. See [Documenting
	changes] for how to do so.

	Common `type`s:

	* `build:` means it affects the building or development workflow.
	* `docs:` means only documentation is being added, updated, or fixed.
	* `feat:` means a user-visible feature is being added. See [Documenting version
	changes] for how to documenAdd `{versionadded}`
	to appropriate docs.
	* `fix:` means a user-visible behavior is being fixed. If the fix is changing
	behavior of a function, add `{versionchanged}` to appropriate docs, as necessary.
	* `refactor:` means some sort of code cleanup that doesn't change user-visible
	behavior. Add `{versionchanged}` to appropriate docs, as necessary.
	* `revert:` means a prior change is being reverted in some way.
	* `test:` means only tests are being added.

	For the full details of types, see
	[Conventional Commits](https://www.conventionalcommits.org/).

	### Documenting changes

	Changes are documented in two places: CHANGELOG.md and API docs.

	CHANGELOG.md contains a brief, human friendly, description. This text is
	intended for easy skimming so that, when people upgrade, they can quickly get a
	sense of what's relevant to them.

	API documentation are the doc strings for functions, fields, attributes, etc.
	When user-visible or notable behavior is added, changed, or removed, the
	`{versionadded}`, `{versionchanged}` or `{versionremoved}` directives should be
	used to note the change. When specifying the version, use the values
	`VERSION_NEXT_FEATURE` or `VERSION_NEXT_PATCH` to indicate what sort of
	version increase the change requires.

	These directives use Sphinx MyST syntax, e.g.

	```
	:::{versionadded} VERSION_NEXT_FEATURE
	The `allow_new_thing` arg was added.
	:::

	:::{versionchanged} VERSION_NEXT_PATCH
	Large numbers no longer consume exponential memory.
	:::

	:::{versionremoved} VERSION_NEXT_FEATURE
	The `legacy_foo` arg was removed
	:::
	```

	## Generated files

	Some checked-in files are generated and need to be updated when a new PR is
	merged:

	* requirements lock files: These are usually generated by a
	`compile_pip_requirements` update target, which is usually in the same directory.
	e.g. `bazel run //docs:requirements.update`

	## Binary artifacts

	Checking in binary artifacts is not allowed. This is because they are extremely
	problematic to verify and ensure they're safe

	Examples include, but aren't limited to: prebuilt binaries, shared libraries,
	zip files, or wheels.


	(breaking-changes)=
	## Breaking Changes

	Breaking changes are generally permitted, but we follow a 3-step process for
	introducing them. The intent behind this process is to balance the difficulty of
	version upgrades for users, maintaining multiple code paths, and being able to
	introduce modern functionality.

	The general process is:

	1. In version `N`, introduce the new behavior, but it must be disabled by
	default. Users can opt into the new functionality when they upgrade to
	version `N`, which lets them try it and verify functionality.
	2. In version `N+1`, the new behavior can be enabled by default. Users can
	opt out if necessary, but doing so causes a warning to be issued.
	3. In version `N+2`, the new behavior is always enabled and cannot be opted out
	of. The API for the control mechanism can be removed in this release.

	Note that the `+1` and `+2` releases are just examples; the steps are not
	required to happen in immediately subsequent releases.

	Once The first major version is released, the process will be:
	1. In `N.M.0` we introduce the new behaviour, but it is disabled by a feature flag.
	2. In `N.M+1.0` we may choose the behaviour to become the default if it is not too
	disruptive.
	3. In `N+1.0.0` we get rid of the old behaviour.

	### How to control breaking changes

	The details of the control mechanism will depend on the situation. Below is
	a summary of some different options.

	* Environment variables are best for repository rule behavior. Environment
	variables can be propagated to rules and macros using the generated
	`@rules_python_internal//:config.bzl` file.
	* Attributes are applicable to macros and regular rules, especially when the
	behavior is likely to vary on a per-target basis.
	* [User defined build settings](https://bazel.build/extending/config#user-defined-build-settings)
	(aka custom build flags) are applicable for rules when the behavior change
	generally wouldn't vary on a per-target basis. They also have the benefit that
	an entire code base can have them easily enabled by a bazel command line flag.
	* Allowlists allow a project to centrally control if something is
	enabled/disabled. Under the hood, they are basically a specialized custom
	build flag.

	Note that attributes and flags can seamlessly interoperate by having the default
	controlled by a flag, and an attribute can override the flag setting. This
	allows a project to enable the new behavior by default while they work to fix
	problematic cases to prepare for the next upgrade.

	### What is considered a breaking change?

	Precisely defining what constitutes a breaking change is hard because it's
	easy for _someone, somewhere_ to depend on _some_ observable behavior, despite
	our best efforts to thoroughly document what is or isn't supported and hiding
	any internal details.

	In general, something is considered a breaking change when it changes the
	direct behavior of a supported public API. Simply being able to observe a
	behavior change doesn't necessarily mean it's a breaking change.

	Long standing undocumented behavior is a large grey area and really depends on
	how load-bearing it has become and what sort of reasonable expectation of
	behavior there is.

	Here's some examples of what would or wouldn't be considered a breaking change.

	Breaking changes:
	* Renaming an function argument for public functions.
	* Enforcing stricter validation than was previously required when there's a
	sensible reason users would run afoul of it.
	* Changing the name of a public rule.

	Not breaking changes:
	* Upgrading dependencies
	* Changing internal details, such as renaming an internal file.
	* Changing a rule to a macro.

	## FAQ

	### Installation errors when during `git commit`

	If you did `pre-commit install`, various tools are run when you do `git commit`.
	This might show as an error such as:

	```
	[INFO] Installing environment for https://github.com/psf/black.
	[INFO] Once installed this environment will be reused.
	[INFO] This may take a few minutes...
	An unexpected error has occurred: CalledProcessError: command: ...
	```

	To fix, you'll need to figure out what command is failing and why. Because these
	are tools that run locally, its likely you'll need to fix something with your
	environment or the installation of the tools. For Python tools (e.g. black or
	isort), you can try using a different Python version in your shell by using
	tools such as [pyenv](https://github.com/pyenv/pyenv).