[v5,1/2] documentation: add tutorial for first contribution
diff mbox series

Message ID 20190507213040.151799-2-emilyshaffer@google.com
State New
Headers show
Series
  • documentation: add lab for first contribution
Related show

Commit Message

Emily Shaffer May 7, 2019, 9:30 p.m. UTC
This tutorial covers how to add a new command to Git and, in the
process, everything from cloning git/git to getting reviewed on the
mailing list. It's meant for new contributors to go through
interactively, learning the techniques generally used by the git/git
development community.

Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
---
 Documentation/Makefile                |    1 +
 Documentation/MyFirstContribution.txt | 1075 +++++++++++++++++++++++++
 2 files changed, 1076 insertions(+)
 create mode 100644 Documentation/MyFirstContribution.txt

Comments

Emily Shaffer May 7, 2019, 11:25 p.m. UTC | #1
> +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_const("user.name", &cfg_name) > 0) {
> +		printf(_("No name is found in config\n"));
> +	} else {
> +		printf(_("Your name: %s\n"), cfg_name);
> +	}

Just noticed the braces here, too. I have removed them from my local
copy and will upload again if I hear other comments warranting a v6.

 - Emily
Junio C Hamano May 8, 2019, 3:46 a.m. UTC | #2
Emily Shaffer <emilyshaffer@google.com> writes:

> +=== 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 official mirror on GitHub.

I didn't want to have to get into fine-grained wordsmithing (let
alone bikeshedding) this late in the iteration of the topic, but
"the official mirror" is not something anybody suggested in the
recent reviews (JTan's rephrasing, which I already said that I am OK
with, said something like "one of the many mirrors").

And "official" is a phrase I have trouble with in this context.  A
mirror does not have to be blessed as official; that's the point of
a mirror---anybody can make one to help users with better
connectivity or availability, as long as its users trust the mirror
maintainer for mirror's correctness and freshness.

So perhaps "... clone from is the mirror maintained by GitHub folks"
or just simply "is the mirror on GitHub"?

> +$ git send-email --to=target@example.com
> +		 --in-reply-to="<foo.12345.author@example.com>"

Very nice attention to the detail here.  I like it (the earlier
round did not have dq around the message ID).

> +		 psuh/v2*
> +----

All other edits relative to the previous round look very sensible to
me.  Thanks.
Emily Shaffer May 8, 2019, 6:58 p.m. UTC | #3
On Wed, May 08, 2019 at 12:46:47PM +0900, Junio C Hamano wrote:
> Emily Shaffer <emilyshaffer@google.com> writes:
> 
> > +=== 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 official mirror on GitHub.
> 
> I didn't want to have to get into fine-grained wordsmithing (let
> alone bikeshedding) this late in the iteration of the topic, but
> "the official mirror" is not something anybody suggested in the
> recent reviews (JTan's rephrasing, which I already said that I am OK
> with, said something like "one of the many mirrors").

I should have waited longer on sending this round of patch out; as it
stands I sent the patch with this fix a few hours before your response
to JTan came out. Sorry for the confusion.

> And "official" is a phrase I have trouble with in this context.  A
> mirror does not have to be blessed as official; that's the point of
> a mirror---anybody can make one to help users with better
> connectivity or availability, as long as its users trust the mirror
> maintainer for mirror's correctness and freshness.

You're right and I'll remove it. However, I've seen at least one
instance of confusion over Git's lack of an "official" mirror (over on
#git on Freenode). I'd like to rephrase this to explain the reasoning
behind having multiple mirrors, none of which are official.

To that end, I propose replacing the phrase with "one of the best places
to clone from is this mirror on GitHub." followed by the clone command
to git/git, then followed by:

	NOTE: As Git is a distributed version control, the Git project also
	follows a distributed model. There is no central official mirror; any
	mirror which you can reasonably trust is being kept correct and fresh to
	the Git source distributed by the Git maintainer is fine to work from.

What do we think?

Alternatively, if the desire is to just be done with it, I have no
problem with Junio rewording however he feels is best and otherwise
applying this patch - if there is value in reducing the churn on the
mailing list for this patch.

> So perhaps "... clone from is the mirror maintained by GitHub folks"
> or just simply "is the mirror on GitHub"?
> 
> > +$ git send-email --to=target@example.com
> > +		 --in-reply-to="<foo.12345.author@example.com>"
> 
> Very nice attention to the detail here.  I like it (the earlier
> round did not have dq around the message ID).
> 
> > +		 psuh/v2*
> > +----
> 
> All other edits relative to the previous round look very sensible to
> me.  Thanks.
Jonathan Tan May 8, 2019, 7:53 p.m. UTC | #4
> > And "official" is a phrase I have trouble with in this context.  A
> > mirror does not have to be blessed as official; that's the point of
> > a mirror---anybody can make one to help users with better
> > connectivity or availability, as long as its users trust the mirror
> > maintainer for mirror's correctness and freshness.
> 
> You're right and I'll remove it. However, I've seen at least one
> instance of confusion over Git's lack of an "official" mirror (over on
> #git on Freenode). I'd like to rephrase this to explain the reasoning
> behind having multiple mirrors, none of which are official.
> 
> To that end, I propose replacing the phrase with "one of the best places
> to clone from is this mirror on GitHub." followed by the clone command
> to git/git, then followed by:
> 
> 	NOTE: As Git is a distributed version control, the Git project also
> 	follows a distributed model. There is no central official mirror; any
> 	mirror which you can reasonably trust is being kept correct and fresh to
> 	the Git source distributed by the Git maintainer is fine to work from.
> 
> What do we think?

In the interest of avoiding mailing list churn, I think we should not
bother with explaining what an "official" mirror is right now, as long
as we already have steps that a newcomer can take (which we do). Someone
else can add it later if they wish.

For me, the "official" mirrors are whatever is listed in the latest "A
note from the maintainer" (e.g. [1]). Even if we want to link to this or
replicate part of its contents, I think we can do it after this patch is
merged.

(Also, with that paragraph, I don't think a newcomer should be expected
to know what mirror is reasonably trusted.)

[1] https://public-inbox.org/git/xmqqwolmcvyb.fsf@gitster-ct.c.googlers.com/

> Alternatively, if the desire is to just be done with it, I have no
> problem with Junio rewording however he feels is best and otherwise
> applying this patch - if there is value in reducing the churn on the
> mailing list for this patch.

This sounds good to me too.

Patch
diff mbox series

diff --git a/Documentation/Makefile b/Documentation/Makefile
index 6d738f831e..360c8051e2 100644
--- a/Documentation/Makefile
+++ b/Documentation/Makefile
@@ -73,6 +73,7 @@  SP_ARTICLES += howto/maintain-git
 API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technical/api-index.txt, $(wildcard technical/api-*.txt)))
 SP_ARTICLES += $(API_DOCS)
 
+TECH_DOCS += MyFirstContribution
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += technical/hash-function-transition
 TECH_DOCS += technical/http-protocol
diff --git a/Documentation/MyFirstContribution.txt b/Documentation/MyFirstContribution.txt
new file mode 100644
index 0000000000..0f9a7fed93
--- /dev/null
+++ b/Documentation/MyFirstContribution.txt
@@ -0,0 +1,1075 @@ 
+My First Contribution to the Git Project
+========================================
+
+== 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
+
+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
+
+This tutorial aims to summarize the following documents, but the reader may find
+useful additional context:
+
+- `Documentation/SubmittingPatches`
+- `Documentation/howto/new-command.txt`
+
+== Getting Started
+
+=== 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 official mirror on GitHub.
+
+----
+$ git clone https://github.com/git/git git
+----
+
+=== 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`.)
+
+=== 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!
+
+NOTE: A reference implementation can be found at
+https://github.com/nasamuffin/git/tree/psuh.
+
+=== 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_push`, and add a new line for `psuh` immediately before it,
+in order to keep the declarations 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/push.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.
+
+NOTE: The Git build is parallelizable. `-j#` is not included above but you can
+use it as you prefer, here and elsewhere.
+
+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.
+
+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 add Makefile builtin.h builtin/psuh.c git.c
+$ 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 line 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
+
+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:
+
+----
+	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_const("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_const()` 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 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 commit -sm "psuh: display the top of origin/master"
+----
+
+=== 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'
+
+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.
+
+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
+----
+
+NOTE: You may need to install the package `asciidoc` to get this to work.
+
+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.
+
+=== 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 usage string and a
+`builtin_psuh_options` array. Add a line to `#include "parse-options.h"`.
+
+At global scope, add your usage:
+
+----
+static const char * const psuh_usage[] = {
+	N_("git psuh"),
+	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.
+
+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
+
+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 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`.
+
+=== 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 &&
+	test_i18ngrep 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.
+
+=== 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.
+
+== Getting Ready to Share
+
+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 patches from
+pull requests, and the patches emailed for review need to be formatted a
+specific way. 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`.
+
+== 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.
+
+=== 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.
+
+=== 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.
+
+=== 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 it's used by GitGitGadget as the cover
+letter for your change. When you're happy, submit your pull request.
+
+=== 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.
+
+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 Your Work
+////
+
+=== 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`.
+
+=== 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.
+
+== 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.
+
+=== 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
+are a number of resources online to help you do so. You will also need to
+determine the right way to configure it to use your SMTP server; again, as this
+configuration can change significantly based on your system and email setup, it
+is out of scope for the context of this tutorial.
+
+=== Preparing Initial Patchset
+
+Sending emails with Git is a two-part process; before you can prepare the emails
+themselves, you'll need to prepare the patches. Luckily, this is pretty simple:
+
+----
+$ git format-patch --cover-letter -o psuh/ master..psuh
+----
+
+The `--cover-letter` parameter tells `format-patch` to create a cover letter
+template for you. You will need to fill in the template before you're ready
+to send - but for now, the template will be next to your other patches.
+
+The `-o psuh/` parameter tells `format-patch` to place the patch files into a
+directory. This is useful because `git send-email` can take a directory and
+send out all the patches from there.
+
+`master..psuh` tells `format-patch` to generate patches for the difference
+between `master` and `psuh`. It will make one patch file per commit. After you
+run, you can go have a look at each of the patches with your favorite text
+editor and make sure everything looks alright; however, it's not recommended to
+make code fixups via the patch file. It's a better idea to make the change the
+normal way using `git rebase -i` or by adding a new commit than by modifying a
+patch.
+
+NOTE: Optionally, you can also use the `--rfc` flag to prefix your patch subject
+with ``[RFC PATCH]'' instead of ``[PATCH]''. RFC stands for ``request for
+comments'' and indicates that while your code isn't quite ready for submission,
+you'd like to begin the code review process. This can also be used when your
+patch is a proposal, but you aren't sure whether the community wants to solve
+the problem with that approach or not - to conduct a sort of design review. You
+may also see on the list patches marked ``WIP'' - this means they are incomplete
+but want reviewers to look at what they have so far. You can add this flag with
+`--subject-prefix=WIP`.
+
+Check and make sure that your patches and cover letter template exist in the
+directory you specified - you're nearly ready to send out your review!
+
+=== Preparing Email
+
+In addition to an email per patch, the Git community also expects your patches
+to come with a cover letter, typically with a subject line [PATCH 0/x] (where
+x is the number of patches you're sending). Since you invoked `format-patch`
+with `--cover-letter`, you've already got a template ready. Open it up in your
+favorite editor.
+
+You should see a number of headers present already. Check that your `From:`
+header is correct. Then modify your `Subject:` to something which succinctly
+covers the purpose of your entire topic branch, for example:
+
+----
+Subject: [PATCH 0/7] adding the 'psuh' command
+----
+
+Make sure you retain the ``[PATCH 0/X]'' part; that's what indicates to the Git
+community that this email is the beginning of a review, and many reviewers
+filter their email for this type of flag.
+
+You'll need to add some extra parameters when you invoke `git send-email` to add
+the cover letter.
+
+Next you'll have to fill out the body of your 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 diff. Be sure to explain anything your diff doesn't make clear
+on its own.
+
+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.
+----
+
+The template created by `git format-patch --cover-letter` includes a diffstat.
+This gives reviewers a summary of what they're in for when reviewing your topic.
+The one generated for `psuh` from the sample implementation looks like this:
+
+----
+ Documentation/git-psuh.txt | 40 +++++++++++++++++++++
+ Makefile                   |  1 +
+ builtin.h                  |  1 +
+ builtin/psuh.c             | 73 ++++++++++++++++++++++++++++++++++++++
+ git.c                      |  1 +
+ t/t9999-psuh-tutorial.sh   | 12 +++++++
+ 6 files changed, 128 insertions(+)
+ create mode 100644 Documentation/git-psuh.txt
+ create mode 100644 builtin/psuh.c
+ create mode 100755 t/t9999-psuh-tutorial.sh
+----
+
+Finally, the letter will include the version of Git used to generate the
+patches. You can leave that string alone.
+
+=== Sending Email
+
+At this point you should have a directory `psuh/` which is filled with your
+patches and a cover letter. Time to mail it out! You can send it like this:
+
+----
+$ git send-email --to=target@example.com psuh/*.patch
+----
+
+NOTE: Check `git help send-email` for some other options which you may find
+valuable, such as changing the Reply-to address or adding more CC and BCC lines.
+
+NOTE: When you are sending a real patch, it will go to git@vger.kernel.org - but
+please don't send your patchset from the tutorial to the real mailing list! For
+now, you can send it to yourself, to make sure you understand how it will look.
+
+After you run the command above, you will be presented with an interactive
+prompt for each patch that's about to go out. This gives you one last chance to
+edit or quit sending something (but again, don't edit code this way). Once you
+press `y` or `a` at these prompts your emails will be sent! Congratulations!
+
+Awesome, now the community will drop everything and review your changes. (Just
+kidding - be patient!)
+
+=== Sending v2
+
+Skip ahead to <<reviewing,Responding to Reviews>> for information on how to
+handle comments from reviewers. Continue this section when your topic branch is
+shaped the way you want it to look for your patchset v2.
+
+When you're ready with the next iteration of your patch, the process is fairly
+similar.
+
+First, generate your v2 patches again:
+
+----
+$ git format-patch -v2 --cover-letter -o psuh/ master..psuh
+----
+
+This will add your v2 patches, all named like `v2-000n-my-commit-subject.patch`,
+to the `psuh/` directory. You may notice that they are sitting alongside the v1
+patches; that's fine, but be careful when you are ready to send them.
+
+Edit your cover letter again. Now is a good time to mention what's different
+between your last version and now, if it's something significant. You do not
+need the exact same body in your second cover letter; focus on explaining to
+reviewers the changes you've made that may not be as visible.
+
+You will also need to go and find the Message-Id of your previous cover letter.
+You can either note it when you send the first series, from the output of `git
+send-email`, or you can look it up on the
+https://public-inbox.org/git[mailing list]. Find your cover letter in the
+archives, click on it, then click "permalink" or "raw" to reveal the Message-Id
+header. It should match:
+
+----
+Message-Id: <foo.12345.author@example.com>
+----
+
+Your Message-Id is `<foo.12345.author@example.com>`. This example will be used
+below as well; make sure to replace it with the correct Message-Id for your
+**previous cover letter** - that is, if you're sending v2, use the Message-Id
+from v1; if you're sending v3, use the Message-Id from v2.
+
+While you're looking at the email, you should also note who is CC'd, as it's
+common practice in the mailing list to keep all CCs on a thread. You can add
+these CC lines directly to your cover letter with a line like so in the header
+(before the Subject line):
+
+----
+CC: author@example.com, Othe R <other@example.com>
+----
+
+Now send the emails again, paying close attention to which messages you pass in
+to the command:
+
+----
+$ git send-email --to=target@example.com
+		 --in-reply-to="<foo.12345.author@example.com>"
+		 psuh/v2*
+----
+
+=== Bonus Chapter: One-Patch Changes
+
+In some cases, your very small change may consist of only one patch. When that
+happens, you only need to send one email. Your commit message should already be
+meaningful and explain at a high level the purpose (what is happening and why)
+of your patch, but if you need to supply even more context, you can do so below
+the `---` in your patch. Take the example below, which was generated with `git
+format-patch` on a single commit, and then edited to add the content between
+the `---` and the diffstat.
+
+----
+From 1345bbb3f7ac74abde040c12e737204689a72723 Mon Sep 17 00:00:00 2001
+From: A U Thor <author@example.com>
+Date: Thu, 18 Apr 2019 15:11:02 -0700
+Subject: [PATCH] README: change the grammar
+
+I think it looks better this way. This part of the commit message will
+end up in the commit-log.
+
+Signed-off-by: A U Thor <author@example.com>
+---
+Let's have a wild discussion about grammar on the mailing list. This
+part of my email will never end up in the commit log. Here is where I
+can add additional context to the mailing list about my intent, outside
+of the context of the commit log. This section was added after `git
+format-patch` was run, by editing the patch file in a text editor.
+
+ README.md | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/README.md b/README.md
+index 88f126184c..38da593a60 100644
+--- a/README.md
++++ b/README.md
+@@ -3,7 +3,7 @@
+ Git - fast, scalable, distributed revision control system
+ =========================================================
+
+-Git is a fast, scalable, distributed revision control system with an
++Git is a fast, scalable, and distributed revision control system with an
+ unusually rich command set that provides both high-level operations
+ and full access to internals.
+
+--
+2.21.0.392.gf8f6787159e-goog
+----
+
+== My Patch Got Emailed - Now What?
+
+[[reviewing]]
+=== Responding to Reviews
+
+After a few days, you will hopefully receive a reply to your patchset with some
+comments. Woohoo! Now you can get back to work.
+
+It's good manners to reply to each comment, notifying the reviewer that you have
+made the change requested, feel the original is better, or that the comment
+inspired you to do something a new way which is superior to both the original
+and the suggested change. This way reviewers don't need to inspect your v2 to
+figure out whether you implemented their comment or not.
+
+If you are going to push back on a comment, be polite and explain why you feel
+your original is better; be prepared that the reviewer may still disagree with
+you, and the rest of the community may weigh in on one side or the other. As
+with all code reviews, it's important to keep an open mind to doing something a
+different way than you originally planned; other reviewers have a different
+perspective on the project than you do, and may be thinking of a valid side
+effect which had not occurred to you. It is always okay to ask for clarification
+if you aren't sure why a change was suggested, or what the reviewer is asking
+you to do.
+
+Make sure your email client has a plaintext email mode and it is turned on; the
+Git list rejects HTML email. Please also follow the mailing list etiquette
+outlined in the
+https://kernel.googlesource.com/pub/scm/git/git/+/todo/MaintNotes[Maintainer's
+Note], which are similar to etiquette rules in most open source communities
+surrounding bottom-posting and inline replies.
+
+When you're making changes to your code, it is cleanest - that is, the resulting
+commits are easiest to look at - if you use `git rebase -i` (interactive
+rebase). Take a look at this
+https://www.oreilly.com/library/view/git-pocket-guide/9781449327507/ch10.html[overview]
+from O'Reilly. The general idea is to modify each commit which requires changes;
+this way, instead of having a patch A with a mistake, a patch B which was fine
+and required no upstream reviews in v1, and a patch C which fixes patch A for
+v2, you can just ship a v2 with a correct patch A and correct patch B. This is
+changing history, but since it's local history which you haven't shared with
+anyone, that is okay for now! (Later, it may not make sense to do this; take a
+look at the section below this one for some context.)
+
+=== After Review Approval
+
+The Git project has four integration branches: `pu`, `next`, `master`, and
+`maint`. Your change will be placed into `pu` fairly early on by the maintainer
+while it is still in the review process; from there, when it is ready for wider
+testing, it will be merged into `next`. Plenty of early testers use `next` and
+may report issues. Eventually, changes in `next` will make it to `master`,
+which is typically considered stable. Finally, when a new release is cut,
+`maint` is used to base bugfixes onto. As mentioned at the beginning of this
+document, you can read `Documents/SubmittingPatches` for some more info about
+the use of the various integration branches.
+
+Back to now: your code has been lauded by the upstream reviewers. It is perfect.
+It is ready to be accepted. You don't need to do anything else; the maintainer
+will merge your topic branch to `next` and life is good.
+
+However, if you discover it isn't so perfect after this point, you may need to
+take some special steps depending on where you are in the process.
+
+If the maintainer has announced in the "What's cooking in git.git" email that
+your topic is marked for `next` - that is, that they plan to merge it to `next`
+but have not yet done so - you should send an email asking the maintainer to
+wait a little longer: "I've sent v4 of my series and you marked it for `next`,
+but I need to change this and that - please wait for v5 before you merge it."
+
+If the topic has already been merged to `next`, rather than modifying your
+patches with `git rebase -i`, you should make further changes incrementally -
+that is, with another commit, based on top of the maintainer's topic branch as
+detailed in https://github.com/gitster/git. Your work is still in the same topic
+but is now incremental, rather than a wholesale rewrite of the topic branch.
+
+The topic branches in the maintainer's GitHub are mirrored in GitGitGadget, so
+if you're sending your reviews out that way, you should be sure to open your PR
+against the appropriate GitGitGadget/Git branch.
+
+If you're using `git send-email`, you can use it the same way as before, but you
+should generate your diffs from `<topic>..<mybranch>` and base your work on
+`<topic>` instead of `master`.