go/doc/contribute.html

<!--{
	"Title": "Contribution Guide"
}-->

<p>
The Go project welcomes all contributors. The process of contributing
to the Go project may be different than many projects you are used to.
This document is intended as a guide to help you through the contribution
process. This guide assumes you have a basic understanding of Git and Go.
</p>

<p>
In addition to the information here, the Go community maintains a
<a href="https://golang.org/wiki/CodeReview">CodeReview</a> wiki page.
Feel free to contribute to the wiki as you learn the review process.
</p>

<p>
Note that the <code>gccgo</code> front end lives elsewhere;
see <a href="gccgo_contribute.html">Contributing to gccgo</a>.
</p>

<h2 id="contributor">Becoming a contributor</h2>

<h3>Overview</h3>

<p>
The first step is registering as a Go contributor and configuring your environment.
Here is a very quick checklist of the required steps, that you will need
to follow:
</p>

<ul>
<li>
<b>Step 0</b>: Decide on a single Google Account you would be using to contribute to Go.
Use that account for all the following steps and make sure that <code>git</code>
is configured to create commits with that account's e-mail address.
</li>
<li>
<b>Step 1</b>: <a href="https://cla.developers.google.com/clas">Sign and submit</a> a
CLA (Contributor License Agreement).
</li>
<li>
<b>Step 2</b>: Configure authentication credentials for our <code>git</code> repository.
Go to <a href="https://go.googlesource.com/">go.googlesource.com</a>, click
on "Generate Password" (top right), and follow the instructions.
</li>
<li>
<b>Step 3</b>: Register to Gerrit, the code review tool used by the Go team, by <a href="https://go-review.googlesource.com/login/">visiting this page</a>. The CLA and the registration
need to be done only once for your account.
</li>
<li>
<b>Step 4</b>: Install <code>git-codereview</code> by running
<code>go get -u golang.org/x/review/git-codereview</code>
</li>
</ul>

<p>
If you prefer, we have an automated tool that walks through these steps. Just
run:
</p>

<pre>
$ go get -u golang.org/x/tools/cmd/go-contrib-init
$ cd /code/to/edit
$ go-contrib-init
</pre>

<p>
The rest of this chapter elaborates on these steps.
If you have completed the steps above (either manually or through the tool), jump to
<a href="#making_a_change">Making a change</a>.
</p>

<h3 id="google_account">Step 0: Select a Google Account</h3>

<p>
A contribution to Go is made through a Google account, with a specific
e-mail address. Make sure to pick one and use it throughout the process and
for all your contributions. You may need to decide whether to
use a personal address or a corporate address. The choice will depend on who
will own the copyright for the code that you will be writing
and submitting. Consider discussing this with your employer.
</p>

<p>
Google Accounts can either be Gmail email accounts, G-Suite organization accounts, or
accounts associated with an external e-mail address. For instance, if you need to use
an existing corporate e-mail that is not managed through G-Suite, you can create
an account associated
<a href="https://accounts.google.com/SignUpWithoutGmail">with your existing
email address</a>.
</p>

<p>
You also need to make sure that <code>git</code> is configured to author commits
using the same e-mail address. You can either configure it globally
(as a default for all projects), or locally (for a single specific project).
You can check the current configuration with this command:
<p>

<pre>
$ git config --global user.email  # check current global config
$ git config user.email           # check current local config
</pre>

<p>To change the configured address:</p>

<pre>
$ git config --global user.email name@example.com   # change global config
$ git config user.email name@example.com            # change local config
</pre>


<h3 id="cla">Step 1: Contributor License Agreement</h3>

<p>
Before sending your first change to the Go project
you must have completed one of the following two CLAs.
Which CLA you should sign depends on who owns the copyright to your work.

<ul>
<li>
If you are the copyright holder, you will need to agree to the
<a href="https://developers.google.com/open-source/cla/individual">individual
contributor license agreement</a>, which can be completed online.
</li>
<li>
If your organization is the copyright holder, the organization
will need to agree to the
<a href="https://developers.google.com/open-source/cla/corporate">corporate
contributor license agreement</a>.<br>
</li>
</ul>

<p>
You can check your currently signed agreements and sign new ones, through
the <a href="https://cla.developers.google.com/clas?pli=1&authuser=1">Google Developers
Contributor License Agreements</a> website.
If the copyright holder for your contribution has already completed the
agreement in connection with another Google open source project,
it does not need to be completed again.
</p>

<p>
If the copyright holder for the code you are submitting changes &mdash; for example,
if you start contributing code on behalf of a new company &mdash; please send email
to golang-dev and let us know, so that we can make sure an appropriate agreement is
completed and update the <code>AUTHORS</code> file.
</p>


<h3 id="auth">Step 2: Configure git authentication</h3>

<p>
Go development happens on <a href="go.googlesource.com">go.googlesource.com</a>,
a <code>git</code> server hosted by Google.
Authentication on the web server is made through your Google account, but
you also need to configure <code>git</code> on your computer to access it.
Follow this steps:
</p>

<ol>
<li>
Visit <a href="https://go.googlesource.com">go.googlesource.com</a>
and click on "Generate Password" in the page's top right menu bar.
You will be redirected to accounts.google.com to sign in.
</li>
<li>
After signing in, you are taken to a page with the title "Configure Git".
This page contains a personalized script that when run locally will configure git
to have your unique authentication key.
This key is paired with one generated server side, analogous to how SSH keys work.
</li>
<li>
Copy and run this script locally in your command line terminal, to store your
secret authentication token in a <code>.gitcookies</code> file.
(On a Windows computer using <code>cmd</code> you should instead follow the instructions
in the yellow box to run the command. If you are using <code>git-bash</code> use the same
script as *nix.).
</li>
</ol>

<h3 id="auth">Step 3: Create a Gerrit account </h3>

<p>
Gerrit is an open-source tool used by Go maintainers to discuss and review
code submissions.
</p>

<p>
To register your account, visit <a href="https://go-review.googlesource.com/login/">
go-review.googlesource.com/login/</a> and sign in once using the same Google Account you used above.
</p>

<h3 id="git-codereview_install">Step 4: Install the git-codereview command</h3>

<p>
Changes to Go must be reviewed before they are accepted, no matter who makes the change.
A custom git command called <code>git-codereview</code>, discussed below,
helps to send changes to Gerrit.
</p>

<p>
Install the <code>git-codereview</code> command by running,
</p>

<pre>
$ go get -u golang.org/x/review/git-codereview
</pre>

<p>
Make sure <code>git-codereview</code> is installed in your shell path, so that the
<code>git</code> command can find it. Check that
</p>

<pre>
$ git codereview help
</pre>

<p>
prints help text, not an error.
</p>

<p>
On Windows, when using git-bash you must make sure that
<code>git-codereview.exe</code> is in your git exec-path.
Run <code>git --exec-path</code> to discover the right location then create a
symbolic link or simply copy the executable from $GOPATH/bin to this directory.
</p>


<h2 id="making_a_contribution">Before contributing code</h2>

<p>
The project welcomes submissions but please let everyone know what
you're working on if you want to change or add to the Go repositories.
</p>

<p>
Before undertaking to write something new for the Go project,
please <a href="https://golang.org/issue/new">file an issue</a>
(or claim an <a href="https://golang.org/issues">existing issue</a>).
</p>

<h3>Check the issue tracker</h3>

<p>Whether you already know what contribution to make, or you are searching for
an idea, the <a href="https://github.com/golang/go/issues">issue tracker</a> is
always the first place to go. Issues are triaged to categorize them and manage
the workflow.
</p>

<p>Most issues will be marked with one of the following workflow labels:
<ul>
	<li><b>NeedsInvestigation</b>: The issue is not fully understood well
	and requires analysis to understand the root cause. </li>
	<li><b>NeedsDecision</b>: the issue is relatively well understood, but the
	Go team hasn't yet decided the best way to fix it or implement it among all
	possible options. It would be better to wait for a decision before
	writing code. If you are interested on working on an issue in this state,
	feel free to ping maintainers here if some time has passed without a decision.</li>
	<li><b>NeedsFix</b>: the issue is fully understood and code can be written
	to fix it.</li>
</ul>
</p>

<h3 id="Design">Open an issue for any new problem</h3>

<p>
Excluding very trivial changes, all contributions should be connected
to an existing issue. Feel free to open one and discuss what your
plans are. This process gives everyone a chance to validate the design,
helps prevent duplication of effort,
and ensures that the idea fits inside the goals for the language and tools.
It also checks that the design is sound before code is written;
the code review tool is not the place for high-level discussions.
</p>

<p>
When planning work, please note that the Go project follows a <a
href="https://golang.org/wiki/Go-Release-Cycle">six-month development cycle</a>.
The latter half of each cycle is a three-month feature freeze during
which only bug fixes and doc updates are accepted. New contributions can be
sent during a feature freeze but will not be accepted until the freeze thaws.
</p>

<p>Significant changes must go through the
<a href="https://golang.org/s/proposal-process">change proposal process</a>
before they can be accepted.</p>

<p>
Sensitive security-related issues should be reported to <a href="mailto:security@golang.org">security@golang.org</a>.
</p>

<h2 id="making_a_contribution">Sending a change via GitHub</h2>

<p>
First-time contributors that are already familiar with the
<a href="https://guides.github.com/introduction/flow/">GitHub flow</a>
are encouraged to use the same process for Go contributions. Even though Go
maintainers use Gerrit for code review, a bot has been created to sync
GitHub pull requests to Gerrit.
</p>

<p>
Open a pull request as you would normally do. Gopherbot will automatically
sync the code and post a link to Gerrit. When somebody comments on the
change, it will be posted in the pull request, so you will also get a notification.
</p>

<p>Some things to keep in mind:

<ul>
<li>
To update the pull request with new code, just push it to the branch; you can either
add more commits, or rebase and force-push (both styles are accepted).
</li>
<li>
If the request is accepted, all the commits will be squashed, and the final
commit description will be composed by concatenating the pull request's
title and description. The individual commits' descriptions will be discarded.
See <a href="#commit_messages">Writing good commit messages</a> for some
suggestions.
</li>
<li>
Gopherbot is unable to sync line-by-line codereview into GitHub: only the
contents of the overall comment on the request will be synced. Remember you
can always to go Gerrit to see the fine-grained review.
</li>
</ul>
</p>

<h2 id="making_a_contribution">Sending a change via Gerrit</h2>

<p>
It is not possible to fully sync Gerrit and GitHub, at least at the moment,
so we recommend learning Gerrit. It's different but powerful and familiarity
with help you understand the flow.
</p>

<h3>Overview</h3>

<p>This is an overview of the overall process:
<ul>
<li><b>Step 1:</b> Clone the Go source code from GitHub or go.googlesource.com, and make sure it's stable by compiling and testing it once:
<pre>
$ git clone https://github.com/golang/go    # or https://go.googlesource.com/go
$ cd go/src
$ ./all.bash                                # compile and test
</pre>
<li><b>Step 2:</b> Prepare changes in a new branch, created from the master branch.
To commit the changes, use <code>git</code> <code>codereview</code> <code>change</code>, that
will create or amend a single commit in the branch.
<pre>
$ git checkout -b mybranch
$ [edit files...]
$ git add [files...]
$ git codereview change   # create commit in the branch
$ [edit again...]
$ git add [files...]
$ git codereview change   # amend the existing commit with new changes
$ [etc.]
</pre>
</li>
<li>
<b>Step 3:</b> Test your changes, re-running <code>all.bash</code>.
<pre>
$ ./all.bash    # recompile and test
</pre>
</li>
<li>
<b>Step 4:</b> Send the changes for review to Gerrit using <code>git</code>
<code>codereview</code> <code>mail</code> (which doesn't use e-mail, despite the name).
<pre>
$ git codereview mail     # send changes to Gerrit
</pre>
</li>
<li>
<b>Step 5:</b> After a review, apply changes to the same single commit, and mail them to Gerrit again:
<pre>
$ [edit files...]
$ git add [files...]
$ git codereview change   # update same commit
$ git codereview mail     # send to Gerrit again
</li>
</ul>
</p>

<p>The rest of this chapter describes these steps in more detail.</p>


<h3 id="checkout_go">Step 1: Clone the Go source code</h3>

<p>
In addition to a recent Go installation, you need to have a local copy of the source
checked out from the correct repository. You should check out the Go source repo anywhere
you want as long as it's outside of your <code>GOPATH</code>. Either clone from
<code>go.googlesource.com</code> or GitHub:
</p>

<pre>
$ git clone https://github.com/golang/go   # or https://go.googlesource.com/go
$ cd go
</pre>

<h3 id="checkout_go">Step 2: Prepare changes in a new branch</h3>

<p>
Each Go change must be made in a separate branch, created from the master branch. You can use
the normal <code>git</code> commands to create a branch and add changes to the
staging area:
</p>

<pre>
$ git checkout -b mybranch
$ [edit files...]
$ git add [files...]
</pre>

<p>
To commit changes, instead of <code>git commit</code>, use <code>git codereview change</code>.
</p>

<pre>
$ git codereview change
(open $EDITOR)
</pre>

<p>
You can edit the commit description in your favorite editor as usual.
<code>git</code> <code>codereview</code> <code>change</code> will automatically
add a <code>Change-Id</code>  line near the bottom. That line is used by
Gerrit to match successive uploads of the same change. Do not edit or delete it.
This is an example:
</p>

<pre>
commit fef82cf89a34935a41bd0e3c1e0c2d9d6de29ee2 (HEAD -> test)
Author: Giovanni Bajo <rasky@develer.com>
Date:   Tue Feb 13 01:07:15 2018 +0100

    cmd/compile: test

    Change-Id: I2fbdbffb3aab626c4b6f56348861b7909e3e8990
</pre>

<p>
<code>git</code> <code>codereview</code> <code>change</code> also checks that you've
run <code>go</code> <code>fmt</code> over the source code, and that
the commit message follows the <a href="#commit_messages">suggested format</a>.
</p>

<p>
If you need to edit the files again, you can stage the new changes and
re-run <code>git</code> <code>codereview</code> <code>change</code>: each subsequent
run will amend the existing commit.
</p>

<p>
Make sure that you always keep a single commit in each branch. If you add more
commits by mistake, you can use <code>git</code> <code>rebase</code> to
<a href="https://stackoverflow.com/questions/31668794/squash-all-your-commits-in-one-before-a-pull-request-in-github">squash them together</a>
into a single one.
</p>


<h3 id="Testing">Step 3: Test changes</h3>

<p>
You've <a href="code.html">written and tested your code</a>, but
before sending code out for review, run all the tests for the whole
tree to make sure the changes don't break other packages or programs:
</p>

<pre>
$ cd go/src
$ ./all.bash
</pre>

<p>
(To build under Windows use <code>all.bat</code>; this also requires
setting the environment variable <code>GOROOT_BOOTSTRAP</code> to the
bootstrap compiler)
</p>

<p>
After running for a while, the command should print:
</p>

<pre>
"ALL TESTS PASSED".
</pre>

<p>Notice that you can use <code>make.bash</code> instead of <code>all.bash</code>
to just build the compiler without running the testsuite. Once the compiler is
built, you can run it directly from <code>&lt;GOCLONEDIR&gt;/bin/go</code>; see also
the section on <a href="#quicktest">quickly test your changes</a>.</p>

<h3 id="mail">Step 4: Send changes for review</h3>

<p>
Once the change is ready, send it for review.
This is done via the <code>mail</code> sub-command which despite its name, doesn't
directly mail anything, it just sends the change to Gerrit:
</p>

<pre>
$ git codereview mail
</pre>

<p>
Gerrit assigns your change a number and URL, which <code>git</code> <code>codereview</code> <code>mail</code> will print, something like:
</p>

<pre>
remote: New Changes:
remote:   https://go-review.googlesource.com/99999 math: improved Sin, Cos and Tan precision for very large arguments
</pre>

<p>
If you get an error instead, check the
<a href="#troubleshooting_mail">Troubleshooting mail errors</a> section.
</p>

<p>
If your change relates to an open GitHub issue and you have followed the <a href="#commit_messages">
suggested commit message format</a>, the issue will be updated in a few minutes by a bot,
linking your Gerrit change in it.
</p>


<h3 id="revise">Step 5: Revise changes after a review</h3>

<p>
Go maintainers will review your code on Gerrit, and you will get notifications via email.
You can see the review on Gerrit, and comment on them. You can also reply
<a href="https://gerrit-review.googlesource.com/Documentation/intro-user.html#reply-by-email">via email</a>
if you prefer.
</p>

<p>
When you're ready to revise your submitted code, edit the files in correct branch,
add them to the git staging area, and then amend the commit with
<code>git</code> <code>codereview</code> <code>change</code>:
</p>

<pre>
$ git codereview change     # amend current commit
(open $EDITOR)
$ git codereview mail       # send new changes to Gerrit
</pre>

<p>
If you don't need to change the commit description, just save and exit from the editor.
Remember not to touch the special <code>Change-Id</code> line.
</p>

<p>
Make sure that you always keep a single commit in each branch. If you add more
commits by mistake, you can use <code>git rebase</code> to
<a href="https://stackoverflow.com/questions/31668794/squash-all-your-commits-in-one-before-a-pull-request-in-github">squash them together</a>
into a single one.
</p>

<h2 id="commit_messages">Writing good commit messages</h2>

<p>Commit messages in Go follow a specific convention. Read this chapter
to learn more about it. This is an example of a good one:

<pre>
math: improve Sin, Cos and Tan precision for very large arguments

The existing implementation has poor numerical properties for
large arguments, so use the McGillicutty algorithm to improve
accuracy above 1e10.

The algorithm is described at http://wikipedia.org/wiki/McGillicutty_Algorithm

Fixes #159
</pre>

</p>

<h3>First line</h3>

<p>
The first line of the change description is conventionally a short one-line
summary of the change, prefixed by the primary affected package.

<p>It should be written so to complete the sentence "This change modifies Go to _____."</p>

<h3>Main content</h3>

<p>The rest of the description elaborates and should provide context for the
change and explain what it does.
Write in complete sentences with correct punctuation, just like
for your comments in Go.
Don't use HTML, Markdown, or any other markup language.
</p>

<h3>Referencing issues</h3>

<p>
The special notation "Fixes #159" associates the change with issue 159 in the
<a href="https://golang.org/issue/159">Go issue tracker</a>.
When this change is eventually applied, the issue
tracker will automatically mark the issue as fixed.
</p>

<p>
If the change is a partial step towards the resolution of the issue,
uses the notation "Updates #159". This will leave a comment in the issue
linking back to the change in Gerrit, but it will not close the issue
when the change is applied.
</p>

<p>
If you are sending a change against a subrepository, you must use
the fully-qualified syntax supported by GitHub, to make sure the change is
linked to the issue in the main repository. The correct form is "Fixes golang/go#159".
</p>


<h2 id="review">The review process</h2>

<p>
This section explains the review process in details, and how to approach
reviews after a change was submitted.
</p>


<h3 id="mistakes">Common beginner mistakes</h3>

<p>
When a change is submitted to Gerrit, it is usually triaged in the next few days.
A maintainer will give a look and submit some initial review, that for first-time
contributors usually focus on basic cosmetics and common mistakes. For instance:
</p>

<ul>
<li>
Commit messages might not follow the <a href="#commit_messages">suggested
format</a>.
</li>
<li>
There might not be a linked GitHub issue. The vast majority of changes
require a linked issue that describes the bug or the feature that the change
fixes or implements, and consensus should have been reached on the tracker
to actually proceed with it. Gerrit reviews do not discuss the merit of the change,
just its implementation.
<br>Only very trivial or cosmetic changes will be accepted without a issue.
</li>
<li>
The change might have been submitted during the freeze phase, when the tree
is closed for some specific kind of change (eg: new features). In this case,
a maintainer might review the code with a line such as <code>R=go1.11</code>,
which means that it will be reviewed later when the tree opens for a new
development window. You can add <code>R=go1.XX</code> as a comment yourself
if you know that it's not the correct timeframe for the change and help the
maintainers.
</li>
</ul>

<h3 id="trybots">Trybots</h3>

<p>After an initial reading of your patch, maintainers will trigger trybots,
a cluster of servers that will run the full testsuite on several different
architectures. Most trybots run complete in a few minutes, and a link will
be posted in Gerrit where you can see the results.</p>

<p>If the trybot run fails, follow the link and check the full logs of the
platforms on which the tests failed. Try to understand what broke, and
update your patch. Maintainers will trigger a new trybot run to see
if the problem was fixed.</p>

<p>Sometimes, the tree can be broken on some platforms for a few hours; if
the failure in trybot logs doesn't seem related to your patch, go to the
<a href="https://build.golang.org">Build Dashboard</a> and check if the same
failures appears in the recent commits, on the same platform. In this case,
feel free to write a comment in Gerrit to mention that the failure is
unrelated to your change, to help maintainers understanding the situation.</p>

<h3 id="reviews">Reviews</h3>

<p>The Go team values very thorough reviews. Consider
each line comment like a ticket: you are expected to somehow "close" it
by acting on it, either by implementing the suggestion or convincing the
reviewer otherwise.</p>

<p>After you update the change, go through line comments and make sure
to reply on every one. You can click the "Done" button to reply
indicating that you've implemented the reviewer's suggestion; otherwise,
click on "Reply" and explain why you have not.</p>

<p>It is absolutely normal for changes to go through several round of reviews,
in which the reviewer make new comments every time and then wait for an updated
change to be uploaded. This also happens for experienced contributors, so
don't feel discouraged by it.</p>

<h3 id="votes">Voting conventions</h3>

<p>
At some point, reviewers will express a vote on your change. This is the
voting convention:
<ul>
	<li><b>+2</b> The change is approved for being merged. Only Go maintainers
	can cast a +2.</li>
	<li><b>+1</b> The change looks good, but either the reviewer is requesting
	more changes before approving it, or they are not a maintainer and cannot
	approve it, but would like to encourage an approval.</li>
	<li><b>-1</b> The change is not good the way it is. -1 are always casted
	with a comment explaining the reason for it.</li>
	<li><b>-2</b> The change is blocked by a maintainer and cannot be approved.
	There will be a comment explaining the decision.</li>
</ul>
</p>

<h3 id="submit">Submitting an approved change</h3>

<p>
After the code has been +2'ed, an approver will
apply it to the master branch using the Gerrit UI. This is
called "submission".
</p>

<p>
The two steps are separate because in some cases maintainers
may want to approve it but not to submit it right away (e.g.
the tree could be temporarily frozen).
</p>

<p>
Submission checks the change into the repository.
The change description will include a link to the code review,
and the code review will be updated with a link to the change
in the repository.
Since the method used to integrate the changes is "Cherry Pick",
the commit hashes in the repository will be changed by
the "Submit" operation.
</p>

<p>If your change has been approved for a few days without being
submitted, feel free to write a comment in Gerrit requesting
submission.</p>


<h3 id="more_information">More information</h3>

<p>
In addition to the information here, the Go community maintains a <a
href="https://golang.org/wiki/CodeReview">CodeReview</a> wiki page.
Feel free to contribute to this page as you learn the review process.
</p>



<h2 id="advanced_topics">Advanced topics</h2>

<p>
This section contains more in-depth topics on how to contribute to Go. Read it to
get a better understanding of the contribution process.
</p>


<h3 id="copyright">Copyright headers</h3>

<p>
Files in the Go repository don't list author names, both to avoid clutter
and to avoid having to keep the lists up to date.
Instead, your name will appear in the
<a href="https://golang.org/change">change log</a> and in the <a
href="/CONTRIBUTORS"><code>CONTRIBUTORS</code></a> file and perhaps the <a
href="/AUTHORS"><code>AUTHORS</code></a> file.
These files are automatically generated from the commit logs periodically.
The <a href="/AUTHORS"><code>AUTHORS</code></a> file defines who &ldquo;The Go
Authors&rdquo;&mdash;the copyright holders&mdash;are.
</p>

<p>New files that you contribute should use the standard copyright header:</p>

<pre>
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
</pre>

<p>
Files in the repository are copyright the year they are added.
Do not update the copyright year on files that you change.
</p>




<h3 id="troubleshooting_mail">Troubleshooting mail errors</h3>

<p>
The most common way that the <code>git</code> <code>codereview</code> <code>mail</code>
command fails is because the email address in the commit does not match the one
that you used during <a href="#google_account">the registration process</a>.

<br>
If you see something like...
</p>

<pre>
remote: Processing changes: refs: 1, done
remote:
remote: ERROR:  In commit ab13517fa29487dcf8b0d48916c51639426c5ee9
remote: ERROR:  author email address XXXXXXXXXXXXXXXXXXX
remote: ERROR:  does not match your user account.
</pre>

<p>
You need to set this repo to use the email address that you registered with.
First, let's change the email address for this repo so this doesn't happen again.
You can change your email address for this repo with the following command:
</p>

<pre>
$ git config user.email email@address.com
</pre>

<p>
Then change the commit to use this alternative email address.
You can do that with:
</p>

<pre>
$ git commit --amend --author="Author Name &lt;email@address.com&gt;"
</pre>

<p>
Finally try to resend with:
</p>

<pre>
$ git codereview mail
</pre>


<h3 id="quicktest">Quickly testing your changes</h3>

<p>Running <code>all.bash</code> for every single change to the code tree
is burdensome. Even though it is strongly suggested to run it before
sending a change, during the normal development cycle you may want
to quickly compile and locally test your change.</p>

<ul>
<li>
In general, you can run <code>make.bash</code> instead of <code>all.bash</code>
to only rebuild the Go toolchain without running the whole testsuite. Or you
can run <code>run.bash</code> to only run the whole testsuite without rebuilding
the toolchain. You can think of <code>all.bash</code> as <code>make.bash</code>
followed by <code>run.bash</code>.
</li>
<li>The just-built compiler is in <code>&lt;GOCLONEDIR&gt;/bin/go</code>; you
can run it directly to test whatever you want to test. For instance, if you
have modified the compiler and you want to test how it affects the
testsuite of your own project, just run <code>go</code> <code>test</code>
using it:

<pre>
$ cd &lt;MYPROJECTDIR&gt;
$ &lt;GOCLONEDIR&gt;/bin/go test
</pre>
</li>

<li>
If you're changing the standard library, you probably don't need to rebuild
the compiler: you can run the tests on the package you have changed.
You can either do that with whatever Go version you normally develop with, or
using the Go compiler built from your clone (which is
sometimes required because the standard library code you're modifying
might require a newer version than the stable one you have installed).

<pre>
$ cd &lt;GOCLONEDIR&gt;/src/hash/sha1
$ [make changes...]
$ &lt;GOCLONEDIR&gt;/bin/go test .
</pre>
</li>

<li>
If you're modyfing the compiler itself, you can just recompile
the <code>compile</code> tool (which is the internal binary invoked
by <code>go</code> <code>build</code> to compile each single package).
After that, you will want to test it by compiling or running something.

<pre>
$ cd &lt;GOCLONEDIR&gt;/src
$ [make changes...]
$ &lt;GOCLONEDIR&gt;/bin/go install cmd/compile
$ &lt;GOCLONEDIR&gt;/bin/go build [something...]   # test the new compiler
$ &lt;GOCLONEDIR&gt;/bin/go run [something...]     # test the new compiler
$ &lt;GOCLONEDIR&gt;/bin/go test [something...]    # test the new compiler
</pre>

The same applies to other internal tools of the Go toolchain,
such as <code>asm</code>, <code>cover</code>, <code>link</code>,
etc. Just recompile and install the tool using <code>go</code>
<code>install</code> <code>cmd/&lt;TOOL&gt;</code> and then use
the built Go binary to test it.
</li>

<li>
In addition to the standard per-package tests, there is a top-level
testsuite in <code>&lt;GOCLONEDIR&gt;/test</code> that contains
several black-box and regression tests. The testsuite is run
by <code>all.bash</code> but you can also run it manually:

<pre>
$ cd &lt;GOCLONEDIR&gt;/test
$ go run run.go
</pre>

Note that this will use the Go compiler found in <code>PATH</code>.
</ul>

<h3 id="subrepos">Contributing to subrepositories (golang.org/x/...)</h3>

<p>
If you are contributing a change to a subrepository, obtain the
Go package using <code>go get</code>. For example, to contribute
to <code>golang.org/x/oauth2</code>, check out the code by running:
</p>

<pre>
$ go get -d golang.org/x/oauth2/...
</pre>

<p>
Then, change your directory to the package's source directory
(<code>$GOPATH/src/golang.org/x/oauth2</code>), and follow the
normal contribution flow.
</p>



<h3 id="cc">Specifying a reviewer / CCing others</h3>

<p>
Unless explicitly told otherwise, such as in the discussion leading
up to sending in the change, it's better not to specify a reviewer.
All changes are automatically CC'ed to the
<a href="https://groups.google.com/group/golang-codereviews">golang-codereviews@googlegroups.com</a>
mailing list. If this is your first ever change, there may be a moderation
delay before it appears on the mailing list, to prevent spam.
</p>

<p>
You can specify a reviewer or CC interested parties
using the <code>-r</code> or <code>-cc</code> options.
Both accept a comma-separated list of email addresses:
</p>

<pre>
$ git codereview mail -r joe@golang.org -cc mabel@example.com,math-nuts@swtch.com
</pre>









<h3 id="sync">Synchronize your client</h3>

<p>
While you were working, others might have submitted changes to the repository.
To update your local branch, run
</p>

<pre>
$ git sync
</pre>

<p>
(In git terms, <code>git</code> <code>sync</code> runs
<code>git</code> <code>pull</code> <code>-r</code>.)
</p>





<h3 id="download">Reviewing code by others</h3>

<p>
As part of the review process reviewers can propose changes directly (in the
GitHub workflow this would be someone else attaching commits to a pull request).

You can import these changes proposed by someone else into your local Git repository.
On the Gerrit review page, click the "Download ▼" link in the upper right
corner, copy the "Checkout" command and run it from your local Git repo. It
should look something like this:
</p>

<pre>
$ git fetch https://go.googlesource.com/review refs/changes/21/1221/1 &amp;&amp; git checkout FETCH_HEAD
</pre>

<p>
To revert, change back to the branch you were working in.
</p>


<h3 id="git-config">Set up git aliases</h2>

<p>
The <code>git-codereview</code> command can be run directly from the shell
by typing, for instance,
</p>

<pre>
$ git codereview sync
</pre>

<p>
but it is more convenient to set up aliases for <code>git-codereview</code>'s own
subcommands, so that the above becomes,
</p>

<pre>
$ git sync
</pre>

<p>
The <code>git-codereview</code> subcommands have been chosen to be distinct from
Git's own, so it's safe to do so. To install them, copy this text into your
Git configuration file (usually <code>.gitconfig</code> in your home directory):
</p>

<pre>
[alias]
	change = codereview change
	gofmt = codereview gofmt
	mail = codereview mail
	pending = codereview pending
	submit = codereview submit
	sync = codereview sync
</pre>


<h3 id="multiple_changes">Sending multiple dependent changes</h3>

<p>Gerrit allows for changes to be dependent on each other, forming a dependency chain.
This is an indication for maintainers to better review your code, even though each
change will technically need to be approved and submitted separately.</p>

<p>To submit a group of dependent changes, keep each change as a different commit under
the same branch, and then run:

<pre>
$ git codereview mail HEAD
</pre>

Make sure to explicitly specify <code>HEAD</code>, which is usually not required when sending
single changes.</p>