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Diffstat (limited to 'Documentation/CodingGuidelines')
| -rw-r--r-- | Documentation/CodingGuidelines | 239 |
1 files changed, 202 insertions, 37 deletions
diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines index 48aa4edfbd..003393ed16 100644 --- a/Documentation/CodingGuidelines +++ b/Documentation/CodingGuidelines @@ -26,6 +26,13 @@ code. For Git in general, a few rough rules are: go and fix it up." Cf. http://lkml.iu.edu/hypermail/linux/kernel/1001.3/01069.html + - Log messages to explain your changes are as important as the + changes themselves. Clearly written code and in-code comments + explain how the code works and what is assumed from the surrounding + context. The log messages explain what the changes wanted to + achieve and why the changes were necessary (more on this in the + accompanying SubmittingPatches document). + Make your code readable and sensible, and don't try to be clever. As for more concrete guidelines, just imitate the existing code @@ -36,7 +43,10 @@ the overall style of existing code. Modifications to existing code is expected to match the style the surrounding code already uses (even if it doesn't match the overall style of existing code). -But if you must have a list of rules, here they are. +But if you must have a list of rules, here are some language +specific ones. Note that Documentation/ToolsForGit.txt document +has a collection of tips to help you use some external tools +to conform to these guidelines. For shell scripts specifically (not exhaustive): @@ -75,7 +85,7 @@ For shell scripts specifically (not exhaustive): - If you want to find out if a command is available on the user's $PATH, you should use 'type <command>', instead of 'which <command>'. - The output of 'which' is not machine parseable and its exit code + The output of 'which' is not machine parsable and its exit code is not reliable across platforms. - We use POSIX compliant parameter substitutions and avoid bashisms; @@ -91,16 +101,10 @@ For shell scripts specifically (not exhaustive): - No shell arrays. - - No strlen ${#parameter}. - - No pattern replacement ${parameter/pattern/string}. - We use Arithmetic Expansion $(( ... )). - - Inside Arithmetic Expansion, spell shell variables with $ in front - of them, as some shells do not grok $((x)) while accepting $(($x)) - just fine (e.g. dash older than 0.5.4). - - We do not use Process Substitution <(list) or >(list). - Do not write control structures on a single line with semicolon. @@ -118,6 +122,24 @@ For shell scripts specifically (not exhaustive): do this fi + - If a command sequence joined with && or || or | spans multiple + lines, put each command on a separate line and put && and || and | + operators at the end of each line, rather than the start. This + means you don't need to use \ to join lines, since the above + operators imply the sequence isn't finished. + + (incorrect) + grep blob verify_pack_result \ + | awk -f print_1.awk \ + | sort >actual && + ... + + (correct) + grep blob verify_pack_result | + awk -f print_1.awk | + sort >actual && + ... + - We prefer "test" over "[ ... ]". - We do not write the noiseword "function" in front of shell @@ -140,8 +162,6 @@ For shell scripts specifically (not exhaustive): - We do not use \{m,n\}; - - We do not use -E; - - We do not use ? or + (which are \{0,1\} and \{1,\} respectively in BRE) but that goes without saying as these are ERE elements not BRE (note that \? and \+ are not even part @@ -163,6 +183,11 @@ For shell scripts specifically (not exhaustive): does not have such a problem. + - Even though "local" is not part of POSIX, we make heavy use of it + in our test suite. We do not use it in scripted Porcelains, and + hopefully nobody starts using "local" before they are reimplemented + in C ;-) + For C programs: @@ -177,10 +202,51 @@ For C programs: by e.g. "echo DEVELOPER=1 >>config.mak". - We try to support a wide range of C compilers to compile Git with, - including old ones. That means that you should not use C99 - initializers, even if a lot of compilers grok it. + including old ones. As of Git v2.35.0 Git requires C99 (we check + "__STDC_VERSION__"). You should not use features from a newer C + standard, even if your compiler groks them. + + New C99 features have been phased in gradually, if something's new + in C99 but not used yet don't assume that it's safe to use, some + compilers we target have only partial support for it. These are + considered safe to use: + + . since around 2007 with 2b6854c863a, we have been using + initializer elements which are not computable at load time. E.g.: + + const char *args[] = {"constant", variable, NULL}; - - Variables have to be declared at the beginning of the block. + . since early 2012 with e1327023ea, we have been using an enum + definition whose last element is followed by a comma. This, like + an array initializer that ends with a trailing comma, can be used + to reduce the patch noise when adding a new identifier at the end. + + . since mid 2017 with cbc0f81d, we have been using designated + initializers for struct (e.g. "struct t v = { .val = 'a' };"). + + . since mid 2017 with 512f41cf, we have been using designated + initializers for array (e.g. "int array[10] = { [5] = 2 }"). + + . since early 2021 with 765dc168882, we have been using variadic + macros, mostly for printf-like trace and debug macros. + + . since late 2021 with 44ba10d6, we have had variables declared in + the for loop "for (int i = 0; i < 10; i++)". + + New C99 features that we cannot use yet: + + . %z and %zu as a printf() argument for a size_t (the %z being for + the POSIX-specific ssize_t). Instead you should use + printf("%"PRIuMAX, (uintmax_t)v). These days the MSVC version we + rely on supports %z, but the C library used by MinGW does not. + + . Shorthand like ".a.b = *c" in struct initializations is known to + trip up an older IBM XLC version, use ".a = { .b = *c }" instead. + See the 33665d98 (reftable: make assignments portable to AIX xlc + v12.01, 2022-03-28). + + - Variables have to be declared at the beginning of the block, before + the first statement (i.e. -Wdeclaration-after-statement). - NULL pointers shall be written as NULL, not as 0. @@ -200,6 +266,18 @@ For C programs: while( condition ) func (bar+1); + - Do not explicitly compare an integral value with constant 0 or '\0', + or a pointer value with constant NULL. For instance, to validate that + counted array <ptr, cnt> is initialized but has no elements, write: + + if (!ptr || cnt) + BUG("empty array expected"); + + and not: + + if (ptr == NULL || cnt != 0); + BUG("empty array expected"); + - We avoid using braces unnecessarily. I.e. if (bla) { @@ -358,11 +436,18 @@ For C programs: string_list for sorted string lists, a hash map (mapping struct objects) named "struct decorate", amongst other things. - - When you come up with an API, document it. + - When you come up with an API, document its functions and structures + in the header file that exposes the API to its callers. Use what is + in "strbuf.h" as a model for the appropriate tone and level of + detail. - The first #include in C files, except in platform specific compat/ - implementations, must be either "git-compat-util.h", "cache.h" or - "builtin.h". You do not have to include more than one of these. + implementations and sha1dc/, must be either "git-compat-util.h" or + one of the approved headers that includes it first for you. (The + approved headers currently include "cache.h", "builtin.h", + "t/helper/test-tool.h", "xdiff/xinclude.h", or + "reftable/system.h"). You do not have to include more than one of + these. - A C file must directly include the header files that declare the functions and the types it uses, except for the functions and types @@ -391,6 +476,12 @@ 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. @@ -421,36 +512,52 @@ For Perl programs: - Learn and use Git.pm if you need that functionality. - - For Emacs, it's useful to put the following in - GIT_CHECKOUT/.dir-locals.el, assuming you use cperl-mode: - - ;; note the first part is useful for C editing, too - ((nil . ((indent-tabs-mode . t) - (tab-width . 8) - (fill-column . 80))) - (cperl-mode . ((cperl-indent-level . 8) - (cperl-extra-newline-before-brace . nil) - (cperl-merge-trailing-else . t)))) - For Python scripts: - We follow PEP-8 (http://www.python.org/dev/peps/pep-0008/). - - As a minimum, we aim to be compatible with Python 2.6 and 2.7. + - As a minimum, we aim to be compatible with Python 2.7. - Where required libraries do not restrict us to Python 2, we try to also be compatible with Python 3.1 and later. - - When you must differentiate between Unicode literals and byte string - literals, it is OK to use the 'b' prefix. Even though the Python - documentation for version 2.6 does not mention this prefix, it has - been supported since version 2.6.0. + +Program Output + + We make a distinction between a Git command's primary output and + output which is merely chatty feedback (for instance, status + messages, running transcript, or progress display), as well as error + messages. Roughly speaking, a Git command's primary output is that + which one might want to capture to a file or send down a pipe; its + chatty output should not interfere with these use-cases. + + As such, primary output should be sent to the standard output stream + (stdout), and chatty output should be sent to the standard error + stream (stderr). Examples of commands which produce primary output + include `git log`, `git show`, and `git branch --list` which generate + output on the stdout stream. + + Not all Git commands have primary output; this is often true of + commands whose main function is to perform an action. Some action + commands are silent, whereas others are chatty. An example of a + chatty action commands is `git clone` with its "Cloning into + '<path>'..." and "Checking connectivity..." status messages which it + sends to the stderr stream. + + Error messages from Git commands should always be sent to the stderr + stream. + Error Messages - Do not end error messages with a full stop. - - Do not capitalize ("unable to open %s", not "Unable to open %s") + - Do not capitalize the first word, only because it is the first word + in the message ("unable to open %s", not "Unable to open %s"). But + "SHA-3 not supported" is fine, because the reason the first word is + capitalized is not because it is at the beginning of the sentence, + but because the word would be spelled in capital letters even when + it appeared in the middle of the sentence. - Say what the error is first ("cannot open %s", not "%s: cannot open") @@ -493,6 +600,51 @@ Writing Documentation: documentation, please see the documentation-related advice in the Documentation/SubmittingPatches file). + In order to ensure the documentation is inclusive, avoid assuming + that an unspecified example person is male or female, and think + twice before using "he", "him", "she", or "her". Here are some + tips to avoid use of gendered pronouns: + + - Prefer succinctness and matter-of-factly describing functionality + in the abstract. E.g. + + --short:: Emit output in the short-format. + + and avoid something like these overly verbose alternatives: + + --short:: Use this to emit output in the short-format. + --short:: You can use this to get output in the short-format. + --short:: A user who prefers shorter output could.... + --short:: Should a person and/or program want shorter output, he + she/they/it can... + + This practice often eliminates the need to involve human actors in + your description, but it is a good practice regardless of the + avoidance of gendered pronouns. + + - When it becomes awkward to stick to this style, prefer "you" when + addressing the hypothetical user, and possibly "we" when + discussing how the program might react to the user. E.g. + + You can use this option instead of --xyz, but we might remove + support for it in future versions. + + while keeping in mind that you can probably be less verbose, e.g. + + Use this instead of --xyz. This option might be removed in future + versions. + + - If you still need to refer to an example person that is + third-person singular, you may resort to "singular they" to avoid + "he/she/him/her", e.g. + + A contributor asks their upstream to pull from them. + + Note that this sounds ungrammatical and unnatural to those who + learned that "they" is only used for third-person plural, e.g. + those who learn English as a second language in some parts of the + world. + Every user-visible change should be reflected in the documentation. The same general rule as for code applies -- imitate the existing conventions. @@ -515,8 +667,8 @@ Writing Documentation: (One or more of <file>.) Optional parts are enclosed in square brackets: - [<extra>] - (Zero or one <extra>.) + [<file>...] + (Zero or more of <file>.) --exec-path[=<path>] (Option with an optional argument. Note that the "=" is inside the @@ -530,6 +682,16 @@ Writing Documentation: [-q | --quiet] [--utf8 | --no-utf8] + Use spacing around "|" token(s), but not immediately after opening or + before closing a [] or () pair: + Do: [-q | --quiet] + Don't: [-q|--quiet] + + Don't use spacing around "|" tokens when they're used to seperate the + alternate arguments of an option: + Do: --track[=(direct|inherit)] + Don't: --track[=(direct | inherit)] + Parentheses are used for grouping: [(<rev> | <range>)...] (Any number of either <rev> or <range>. Parens are needed to make @@ -559,11 +721,14 @@ Writing Documentation: or commands: Literal examples (e.g. use of command-line options, command names, - branch names, configuration and environment variables) must be - typeset in monospace (i.e. wrapped with backticks): + branch names, URLs, pathnames (files and directories), configuration and + environment variables) must be typeset in monospace (i.e. wrapped with + backticks): `--pretty=oneline` `git rev-list` `remote.pushDefault` + `http://git.example.com` + `.git/config` `GIT_DIR` `HEAD` |