doc: MyFirstContribution: fix cmd placement instructions
[git/git.git] / Documentation / MyFirstContribution.txt
1 My First Contribution to the Git Project
2 ========================================
3 :sectanchors:
5 [[summary]]
6 == Summary
8 This is a tutorial demonstrating the end-to-end workflow of creating a change to
9 the Git tree, sending it for review, and making changes based on comments.
11 [[prerequisites]]
12 === Prerequisites
14 This tutorial assumes you're already fairly familiar with using Git to manage
15 source code. The Git workflow steps will largely remain unexplained.
17 [[related-reading]]
18 === Related Reading
20 This tutorial aims to summarize the following documents, but the reader may find
21 useful additional context:
23 - `Documentation/SubmittingPatches`
24 - `Documentation/howto/new-command.txt`
26 [[getting-started]]
27 == Getting Started
29 [[cloning]]
30 === Clone the Git Repository
32 Git is mirrored in a number of locations. Clone the repository from one of them;
33 suggests one of the best places to clone from is
34 the mirror on GitHub.
36 ----
37 $ git clone git
38 $ cd git
39 ----
41 [[identify-problem]]
42 === Identify Problem to Solve
44 ////
45 Use + to indicate fixed-width here; couldn't get ` to work nicely with the
46 quotes around "Pony Saying 'Um, Hello'".
47 ////
48 In this tutorial, we will add a new command, +git psuh+, short for ``Pony Saying
49 `Um, Hello''' - a feature which has gone unimplemented despite a high frequency
50 of invocation during users' typical daily workflow.
52 (We've seen some other effort in this space with the implementation of popular
53 commands such as `sl`.)
55 [[setup-workspace]]
56 === Set Up Your Workspace
58 Let's start by making a development branch to work on our changes. Per
59 `Documentation/SubmittingPatches`, since a brand new command is a new feature,
60 it's fine to base your work on `master`. However, in the future for bugfixes,
61 etc., you should check that document and base it on the appropriate branch.
63 For the purposes of this document, we will base all our work on the `master`
64 branch of the upstream project. Create the `psuh` branch you will use for
65 development like so:
67 ----
68 $ git checkout -b psuh origin/master
69 ----
71 We'll make a number of commits here in order to demonstrate how to send a topic
72 with multiple patches up for review simultaneously.
74 [[code-it-up]]
75 == Code It Up!
77 NOTE: A reference implementation can be found at
80 [[add-new-command]]
81 === Adding a New Command
83 Lots of the subcommands are written as builtins, which means they are
84 implemented in C and compiled into the main `git` executable. Implementing the
85 very simple `psuh` command as a built-in will demonstrate the structure of the
86 codebase, the internal API, and the process of working together as a contributor
87 with the reviewers and maintainer to integrate this change into the system.
89 Built-in subcommands are typically implemented in a function named "cmd_"
90 followed by the name of the subcommand, in a source file named after the
91 subcommand and contained within `builtin/`. So it makes sense to implement your
92 command in `builtin/psuh.c`. Create that file, and within it, write the entry
93 point for your command in a function matching the style and signature:
95 ----
96 int cmd_psuh(int argc, const char **argv, const char *prefix)
97 ----
99 We'll also need to add the declaration of psuh; open up `builtin.h`, find the
100 declaration for `cmd_pull`, and add a new line for `psuh` immediately before it,
101 in order to keep the declarations alphabetically sorted:
103 ----
104 int cmd_psuh(int argc, const char **argv, const char *prefix);
105 ----
107 Be sure to `#include "builtin.h"` in your `psuh.c`.
109 Go ahead and add some throwaway printf to that function. This is a decent
110 starting point as we can now add build rules and register the command.
112 NOTE: Your throwaway text, as well as much of the text you will be adding over
113 the course of this tutorial, is user-facing. That means it needs to be
114 localizable. Take a look at `po/README` under "Marking strings for translation".
115 Throughout the tutorial, we will mark strings for translation as necessary; you
116 should also do so when writing your user-facing commands in the future.
118 ----
119 int cmd_psuh(int argc, const char **argv, const char *prefix)
120 {
121 printf(_("Pony saying hello goes here.\n"));
122 return 0;
123 }
124 ----
126 Let's try to build it. Open `Makefile`, find where `builtin/pull.o` is added
127 to `BUILTIN_OBJS`, and add `builtin/psuh.o` in the same way next to it in
128 alphabetical order. Once you've done so, move to the top-level directory and
129 build simply with `make`. Also add the `DEVELOPER=1` variable to turn on
130 some additional warnings:
132 ----
133 $ echo DEVELOPER=1 >config.mak
134 $ make
135 ----
137 NOTE: When you are developing the Git project, it's preferred that you use the
138 `DEVELOPER` flag; if there's some reason it doesn't work for you, you can turn
139 it off, but it's a good idea to mention the problem to the mailing list.
141 NOTE: The Git build is parallelizable. `-j#` is not included above but you can
142 use it as you prefer, here and elsewhere.
144 Great, now your new command builds happily on its own. But nobody invokes it.
145 Let's change that.
147 The list of commands lives in `git.c`. We can register a new command by adding
148 a `cmd_struct` to the `commands[]` array. `struct cmd_struct` takes a string
149 with the command name, a function pointer to the command implementation, and a
150 setup option flag. For now, let's keep mimicking `push`. Find the line where
151 `cmd_push` is registered, copy it, and modify it for `cmd_psuh`, placing the new
152 line in alphabetical order (immediately before `cmd_pull`).
154 The options are documented in `builtin.h` under "Adding a new built-in." Since
155 we hope to print some data about the user's current workspace context later,
156 we need a Git directory, so choose `RUN_SETUP` as your only option.
158 Go ahead and build again. You should see a clean build, so let's kick the tires
159 and see if it works. There's a binary you can use to test with in the
160 `bin-wrappers` directory.
162 ----
163 $ ./bin-wrappers/git psuh
164 ----
166 Check it out! You've got a command! Nice work! Let's commit this.
168 `git status` reveals modified `Makefile`, `builtin.h`, and `git.c` as well as
169 untracked `builtin/psuh.c` and `git-psuh`. First, let's take care of the binary,
170 which should be ignored. Open `.gitignore` in your editor, find `/git-pull`, and
171 add an entry for your new command in alphabetical order:
173 ----
174 ...
175 /git-prune-packed
176 /git-psuh
177 /git-pull
178 /git-push
179 /git-quiltimport
180 /git-range-diff
181 ...
182 ----
184 Checking `git status` again should show that `git-psuh` has been removed from
185 the untracked list and `.gitignore` has been added to the modified list. Now we
186 can stage and commit:
188 ----
189 $ git add Makefile builtin.h builtin/psuh.c git.c .gitignore
190 $ git commit -s
191 ----
193 You will be presented with your editor in order to write a commit message. Start
194 the commit with a 50-column or less subject line, including the name of the
195 component you're working on, followed by a blank line (always required) and then
196 the body of your commit message, which should provide the bulk of the context.
197 Remember to be explicit and provide the "Why" of your change, especially if it
198 couldn't easily be understood from your diff. When editing your commit message,
199 don't remove the Signed-off-by line which was added by `-s` above.
201 ----
202 psuh: add a built-in by popular demand
204 Internal metrics indicate this is a command many users expect to be
205 present. So here's an implementation to help drive customer
206 satisfaction and engagement: a pony which doubtfully greets the user,
207 or, a Pony Saying "Um, Hello" (PSUH).
209 This commit message is intentionally formatted to 72 columns per line,
210 starts with a single line as "commit message subject" that is written as
211 if to command the codebase to do something (add this, teach a command
212 that). The body of the message is designed to add information about the
213 commit that is not readily deduced from reading the associated diff,
214 such as answering the question "why?".
216 Signed-off-by: A U Thor <>
217 ----
219 Go ahead and inspect your new commit with `git show`. "psuh:" indicates you
220 have modified mainly the `psuh` command. The subject line gives readers an idea
221 of what you've changed. The sign-off line (`-s`) indicates that you agree to
222 the Developer's Certificate of Origin 1.1 (see the
223 `Documentation/SubmittingPatches` +++[[dco]]+++ header).
225 For the remainder of the tutorial, the subject line only will be listed for the
226 sake of brevity. However, fully-fleshed example commit messages are available
227 on the reference implementation linked at the top of this document.
229 [[implementation]]
230 === Implementation
232 It's probably useful to do at least something besides printing out a string.
233 Let's start by having a look at everything we get.
235 Modify your `cmd_psuh` implementation to dump the args you're passed, keeping
236 existing `printf()` calls in place:
238 ----
239 int i;
241 ...
243 printf(Q_("Your args (there is %d):\n",
244 "Your args (there are %d):\n",
245 argc),
246 argc);
247 for (i = 0; i < argc; i++)
248 printf("%d: %s\n", i, argv[i]);
250 printf(_("Your current working directory:\n<top-level>%s%s\n"),
251 prefix ? "/" : "", prefix ? prefix : "");
253 ----
255 Build and try it. As you may expect, there's pretty much just whatever we give
256 on the command line, including the name of our command. (If `prefix` is empty
257 for you, try `cd Documentation/ && ../bin-wrappers/git psuh`). That's not so
258 helpful. So what other context can we get?
260 Add a line to `#include "config.h"`. Then, add the following bits to the
261 function body:
263 ----
264 const char *cfg_name;
266 ...
268 git_config(git_default_config, NULL);
269 if (git_config_get_string_const("", &cfg_name) > 0)
270 printf(_("No name is found in config\n"));
271 else
272 printf(_("Your name: %s\n"), cfg_name);
273 ----
275 `git_config()` will grab the configuration from config files known to Git and
276 apply standard precedence rules. `git_config_get_string_const()` will look up
277 a specific key ("") and give you the value. There are a number of
278 single-key lookup functions like this one; you can see them all (and more info
279 about how to use `git_config()`) in `Documentation/technical/api-config.txt`.
281 You should see that the name printed matches the one you see when you run:
283 ----
284 $ git config --get
285 ----
287 Great! Now we know how to check for values in the Git config. Let's commit this
288 too, so we don't lose our progress.
290 ----
291 $ git add builtin/psuh.c
292 $ git commit -sm "psuh: show parameters & config opts"
293 ----
295 NOTE: Again, the above is for sake of brevity in this tutorial. In a real change
296 you should not use `-m` but instead use the editor to write a meaningful
297 message.
299 Still, it'd be nice to know what the user's working context is like. Let's see
300 if we can print the name of the user's current branch. We can mimic the
301 `git status` implementation; the printer is located in `wt-status.c` and we can
302 see that the branch is held in a `struct wt_status`.
304 `wt_status_print()` gets invoked by `cmd_status()` in `builtin/commit.c`.
305 Looking at that implementation we see the status config being populated like so:
307 ----
308 status_init_config(&s, git_status_config);
309 ----
311 But as we drill down, we can find that `status_init_config()` wraps a call
312 to `git_config()`. Let's modify the code we wrote in the previous commit.
314 Be sure to include the header to allow you to use `struct wt_status`:
315 ----
316 #include "wt-status.h"
317 ----
319 Then modify your `cmd_psuh` implementation to declare your `struct wt_status`,
320 prepare it, and print its contents:
322 ----
323 struct wt_status status;
325 ...
327 wt_status_prepare(the_repository, &status);
328 git_config(git_default_config, &status);
330 ...
332 printf(_("Your current branch: %s\n"), status.branch);
333 ----
335 Run it again. Check it out - here's the (verbose) name of your current branch!
337 Let's commit this as well.
339 ----
340 $ git add builtin/psuh.c
341 $ git commit -sm "psuh: print the current branch"
342 ----
344 Now let's see if we can get some info about a specific commit.
346 Luckily, there are some helpers for us here. `commit.h` has a function called
347 `lookup_commit_reference_by_name` to which we can simply provide a hardcoded
348 string; `pretty.h` has an extremely handy `pp_commit_easy()` call which doesn't
349 require a full format object to be passed.
351 Add the following includes:
353 ----
354 #include "commit.h"
355 #include "pretty.h"
356 ----
358 Then, add the following lines within your implementation of `cmd_psuh()` near
359 the declarations and the logic, respectively.
361 ----
362 struct commit *c = NULL;
363 struct strbuf commitline = STRBUF_INIT;
365 ...
367 c = lookup_commit_reference_by_name("origin/master");
369 if (c != NULL) {
370 pp_commit_easy(CMIT_FMT_ONELINE, c, &commitline);
371 printf(_("Current commit: %s\n"), commitline.buf);
372 }
373 ----
375 The `struct strbuf` provides some safety belts to your basic `char*`, one of
376 which is a length member to prevent buffer overruns. It needs to be initialized
377 nicely with `STRBUF_INIT`. Keep it in mind when you need to pass around `char*`.
379 `lookup_commit_reference_by_name` resolves the name you pass it, so you can play
380 with the value there and see what kind of things you can come up with.
382 `pp_commit_easy` is a convenience wrapper in `pretty.h` that takes a single
383 format enum shorthand, rather than an entire format struct. It then
384 pretty-prints the commit according to that shorthand. These are similar to the
385 formats available with `--pretty=FOO` in many Git commands.
387 Build it and run, and if you're using the same name in the example, you should
388 see the subject line of the most recent commit in `origin/master` that you know
389 about. Neat! Let's commit that as well.
391 ----
392 $ git add builtin/psuh.c
393 $ git commit -sm "psuh: display the top of origin/master"
394 ----
396 [[add-documentation]]
397 === Adding Documentation
399 Awesome! You've got a fantastic new command that you're ready to share with the
400 community. But hang on just a minute - this isn't very user-friendly. Run the
401 following:
403 ----
404 $ ./bin-wrappers/git help psuh
405 ----
407 Your new command is undocumented! Let's fix that.
409 Take a look at `Documentation/git-*.txt`. These are the manpages for the
410 subcommands that Git knows about. You can open these up and take a look to get
411 acquainted with the format, but then go ahead and make a new file
412 `Documentation/git-psuh.txt`. Like with most of the documentation in the Git
413 project, help pages are written with AsciiDoc (see CodingGuidelines, "Writing
414 Documentation" section). Use the following template to fill out your own
415 manpage:
417 // Surprisingly difficult to embed AsciiDoc source within AsciiDoc.
418 [listing]
419 ....
420 git-psuh(1)
421 ===========
423 NAME
424 ----
425 git-psuh - Delight users' typo with a shy horse
429 --------
430 [verse]
431 'git-psuh [<arg>...]'
434 -----------
435 ...
438 ------------------
439 ...
442 ------
443 ...
445 GIT
446 ---
447 Part of the linkgit:git[1] suite
448 ....
450 The most important pieces of this to note are the file header, underlined by =,
451 the NAME section, and the SYNOPSIS, which would normally contain the grammar if
452 your command took arguments. Try to use well-established manpage headers so your
453 documentation is consistent with other Git and UNIX manpages; this makes life
454 easier for your user, who can skip to the section they know contains the
455 information they need.
457 Now that you've written your manpage, you'll need to build it explicitly. We
458 convert your AsciiDoc to troff which is man-readable like so:
460 ----
461 $ make all doc
462 $ man Documentation/git-psuh.1
463 ----
465 or
467 ----
468 $ make -C Documentation/ git-psuh.1
469 $ man Documentation/git-psuh.1
470 ----
472 NOTE: You may need to install the package `asciidoc` to get this to work.
474 While this isn't as satisfying as running through `git help`, you can at least
475 check that your help page looks right.
477 You can also check that the documentation coverage is good (that is, the project
478 sees that your command has been implemented as well as documented) by running
479 `make check-docs` from the top-level.
481 Go ahead and commit your new documentation change.
483 [[add-usage]]
484 === Adding Usage Text
486 Try and run `./bin-wrappers/git psuh -h`. Your command should crash at the end.
487 That's because `-h` is a special case which your command should handle by
488 printing usage.
490 Take a look at `Documentation/technical/api-parse-options.txt`. This is a handy
491 tool for pulling out options you need to be able to handle, and it takes a
492 usage string.
494 In order to use it, we'll need to prepare a NULL-terminated array of usage
495 strings and a `builtin_psuh_options` array.
497 Add a line to `#include "parse-options.h"`.
499 At global scope, add your array of usage strings:
501 ----
502 static const char * const psuh_usage[] = {
503 N_("git psuh [<arg>...]"),
504 NULL,
505 };
506 ----
508 Then, within your `cmd_psuh()` implementation, we can declare and populate our
509 `option` struct. Ours is pretty boring but you can add more to it if you want to
510 explore `parse_options()` in more detail:
512 ----
513 struct option options[] = {
514 OPT_END()
515 };
516 ----
518 Finally, before you print your args and prefix, add the call to
519 `parse-options()`:
521 ----
522 argc = parse_options(argc, argv, prefix, options, psuh_usage, 0);
523 ----
525 This call will modify your `argv` parameter. It will strip the options you
526 specified in `options` from `argv` and the locations pointed to from `options`
527 entries will be updated. Be sure to replace your `argc` with the result from
528 `parse_options()`, or you will be confused if you try to parse `argv` later.
530 It's worth noting the special argument `--`. As you may be aware, many Unix
531 commands use `--` to indicate "end of named parameters" - all parameters after
532 the `--` are interpreted merely as positional arguments. (This can be handy if
533 you want to pass as a parameter something which would usually be interpreted as
534 a flag.) `parse_options()` will terminate parsing when it reaches `--` and give
535 you the rest of the options afterwards, untouched.
537 Build again. Now, when you run with `-h`, you should see your usage printed and
538 your command terminated before anything else interesting happens. Great!
540 Go ahead and commit this one, too.
542 [[testing]]
543 == Testing
545 It's important to test your code - even for a little toy command like this one.
546 Moreover, your patch won't be accepted into the Git tree without tests. Your
547 tests should:
549 * Illustrate the current behavior of the feature
550 * Prove the current behavior matches the expected behavior
551 * Ensure the externally-visible behavior isn't broken in later changes
553 So let's write some tests.
555 Related reading: `t/README`
557 [[overview-test-structure]]
558 === Overview of Testing Structure
560 The tests in Git live in `t/` and are named with a 4-digit decimal number using
561 the schema shown in the Naming Tests section of `t/README`.
563 [[write-new-test]]
564 === Writing Your Test
566 Since this a toy command, let's go ahead and name the test with t9999. However,
567 as many of the family/subcmd combinations are full, best practice seems to be
568 to find a command close enough to the one you've added and share its naming
569 space.
571 Create a new file `t/`. Begin with the header as so (see
572 "Writing Tests" and "Source ''" in `t/README`):
574 ----
575 #!/bin/sh
577 test_description='git-psuh test
579 This test runs git-psuh and makes sure it does not crash.'
581 . ./
582 ----
584 Tests are framed inside of a `test_expect_success` in order to output TAP
585 formatted results. Let's make sure that `git psuh` doesn't exit poorly and does
586 mention the right animal somewhere:
588 ----
589 test_expect_success 'runs correctly with no args and good output' '
590 git psuh >actual &&
591 test_i18ngrep Pony actual
592 '
593 ----
595 Indicate that you've run everything you wanted by adding the following at the
596 bottom of your script:
598 ----
599 test_done
600 ----
602 Make sure you mark your test script executable:
604 ----
605 $ chmod +x t/
606 ----
608 You can get an idea of whether you created your new test script successfully
609 by running `make -C t test-lint`, which will check for things like test number
610 uniqueness, executable bit, and so on.
612 [[local-test]]
613 === Running Locally
615 Let's try and run locally:
617 ----
618 $ make
619 $ cd t/ && prove
620 ----
622 You can run the full test suite and ensure `git-psuh` didn't break anything:
624 ----
625 $ cd t/
626 $ prove -j$(nproc) --shuffle t[0-9]*.sh
627 ----
629 NOTE: You can also do this with `make test` or use any testing harness which can
630 speak TAP. `prove` can run concurrently. `shuffle` randomizes the order the
631 tests are run in, which makes them resilient against unwanted inter-test
632 dependencies. `prove` also makes the output nicer.
634 Go ahead and commit this change, as well.
636 [[ready-to-share]]
637 == Getting Ready to Share
639 You may have noticed already that the Git project performs its code reviews via
640 emailed patches, which are then applied by the maintainer when they are ready
641 and approved by the community. The Git project does not accept patches from
642 pull requests, and the patches emailed for review need to be formatted a
643 specific way. At this point the tutorial diverges, in order to demonstrate two
644 different methods of formatting your patchset and getting it reviewed.
646 The first method to be covered is GitGitGadget, which is useful for those
647 already familiar with GitHub's common pull request workflow. This method
648 requires a GitHub account.
650 The second method to be covered is `git send-email`, which can give slightly
651 more fine-grained control over the emails to be sent. This method requires some
652 setup which can change depending on your system and will not be covered in this
653 tutorial.
655 Regardless of which method you choose, your engagement with reviewers will be
656 the same; the review process will be covered after the sections on GitGitGadget
657 and `git send-email`.
659 [[howto-ggg]]
660 == Sending Patches via GitGitGadget
662 One option for sending patches is to follow a typical pull request workflow and
663 send your patches out via GitGitGadget. GitGitGadget is a tool created by
664 Johannes Schindelin to make life as a Git contributor easier for those used to
665 the GitHub PR workflow. It allows contributors to open pull requests against its
666 mirror of the Git project, and does some magic to turn the PR into a set of
667 emails and send them out for you. It also runs the Git continuous integration
668 suite for you. It's documented at
670 [[create-fork]]
671 === Forking `git/git` on GitHub
673 Before you can send your patch off to be reviewed using GitGitGadget, you will
674 need to fork the Git project and upload your changes. First thing - make sure
675 you have a GitHub account.
677 Head to the[GitHub mirror] and look for the Fork
678 button. Place your fork wherever you deem appropriate and create it.
680 [[upload-to-fork]]
681 === Uploading to Your Own Fork
683 To upload your branch to your own fork, you'll need to add the new fork as a
684 remote. You can use `git remote -v` to show the remotes you have added already.
685 From your new fork's page on GitHub, you can press "Clone or download" to get
686 the URL; then you need to run the following to add, replacing your own URL and
687 remote name for the examples provided:
689 ----
690 $ git remote add remotename
691 ----
693 or to use the HTTPS URL:
695 ----
696 $ git remote add remotename
697 ----
699 Run `git remote -v` again and you should see the new remote showing up.
700 `git fetch remotename` (with the real name of your remote replaced) in order to
701 get ready to push.
703 Next, double-check that you've been doing all your development in a new branch
704 by running `git branch`. If you didn't, now is a good time to move your new
705 commits to their own branch.
707 As mentioned briefly at the beginning of this document, we are basing our work
708 on `master`, so go ahead and update as shown below, or using your preferred
709 workflow.
711 ----
712 $ git checkout master
713 $ git pull -r
714 $ git rebase master psuh
715 ----
717 Finally, you're ready to push your new topic branch! (Due to our branch and
718 command name choices, be careful when you type the command below.)
720 ----
721 $ git push remotename psuh
722 ----
724 Now you should be able to go and check out your newly created branch on GitHub.
726 [[send-pr-ggg]]
727 === Sending a PR to GitGitGadget
729 In order to have your code tested and formatted for review, you need to start by
730 opening a Pull Request against `gitgitgadget/git`. Head to
731 and open a PR either with the "New pull
732 request" button or the convenient "Compare & pull request" button that may
733 appear with the name of your newly pushed branch.
735 Review the PR's title and description, as it's used by GitGitGadget as the cover
736 letter for your change. When you're happy, submit your pull request.
738 [[run-ci-ggg]]
739 === Running CI and Getting Ready to Send
741 If it's your first time using GitGitGadget (which is likely, as you're using
742 this tutorial) then someone will need to give you permission to use the tool.
743 As mentioned in the GitGitGadget documentation, you just need someone who
744 already uses it to comment on your PR with `/allow <username>`. GitGitGadget
745 will automatically run your PRs through the CI even without the permission given
746 but you will not be able to `/submit` your changes until someone allows you to
747 use the tool.
749 If the CI fails, you can update your changes with `git rebase -i` and push your
750 branch again:
752 ----
753 $ git push -f remotename psuh
754 ----
756 In fact, you should continue to make changes this way up until the point when
757 your patch is accepted into `next`.
759 ////
760 TODO
761 It'd be nice to be able to verify that the patch looks good before sending it
762 to everyone on Git mailing list.
763 [[check-work-ggg]]
764 === Check Your Work
765 ////
767 [[send-mail-ggg]]
768 === Sending Your Patches
770 Now that your CI is passing and someone has granted you permission to use
771 GitGitGadget with the `/allow` command, sending out for review is as simple as
772 commenting on your PR with `/submit`.
774 [[responding-ggg]]
775 === Updating With Comments
777 Skip ahead to <<reviewing,Responding to Reviews>> for information on how to
778 reply to review comments you will receive on the mailing list.
780 Once you have your branch again in the shape you want following all review
781 comments, you can submit again:
783 ----
784 $ git push -f remotename psuh
785 ----
787 Next, go look at your pull request against GitGitGadget; you should see the CI
788 has been kicked off again. Now while the CI is running is a good time for you
789 to modify your description at the top of the pull request thread; it will be
790 used again as the cover letter. You should use this space to describe what
791 has changed since your previous version, so that your reviewers have some idea
792 of what they're looking at. When the CI is done running, you can comment once
793 more with `/submit` - GitGitGadget will automatically add a v2 mark to your
794 changes.
796 [[howto-git-send-email]]
797 == Sending Patches with `git send-email`
799 If you don't want to use GitGitGadget, you can also use Git itself to mail your
800 patches. Some benefits of using Git this way include finer grained control of
801 subject line (for example, being able to use the tag [RFC PATCH] in the subject)
802 and being able to send a ``dry run'' mail to yourself to ensure it all looks
803 good before going out to the list.
805 [[setup-git-send-email]]
806 === Prerequisite: Setting Up `git send-email`
808 Configuration for `send-email` can vary based on your operating system and email
809 provider, and so will not be covered in this tutorial, beyond stating that in
810 many distributions of Linux, `git-send-email` is not packaged alongside the
811 typical `git` install. You may need to install this additional package; there
812 are a number of resources online to help you do so. You will also need to
813 determine the right way to configure it to use your SMTP server; again, as this
814 configuration can change significantly based on your system and email setup, it
815 is out of scope for the context of this tutorial.
817 [[format-patch]]
818 === Preparing Initial Patchset
820 Sending emails with Git is a two-part process; before you can prepare the emails
821 themselves, you'll need to prepare the patches. Luckily, this is pretty simple:
823 ----
824 $ git format-patch --cover-letter -o psuh/ master..psuh
825 ----
827 The `--cover-letter` parameter tells `format-patch` to create a cover letter
828 template for you. You will need to fill in the template before you're ready
829 to send - but for now, the template will be next to your other patches.
831 The `-o psuh/` parameter tells `format-patch` to place the patch files into a
832 directory. This is useful because `git send-email` can take a directory and
833 send out all the patches from there.
835 `master..psuh` tells `format-patch` to generate patches for the difference
836 between `master` and `psuh`. It will make one patch file per commit. After you
837 run, you can go have a look at each of the patches with your favorite text
838 editor and make sure everything looks alright; however, it's not recommended to
839 make code fixups via the patch file. It's a better idea to make the change the
840 normal way using `git rebase -i` or by adding a new commit than by modifying a
841 patch.
843 NOTE: Optionally, you can also use the `--rfc` flag to prefix your patch subject
844 with ``[RFC PATCH]'' instead of ``[PATCH]''. RFC stands for ``request for
845 comments'' and indicates that while your code isn't quite ready for submission,
846 you'd like to begin the code review process. This can also be used when your
847 patch is a proposal, but you aren't sure whether the community wants to solve
848 the problem with that approach or not - to conduct a sort of design review. You
849 may also see on the list patches marked ``WIP'' - this means they are incomplete
850 but want reviewers to look at what they have so far. You can add this flag with
851 `--subject-prefix=WIP`.
853 Check and make sure that your patches and cover letter template exist in the
854 directory you specified - you're nearly ready to send out your review!
856 [[cover-letter]]
857 === Preparing Email
859 In addition to an email per patch, the Git community also expects your patches
860 to come with a cover letter, typically with a subject line [PATCH 0/x] (where
861 x is the number of patches you're sending). Since you invoked `format-patch`
862 with `--cover-letter`, you've already got a template ready. Open it up in your
863 favorite editor.
865 You should see a number of headers present already. Check that your `From:`
866 header is correct. Then modify your `Subject:` to something which succinctly
867 covers the purpose of your entire topic branch, for example:
869 ----
870 Subject: [PATCH 0/7] adding the 'psuh' command
871 ----
873 Make sure you retain the ``[PATCH 0/X]'' part; that's what indicates to the Git
874 community that this email is the beginning of a review, and many reviewers
875 filter their email for this type of flag.
877 You'll need to add some extra parameters when you invoke `git send-email` to add
878 the cover letter.
880 Next you'll have to fill out the body of your cover letter. This is an important
881 component of change submission as it explains to the community from a high level
882 what you're trying to do, and why, in a way that's more apparent than just
883 looking at your diff. Be sure to explain anything your diff doesn't make clear
884 on its own.
886 Here's an example body for `psuh`:
888 ----
889 Our internal metrics indicate widespread interest in the command
890 git-psuh - that is, many users are trying to use it, but finding it is
891 unavailable, using some unknown workaround instead.
893 The following handful of patches add the psuh command and implement some
894 handy features on top of it.
896 This patchset is part of the MyFirstContribution tutorial and should not
897 be merged.
898 ----
900 The template created by `git format-patch --cover-letter` includes a diffstat.
901 This gives reviewers a summary of what they're in for when reviewing your topic.
902 The one generated for `psuh` from the sample implementation looks like this:
904 ----
905 Documentation/git-psuh.txt | 40 +++++++++++++++++++++
906 Makefile | 1 +
907 builtin.h | 1 +
908 builtin/psuh.c | 73 ++++++++++++++++++++++++++++++++++++++
909 git.c | 1 +
910 t/ | 12 +++++++
911 6 files changed, 128 insertions(+)
912 create mode 100644 Documentation/git-psuh.txt
913 create mode 100644 builtin/psuh.c
914 create mode 100755 t/
915 ----
917 Finally, the letter will include the version of Git used to generate the
918 patches. You can leave that string alone.
920 [[sending-git-send-email]]
921 === Sending Email
923 At this point you should have a directory `psuh/` which is filled with your
924 patches and a cover letter. Time to mail it out! You can send it like this:
926 ----
927 $ git send-email psuh/*.patch
928 ----
930 NOTE: Check `git help send-email` for some other options which you may find
931 valuable, such as changing the Reply-to address or adding more CC and BCC lines.
933 NOTE: When you are sending a real patch, it will go to - but
934 please don't send your patchset from the tutorial to the real mailing list! For
935 now, you can send it to yourself, to make sure you understand how it will look.
937 After you run the command above, you will be presented with an interactive
938 prompt for each patch that's about to go out. This gives you one last chance to
939 edit or quit sending something (but again, don't edit code this way). Once you
940 press `y` or `a` at these prompts your emails will be sent! Congratulations!
942 Awesome, now the community will drop everything and review your changes. (Just
943 kidding - be patient!)
945 [[v2-git-send-email]]
946 === Sending v2
948 Skip ahead to <<reviewing,Responding to Reviews>> for information on how to
949 handle comments from reviewers. Continue this section when your topic branch is
950 shaped the way you want it to look for your patchset v2.
952 When you're ready with the next iteration of your patch, the process is fairly
953 similar.
955 First, generate your v2 patches again:
957 ----
958 $ git format-patch -v2 --cover-letter -o psuh/ master..psuh
959 ----
961 This will add your v2 patches, all named like `v2-000n-my-commit-subject.patch`,
962 to the `psuh/` directory. You may notice that they are sitting alongside the v1
963 patches; that's fine, but be careful when you are ready to send them.
965 Edit your cover letter again. Now is a good time to mention what's different
966 between your last version and now, if it's something significant. You do not
967 need the exact same body in your second cover letter; focus on explaining to
968 reviewers the changes you've made that may not be as visible.
970 You will also need to go and find the Message-Id of your previous cover letter.
971 You can either note it when you send the first series, from the output of `git
972 send-email`, or you can look it up on the
973[mailing list]. Find your cover letter in the
974 archives, click on it, then click "permalink" or "raw" to reveal the Message-Id
975 header. It should match:
977 ----
978 Message-Id: <>
979 ----
981 Your Message-Id is `<>`. This example will be used
982 below as well; make sure to replace it with the correct Message-Id for your
983 **previous cover letter** - that is, if you're sending v2, use the Message-Id
984 from v1; if you're sending v3, use the Message-Id from v2.
986 While you're looking at the email, you should also note who is CC'd, as it's
987 common practice in the mailing list to keep all CCs on a thread. You can add
988 these CC lines directly to your cover letter with a line like so in the header
989 (before the Subject line):
991 ----
992 CC:, Othe R <>
993 ----
995 Now send the emails again, paying close attention to which messages you pass in
996 to the command:
998 ----
999 $ git send-email
1000 --in-reply-to="<>"
1001 psuh/v2*
1002 ----
1004 [[single-patch]]
1005 === Bonus Chapter: One-Patch Changes
1007 In some cases, your very small change may consist of only one patch. When that
1008 happens, you only need to send one email. Your commit message should already be
1009 meaningful and explain at a high level the purpose (what is happening and why)
1010 of your patch, but if you need to supply even more context, you can do so below
1011 the `---` in your patch. Take the example below, which was generated with `git
1012 format-patch` on a single commit, and then edited to add the content between
1013 the `---` and the diffstat.
1015 ----
1016 From 1345bbb3f7ac74abde040c12e737204689a72723 Mon Sep 17 00:00:00 2001
1017 From: A U Thor <>
1018 Date: Thu, 18 Apr 2019 15:11:02 -0700
1019 Subject: [PATCH] README: change the grammar
1021 I think it looks better this way. This part of the commit message will
1022 end up in the commit-log.
1024 Signed-off-by: A U Thor <>
1025 ---
1026 Let's have a wild discussion about grammar on the mailing list. This
1027 part of my email will never end up in the commit log. Here is where I
1028 can add additional context to the mailing list about my intent, outside
1029 of the context of the commit log. This section was added after `git
1030 format-patch` was run, by editing the patch file in a text editor.
1032 | 2 +-
1033 1 file changed, 1 insertion(+), 1 deletion(-)
1035 diff --git a/ b/
1036 index 88f126184c..38da593a60 100644
1037 --- a/
1038 +++ b/
1039 @@ -3,7 +3,7 @@
1040 Git - fast, scalable, distributed revision control system
1041 =========================================================
1043 -Git is a fast, scalable, distributed revision control system with an
1044 +Git is a fast, scalable, and distributed revision control system with an
1045 unusually rich command set that provides both high-level operations
1046 and full access to internals.
1048 --
1050 ----
1052 [[now-what]]
1053 == My Patch Got Emailed - Now What?
1055 [[reviewing]]
1056 === Responding to Reviews
1058 After a few days, you will hopefully receive a reply to your patchset with some
1059 comments. Woohoo! Now you can get back to work.
1061 It's good manners to reply to each comment, notifying the reviewer that you have
1062 made the change requested, feel the original is better, or that the comment
1063 inspired you to do something a new way which is superior to both the original
1064 and the suggested change. This way reviewers don't need to inspect your v2 to
1065 figure out whether you implemented their comment or not.
1067 If you are going to push back on a comment, be polite and explain why you feel
1068 your original is better; be prepared that the reviewer may still disagree with
1069 you, and the rest of the community may weigh in on one side or the other. As
1070 with all code reviews, it's important to keep an open mind to doing something a
1071 different way than you originally planned; other reviewers have a different
1072 perspective on the project than you do, and may be thinking of a valid side
1073 effect which had not occurred to you. It is always okay to ask for clarification
1074 if you aren't sure why a change was suggested, or what the reviewer is asking
1075 you to do.
1077 Make sure your email client has a plaintext email mode and it is turned on; the
1078 Git list rejects HTML email. Please also follow the mailing list etiquette
1079 outlined in the
1081 Note], which are similar to etiquette rules in most open source communities
1082 surrounding bottom-posting and inline replies.
1084 When you're making changes to your code, it is cleanest - that is, the resulting
1085 commits are easiest to look at - if you use `git rebase -i` (interactive
1086 rebase). Take a look at this
1088 from O'Reilly. The general idea is to modify each commit which requires changes;
1089 this way, instead of having a patch A with a mistake, a patch B which was fine
1090 and required no upstream reviews in v1, and a patch C which fixes patch A for
1091 v2, you can just ship a v2 with a correct patch A and correct patch B. This is
1092 changing history, but since it's local history which you haven't shared with
1093 anyone, that is okay for now! (Later, it may not make sense to do this; take a
1094 look at the section below this one for some context.)
1096 [[after-approval]]
1097 === After Review Approval
1099 The Git project has four integration branches: `pu`, `next`, `master`, and
1100 `maint`. Your change will be placed into `pu` fairly early on by the maintainer
1101 while it is still in the review process; from there, when it is ready for wider
1102 testing, it will be merged into `next`. Plenty of early testers use `next` and
1103 may report issues. Eventually, changes in `next` will make it to `master`,
1104 which is typically considered stable. Finally, when a new release is cut,
1105 `maint` is used to base bugfixes onto. As mentioned at the beginning of this
1106 document, you can read `Documents/SubmittingPatches` for some more info about
1107 the use of the various integration branches.
1109 Back to now: your code has been lauded by the upstream reviewers. It is perfect.
1110 It is ready to be accepted. You don't need to do anything else; the maintainer
1111 will merge your topic branch to `next` and life is good.
1113 However, if you discover it isn't so perfect after this point, you may need to
1114 take some special steps depending on where you are in the process.
1116 If the maintainer has announced in the "What's cooking in git.git" email that
1117 your topic is marked for `next` - that is, that they plan to merge it to `next`
1118 but have not yet done so - you should send an email asking the maintainer to
1119 wait a little longer: "I've sent v4 of my series and you marked it for `next`,
1120 but I need to change this and that - please wait for v5 before you merge it."
1122 If the topic has already been merged to `next`, rather than modifying your
1123 patches with `git rebase -i`, you should make further changes incrementally -
1124 that is, with another commit, based on top of the maintainer's topic branch as
1125 detailed in Your work is still in the same topic
1126 but is now incremental, rather than a wholesale rewrite of the topic branch.
1128 The topic branches in the maintainer's GitHub are mirrored in GitGitGadget, so
1129 if you're sending your reviews out that way, you should be sure to open your PR
1130 against the appropriate GitGitGadget/Git branch.
1132 If you're using `git send-email`, you can use it the same way as before, but you
1133 should generate your diffs from `<topic>..<mybranch>` and base your work on
1134 `<topic>` instead of `master`.