My First Contribution to the Git Project

========================================

:sectanchors:

[[summary]]

== Summary

This is a tutorial demonstrating the end-to-end workflow of creating a change to

the Git tree, sending it for review, and making changes based on comments.

[[prerequisites]]

=== Prerequisites

This tutorial assumes you're already fairly familiar with using Git to manage

source code. The Git workflow steps will largely remain unexplained.

[[related-reading]]

=== Related Reading

This tutorial aims to summarize the following documents, but the reader may find

useful additional context:

- `Documentation/SubmittingPatches`

- `Documentation/howto/new-command.txt`

[[getting-help]]

=== Getting Help

If you get stuck, you can seek help in the following places.

==== git@vger.kernel.org

This is the main Git project mailing list where code reviews, version

announcements, design discussions, and more take place. Those interested in

contributing are welcome to post questions here. The Git list requires

plain-text-only emails and prefers inline and bottom-posting when replying to

mail; you will be CC'd in all replies to you. Optionally, you can subscribe to

the list by sending an email to majordomo@vger.kernel.org with "subscribe git"

in the body. The https://lore.kernel.org/git[archive] of this mailing list is

available to view in a browser.

==== https://groups.google.com/forum/#!forum/git-mentoring[git-mentoring@googlegroups.com]

This mailing list is targeted to new contributors and was created as a place to

post questions and receive answers outside of the public eye of the main list.

Veteran contributors who are especially interested in helping mentor newcomers

are present on the list. In order to avoid search indexers, group membership is

required to view messages; anyone can join and no approval is required.

==== https://web.libera.chat/#git-devel[#git-devel] on Libera Chat

This IRC channel is for conversations between Git contributors. If someone is

currently online and knows the answer to your question, you can receive help

in real time. Otherwise, you can read the

https://colabti.org/irclogger/irclogger_logs/git-devel[scrollback] to see

whether someone answered you. IRC does not allow offline private messaging, so

if you try to private message someone and then log out of IRC, they cannot

respond to you. It's better to ask your questions in the channel so that you

can be answered if you disconnect and so that others can learn from the

conversation.

[[getting-started]]

== Getting Started

[[cloning]]

=== Clone the Git Repository

Git is mirrored in a number of locations. Clone the repository from one of them;

https://git-scm.com/downloads suggests one of the best places to clone from is

the mirror on GitHub.

----

$ git clone https://github.com/git/git git

$ cd git

----

[[dependencies]]

=== Installing Dependencies

To build Git from source, you need to have a handful of dependencies installed

on your system. For a hint of what's needed, you can take a look at

`INSTALL`, paying close attention to the section about Git's dependencies on

external programs and libraries. That document mentions a way to "test-drive"

our freshly built Git without installing; that's the method we'll be using in

this tutorial.

Make sure that your environment has everything you need by building your brand

new clone of Git from the above step:

----

$ make

----

NOTE: The Git build is parallelizable. `-j#` is not included above but you can

use it as you prefer, here and elsewhere.

[[identify-problem]]

=== Identify Problem to Solve

////

Use + to indicate fixed-width here; couldn't get ` to work nicely with the

quotes around "Pony Saying 'Um, Hello'".

////

In this tutorial, we will add a new command, +git psuh+, short for ``Pony Saying

`Um, Hello''' - a feature which has gone unimplemented despite a high frequency

of invocation during users' typical daily workflow.

(We've seen some other effort in this space with the implementation of popular

commands such as `sl`.)

[[setup-workspace]]

=== Set Up Your Workspace

Let's start by making a development branch to work on our changes. Per

`Documentation/SubmittingPatches`, since a brand new command is a new feature,

it's fine to base your work on `master`. However, in the future for bugfixes,

etc., you should check that document and base it on the appropriate branch.

For the purposes of this document, we will base all our work on the `master`

branch of the upstream project. Create the `psuh` branch you will use for

development like so:

----

$ git checkout -b psuh origin/master

----

We'll make a number of commits here in order to demonstrate how to send a topic

with multiple patches up for review simultaneously.

[[code-it-up]]

== Code It Up!

NOTE: A reference implementation can be found at

https://github.com/nasamuffin/git/tree/psuh.

[[add-new-command]]

=== Adding a New Command

Lots of the subcommands are written as builtins, which means they are

implemented in C and compiled into the main `git` executable. Implementing the

very simple `psuh` command as a built-in will demonstrate the structure of the

codebase, the internal API, and the process of working together as a contributor

with the reviewers and maintainer to integrate this change into the system.

Built-in subcommands are typically implemented in a function named "cmd_"

followed by the name of the subcommand, in a source file named after the

subcommand and contained within `builtin/`. So it makes sense to implement your

command in `builtin/psuh.c`. Create that file, and within it, write the entry

point for your command in a function matching the style and signature:

----

int cmd_psuh(int argc, const char **argv, const char *prefix)

----

We'll also need to add the declaration of psuh; open up `builtin.h`, find the

declaration for `cmd_pull`, and add a new line for `psuh` immediately before it,

in order to keep the declarations alphabetically sorted:

----

int cmd_psuh(int argc, const char **argv, const char *prefix);

----

Be sure to `#include "builtin.h"` in your `psuh.c`.

Go ahead and add some throwaway printf to that function. This is a decent

starting point as we can now add build rules and register the command.

NOTE: Your throwaway text, as well as much of the text you will be adding over

the course of this tutorial, is user-facing. That means it needs to be

localizable. Take a look at `po/README` under "Marking strings for translation".

Throughout the tutorial, we will mark strings for translation as necessary; you

should also do so when writing your user-facing commands in the future.

----

int cmd_psuh(int argc, const char **argv, const char *prefix)

{

printf(_("Pony saying hello goes here.\n"));

return 0;

}

----

Let's try to build it. Open `Makefile`, find where `builtin/pull.o` is added

to `BUILTIN_OBJS`, and add `builtin/psuh.o` in the same way next to it in

alphabetical order. Once you've done so, move to the top-level directory and

build simply with `make`. Also add the `DEVELOPER=1` variable to turn on

some additional warnings:

----

$ echo DEVELOPER=1 >config.mak

$ make

----

NOTE: When you are developing the Git project, it's preferred that you use the

`DEVELOPER` flag; if there's some reason it doesn't work for you, you can turn

it off, but it's a good idea to mention the problem to the mailing list.

Great, now your new command builds happily on its own. But nobody invokes it.

Let's change that.

The list of commands lives in `git.c`. We can register a new command by adding

a `cmd_struct` to the `commands[]` array. `struct cmd_struct` takes a string

with the command name, a function pointer to the command implementation, and a

setup option flag. For now, let's keep mimicking `push`. Find the line where

`cmd_push` is registered, copy it, and modify it for `cmd_psuh`, placing the new

line in alphabetical order (immediately before `cmd_pull`).

The options are documented in `builtin.h` under "Adding a new built-in." Since

we hope to print some data about the user's current workspace context later,

we need a Git directory, so choose `RUN_SETUP` as your only option.

Go ahead and build again. You should see a clean build, so let's kick the tires

and see if it works. There's a binary you can use to test with in the

`bin-wrappers` directory.

----

$ ./bin-wrappers/git psuh

----

Check it out! You've got a command! Nice work! Let's commit this.

`git status` reveals modified `Makefile`, `builtin.h`, and `git.c` as well as

untracked `builtin/psuh.c` and `git-psuh`. First, let's take care of the binary,

which should be ignored. Open `.gitignore` in your editor, find `/git-pull`, and

add an entry for your new command in alphabetical order:

----

...

/git-prune-packed

/git-psuh

/git-pull

/git-push

/git-quiltimport

/git-range-diff

...

----

Checking `git status` again should show that `git-psuh` has been removed from

the untracked list and `.gitignore` has been added to the modified list. Now we

can stage and commit:

----

$ git add Makefile builtin.h builtin/psuh.c git.c .gitignore

$ git commit -s

----

You will be presented with your editor in order to write a commit message. Start

the commit with a 50-column or less subject line, including the name of the

component you're working on, followed by a blank line (always required) and then

the body of your commit message, which should provide the bulk of the context.

Remember to be explicit and provide the "Why" of your change, especially if it

couldn't easily be understood from your diff. When editing your commit message,

don't remove the `Signed-off-by` trailer which was added by `-s` above.

----

psuh: add a built-in by popular demand

Internal metrics indicate this is a command many users expect to be

present. So here's an implementation to help drive customer

satisfaction and engagement: a pony which doubtfully greets the user,

or, a Pony Saying "Um, Hello" (PSUH).

This commit message is intentionally formatted to 72 columns per line,

starts with a single line as "commit message subject" that is written as

if to command the codebase to do something (add this, teach a command

that). The body of the message is designed to add information about the

commit that is not readily deduced from reading the associated diff,

such as answering the question "why?".

Signed-off-by: A U Thor <author@example.com>

----

Go ahead and inspect your new commit with `git show`. "psuh:" indicates you

have modified mainly the `psuh` command. The subject line gives readers an idea

of what you've changed. The sign-off line (`-s`) indicates that you agree to

the Developer's Certificate of Origin 1.1 (see the

`Documentation/SubmittingPatches` +++[[dco]]+++ header).

For the remainder of the tutorial, the subject line only will be listed for the

sake of brevity. However, fully-fleshed example commit messages are available

on the reference implementation linked at the top of this document.

[[implementation]]

=== Implementation

It's probably useful to do at least something besides printing out a string.

Let's start by having a look at everything we get.

Modify your `cmd_psuh` implementation to dump the args you're passed, keeping

existing `printf()` calls in place:

----

int i;

...

printf(Q_("Your args (there is %d):\n",

"Your args (there are %d):\n",

argc),

argc);

for (i = 0; i < argc; i++)

printf("%d: %s\n", i, argv[i]);

printf(_("Your current working directory:\n<top-level>%s%s\n"),

prefix ? "/" : "", prefix ? prefix : "");

----

Build and try it. As you may expect, there's pretty much just whatever we give

on the command line, including the name of our command. (If `prefix` is empty

for you, try `cd Documentation/ && ../bin-wrappers/git psuh`). That's not so

helpful. So what other context can we get?

Add a line to `#include "config.h"`. Then, add the following bits to the

function body:

----

const char *cfg_name;

...

git_config(git_default_config, NULL);

if (git_config_get_string_tmp("user.name", &cfg_name) > 0)

printf(_("No name is found in config\n"));

else

printf(_("Your name: %s\n"), cfg_name);

----

`git_config()` will grab the configuration from config files known to Git and

apply standard precedence rules. `git_config_get_string_tmp()` will look up

a specific key ("user.name") and give you the value. There are a number of

single-key lookup functions like this one; you can see them all (and more info

about how to use `git_config()`) in `Documentation/technical/api-config.txt`.

You should see that the name printed matches the one you see when you run:

----

$ git config --get user.name

----

Great! Now we know how to check for values in the Git config. Let's commit this

too, so we don't lose our progress.

----

$ git add builtin/psuh.c

$ git commit -sm "psuh: show parameters & config opts"

----

NOTE: Again, the above is for sake of brevity in this tutorial. In a real change

you should not use `-m` but instead use the editor to write a meaningful

message.

Still, it'd be nice to know what the user's working context is like. Let's see

if we can print the name of the user's current branch. We can mimic the

`git status` implementation; the printer is located in `wt-status.c` and we can

see that the branch is held in a `struct wt_status`.

`wt_status_print()` gets invoked by `cmd_status()` in `builtin/commit.c`.

Looking at that implementation we see the status config being populated like so:

----

status_init_config(&s, git_status_config);

----

But as we drill down, we can find that `status_init_config()` wraps a call

to `git_config()`. Let's modify the code we wrote in the previous commit.

Be sure to include the header to allow you to use `struct wt_status`:

----

#include "wt-status.h"

----

Then modify your `cmd_psuh` implementation to declare your `struct wt_status`,

prepare it, and print its contents:

----

struct wt_status status;

...

wt_status_prepare(the_repository, &status);

git_config(git_default_config, &status);

...

printf(_("Your current branch: %s\n"), status.branch);

----

Run it again. Check it out - here's the (verbose) name of your current branch!

Let's commit this as well.

----

$ git add builtin/psuh.c

$ git commit -sm "psuh: print the current branch"

----

Now let's see if we can get some info about a specific commit.

Luckily, there are some helpers for us here. `commit.h` has a function called

`lookup_commit_reference_by_name` to which we can simply provide a hardcoded

string; `pretty.h` has an extremely handy `pp_commit_easy()` call which doesn't

require a full format object to be passed.

Add the following includes:

----

#include "commit.h"

#include "pretty.h"

----

Then, add the following lines within your implementation of `cmd_psuh()` near

the declarations and the logic, respectively.

----

struct commit *c = NULL;

struct strbuf commitline = STRBUF_INIT;

...

c = lookup_commit_reference_by_name("origin/master");

if (c != NULL) {

pp_commit_easy(CMIT_FMT_ONELINE, c, &commitline);

printf(_("Current commit: %s\n"), commitline.buf);

}

----

The `struct strbuf` provides some safety belts to your basic `char*`, one of

which is a length member to prevent buffer overruns. It needs to be initialized

nicely with `STRBUF_INIT`. Keep it in mind when you need to pass around `char*`.

`lookup_commit_reference_by_name` resolves the name you pass it, so you can play

with the value there and see what kind of things you can come up with.

`pp_commit_easy` is a convenience wrapper in `pretty.h` that takes a single

format enum shorthand, rather than an entire format struct. It then

pretty-prints the commit according to that shorthand. These are similar to the

formats available with `--pretty=FOO` in many Git commands.

Build it and run, and if you're using the same name in the example, you should

see the subject line of the most recent commit in `origin/master` that you know

about. Neat! Let's commit that as well.

----

$ git add builtin/psuh.c

$ git commit -sm "psuh: display the top of origin/master"

----

[[add-documentation]]

=== Adding Documentation

Awesome! You've got a fantastic new command that you're ready to share with the

community. But hang on just a minute - this isn't very user-friendly. Run the

following:

----

$ ./bin-wrappers/git help psuh

----

Your new command is undocumented! Let's fix that.

Take a look at `Documentation/git-*.txt`. These are the manpages for the

subcommands that Git knows about. You can open these up and take a look to get

acquainted with the format, but then go ahead and make a new file

`Documentation/git-psuh.txt`. Like with most of the documentation in the Git

project, help pages are written with AsciiDoc (see CodingGuidelines, "Writing

Documentation" section). Use the following template to fill out your own

manpage:

// Surprisingly difficult to embed AsciiDoc source within AsciiDoc.

[listing]

....

git-psuh(1)

===========

NAME

----

git-psuh - Delight users' typo with a shy horse

SYNOPSIS

--------

[verse]

'git-psuh [<arg>...]'

DESCRIPTION

-----------

...

OPTIONS[[OPTIONS]]

------------------

...

OUTPUT

------

...

GIT

---

Part of the linkgit:git[1] suite

....

The most important pieces of this to note are the file header, underlined by =,

the NAME section, and the SYNOPSIS, which would normally contain the grammar if

your command took arguments. Try to use well-established manpage headers so your

documentation is consistent with other Git and UNIX manpages; this makes life

easier for your user, who can skip to the section they know contains the

information they need.

NOTE: Before trying to build the docs, make sure you have the package `asciidoc`

installed.

Now that you've written your manpage, you'll need to build it explicitly. We

convert your AsciiDoc to troff which is man-readable like so:

----

$ make all doc

$ man Documentation/git-psuh.1

----

or

----

$ make -C Documentation/ git-psuh.1

$ man Documentation/git-psuh.1

----

While this isn't as satisfying as running through `git help`, you can at least

check that your help page looks right.

You can also check that the documentation coverage is good (that is, the project

sees that your command has been implemented as well as documented) by running

`make check-docs` from the top-level.

Go ahead and commit your new documentation change.

[[add-usage]]

=== Adding Usage Text

Try and run `./bin-wrappers/git psuh -h`. Your command should crash at the end.

That's because `-h` is a special case which your command should handle by

printing usage.

Take a look at `Documentation/technical/api-parse-options.txt`. This is a handy

tool for pulling out options you need to be able to handle, and it takes a

usage string.

In order to use it, we'll need to prepare a NULL-terminated array of usage

strings and a `builtin_psuh_options` array.

Add a line to `#include "parse-options.h"`.

At global scope, add your array of usage strings:

----

static const char * const psuh_usage[] = {

N_("git psuh [<arg>...]"),

NULL,

};

----

Then, within your `cmd_psuh()` implementation, we can declare and populate our

`option` struct. Ours is pretty boring but you can add more to it if you want to

explore `parse_options()` in more detail:

----

struct option options[] = {

OPT_END()

};

----

Finally, before you print your args and prefix, add the call to

`parse-options()`:

----

argc = parse_options(argc, argv, prefix, options, psuh_usage, 0);

----

This call will modify your `argv` parameter. It will strip the options you

specified in `options` from `argv` and the locations pointed to from `options`

entries will be updated. Be sure to replace your `argc` with the result from

`parse_options()`, or you will be confused if you try to parse `argv` later.

It's worth noting the special argument `--`. As you may be aware, many Unix

commands use `--` to indicate "end of named parameters" - all parameters after

the `--` are interpreted merely as positional arguments. (This can be handy if

you want to pass as a parameter something which would usually be interpreted as

a flag.) `parse_options()` will terminate parsing when it reaches `--` and give

you the rest of the options afterwards, untouched.

Now that you have a usage hint, you can teach Git how to show it in the general

command list shown by `git help git` or `git help -a`, which is generated from

`command-list.txt`. Find the line for 'git-pull' so you can add your 'git-psuh'

line above it in alphabetical order. Now, we can add some attributes about the

command which impacts where it shows up in the aforementioned help commands. The

top of `command-list.txt` shares some information about what each attribute

means; in those help pages, the commands are sorted according to these

attributes. `git psuh` is user-facing, or porcelain - so we will mark it as

"mainporcelain". For "mainporcelain" commands, the comments at the top of

`command-list.txt` indicate we can also optionally add an attribute from another

list; since `git psuh` shows some information about the user's workspace but

doesn't modify anything, let's mark it as "info". Make sure to keep your

attributes in the same style as the rest of `command-list.txt` using spaces to

align and delineate them:

----

git-prune-packed plumbingmanipulators

git-psuh mainporcelain info

git-pull mainporcelain remote

git-push mainporcelain remote

----

Build again. Now, when you run with `-h`, you should see your usage printed and

your command terminated before anything else interesting happens. Great!

Go ahead and commit this one, too.

[[testing]]

== Testing

It's important to test your code - even for a little toy command like this one.

Moreover, your patch won't be accepted into the Git tree without tests. Your

tests should:

* Illustrate the current behavior of the feature

* Prove the current behavior matches the expected behavior

* Ensure the externally-visible behavior isn't broken in later changes

So let's write some tests.

Related reading: `t/README`

[[overview-test-structure]]

=== Overview of Testing Structure

The tests in Git live in `t/` and are named with a 4-digit decimal number using

the schema shown in the Naming Tests section of `t/README`.

[[write-new-test]]

=== Writing Your Test

Since this a toy command, let's go ahead and name the test with t9999. However,

as many of the family/subcmd combinations are full, best practice seems to be

to find a command close enough to the one you've added and share its naming

space.

Create a new file `t/t9999-psuh-tutorial.sh`. Begin with the header as so (see

"Writing Tests" and "Source 'test-lib.sh'" in `t/README`):

----

#!/bin/sh

test_description='git-psuh test

This test runs git-psuh and makes sure it does not crash.'

. ./test-lib.sh

----

Tests are framed inside of a `test_expect_success` in order to output TAP

formatted results. Let's make sure that `git psuh` doesn't exit poorly and does

mention the right animal somewhere:

----

test_expect_success 'runs correctly with no args and good output' '

git psuh >actual &&

grep Pony actual

'

----

Indicate that you've run everything you wanted by adding the following at the

bottom of your script:

----

test_done

----

Make sure you mark your test script executable:

----

$ chmod +x t/t9999-psuh-tutorial.sh

----

You can get an idea of whether you created your new test script successfully

by running `make -C t test-lint`, which will check for things like test number

uniqueness, executable bit, and so on.

[[local-test]]

=== Running Locally

Let's try and run locally:

----

$ make

$ cd t/ && prove t9999-psuh-tutorial.sh

----

You can run the full test suite and ensure `git-psuh` didn't break anything:

----

$ cd t/

$ prove -j$(nproc) --shuffle t[0-9]*.sh

----

NOTE: You can also do this with `make test` or use any testing harness which can

speak TAP. `prove` can run concurrently. `shuffle` randomizes the order the

tests are run in, which makes them resilient against unwanted inter-test

dependencies. `prove` also makes the output nicer.

Go ahead and commit this change, as well.

[[ready-to-share]]

== Getting Ready to Share: Anatomy of a Patch Series

You may have noticed already that the Git project performs its code reviews via

emailed patches, which are then applied by the maintainer when they are ready

and approved by the community. The Git project does not accept contributions from

pull requests, and the patches emailed for review need to be formatted a

specific way.

:patch-series: https://lore.kernel.org/git/pull.1218.git.git.1645209647.gitgitgadget@gmail.com/

:lore: https://lore.kernel.org/git/

Before taking a look at how to convert your commits into emailed patches,

let's analyze what the end result, a "patch series", looks like. Here is an

{patch-series}[example] of the summary view for a patch series on the web interface of

the {lore}[Git mailing list archive]:

----

2022-02-18 18:40 [PATCH 0/3] libify reflog John Cai via GitGitGadget

2022-02-18 18:40 ` [PATCH 1/3] reflog: libify delete reflog function and helpers John Cai via GitGitGadget

2022-02-18 19:10 ` Ævar Arnfjörð Bjarmason [this message]

2022-02-18 19:39 ` Taylor Blau

2022-02-18 19:48 ` Ævar Arnfjörð Bjarmason

2022-02-18 19:35 ` Taylor Blau

2022-02-21 1:43 ` John Cai

2022-02-21 1:50 ` Taylor Blau

2022-02-23 19:50 ` John Cai

2022-02-18 20:00 ` // other replies ellided

2022-02-18 18:40 ` [PATCH 2/3] reflog: call reflog_delete from reflog.c John Cai via GitGitGadget

2022-02-18 19:15 ` Ævar Arnfjörð Bjarmason

2022-02-18 20:26 ` Junio C Hamano

2022-02-18 18:40 ` [PATCH 3/3] stash: call reflog_delete from reflog.c John Cai via GitGitGadget

2022-02-18 19:20 ` Ævar Arnfjörð Bjarmason

2022-02-19 0:21 ` Taylor Blau

2022-02-22 2:36 ` John Cai

2022-02-22 10:51 ` Ævar Arnfjörð Bjarmason

2022-02-18 19:29 ` [PATCH 0/3] libify reflog Ævar Arnfjörð Bjarmason

2022-02-22 18:30 ` [PATCH v2 0/3] libify reflog John Cai via GitGitGadget

2022-02-22 18:30 ` [PATCH v2 1/3] stash: add test to ensure reflog --rewrite --updatref behavior John Cai via GitGitGadget

2022-02-23 8:54 ` Ævar Arnfjörð Bjarmason

2022-02-23 21:27 ` Junio C Hamano

// continued

----

We can note a few things:

- Each commit is sent as a separate email, with the commit message title as

subject, prefixed with "[PATCH _i_/_n_]" for the _i_-th commit of an

_n_-commit series.

- Each patch is sent as a reply to an introductory email called the _cover

letter_ of the series, prefixed "[PATCH 0/_n_]".

- Subsequent iterations of the patch series are labelled "PATCH v2", "PATCH

v3", etc. in place of "PATCH". For example, "[PATCH v2 1/3]" would be the first of

three patches in the second iteration. Each iteration is sent with a new cover

letter (like "[PATCH v2 0/3]" above), itself a reply to the cover letter of the

previous iteration (more on that below).

NOTE: A single-patch topic is sent with "[PATCH]", "[PATCH v2]", etc. without

_i_/_n_ numbering (in the above thread overview, no single-patch topic appears,

though).

[[cover-letter]]

=== The cover letter

In addition to an email per patch, the Git community also expects your patches

to come with a cover letter. This is an important component of change

submission as it explains to the community from a high level what you're trying

to do, and why, in a way that's more apparent than just looking at your

patches.

The title of your cover letter should be something which succinctly covers the

purpose of your entire topic branch. It's often in the imperative mood, just

like our commit message titles. Here is how we'll title our series:

---

Add the 'psuh' command

---

The body of the cover letter is used to give additional context to reviewers.

Be sure to explain anything your patches don't make clear on their own, but

remember that since the cover letter is not recorded in the commit history,

anything that might be useful to future readers of the repository's history

should also be in your commit messages.

Here's an example body for `psuh`:

----

Our internal metrics indicate widespread interest in the command

git-psuh - that is, many users are trying to use it, but finding it is

unavailable, using some unknown workaround instead.

The following handful of patches add the psuh command and implement some

handy features on top of it.

This patchset is part of the MyFirstContribution tutorial and should not

be merged.

----

At this point the tutorial diverges, in order to demonstrate two

different methods of formatting your patchset and getting it reviewed.

The first method to be covered is GitGitGadget, which is useful for those

already familiar with GitHub's common pull request workflow. This method

requires a GitHub account.

The second method to be covered is `git send-email`, which can give slightly

more fine-grained control over the emails to be sent. This method requires some

setup which can change depending on your system and will not be covered in this

tutorial.

Regardless of which method you choose, your engagement with reviewers will be

the same; the review process will be covered after the sections on GitGitGadget

and `git send-email`.

[[howto-ggg]]

== Sending Patches via GitGitGadget

One option for sending patches is to follow a typical pull request workflow and

send your patches out via GitGitGadget. GitGitGadget is a tool created by

Johannes Schindelin to make life as a Git contributor easier for those used to

the GitHub PR workflow. It allows contributors to open pull requests against its

mirror of the Git project, and does some magic to turn the PR into a set of

emails and send them out for you. It also runs the Git continuous integration

suite for you. It's documented at http://gitgitgadget.github.io.

[[create-fork]]

=== Forking `git/git` on GitHub

Before you can send your patch off to be reviewed using GitGitGadget, you will

need to fork the Git project and upload your changes. First thing - make sure

you have a GitHub account.

Head to the https://github.com/git/git[GitHub mirror] and look for the Fork

button. Place your fork wherever you deem appropriate and create it.

[[upload-to-fork]]

=== Uploading to Your Own Fork

To upload your branch to your own fork, you'll need to add the new fork as a

remote. You can use `git remote -v` to show the remotes you have added already.

From your new fork's page on GitHub, you can press "Clone or download" to get

the URL; then you need to run the following to add, replacing your own URL and

remote name for the examples provided:

----

$ git remote add remotename git@github.com:remotename/git.git

----

or to use the HTTPS URL:

----

$ git remote add remotename https://github.com/remotename/git/.git

----

Run `git remote -v` again and you should see the new remote showing up.

`git fetch remotename` (with the real name of your remote replaced) in order to

get ready to push.

Next, double-check that you've been doing all your development in a new branch

by running `git branch`. If you didn't, now is a good time to move your new

commits to their own branch.

As mentioned briefly at the beginning of this document, we are basing our work

on `master`, so go ahead and update as shown below, or using your preferred

workflow.

----

$ git checkout master

$ git pull -r

$ git rebase master psuh

----

Finally, you're ready to push your new topic branch! (Due to our branch and

command name choices, be careful when you type the command below.)

----

$ git push remotename psuh

----

Now you should be able to go and check out your newly created branch on GitHub.

[[send-pr-ggg]]

=== Sending a PR to GitGitGadget

In order to have your code tested and formatted for review, you need to start by

opening a Pull Request against `gitgitgadget/git`. Head to

https://github.com/gitgitgadget/git and open a PR either with the "New pull

request" button or the convenient "Compare & pull request" button that may

appear with the name of your newly pushed branch.

Review the PR's title and description, as they're used by GitGitGadget

respectively as the subject and body of the cover letter for your change. Refer

to <<cover-letter,"The cover letter">> above for advice on how to title your

submission and what content to include in the description.

NOTE: For single-patch contributions, your commit message should already be

meaningful and explain at a high level the purpose (what is happening and why)

of your patch, so you usually do not need any additional context. In that case,

remove the PR description that GitHub automatically generates from your commit

message (your PR description should be empty). If you do need to supply even

more context, you can do so in that space and it will be appended to the email

that GitGitGadget will send, between the three-dash line and the diffstat

(see <<single-patch,Bonus Chapter: One-Patch Changes>> for how this looks once

submitted).

When you're happy, submit your pull request.

[[run-ci-ggg]]

=== Running CI and Getting Ready to Send

If it's your first time using GitGitGadget (which is likely, as you're using

this tutorial) then someone will need to give you permission to use the tool.

As mentioned in the GitGitGadget documentation, you just need someone who

already uses it to comment on your PR with `/allow <username>`. GitGitGadget

will automatically run your PRs through the CI even without the permission given

but you will not be able to `/submit` your changes until someone allows you to

use the tool.

NOTE: You can typically find someone who can `/allow` you on GitGitGadget by

either examining recent pull requests where someone has been granted `/allow`

(https://github.com/gitgitgadget/git/pulls?utf8=%E2%9C%93&q=is%3Apr+is%3Aopen+%22%2Fallow%22[Search:

is:pr is:open "/allow"]), in which case both the author and the person who

granted the `/allow` can now `/allow` you, or by inquiring on the

https://web.libera.chat/#git-devel[#git-devel] IRC channel on Libera Chat

linking your pull request and asking for someone to `/allow` you.

If the CI fails, you can update your changes with `git rebase -i` and push your

branch again:

----

$ git push -f remotename psuh

----

In fact, you should continue to make changes this way up until the point when

your patch is accepted into `next`.

////

TODO https://github.com/gitgitgadget/gitgitgadget/issues/83

It'd be nice to be able to verify that the patch looks good before sending it

to everyone on Git mailing list.

[[check-work-ggg]]

=== Check Your Work

////

[[send-mail-ggg]]

=== Sending Your Patches

Now that your CI is passing and someone has granted you permission to use

GitGitGadget with the `/allow` command, sending out for review is as simple as

commenting on your PR with `/submit`.

[[responding-ggg]]

=== Updating With Comments

Skip ahead to <<reviewing,Responding to Reviews>> for information on how to

reply to review comments you will receive on the mailing list.

Once you have your branch again in the shape you want following all review

comments, you can submit again:

----

$ git push -f remotename psuh

----

Next, go look at your pull request against GitGitGadget; you should see the CI

has been kicked off again. Now while the CI is running is a good time for you

to modify your description at the top of the pull request thread; it will be

used again as the cover letter. You should use this space to describe what

has changed since your previous version, so that your reviewers have some idea

of what they're looking at. When the CI is done running, you can comment once

more with `/submit` - GitGitGadget will automatically add a v2 mark to your

changes.

[[howto-git-send-email]]

== Sending Patches with `git send-email`

If you don't want to use GitGitGadget, you can also use Git itself to mail your

patches. Some benefits of using Git this way include finer grained control of

subject line (for example, being able to use the tag [RFC PATCH] in the subject)

and being able to send a ``dry run'' mail to yourself to ensure it all looks

good before going out to the list.

[[setup-git-send-email]]

=== Prerequisite: Setting Up `git send-email`

Configuration for `send-email` can vary based on your operating system and email

provider, and so will not be covered in this tutorial, beyond stating that in

many distributions of Linux, `git-send-email` is not packaged alongside the

typical `git` install. You may need to install this additional package; there