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Document cross-module internal package rule (#4427) 
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Contributing to opentelemetry-go

The Go special interest group (SIG) meets regularly. See the OpenTelemetry community repo for information on this and other language SIGs.

See the public meeting notes for a summary description of past meetings. To request edit access, join the meeting or get in touch on Slack.

Development

You can view and edit the source code by cloning this repository:

git clone https://github.com/open-telemetry/opentelemetry-go.git

Run make test to run the tests instead of go test.

There are some generated files checked into the repo. To make sure that the generated files are up-to-date, run make (or make precommit - the precommit target is the default).

The precommit target also fixes the formatting of the code and checks the status of the go module files.

Additionally, there is a codespell target that checks for common typos in the code. It is not run by default, but you can run it manually with make codespell. It will set up a virtual environment in venv and install codespell there.

If after running make precommit the output of git status contains nothing to commit, working tree clean then it means that everything is up-to-date and properly formatted.

Pull Requests

How to Send Pull Requests

Everyone is welcome to contribute code to opentelemetry-go via GitHub pull requests (PRs).

To create a new PR, fork the project in GitHub and clone the upstream repo:

go get -d go.opentelemetry.io/otel

(This may print some warning about "build constraints exclude all Go files", just ignore it.)

This will put the project in ${GOPATH}/src/go.opentelemetry.io/otel. You can alternatively use git directly with:

git clone https://github.com/open-telemetry/opentelemetry-go

(Note that git clone is not using the go.opentelemetry.io/otel name - that name is a kind of a redirector to GitHub that go get can understand, but git does not.)

This would put the project in the opentelemetry-go directory in current working directory.

Enter the newly created directory and add your fork as a new remote:

git remote add <YOUR_FORK> git@github.com:<YOUR_GITHUB_USERNAME>/opentelemetry-go

Check out a new branch, make modifications, run linters and tests, update CHANGELOG.md, and push the branch to your fork:

git checkout -b <YOUR_BRANCH_NAME>
# edit files
# update changelog
make precommit
git add -p
git commit
git push <YOUR_FORK> <YOUR_BRANCH_NAME>

Open a pull request against the main opentelemetry-go repo. Be sure to add the pull request ID to the entry you added to CHANGELOG.md.

How to Receive Comments

  • If the PR is not ready for review, please put [WIP] in the title, tag it as work-in-progress, or mark it as draft.
  • Make sure CLA is signed and CI is clear.

How to Get PRs Merged

A PR is considered ready to merge when:

  • It has received two qualified approvals1.

    This is not enforced through automation, but needs to be validated by the maintainer merging.

    • The qualified approvals need to be from Approvers/Maintainers affiliated with different companies. Two qualified approvals from Approvers or Maintainers affiliated with the same company counts as a single qualified approval.
    • PRs introducing changes that have already been discussed and consensus reached only need one qualified approval. The discussion and resolution needs to be linked to the PR.
    • Trivial changes2 only need one qualified approval.

  • All feedback has been addressed.

    • All PR comments and suggestions are resolved.
    • All GitHub Pull Request reviews with a status of "Request changes" have been addressed. Another review by the objecting reviewer with a different status can be submitted to clear the original review, or the review can be dismissed by a Maintainer when the issues from the original review have been addressed.
    • Any comments or reviews that cannot be resolved between the PR author and reviewers can be submitted to the community Approvers and Maintainers during the weekly SIG meeting. If consensus is reached among the Approvers and Maintainers during the SIG meeting the objections to the PR may be dismissed or resolved or the PR closed by a Maintainer.
    • Any substantive changes to the PR require existing Approval reviews be cleared unless the approver explicitly states that their approval persists across changes. This includes changes resulting from other feedback. Approvers and Maintainers can help in clearing reviews and they should be consulted if there are any questions.

  • The PR branch is up to date with the base branch it is merging into.

    • To ensure this does not block the PR, it should be configured to allow maintainers to update it.

  • It has been open for review for at least one working day. This gives people reasonable time to review.

    • Trivial changes2 do not have to wait for one day and may be merged with a single Maintainer's approval.

  • All required GitHub workflows have succeeded.

  • Urgent fix can take exception as long as it has been actively communicated among Maintainers.

Any Maintainer can merge the PR once the above criteria have been met.

Design Choices

As with other OpenTelemetry clients, opentelemetry-go follows the OpenTelemetry Specification.

It's especially valuable to read through the library guidelines.

Focus on Capabilities, Not Structure Compliance

OpenTelemetry is an evolving specification, one where the desires and use cases are clear, but the method to satisfy those uses cases are not.

As such, Contributions should provide functionality and behavior that conforms to the specification, but the interface and structure is flexible.

It is preferable to have contributions follow the idioms of the language rather than conform to specific API names or argument patterns in the spec.

For a deeper discussion, see this.

Documentation

Each (non-internal, non-test) package must be documented using Go Doc Comments, preferably in a doc.go file.

Prefer using Examples instead of putting code snippets in Go doc comments. In some cases, you can even create Testable Examples.

You can install and run a "local Go Doc site" in the following way:

go install golang.org/x/pkgsite/cmd/pkgsite@latest
pkgsite

go.opentelemetry.io/otel/metric is an example of a very well-documented package.

Style Guide

One of the primary goals of this project is that it is actually used by developers. With this goal in mind the project strives to build user-friendly and idiomatic Go code adhering to the Go community's best practices.

For a non-comprehensive but foundational overview of these best practices the Effective Go documentation is an excellent starting place.

As a convenience for developers building this project the make precommit will format, lint, validate, and in some cases fix the changes you plan to submit. This check will need to pass for your changes to be able to be merged.

In addition to idiomatic Go, the project has adopted certain standards for implementations of common patterns. These standards should be followed as a default, and if they are not followed documentation needs to be included as to the reasons why.

Configuration

When creating an instantiation function for a complex type T struct, it is useful to allow variable number of options to be applied. However, the strong type system of Go restricts the function design options. There are a few ways to solve this problem, but we have landed on the following design.

config

Configuration should be held in a struct named config, or prefixed with specific type name this Configuration applies to if there are multiple config in the package. This type must contain configuration options.

// config contains configuration options for a thing.
type config struct {
	// options ...
}

In general the config type will not need to be used externally to the package and should be unexported. If, however, it is expected that the user will likely want to build custom options for the configuration, the config should be exported. Please, include in the documentation for the config how the user can extend the configuration.

It is important that internal config are not shared across package boundaries. Meaning a config from one package should not be directly used by another. The one exception is the API packages. The configs from the base API, eg. go.opentelemetry.io/otel/trace.TracerConfig and go.opentelemetry.io/otel/metric.InstrumentConfig, are intended to be consumed by the SDK therefore it is expected that these are exported.

When a config is exported we want to maintain forward and backward compatibility, to achieve this no fields should be exported but should instead be accessed by methods.

Optionally, it is common to include a newConfig function (with the same naming scheme). This function wraps any defaults setting and looping over all options to create a configured config.

// newConfig returns an appropriately configured config.
func newConfig(options ...Option) config {
	// Set default values for config.
	config := config{/* […] */}
	for _, option := range options {
		config = option.apply(config)
	}
	// Perform any validation here.
	return config
}

If validation of the config options is also performed this can return an error as well that is expected to be handled by the instantiation function or propagated to the user.

Given the design goal of not having the user need to work with the config, the newConfig function should also be unexported.

Option

To set the value of the options a config contains, a corresponding Option interface type should be used.

type Option interface {
	apply(config) config
}

Having apply unexported makes sure that it will not be used externally. Moreover, the interface becomes sealed so the user cannot easily implement the interface on its own.

The apply method should return a modified version of the passed config. This approach, instead of passing a pointer, is used to prevent the config from being allocated to the heap.

The name of the interface should be prefixed in the same way the corresponding config is (if at all).

Options

All user configurable options for a config must have a related unexported implementation of the Option interface and an exported configuration function that wraps this implementation.

The wrapping function name should be prefixed with With* (or in the special case of a boolean options Without*) and should have the following function signature.

func With*(…) Option { … }
bool Options
type defaultFalseOption bool

func (o defaultFalseOption) apply(c config) config {
	c.Bool = bool(o)
    return c
}

// WithOption sets a T to have an option included.
func WithOption() Option {
	return defaultFalseOption(true)
}

type defaultTrueOption bool

func (o defaultTrueOption) apply(c config) config {
	c.Bool = bool(o)
    return c
}

// WithoutOption sets a T to have Bool option excluded.
func WithoutOption() Option {
	return defaultTrueOption(false)
}
Declared Type Options
type myTypeOption struct {
	MyType MyType
}

func (o myTypeOption) apply(c config) config {
	c.MyType = o.MyType
    return c
}

// WithMyType sets T to have include MyType.
func WithMyType(t MyType) Option {
	return myTypeOption{t}
}
Functional Options
type optionFunc func(config) config

func (fn optionFunc) apply(c config) config {
	return fn(c)
}

// WithMyType sets t as MyType.
func WithMyType(t MyType) Option {
	return optionFunc(func(c config) config {
		c.MyType = t
        return c
	})
}

Instantiation

Using this configuration pattern to configure instantiation with a NewT function.

func NewT(options ...Option) T {…}

Any required parameters can be declared before the variadic options.

Dealing with Overlap

Sometimes there are multiple complex struct that share common configuration and also have distinct configuration. To avoid repeated portions of configs, a common config can be used with the union of options being handled with the Option interface.

For example.

// config holds options for all animals.
type config struct {
	Weight      float64
	Color       string
	MaxAltitude float64
}

// DogOption apply Dog specific options.
type DogOption interface {
	applyDog(config) config
}

// BirdOption apply Bird specific options.
type BirdOption interface {
	applyBird(config) config
}

// Option apply options for all animals.
type Option interface {
	BirdOption
	DogOption
}

type weightOption float64

func (o weightOption) applyDog(c config) config {
	c.Weight = float64(o)
	return c
}

func (o weightOption) applyBird(c config) config {
	c.Weight = float64(o)
	return c
}

func WithWeight(w float64) Option { return weightOption(w) }

type furColorOption string

func (o furColorOption) applyDog(c config) config {
	c.Color = string(o)
	return c
}

func WithFurColor(c string) DogOption { return furColorOption(c) }

type maxAltitudeOption float64

func (o maxAltitudeOption) applyBird(c config) config {
	c.MaxAltitude = float64(o)
	return c
}

func WithMaxAltitude(a float64) BirdOption { return maxAltitudeOption(a) }

func NewDog(name string, o ...DogOption) Dog    {…}
func NewBird(name string, o ...BirdOption) Bird {…}

Interfaces

To allow other developers to better comprehend the code, it is important to ensure it is sufficiently documented. One simple measure that contributes to this aim is self-documenting by naming method parameters. Therefore, where appropriate, methods of every exported interface type should have their parameters appropriately named.

Interface Stability

All exported stable interfaces that include the following warning in their documentation are allowed to be extended with additional methods.

Warning: methods may be added to this interface in minor releases.

These interfaces are defined by the OpenTelemetry specification and will be updated as the specification evolves.

Otherwise, stable interfaces MUST NOT be modified.

How to Change Specification Interfaces

When an API change must be made, we will update the SDK with the new method one release before the API change. This will allow the SDK one version before the API change to work seamlessly with the new API.

If an incompatible version of the SDK is used with the new API the application will fail to compile.

How Not to Change Specification Interfaces

We have explored using a v2 of the API to change interfaces and found that there was no way to introduce a v2 and have it work seamlessly with the v1 of the API. Problems happened with libraries that upgraded to v2 when an application did not, and would not produce any telemetry.

More detail of the approaches considered and their limitations can be found in the Use a V2 API to evolve interfaces issue.

How to Change Other Interfaces

If new functionality is needed for an interface that cannot be changed it MUST be added by including an additional interface. That added interface can be a simple interface for the specific functionality that you want to add or it can be a super-set of the original interface. For example, if you wanted to a Close method to the Exporter interface:

type Exporter interface {
	Export()
}

A new interface, Closer, can be added:

type Closer interface {
	Close()
}

Code that is passed the Exporter interface can now check to see if the passed value also satisfies the new interface. E.g.

func caller(e Exporter) {
	/* ... */
	if c, ok := e.(Closer); ok {
		c.Close()
	}
	/* ... */
}

Alternatively, a new type that is the super-set of an Exporter can be created.

type ClosingExporter struct {
	Exporter
	Close()
}

This new type can be used similar to the simple interface above in that a passed Exporter type can be asserted to satisfy the ClosingExporter type and the Close method called.

This super-set approach can be useful if there is explicit behavior that needs to be coupled with the original type and passed as a unified type to a new function, but, because of this coupling, it also limits the applicability of the added functionality. If there exist other interfaces where this functionality should be added, each one will need their own super-set interfaces and will duplicate the pattern. For this reason, the simple targeted interface that defines the specific functionality should be preferred.

Testing

The tests should never leak goroutines.

Use the term ConcurrentSafe in the test name when it aims to verify the absence of race conditions.

Internal packages

The use of internal packages should be scoped to a single module. A sub-module should never import from a parent internal package. This creates a coupling between the two modules where a user can upgrade the parent without the child and if the internal package API has changed it will fail to upgrade3.

There are two known exceptions to this rule:

  • go.opentelemetry.io/otel/internal/global
    • This package manages global state for all of opentelemetry-go. It needs to be a single package in order to ensure the uniqueness of the global state.
  • go.opentelemetry.io/otel/internal/baggage
    • This package provides values in a context.Context that need to be recognized by go.opentelemetry.io/otel/baggage and go.opentelemetry.io/otel/bridge/opentracing but remain private.

If you have duplicate code in multiple modules, make that code into a Go template stored in go.opentelemetry.io/otel/internal/shared and use gotmpl to render the templates in the desired locations. See #4404 for an example of this.

Approvers and Maintainers

Approvers

Maintainers

Emeritus

Become an Approver or a Maintainer

See the community membership document in OpenTelemetry community repo.

  1. A qualified approval is a GitHub Pull Request review with "Approve" status from an OpenTelemetry Go Approver or Maintainer. ↩︎

  2. Trivial changes include: typo corrections, cosmetic non-substantive changes, documentation corrections or updates, dependency updates, etc. ↩︎

  3. https://github.com/open-telemetry/opentelemetry-go/issues/3548 ↩︎