doc: MyFirstContribution: fix cmd placement instructions
[git/git.git] / Documentation / MyFirstContribution.txt
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1My First Contribution to the Git Project
2========================================
5ef811ac 3:sectanchors:
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5ef811ac 5[[summary]]
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6== Summary
7
8This is a tutorial demonstrating the end-to-end workflow of creating a change to
9the Git tree, sending it for review, and making changes based on comments.
10
5ef811ac 11[[prerequisites]]
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12=== Prerequisites
13
14This tutorial assumes you're already fairly familiar with using Git to manage
15source code. The Git workflow steps will largely remain unexplained.
16
5ef811ac 17[[related-reading]]
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18=== Related Reading
19
20This tutorial aims to summarize the following documents, but the reader may find
21useful additional context:
22
23- `Documentation/SubmittingPatches`
24- `Documentation/howto/new-command.txt`
25
5ef811ac 26[[getting-started]]
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27== Getting Started
28
5ef811ac 29[[cloning]]
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30=== Clone the Git Repository
31
32Git is mirrored in a number of locations. Clone the repository from one of them;
33https://git-scm.com/downloads suggests one of the best places to clone from is
34the mirror on GitHub.
35
36----
37$ git clone https://github.com/git/git git
2656fb16 38$ cd git
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39----
40
5ef811ac 41[[identify-problem]]
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42=== Identify Problem to Solve
43
44////
45Use + to indicate fixed-width here; couldn't get ` to work nicely with the
46quotes around "Pony Saying 'Um, Hello'".
47////
48In 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
50of invocation during users' typical daily workflow.
51
52(We've seen some other effort in this space with the implementation of popular
53commands such as `sl`.)
54
5ef811ac 55[[setup-workspace]]
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56=== Set Up Your Workspace
57
58Let'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,
60it's fine to base your work on `master`. However, in the future for bugfixes,
61etc., you should check that document and base it on the appropriate branch.
62
63For the purposes of this document, we will base all our work on the `master`
64branch of the upstream project. Create the `psuh` branch you will use for
65development like so:
66
67----
68$ git checkout -b psuh origin/master
69----
70
71We'll make a number of commits here in order to demonstrate how to send a topic
72with multiple patches up for review simultaneously.
73
5ef811ac 74[[code-it-up]]
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75== Code It Up!
76
77NOTE: A reference implementation can be found at
78https://github.com/nasamuffin/git/tree/psuh.
79
5ef811ac 80[[add-new-command]]
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81=== Adding a New Command
82
83Lots of the subcommands are written as builtins, which means they are
84implemented in C and compiled into the main `git` executable. Implementing the
85very simple `psuh` command as a built-in will demonstrate the structure of the
86codebase, the internal API, and the process of working together as a contributor
87with the reviewers and maintainer to integrate this change into the system.
88
89Built-in subcommands are typically implemented in a function named "cmd_"
90followed by the name of the subcommand, in a source file named after the
91subcommand and contained within `builtin/`. So it makes sense to implement your
92command in `builtin/psuh.c`. Create that file, and within it, write the entry
93point for your command in a function matching the style and signature:
94
95----
96int cmd_psuh(int argc, const char **argv, const char *prefix)
97----
98
99We'll also need to add the declaration of psuh; open up `builtin.h`, find the
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100declaration for `cmd_pull`, and add a new line for `psuh` immediately before it,
101in order to keep the declarations alphabetically sorted:
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102
103----
104int cmd_psuh(int argc, const char **argv, const char *prefix);
105----
106
107Be sure to `#include "builtin.h"` in your `psuh.c`.
108
109Go ahead and add some throwaway printf to that function. This is a decent
110starting point as we can now add build rules and register the command.
111
112NOTE: Your throwaway text, as well as much of the text you will be adding over
113the course of this tutorial, is user-facing. That means it needs to be
114localizable. Take a look at `po/README` under "Marking strings for translation".
115Throughout the tutorial, we will mark strings for translation as necessary; you
116should also do so when writing your user-facing commands in the future.
117
118----
119int cmd_psuh(int argc, const char **argv, const char *prefix)
120{
121 printf(_("Pony saying hello goes here.\n"));
122 return 0;
123}
124----
125
24c68179 126Let's try to build it. Open `Makefile`, find where `builtin/pull.o` is added
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127to `BUILTIN_OBJS`, and add `builtin/psuh.o` in the same way next to it in
128alphabetical order. Once you've done so, move to the top-level directory and
129build simply with `make`. Also add the `DEVELOPER=1` variable to turn on
130some additional warnings:
131
132----
133$ echo DEVELOPER=1 >config.mak
134$ make
135----
136
137NOTE: 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
139it off, but it's a good idea to mention the problem to the mailing list.
140
141NOTE: The Git build is parallelizable. `-j#` is not included above but you can
142use it as you prefer, here and elsewhere.
143
144Great, now your new command builds happily on its own. But nobody invokes it.
145Let's change that.
146
147The list of commands lives in `git.c`. We can register a new command by adding
148a `cmd_struct` to the `commands[]` array. `struct cmd_struct` takes a string
149with the command name, a function pointer to the command implementation, and a
150setup 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
24c68179 152line in alphabetical order (immediately before `cmd_pull`).
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153
154The options are documented in `builtin.h` under "Adding a new built-in." Since
155we hope to print some data about the user's current workspace context later,
156we need a Git directory, so choose `RUN_SETUP` as your only option.
157
158Go ahead and build again. You should see a clean build, so let's kick the tires
159and see if it works. There's a binary you can use to test with in the
160`bin-wrappers` directory.
161
162----
163$ ./bin-wrappers/git psuh
164----
165
166Check it out! You've got a command! Nice work! Let's commit this.
167
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168`git status` reveals modified `Makefile`, `builtin.h`, and `git.c` as well as
169untracked `builtin/psuh.c` and `git-psuh`. First, let's take care of the binary,
24c68179 170which should be ignored. Open `.gitignore` in your editor, find `/git-pull`, and
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171add an entry for your new command in alphabetical order:
172
173----
174...
175/git-prune-packed
176/git-psuh
177/git-pull
178/git-push
179/git-quiltimport
180/git-range-diff
181...
182----
183
184Checking `git status` again should show that `git-psuh` has been removed from
185the untracked list and `.gitignore` has been added to the modified list. Now we
186can stage and commit:
187
76644e32 188----
2656fb16 189$ git add Makefile builtin.h builtin/psuh.c git.c .gitignore
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190$ git commit -s
191----
192
193You will be presented with your editor in order to write a commit message. Start
194the commit with a 50-column or less subject line, including the name of the
195component you're working on, followed by a blank line (always required) and then
196the body of your commit message, which should provide the bulk of the context.
197Remember to be explicit and provide the "Why" of your change, especially if it
198couldn't easily be understood from your diff. When editing your commit message,
199don't remove the Signed-off-by line which was added by `-s` above.
200
201----
202psuh: add a built-in by popular demand
203
204Internal metrics indicate this is a command many users expect to be
205present. So here's an implementation to help drive customer
206satisfaction and engagement: a pony which doubtfully greets the user,
207or, a Pony Saying "Um, Hello" (PSUH).
208
209This commit message is intentionally formatted to 72 columns per line,
210starts with a single line as "commit message subject" that is written as
211if to command the codebase to do something (add this, teach a command
212that). The body of the message is designed to add information about the
213commit that is not readily deduced from reading the associated diff,
214such as answering the question "why?".
215
216Signed-off-by: A U Thor <author@example.com>
217----
218
219Go ahead and inspect your new commit with `git show`. "psuh:" indicates you
220have modified mainly the `psuh` command. The subject line gives readers an idea
221of what you've changed. The sign-off line (`-s`) indicates that you agree to
222the Developer's Certificate of Origin 1.1 (see the
223`Documentation/SubmittingPatches` +++[[dco]]+++ header).
224
225For the remainder of the tutorial, the subject line only will be listed for the
226sake of brevity. However, fully-fleshed example commit messages are available
227on the reference implementation linked at the top of this document.
228
5ef811ac 229[[implementation]]
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230=== Implementation
231
232It's probably useful to do at least something besides printing out a string.
233Let's start by having a look at everything we get.
234
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235Modify your `cmd_psuh` implementation to dump the args you're passed, keeping
236existing `printf()` calls in place:
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237
238----
239 int i;
240
241 ...
242
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]);
249
250 printf(_("Your current working directory:\n<top-level>%s%s\n"),
251 prefix ? "/" : "", prefix ? prefix : "");
252
253----
254
255Build and try it. As you may expect, there's pretty much just whatever we give
256on the command line, including the name of our command. (If `prefix` is empty
257for you, try `cd Documentation/ && ../bin-wrappers/git psuh`). That's not so
258helpful. So what other context can we get?
259
260Add a line to `#include "config.h"`. Then, add the following bits to the
261function body:
262
263----
264 const char *cfg_name;
265
266...
267
2656fb16 268 git_config(git_default_config, NULL);
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269 if (git_config_get_string_const("user.name", &cfg_name) > 0)
270 printf(_("No name is found in config\n"));
271 else
272 printf(_("Your name: %s\n"), cfg_name);
273----
274
275`git_config()` will grab the configuration from config files known to Git and
276apply standard precedence rules. `git_config_get_string_const()` will look up
277a specific key ("user.name") and give you the value. There are a number of
278single-key lookup functions like this one; you can see them all (and more info
279about how to use `git_config()`) in `Documentation/technical/api-config.txt`.
280
281You should see that the name printed matches the one you see when you run:
282
283----
284$ git config --get user.name
285----
286
287Great! Now we know how to check for values in the Git config. Let's commit this
288too, so we don't lose our progress.
289
290----
291$ git add builtin/psuh.c
292$ git commit -sm "psuh: show parameters & config opts"
293----
294
295NOTE: Again, the above is for sake of brevity in this tutorial. In a real change
296you should not use `-m` but instead use the editor to write a meaningful
297message.
298
299Still, it'd be nice to know what the user's working context is like. Let's see
300if 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
302see that the branch is held in a `struct wt_status`.
303
304`wt_status_print()` gets invoked by `cmd_status()` in `builtin/commit.c`.
305Looking at that implementation we see the status config being populated like so:
306
307----
308status_init_config(&s, git_status_config);
309----
310
311But as we drill down, we can find that `status_init_config()` wraps a call
312to `git_config()`. Let's modify the code we wrote in the previous commit.
313
314Be sure to include the header to allow you to use `struct wt_status`:
315----
316#include "wt-status.h"
317----
318
319Then modify your `cmd_psuh` implementation to declare your `struct wt_status`,
320prepare it, and print its contents:
321
322----
323 struct wt_status status;
324
325...
326
327 wt_status_prepare(the_repository, &status);
328 git_config(git_default_config, &status);
329
330...
331
332 printf(_("Your current branch: %s\n"), status.branch);
333----
334
335Run it again. Check it out - here's the (verbose) name of your current branch!
336
337Let's commit this as well.
338
339----
2656fb16 340$ git add builtin/psuh.c
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341$ git commit -sm "psuh: print the current branch"
342----
343
344Now let's see if we can get some info about a specific commit.
345
346Luckily, 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
348string; `pretty.h` has an extremely handy `pp_commit_easy()` call which doesn't
349require a full format object to be passed.
350
351Add the following includes:
352
353----
354#include "commit.h"
355#include "pretty.h"
356----
357
358Then, add the following lines within your implementation of `cmd_psuh()` near
359the declarations and the logic, respectively.
360
361----
362 struct commit *c = NULL;
363 struct strbuf commitline = STRBUF_INIT;
364
365...
366
367 c = lookup_commit_reference_by_name("origin/master");
368
369 if (c != NULL) {
370 pp_commit_easy(CMIT_FMT_ONELINE, c, &commitline);
371 printf(_("Current commit: %s\n"), commitline.buf);
372 }
373----
374
375The `struct strbuf` provides some safety belts to your basic `char*`, one of
376which is a length member to prevent buffer overruns. It needs to be initialized
377nicely with `STRBUF_INIT`. Keep it in mind when you need to pass around `char*`.
378
379`lookup_commit_reference_by_name` resolves the name you pass it, so you can play
380with the value there and see what kind of things you can come up with.
381
382`pp_commit_easy` is a convenience wrapper in `pretty.h` that takes a single
383format enum shorthand, rather than an entire format struct. It then
384pretty-prints the commit according to that shorthand. These are similar to the
385formats available with `--pretty=FOO` in many Git commands.
386
387Build it and run, and if you're using the same name in the example, you should
388see the subject line of the most recent commit in `origin/master` that you know
389about. Neat! Let's commit that as well.
390
391----
2656fb16 392$ git add builtin/psuh.c
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393$ git commit -sm "psuh: display the top of origin/master"
394----
395
5ef811ac 396[[add-documentation]]
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397=== Adding Documentation
398
399Awesome! You've got a fantastic new command that you're ready to share with the
400community. But hang on just a minute - this isn't very user-friendly. Run the
401following:
402
403----
404$ ./bin-wrappers/git help psuh
405----
406
407Your new command is undocumented! Let's fix that.
408
409Take a look at `Documentation/git-*.txt`. These are the manpages for the
410subcommands that Git knows about. You can open these up and take a look to get
411acquainted 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
413project, help pages are written with AsciiDoc (see CodingGuidelines, "Writing
414Documentation" section). Use the following template to fill out your own
415manpage:
416
417// Surprisingly difficult to embed AsciiDoc source within AsciiDoc.
418[listing]
419....
420git-psuh(1)
421===========
422
423NAME
424----
425git-psuh - Delight users' typo with a shy horse
426
427
428SYNOPSIS
429--------
430[verse]
b37e0ec3 431'git-psuh [<arg>...]'
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432
433DESCRIPTION
434-----------
435...
436
437OPTIONS[[OPTIONS]]
438------------------
439...
440
441OUTPUT
442------
443...
444
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445GIT
446---
447Part of the linkgit:git[1] suite
448....
449
450The most important pieces of this to note are the file header, underlined by =,
451the NAME section, and the SYNOPSIS, which would normally contain the grammar if
452your command took arguments. Try to use well-established manpage headers so your
453documentation is consistent with other Git and UNIX manpages; this makes life
454easier for your user, who can skip to the section they know contains the
455information they need.
456
457Now that you've written your manpage, you'll need to build it explicitly. We
458convert your AsciiDoc to troff which is man-readable like so:
459
460----
461$ make all doc
462$ man Documentation/git-psuh.1
463----
464
465or
466
467----
468$ make -C Documentation/ git-psuh.1
469$ man Documentation/git-psuh.1
470----
471
472NOTE: You may need to install the package `asciidoc` to get this to work.
473
474While this isn't as satisfying as running through `git help`, you can at least
475check that your help page looks right.
476
477You can also check that the documentation coverage is good (that is, the project
478sees that your command has been implemented as well as documented) by running
479`make check-docs` from the top-level.
480
481Go ahead and commit your new documentation change.
482
5ef811ac 483[[add-usage]]
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484=== Adding Usage Text
485
486Try and run `./bin-wrappers/git psuh -h`. Your command should crash at the end.
487That's because `-h` is a special case which your command should handle by
488printing usage.
489
490Take a look at `Documentation/technical/api-parse-options.txt`. This is a handy
491tool for pulling out options you need to be able to handle, and it takes a
492usage string.
493
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494In order to use it, we'll need to prepare a NULL-terminated array of usage
495strings and a `builtin_psuh_options` array.
76644e32 496
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497Add a line to `#include "parse-options.h"`.
498
499At global scope, add your array of usage strings:
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500
501----
502static const char * const psuh_usage[] = {
b37e0ec3 503 N_("git psuh [<arg>...]"),
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504 NULL,
505};
506----
507
508Then, 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
510explore `parse_options()` in more detail:
511
512----
513 struct option options[] = {
514 OPT_END()
515 };
516----
517
518Finally, before you print your args and prefix, add the call to
519`parse-options()`:
520
521----
522 argc = parse_options(argc, argv, prefix, options, psuh_usage, 0);
523----
524
525This call will modify your `argv` parameter. It will strip the options you
526specified in `options` from `argv` and the locations pointed to from `options`
527entries 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.
529
530It's worth noting the special argument `--`. As you may be aware, many Unix
531commands use `--` to indicate "end of named parameters" - all parameters after
532the `--` are interpreted merely as positional arguments. (This can be handy if
533you want to pass as a parameter something which would usually be interpreted as
534a flag.) `parse_options()` will terminate parsing when it reaches `--` and give
535you the rest of the options afterwards, untouched.
536
537Build again. Now, when you run with `-h`, you should see your usage printed and
538your command terminated before anything else interesting happens. Great!
539
540Go ahead and commit this one, too.
541
5ef811ac 542[[testing]]
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543== Testing
544
545It's important to test your code - even for a little toy command like this one.
546Moreover, your patch won't be accepted into the Git tree without tests. Your
547tests should:
548
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
552
553So let's write some tests.
554
555Related reading: `t/README`
556
5ef811ac 557[[overview-test-structure]]
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558=== Overview of Testing Structure
559
560The tests in Git live in `t/` and are named with a 4-digit decimal number using
561the schema shown in the Naming Tests section of `t/README`.
562
5ef811ac 563[[write-new-test]]
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564=== Writing Your Test
565
566Since this a toy command, let's go ahead and name the test with t9999. However,
567as many of the family/subcmd combinations are full, best practice seems to be
568to find a command close enough to the one you've added and share its naming
569space.
570
571Create a new file `t/t9999-psuh-tutorial.sh`. Begin with the header as so (see
572"Writing Tests" and "Source 'test-lib.sh'" in `t/README`):
573
574----
575#!/bin/sh
576
577test_description='git-psuh test
578
579This test runs git-psuh and makes sure it does not crash.'
580
581. ./test-lib.sh
582----
583
584Tests are framed inside of a `test_expect_success` in order to output TAP
585formatted results. Let's make sure that `git psuh` doesn't exit poorly and does
586mention the right animal somewhere:
587
588----
589test_expect_success 'runs correctly with no args and good output' '
590 git psuh >actual &&
591 test_i18ngrep Pony actual
592'
593----
594
595Indicate that you've run everything you wanted by adding the following at the
596bottom of your script:
597
598----
599test_done
600----
601
602Make sure you mark your test script executable:
603
604----
605$ chmod +x t/t9999-psuh-tutorial.sh
606----
607
608You can get an idea of whether you created your new test script successfully
609by running `make -C t test-lint`, which will check for things like test number
610uniqueness, executable bit, and so on.
611
5ef811ac 612[[local-test]]
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613=== Running Locally
614
615Let's try and run locally:
616
617----
618$ make
619$ cd t/ && prove t9999-psuh-tutorial.sh
620----
621
622You can run the full test suite and ensure `git-psuh` didn't break anything:
623
624----
625$ cd t/
626$ prove -j$(nproc) --shuffle t[0-9]*.sh
627----
628
629NOTE: You can also do this with `make test` or use any testing harness which can
630speak TAP. `prove` can run concurrently. `shuffle` randomizes the order the
631tests are run in, which makes them resilient against unwanted inter-test
632dependencies. `prove` also makes the output nicer.
633
634Go ahead and commit this change, as well.
635
5ef811ac 636[[ready-to-share]]
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637== Getting Ready to Share
638
639You may have noticed already that the Git project performs its code reviews via
640emailed patches, which are then applied by the maintainer when they are ready
641and approved by the community. The Git project does not accept patches from
642pull requests, and the patches emailed for review need to be formatted a
643specific way. At this point the tutorial diverges, in order to demonstrate two
644different methods of formatting your patchset and getting it reviewed.
645
646The first method to be covered is GitGitGadget, which is useful for those
647already familiar with GitHub's common pull request workflow. This method
648requires a GitHub account.
649
650The second method to be covered is `git send-email`, which can give slightly
651more fine-grained control over the emails to be sent. This method requires some
652setup which can change depending on your system and will not be covered in this
653tutorial.
654
655Regardless of which method you choose, your engagement with reviewers will be
656the same; the review process will be covered after the sections on GitGitGadget
657and `git send-email`.
658
5ef811ac 659[[howto-ggg]]
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660== Sending Patches via GitGitGadget
661
662One option for sending patches is to follow a typical pull request workflow and
663send your patches out via GitGitGadget. GitGitGadget is a tool created by
664Johannes Schindelin to make life as a Git contributor easier for those used to
665the GitHub PR workflow. It allows contributors to open pull requests against its
666mirror of the Git project, and does some magic to turn the PR into a set of
667emails and send them out for you. It also runs the Git continuous integration
668suite for you. It's documented at http://gitgitgadget.github.io.
669
5ef811ac 670[[create-fork]]
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671=== Forking `git/git` on GitHub
672
673Before you can send your patch off to be reviewed using GitGitGadget, you will
674need to fork the Git project and upload your changes. First thing - make sure
675you have a GitHub account.
676
677Head to the https://github.com/git/git[GitHub mirror] and look for the Fork
678button. Place your fork wherever you deem appropriate and create it.
679
5ef811ac 680[[upload-to-fork]]
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681=== Uploading to Your Own Fork
682
683To upload your branch to your own fork, you'll need to add the new fork as a
684remote. You can use `git remote -v` to show the remotes you have added already.
685From your new fork's page on GitHub, you can press "Clone or download" to get
686the URL; then you need to run the following to add, replacing your own URL and
687remote name for the examples provided:
688
689----
690$ git remote add remotename git@github.com:remotename/git.git
691----
692
693or to use the HTTPS URL:
694
695----
696$ git remote add remotename https://github.com/remotename/git/.git
697----
698
699Run `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
701get ready to push.
702
703Next, double-check that you've been doing all your development in a new branch
704by running `git branch`. If you didn't, now is a good time to move your new
705commits to their own branch.
706
707As mentioned briefly at the beginning of this document, we are basing our work
708on `master`, so go ahead and update as shown below, or using your preferred
709workflow.
710
711----
712$ git checkout master
713$ git pull -r
714$ git rebase master psuh
715----
716
717Finally, you're ready to push your new topic branch! (Due to our branch and
718command name choices, be careful when you type the command below.)
719
720----
721$ git push remotename psuh
722----
723
724Now you should be able to go and check out your newly created branch on GitHub.
725
5ef811ac 726[[send-pr-ggg]]
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727=== Sending a PR to GitGitGadget
728
729In order to have your code tested and formatted for review, you need to start by
730opening a Pull Request against `gitgitgadget/git`. Head to
731https://github.com/gitgitgadget/git and open a PR either with the "New pull
732request" button or the convenient "Compare & pull request" button that may
733appear with the name of your newly pushed branch.
734
735Review the PR's title and description, as it's used by GitGitGadget as the cover
736letter for your change. When you're happy, submit your pull request.
737
5ef811ac 738[[run-ci-ggg]]
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739=== Running CI and Getting Ready to Send
740
741If it's your first time using GitGitGadget (which is likely, as you're using
742this tutorial) then someone will need to give you permission to use the tool.
743As mentioned in the GitGitGadget documentation, you just need someone who
744already uses it to comment on your PR with `/allow <username>`. GitGitGadget
745will automatically run your PRs through the CI even without the permission given
746but you will not be able to `/submit` your changes until someone allows you to
747use the tool.
748
749If the CI fails, you can update your changes with `git rebase -i` and push your
750branch again:
751
752----
753$ git push -f remotename psuh
754----
755
756In fact, you should continue to make changes this way up until the point when
757your patch is accepted into `next`.
758
759////
760TODO https://github.com/gitgitgadget/gitgitgadget/issues/83
761It'd be nice to be able to verify that the patch looks good before sending it
762to everyone on Git mailing list.
5ef811ac 763[[check-work-ggg]]
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764=== Check Your Work
765////
766
5ef811ac 767[[send-mail-ggg]]
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768=== Sending Your Patches
769
770Now that your CI is passing and someone has granted you permission to use
771GitGitGadget with the `/allow` command, sending out for review is as simple as
772commenting on your PR with `/submit`.
773
5ef811ac 774[[responding-ggg]]
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775=== Updating With Comments
776
777Skip ahead to <<reviewing,Responding to Reviews>> for information on how to
778reply to review comments you will receive on the mailing list.
779
780Once you have your branch again in the shape you want following all review
781comments, you can submit again:
782
783----
784$ git push -f remotename psuh
785----
786
787Next, go look at your pull request against GitGitGadget; you should see the CI
788has been kicked off again. Now while the CI is running is a good time for you
789to modify your description at the top of the pull request thread; it will be
790used again as the cover letter. You should use this space to describe what
791has changed since your previous version, so that your reviewers have some idea
792of what they're looking at. When the CI is done running, you can comment once
793more with `/submit` - GitGitGadget will automatically add a v2 mark to your
794changes.
795
5ef811ac 796[[howto-git-send-email]]
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797== Sending Patches with `git send-email`
798
799If you don't want to use GitGitGadget, you can also use Git itself to mail your
800patches. Some benefits of using Git this way include finer grained control of
801subject line (for example, being able to use the tag [RFC PATCH] in the subject)
802and being able to send a ``dry run'' mail to yourself to ensure it all looks
803good before going out to the list.
804
5ef811ac 805[[setup-git-send-email]]
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806=== Prerequisite: Setting Up `git send-email`
807
808Configuration for `send-email` can vary based on your operating system and email
809provider, and so will not be covered in this tutorial, beyond stating that in
810many distributions of Linux, `git-send-email` is not packaged alongside the
811typical `git` install. You may need to install this additional package; there
812are a number of resources online to help you do so. You will also need to
813determine the right way to configure it to use your SMTP server; again, as this
814configuration can change significantly based on your system and email setup, it
815is out of scope for the context of this tutorial.
816
5ef811ac 817[[format-patch]]
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818=== Preparing Initial Patchset
819
820Sending emails with Git is a two-part process; before you can prepare the emails
821themselves, you'll need to prepare the patches. Luckily, this is pretty simple:
822
823----
824$ git format-patch --cover-letter -o psuh/ master..psuh
825----
826
827The `--cover-letter` parameter tells `format-patch` to create a cover letter
828template for you. You will need to fill in the template before you're ready
829to send - but for now, the template will be next to your other patches.
830
831The `-o psuh/` parameter tells `format-patch` to place the patch files into a
832directory. This is useful because `git send-email` can take a directory and
833send out all the patches from there.
834
835`master..psuh` tells `format-patch` to generate patches for the difference
836between `master` and `psuh`. It will make one patch file per commit. After you
837run, you can go have a look at each of the patches with your favorite text
838editor and make sure everything looks alright; however, it's not recommended to
839make code fixups via the patch file. It's a better idea to make the change the
840normal way using `git rebase -i` or by adding a new commit than by modifying a
841patch.
842
843NOTE: Optionally, you can also use the `--rfc` flag to prefix your patch subject
844with ``[RFC PATCH]'' instead of ``[PATCH]''. RFC stands for ``request for
845comments'' and indicates that while your code isn't quite ready for submission,
846you'd like to begin the code review process. This can also be used when your
847patch is a proposal, but you aren't sure whether the community wants to solve
848the problem with that approach or not - to conduct a sort of design review. You
849may also see on the list patches marked ``WIP'' - this means they are incomplete
850but want reviewers to look at what they have so far. You can add this flag with
851`--subject-prefix=WIP`.
852
853Check and make sure that your patches and cover letter template exist in the
854directory you specified - you're nearly ready to send out your review!
855
5ef811ac 856[[cover-letter]]
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857=== Preparing Email
858
859In addition to an email per patch, the Git community also expects your patches
860to come with a cover letter, typically with a subject line [PATCH 0/x] (where
861x is the number of patches you're sending). Since you invoked `format-patch`
862with `--cover-letter`, you've already got a template ready. Open it up in your
863favorite editor.
864
865You should see a number of headers present already. Check that your `From:`
866header is correct. Then modify your `Subject:` to something which succinctly
867covers the purpose of your entire topic branch, for example:
868
869----
870Subject: [PATCH 0/7] adding the 'psuh' command
871----
872
873Make sure you retain the ``[PATCH 0/X]'' part; that's what indicates to the Git
874community that this email is the beginning of a review, and many reviewers
875filter their email for this type of flag.
876
877You'll need to add some extra parameters when you invoke `git send-email` to add
878the cover letter.
879
880Next you'll have to fill out the body of your cover letter. This is an important
881component of change submission as it explains to the community from a high level
882what you're trying to do, and why, in a way that's more apparent than just
883looking at your diff. Be sure to explain anything your diff doesn't make clear
884on its own.
885
886Here's an example body for `psuh`:
887
888----
889Our internal metrics indicate widespread interest in the command
890git-psuh - that is, many users are trying to use it, but finding it is
891unavailable, using some unknown workaround instead.
892
893The following handful of patches add the psuh command and implement some
894handy features on top of it.
895
896This patchset is part of the MyFirstContribution tutorial and should not
897be merged.
898----
899
900The template created by `git format-patch --cover-letter` includes a diffstat.
901This gives reviewers a summary of what they're in for when reviewing your topic.
902The one generated for `psuh` from the sample implementation looks like this:
903
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/t9999-psuh-tutorial.sh | 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/t9999-psuh-tutorial.sh
915----
916
917Finally, the letter will include the version of Git used to generate the
918patches. You can leave that string alone.
919
5ef811ac 920[[sending-git-send-email]]
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921=== Sending Email
922
923At this point you should have a directory `psuh/` which is filled with your
924patches and a cover letter. Time to mail it out! You can send it like this:
925
926----
927$ git send-email --to=target@example.com psuh/*.patch
928----
929
930NOTE: Check `git help send-email` for some other options which you may find
931valuable, such as changing the Reply-to address or adding more CC and BCC lines.
932
933NOTE: When you are sending a real patch, it will go to git@vger.kernel.org - but
934please don't send your patchset from the tutorial to the real mailing list! For
935now, you can send it to yourself, to make sure you understand how it will look.
936
937After you run the command above, you will be presented with an interactive
938prompt for each patch that's about to go out. This gives you one last chance to
939edit or quit sending something (but again, don't edit code this way). Once you
940press `y` or `a` at these prompts your emails will be sent! Congratulations!
941
942Awesome, now the community will drop everything and review your changes. (Just
943kidding - be patient!)
944
5ef811ac 945[[v2-git-send-email]]
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946=== Sending v2
947
948Skip ahead to <<reviewing,Responding to Reviews>> for information on how to
949handle comments from reviewers. Continue this section when your topic branch is
950shaped the way you want it to look for your patchset v2.
951
952When you're ready with the next iteration of your patch, the process is fairly
953similar.
954
955First, generate your v2 patches again:
956
957----
958$ git format-patch -v2 --cover-letter -o psuh/ master..psuh
959----
960
961This will add your v2 patches, all named like `v2-000n-my-commit-subject.patch`,
962to the `psuh/` directory. You may notice that they are sitting alongside the v1
963patches; that's fine, but be careful when you are ready to send them.
964
965Edit your cover letter again. Now is a good time to mention what's different
966between your last version and now, if it's something significant. You do not
967need the exact same body in your second cover letter; focus on explaining to
968reviewers the changes you've made that may not be as visible.
969
970You will also need to go and find the Message-Id of your previous cover letter.
971You can either note it when you send the first series, from the output of `git
972send-email`, or you can look it up on the
973https://public-inbox.org/git[mailing list]. Find your cover letter in the
974archives, click on it, then click "permalink" or "raw" to reveal the Message-Id
975header. It should match:
976
977----
978Message-Id: <foo.12345.author@example.com>
979----
980
981Your Message-Id is `<foo.12345.author@example.com>`. This example will be used
982below 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
984from v1; if you're sending v3, use the Message-Id from v2.
985
986While you're looking at the email, you should also note who is CC'd, as it's
987common practice in the mailing list to keep all CCs on a thread. You can add
988these CC lines directly to your cover letter with a line like so in the header
989(before the Subject line):
990
991----
992CC: author@example.com, Othe R <other@example.com>
993----
994
995Now send the emails again, paying close attention to which messages you pass in
996to the command:
997
998----
999$ git send-email --to=target@example.com
1000 --in-reply-to="<foo.12345.author@example.com>"
1001 psuh/v2*
1002----
1003
5ef811ac 1004[[single-patch]]
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1005=== Bonus Chapter: One-Patch Changes
1006
1007In some cases, your very small change may consist of only one patch. When that
1008happens, you only need to send one email. Your commit message should already be
1009meaningful and explain at a high level the purpose (what is happening and why)
1010of your patch, but if you need to supply even more context, you can do so below
1011the `---` in your patch. Take the example below, which was generated with `git
1012format-patch` on a single commit, and then edited to add the content between
1013the `---` and the diffstat.
1014
1015----
1016From 1345bbb3f7ac74abde040c12e737204689a72723 Mon Sep 17 00:00:00 2001
1017From: A U Thor <author@example.com>
1018Date: Thu, 18 Apr 2019 15:11:02 -0700
1019Subject: [PATCH] README: change the grammar
1020
1021I think it looks better this way. This part of the commit message will
1022end up in the commit-log.
1023
1024Signed-off-by: A U Thor <author@example.com>
1025---
1026Let's have a wild discussion about grammar on the mailing list. This
1027part of my email will never end up in the commit log. Here is where I
1028can add additional context to the mailing list about my intent, outside
1029of the context of the commit log. This section was added after `git
1030format-patch` was run, by editing the patch file in a text editor.
1031
1032 README.md | 2 +-
1033 1 file changed, 1 insertion(+), 1 deletion(-)
1034
1035diff --git a/README.md b/README.md
1036index 88f126184c..38da593a60 100644
1037--- a/README.md
1038+++ b/README.md
1039@@ -3,7 +3,7 @@
1040 Git - fast, scalable, distributed revision control system
1041 =========================================================
1042
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.
1047
1048--
10492.21.0.392.gf8f6787159e-goog
1050----
1051
5ef811ac 1052[[now-what]]
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1053== My Patch Got Emailed - Now What?
1054
1055[[reviewing]]
1056=== Responding to Reviews
1057
1058After a few days, you will hopefully receive a reply to your patchset with some
1059comments. Woohoo! Now you can get back to work.
1060
1061It's good manners to reply to each comment, notifying the reviewer that you have
1062made the change requested, feel the original is better, or that the comment
1063inspired you to do something a new way which is superior to both the original
1064and the suggested change. This way reviewers don't need to inspect your v2 to
1065figure out whether you implemented their comment or not.
1066
1067If you are going to push back on a comment, be polite and explain why you feel
1068your original is better; be prepared that the reviewer may still disagree with
1069you, and the rest of the community may weigh in on one side or the other. As
1070with all code reviews, it's important to keep an open mind to doing something a
1071different way than you originally planned; other reviewers have a different
1072perspective on the project than you do, and may be thinking of a valid side
1073effect which had not occurred to you. It is always okay to ask for clarification
1074if you aren't sure why a change was suggested, or what the reviewer is asking
1075you to do.
1076
1077Make sure your email client has a plaintext email mode and it is turned on; the
1078Git list rejects HTML email. Please also follow the mailing list etiquette
1079outlined in the
1080https://kernel.googlesource.com/pub/scm/git/git/+/todo/MaintNotes[Maintainer's
1081Note], which are similar to etiquette rules in most open source communities
1082surrounding bottom-posting and inline replies.
1083
1084When you're making changes to your code, it is cleanest - that is, the resulting
1085commits are easiest to look at - if you use `git rebase -i` (interactive
1086rebase). Take a look at this
1087https://www.oreilly.com/library/view/git-pocket-guide/9781449327507/ch10.html[overview]
1088from O'Reilly. The general idea is to modify each commit which requires changes;
1089this way, instead of having a patch A with a mistake, a patch B which was fine
1090and required no upstream reviews in v1, and a patch C which fixes patch A for
1091v2, you can just ship a v2 with a correct patch A and correct patch B. This is
1092changing history, but since it's local history which you haven't shared with
1093anyone, that is okay for now! (Later, it may not make sense to do this; take a
1094look at the section below this one for some context.)
1095
5ef811ac 1096[[after-approval]]
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1097=== After Review Approval
1098
1099The 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
1101while it is still in the review process; from there, when it is ready for wider
1102testing, it will be merged into `next`. Plenty of early testers use `next` and
1103may report issues. Eventually, changes in `next` will make it to `master`,
1104which 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
1106document, you can read `Documents/SubmittingPatches` for some more info about
1107the use of the various integration branches.
1108
1109Back to now: your code has been lauded by the upstream reviewers. It is perfect.
1110It is ready to be accepted. You don't need to do anything else; the maintainer
1111will merge your topic branch to `next` and life is good.
1112
1113However, if you discover it isn't so perfect after this point, you may need to
1114take some special steps depending on where you are in the process.
1115
1116If the maintainer has announced in the "What's cooking in git.git" email that
1117your topic is marked for `next` - that is, that they plan to merge it to `next`
1118but have not yet done so - you should send an email asking the maintainer to
1119wait a little longer: "I've sent v4 of my series and you marked it for `next`,
1120but I need to change this and that - please wait for v5 before you merge it."
1121
1122If the topic has already been merged to `next`, rather than modifying your
1123patches with `git rebase -i`, you should make further changes incrementally -
1124that is, with another commit, based on top of the maintainer's topic branch as
1125detailed in https://github.com/gitster/git. Your work is still in the same topic
1126but is now incremental, rather than a wholesale rewrite of the topic branch.
1127
1128The topic branches in the maintainer's GitHub are mirrored in GitGitGadget, so
1129if you're sending your reviews out that way, you should be sure to open your PR
1130against the appropriate GitGitGadget/Git branch.
1131
1132If you're using `git send-email`, you can use it the same way as before, but you
1133should generate your diffs from `<topic>..<mybranch>` and base your work on
1134`<topic>` instead of `master`.