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Diffstat (limited to 'Documentation')
69 files changed, 2832 insertions, 352 deletions
diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines index 37705544fc..f45db5b727 100644 --- a/Documentation/CodingGuidelines +++ b/Documentation/CodingGuidelines @@ -432,6 +432,12 @@ For C programs: must be declared with "extern" in header files. However, function declarations should not use "extern", as that is already the default. + - You can launch gdb around your program using the shorthand GIT_DEBUGGER. + Run `GIT_DEBUGGER=1 ./bin-wrappers/git foo` to simply use gdb as is, or + run `GIT_DEBUGGER="<debugger> <debugger-args>" ./bin-wrappers/git foo` to + use your own debugger and arguments. Example: `GIT_DEBUGGER="ddd --gdb" + ./bin-wrappers/git log` (See `wrap-for-bin.sh`.) + For Perl programs: - Most of the C guidelines above apply. diff --git a/Documentation/Makefile b/Documentation/Makefile index dbf5a0f276..76f2ecfc1b 100644 --- a/Documentation/Makefile +++ b/Documentation/Makefile @@ -76,6 +76,7 @@ SP_ARTICLES += howto/maintain-git API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technical/api-index.txt, $(wildcard technical/api-*.txt))) SP_ARTICLES += $(API_DOCS) +TECH_DOCS += MyFirstContribution TECH_DOCS += SubmittingPatches TECH_DOCS += technical/hash-function-transition TECH_DOCS += technical/http-protocol diff --git a/Documentation/MyFirstContribution.txt b/Documentation/MyFirstContribution.txt new file mode 100644 index 0000000000..f8670379c0 --- /dev/null +++ b/Documentation/MyFirstContribution.txt @@ -0,0 +1,1134 @@ +My First Contribution to the Git Project +======================================== +:sectanchors: + +[[summary]] +== Summary + +This is a tutorial demonstrating the end-to-end workflow of creating a change to +the Git tree, sending it for review, and making changes based on comments. + +[[prerequisites]] +=== Prerequisites + +This tutorial assumes you're already fairly familiar with using Git to manage +source code. The Git workflow steps will largely remain unexplained. + +[[related-reading]] +=== Related Reading + +This tutorial aims to summarize the following documents, but the reader may find +useful additional context: + +- `Documentation/SubmittingPatches` +- `Documentation/howto/new-command.txt` + +[[getting-started]] +== Getting Started + +[[cloning]] +=== Clone the Git Repository + +Git is mirrored in a number of locations. Clone the repository from one of them; +https://git-scm.com/downloads suggests one of the best places to clone from is +the mirror on GitHub. + +---- +$ git clone https://github.com/git/git git +$ cd git +---- + +[[identify-problem]] +=== Identify Problem to Solve + +//// +Use + to indicate fixed-width here; couldn't get ` to work nicely with the +quotes around "Pony Saying 'Um, Hello'". +//// +In this tutorial, we will add a new command, +git psuh+, short for ``Pony Saying +`Um, Hello''' - a feature which has gone unimplemented despite a high frequency +of invocation during users' typical daily workflow. + +(We've seen some other effort in this space with the implementation of popular +commands such as `sl`.) + +[[setup-workspace]] +=== Set Up Your Workspace + +Let's start by making a development branch to work on our changes. Per +`Documentation/SubmittingPatches`, since a brand new command is a new feature, +it's fine to base your work on `master`. However, in the future for bugfixes, +etc., you should check that document and base it on the appropriate branch. + +For the purposes of this document, we will base all our work on the `master` +branch of the upstream project. Create the `psuh` branch you will use for +development like so: + +---- +$ git checkout -b psuh origin/master +---- + +We'll make a number of commits here in order to demonstrate how to send a topic +with multiple patches up for review simultaneously. + +[[code-it-up]] +== Code It Up! + +NOTE: A reference implementation can be found at +https://github.com/nasamuffin/git/tree/psuh. + +[[add-new-command]] +=== Adding a New Command + +Lots of the subcommands are written as builtins, which means they are +implemented in C and compiled into the main `git` executable. Implementing the +very simple `psuh` command as a built-in will demonstrate the structure of the +codebase, the internal API, and the process of working together as a contributor +with the reviewers and maintainer to integrate this change into the system. + +Built-in subcommands are typically implemented in a function named "cmd_" +followed by the name of the subcommand, in a source file named after the +subcommand and contained within `builtin/`. So it makes sense to implement your +command in `builtin/psuh.c`. Create that file, and within it, write the entry +point for your command in a function matching the style and signature: + +---- +int cmd_psuh(int argc, const char **argv, const char *prefix) +---- + +We'll also need to add the declaration of psuh; open up `builtin.h`, find the +declaration for `cmd_push`, and add a new line for `psuh` immediately before it, +in order to keep the declarations sorted: + +---- +int cmd_psuh(int argc, const char **argv, const char *prefix); +---- + +Be sure to `#include "builtin.h"` in your `psuh.c`. + +Go ahead and add some throwaway printf to that function. This is a decent +starting point as we can now add build rules and register the command. + +NOTE: Your throwaway text, as well as much of the text you will be adding over +the course of this tutorial, is user-facing. That means it needs to be +localizable. Take a look at `po/README` under "Marking strings for translation". +Throughout the tutorial, we will mark strings for translation as necessary; you +should also do so when writing your user-facing commands in the future. + +---- +int cmd_psuh(int argc, const char **argv, const char *prefix) +{ + printf(_("Pony saying hello goes here.\n")); + return 0; +} +---- + +Let's try to build it. Open `Makefile`, find where `builtin/push.o` is added +to `BUILTIN_OBJS`, and add `builtin/psuh.o` in the same way next to it in +alphabetical order. Once you've done so, move to the top-level directory and +build simply with `make`. Also add the `DEVELOPER=1` variable to turn on +some additional warnings: + +---- +$ echo DEVELOPER=1 >config.mak +$ make +---- + +NOTE: When you are developing the Git project, it's preferred that you use the +`DEVELOPER` flag; if there's some reason it doesn't work for you, you can turn +it off, but it's a good idea to mention the problem to the mailing list. + +NOTE: The Git build is parallelizable. `-j#` is not included above but you can +use it as you prefer, here and elsewhere. + +Great, now your new command builds happily on its own. But nobody invokes it. +Let's change that. + +The list of commands lives in `git.c`. We can register a new command by adding +a `cmd_struct` to the `commands[]` array. `struct cmd_struct` takes a string +with the command name, a function pointer to the command implementation, and a +setup option flag. For now, let's keep mimicking `push`. Find the line where +`cmd_push` is registered, copy it, and modify it for `cmd_psuh`, placing the new +line in alphabetical order. + +The options are documented in `builtin.h` under "Adding a new built-in." Since +we hope to print some data about the user's current workspace context later, +we need a Git directory, so choose `RUN_SETUP` as your only option. + +Go ahead and build again. You should see a clean build, so let's kick the tires +and see if it works. There's a binary you can use to test with in the +`bin-wrappers` directory. + +---- +$ ./bin-wrappers/git psuh +---- + +Check it out! You've got a command! Nice work! Let's commit this. + +`git status` reveals modified `Makefile`, `builtin.h`, and `git.c` as well as +untracked `builtin/psuh.c` and `git-psuh`. First, let's take care of the binary, +which should be ignored. Open `.gitignore` in your editor, find `/git-push`, and +add an entry for your new command in alphabetical order: + +---- +... +/git-prune-packed +/git-psuh +/git-pull +/git-push +/git-quiltimport +/git-range-diff +... +---- + +Checking `git status` again should show that `git-psuh` has been removed from +the untracked list and `.gitignore` has been added to the modified list. Now we +can stage and commit: + +---- +$ git add Makefile builtin.h builtin/psuh.c git.c .gitignore +$ git commit -s +---- + +You will be presented with your editor in order to write a commit message. Start +the commit with a 50-column or less subject line, including the name of the +component you're working on, followed by a blank line (always required) and then +the body of your commit message, which should provide the bulk of the context. +Remember to be explicit and provide the "Why" of your change, especially if it +couldn't easily be understood from your diff. When editing your commit message, +don't remove the Signed-off-by line which was added by `-s` above. + +---- +psuh: add a built-in by popular demand + +Internal metrics indicate this is a command many users expect to be +present. So here's an implementation to help drive customer +satisfaction and engagement: a pony which doubtfully greets the user, +or, a Pony Saying "Um, Hello" (PSUH). + +This commit message is intentionally formatted to 72 columns per line, +starts with a single line as "commit message subject" that is written as +if to command the codebase to do something (add this, teach a command +that). The body of the message is designed to add information about the +commit that is not readily deduced from reading the associated diff, +such as answering the question "why?". + +Signed-off-by: A U Thor <author@example.com> +---- + +Go ahead and inspect your new commit with `git show`. "psuh:" indicates you +have modified mainly the `psuh` command. The subject line gives readers an idea +of what you've changed. The sign-off line (`-s`) indicates that you agree to +the Developer's Certificate of Origin 1.1 (see the +`Documentation/SubmittingPatches` +++[[dco]]+++ header). + +For the remainder of the tutorial, the subject line only will be listed for the +sake of brevity. However, fully-fleshed example commit messages are available +on the reference implementation linked at the top of this document. + +[[implementation]] +=== Implementation + +It's probably useful to do at least something besides printing out a string. +Let's start by having a look at everything we get. + +Modify your `cmd_psuh` implementation to dump the args you're passed, keeping +existing `printf()` calls in place: + +---- + int i; + + ... + + printf(Q_("Your args (there is %d):\n", + "Your args (there are %d):\n", + argc), + argc); + for (i = 0; i < argc; i++) + printf("%d: %s\n", i, argv[i]); + + printf(_("Your current working directory:\n<top-level>%s%s\n"), + prefix ? "/" : "", prefix ? prefix : ""); + +---- + +Build and try it. As you may expect, there's pretty much just whatever we give +on the command line, including the name of our command. (If `prefix` is empty +for you, try `cd Documentation/ && ../bin-wrappers/git psuh`). That's not so +helpful. So what other context can we get? + +Add a line to `#include "config.h"`. Then, add the following bits to the +function body: + +---- + const char *cfg_name; + +... + + git_config(git_default_config, NULL); + if (git_config_get_string_const("user.name", &cfg_name) > 0) + printf(_("No name is found in config\n")); + else + printf(_("Your name: %s\n"), cfg_name); +---- + +`git_config()` will grab the configuration from config files known to Git and +apply standard precedence rules. `git_config_get_string_const()` will look up +a specific key ("user.name") and give you the value. There are a number of +single-key lookup functions like this one; you can see them all (and more info +about how to use `git_config()`) in `Documentation/technical/api-config.txt`. + +You should see that the name printed matches the one you see when you run: + +---- +$ git config --get user.name +---- + +Great! Now we know how to check for values in the Git config. Let's commit this +too, so we don't lose our progress. + +---- +$ git add builtin/psuh.c +$ git commit -sm "psuh: show parameters & config opts" +---- + +NOTE: Again, the above is for sake of brevity in this tutorial. In a real change +you should not use `-m` but instead use the editor to write a meaningful +message. + +Still, it'd be nice to know what the user's working context is like. Let's see +if we can print the name of the user's current branch. We can mimic the +`git status` implementation; the printer is located in `wt-status.c` and we can +see that the branch is held in a `struct wt_status`. + +`wt_status_print()` gets invoked by `cmd_status()` in `builtin/commit.c`. +Looking at that implementation we see the status config being populated like so: + +---- +status_init_config(&s, git_status_config); +---- + +But as we drill down, we can find that `status_init_config()` wraps a call +to `git_config()`. Let's modify the code we wrote in the previous commit. + +Be sure to include the header to allow you to use `struct wt_status`: +---- +#include "wt-status.h" +---- + +Then modify your `cmd_psuh` implementation to declare your `struct wt_status`, +prepare it, and print its contents: + +---- + struct wt_status status; + +... + + wt_status_prepare(the_repository, &status); + git_config(git_default_config, &status); + +... + + printf(_("Your current branch: %s\n"), status.branch); +---- + +Run it again. Check it out - here's the (verbose) name of your current branch! + +Let's commit this as well. + +---- +$ git add builtin/psuh.c +$ git commit -sm "psuh: print the current branch" +---- + +Now let's see if we can get some info about a specific commit. + +Luckily, there are some helpers for us here. `commit.h` has a function called +`lookup_commit_reference_by_name` to which we can simply provide a hardcoded +string; `pretty.h` has an extremely handy `pp_commit_easy()` call which doesn't +require a full format object to be passed. + +Add the following includes: + +---- +#include "commit.h" +#include "pretty.h" +---- + +Then, add the following lines within your implementation of `cmd_psuh()` near +the declarations and the logic, respectively. + +---- + struct commit *c = NULL; + struct strbuf commitline = STRBUF_INIT; + +... + + c = lookup_commit_reference_by_name("origin/master"); + + if (c != NULL) { + pp_commit_easy(CMIT_FMT_ONELINE, c, &commitline); + printf(_("Current commit: %s\n"), commitline.buf); + } +---- + +The `struct strbuf` provides some safety belts to your basic `char*`, one of +which is a length member to prevent buffer overruns. It needs to be initialized +nicely with `STRBUF_INIT`. Keep it in mind when you need to pass around `char*`. + +`lookup_commit_reference_by_name` resolves the name you pass it, so you can play +with the value there and see what kind of things you can come up with. + +`pp_commit_easy` is a convenience wrapper in `pretty.h` that takes a single +format enum shorthand, rather than an entire format struct. It then +pretty-prints the commit according to that shorthand. These are similar to the +formats available with `--pretty=FOO` in many Git commands. + +Build it and run, and if you're using the same name in the example, you should +see the subject line of the most recent commit in `origin/master` that you know +about. Neat! Let's commit that as well. + +---- +$ git add builtin/psuh.c +$ git commit -sm "psuh: display the top of origin/master" +---- + +[[add-documentation]] +=== Adding Documentation + +Awesome! You've got a fantastic new command that you're ready to share with the +community. But hang on just a minute - this isn't very user-friendly. Run the +following: + +---- +$ ./bin-wrappers/git help psuh +---- + +Your new command is undocumented! Let's fix that. + +Take a look at `Documentation/git-*.txt`. These are the manpages for the +subcommands that Git knows about. You can open these up and take a look to get +acquainted with the format, but then go ahead and make a new file +`Documentation/git-psuh.txt`. Like with most of the documentation in the Git +project, help pages are written with AsciiDoc (see CodingGuidelines, "Writing +Documentation" section). Use the following template to fill out your own +manpage: + +// Surprisingly difficult to embed AsciiDoc source within AsciiDoc. +[listing] +.... +git-psuh(1) +=========== + +NAME +---- +git-psuh - Delight users' typo with a shy horse + + +SYNOPSIS +-------- +[verse] +'git-psuh [<arg>...]'< |