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6d0618a8 | 1 | Like other projects, we also have some guidelines to keep to the |
6c3b2afe | 2 | code. For Git in general, a few rough rules are: |
6d0618a8 JS |
3 | |
4 | - Most importantly, we never say "It's in POSIX; we'll happily | |
5 | ignore your needs should your system not conform to it." | |
6 | We live in the real world. | |
7 | ||
8 | - However, we often say "Let's stay away from that construct, | |
9 | it's not even in POSIX". | |
10 | ||
11 | - In spite of the above two rules, we sometimes say "Although | |
12 | this is not in POSIX, it (is so convenient | makes the code | |
13 | much more readable | has other good characteristics) and | |
14 | practically all the platforms we care about support it, so | |
15 | let's use it". | |
16 | ||
17 | Again, we live in the real world, and it is sometimes a | |
18 | judgement call, the decision based more on real world | |
19 | constraints people face than what the paper standard says. | |
20 | ||
dd30800b JH |
21 | - Fixing style violations while working on a real change as a |
22 | preparatory clean-up step is good, but otherwise avoid useless code | |
23 | churn for the sake of conforming to the style. | |
24 | ||
25 | "Once it _is_ in the tree, it's not really worth the patch noise to | |
26 | go and fix it up." | |
27 | Cf. http://article.gmane.org/gmane.linux.kernel/943020 | |
28 | ||
c5e366b1 | 29 | Make your code readable and sensible, and don't try to be clever. |
6d0618a8 JS |
30 | |
31 | As for more concrete guidelines, just imitate the existing code | |
32 | (this is a good guideline, no matter which project you are | |
dfb047b9 | 33 | contributing to). It is always preferable to match the _local_ |
2de9b711 | 34 | convention. New code added to Git suite is expected to match |
dfb047b9 NS |
35 | the overall style of existing code. Modifications to existing |
36 | code is expected to match the style the surrounding code already | |
37 | uses (even if it doesn't match the overall style of existing code). | |
38 | ||
39 | But if you must have a list of rules, here they are. | |
6d0618a8 JS |
40 | |
41 | For shell scripts specifically (not exhaustive): | |
42 | ||
f36a4fa8 GB |
43 | - We use tabs for indentation. |
44 | ||
79fc3ca1 JH |
45 | - Case arms are indented at the same depth as case and esac lines, |
46 | like this: | |
47 | ||
48 | case "$variable" in | |
49 | pattern1) | |
50 | do this | |
51 | ;; | |
52 | pattern2) | |
53 | do that | |
54 | ;; | |
55 | esac | |
f36a4fa8 | 56 | |
48f359bf TH |
57 | - Redirection operators should be written with space before, but no |
58 | space after them. In other words, write 'echo test >"$file"' | |
59 | instead of 'echo test> $file' or 'echo test > $file'. Note that | |
60 | even though it is not required by POSIX to double-quote the | |
61 | redirection target in a variable (as shown above), our code does so | |
62 | because some versions of bash issue a warning without the quotes. | |
63 | ||
6a49909b JH |
64 | (incorrect) |
65 | cat hello > world < universe | |
66 | echo hello >$world | |
67 | ||
68 | (correct) | |
69 | cat hello >world <universe | |
70 | echo hello >"$world" | |
71 | ||
6d0618a8 JS |
72 | - We prefer $( ... ) for command substitution; unlike ``, it |
73 | properly nests. It should have been the way Bourne spelled | |
74 | it from day one, but unfortunately isn't. | |
75 | ||
860f70f9 TH |
76 | - If you want to find out if a command is available on the user's |
77 | $PATH, you should use 'type <command>', instead of 'which <command>'. | |
78 | The output of 'which' is not machine parseable and its exit code | |
79 | is not reliable across platforms. | |
80 | ||
bc979945 JH |
81 | - We use POSIX compliant parameter substitutions and avoid bashisms; |
82 | namely: | |
6d0618a8 | 83 | |
bc979945 JH |
84 | - We use ${parameter-word} and its [-=?+] siblings, and their |
85 | colon'ed "unset or null" form. | |
6d0618a8 | 86 | |
bc979945 JH |
87 | - We use ${parameter#word} and its [#%] siblings, and their |
88 | doubled "longest matching" form. | |
6d0618a8 | 89 | |
bc979945 | 90 | - No "Substring Expansion" ${parameter:offset:length}. |
055467dd | 91 | |
bc979945 | 92 | - No shell arrays. |
6d0618a8 | 93 | |
bc979945 | 94 | - No strlen ${#parameter}. |
6d0618a8 | 95 | |
bc979945 | 96 | - No pattern replacement ${parameter/pattern/string}. |
6d0618a8 | 97 | |
bc979945 JH |
98 | - We use Arithmetic Expansion $(( ... )). |
99 | ||
100 | - Inside Arithmetic Expansion, spell shell variables with $ in front | |
101 | of them, as some shells do not grok $((x)) while accepting $(($x)) | |
102 | just fine (e.g. dash older than 0.5.4). | |
6d0618a8 JS |
103 | |
104 | - We do not use Process Substitution <(list) or >(list). | |
105 | ||
03b05c7d HV |
106 | - Do not write control structures on a single line with semicolon. |
107 | "then" should be on the next line for if statements, and "do" | |
108 | should be on the next line for "while" and "for". | |
109 | ||
9dbe7801 JH |
110 | (incorrect) |
111 | if test -f hello; then | |
112 | do this | |
113 | fi | |
114 | ||
115 | (correct) | |
116 | if test -f hello | |
117 | then | |
118 | do this | |
119 | fi | |
120 | ||
6d0618a8 JS |
121 | - We prefer "test" over "[ ... ]". |
122 | ||
123 | - We do not write the noiseword "function" in front of shell | |
124 | functions. | |
125 | ||
6117a3d4 JH |
126 | - We prefer a space between the function name and the parentheses, |
127 | and no space inside the parentheses. The opening "{" should also | |
128 | be on the same line. | |
129 | ||
130 | (incorrect) | |
131 | my_function(){ | |
132 | ... | |
133 | ||
134 | (correct) | |
135 | my_function () { | |
136 | ... | |
03b05c7d | 137 | |
009c98ee | 138 | - As to use of grep, stick to a subset of BRE (namely, no \{m,n\}, |
a58088ab | 139 | [::], [==], or [..]) for portability. |
009c98ee JH |
140 | |
141 | - We do not use \{m,n\}; | |
142 | ||
143 | - We do not use -E; | |
144 | ||
a58088ab | 145 | - We do not use ? or + (which are \{0,1\} and \{1,\} |
009c98ee JH |
146 | respectively in BRE) but that goes without saying as these |
147 | are ERE elements not BRE (note that \? and \+ are not even part | |
148 | of BRE -- making them accessible from BRE is a GNU extension). | |
149 | ||
5e9637c6 ÆAB |
150 | - Use Git's gettext wrappers in git-sh-i18n to make the user |
151 | interface translatable. See "Marking strings for translation" in | |
152 | po/README. | |
153 | ||
897f964c JH |
154 | - We do not write our "test" command with "-a" and "-o" and use "&&" |
155 | or "||" to concatenate multiple "test" commands instead, because | |
156 | the use of "-a/-o" is often error-prone. E.g. | |
157 | ||
158 | test -n "$x" -a "$a" = "$b" | |
159 | ||
160 | is buggy and breaks when $x is "=", but | |
161 | ||
162 | test -n "$x" && test "$a" = "$b" | |
163 | ||
164 | does not have such a problem. | |
165 | ||
166 | ||
6d0618a8 JS |
167 | For C programs: |
168 | ||
169 | - We use tabs to indent, and interpret tabs as taking up to | |
170 | 8 spaces. | |
171 | ||
172 | - We try to keep to at most 80 characters per line. | |
173 | ||
658df95a LS |
174 | - As a Git developer we assume you have a reasonably modern compiler |
175 | and we recommend you to enable the DEVELOPER makefile knob to | |
176 | ensure your patch is clear of all compiler warnings we care about, | |
177 | by e.g. "echo DEVELOPER=1 >>config.mak". | |
178 | ||
2de9b711 | 179 | - We try to support a wide range of C compilers to compile Git with, |
a26fd033 AS |
180 | including old ones. That means that you should not use C99 |
181 | initializers, even if a lot of compilers grok it. | |
182 | ||
183 | - Variables have to be declared at the beginning of the block. | |
184 | ||
185 | - NULL pointers shall be written as NULL, not as 0. | |
186 | ||
6d0618a8 JS |
187 | - When declaring pointers, the star sides with the variable |
188 | name, i.e. "char *string", not "char* string" or | |
189 | "char * string". This makes it easier to understand code | |
190 | like "char *string, c;". | |
191 | ||
f57b6cfd JK |
192 | - Use whitespace around operators and keywords, but not inside |
193 | parentheses and not around functions. So: | |
194 | ||
195 | while (condition) | |
196 | func(bar + 1); | |
197 | ||
198 | and not: | |
199 | ||
200 | while( condition ) | |
201 | func (bar+1); | |
202 | ||
6d0618a8 JS |
203 | - We avoid using braces unnecessarily. I.e. |
204 | ||
205 | if (bla) { | |
206 | x = 1; | |
207 | } | |
208 | ||
209 | is frowned upon. A gray area is when the statement extends | |
210 | over a few lines, and/or you have a lengthy comment atop of | |
211 | it. Also, like in the Linux kernel, if there is a long list | |
212 | of "else if" statements, it can make sense to add braces to | |
213 | single line blocks. | |
214 | ||
691d0dd0 | 215 | - We try to avoid assignments in the condition of an "if" statement. |
0b0b8cd7 | 216 | |
6d0618a8 JS |
217 | - Try to make your code understandable. You may put comments |
218 | in, but comments invariably tend to stale out when the code | |
219 | they were describing changes. Often splitting a function | |
220 | into two makes the intention of the code much clearer. | |
221 | ||
b75a6ca7 | 222 | - Multi-line comments include their delimiters on separate lines from |
223 | the text. E.g. | |
224 | ||
225 | /* | |
226 | * A very long | |
227 | * multi-line comment. | |
228 | */ | |
229 | ||
cbcfd4e3 JH |
230 | Note however that a comment that explains a translatable string to |
231 | translators uses a convention of starting with a magic token | |
232 | "TRANSLATORS: " immediately after the opening delimiter, even when | |
233 | it spans multiple lines. We do not add an asterisk at the beginning | |
234 | of each line, either. E.g. | |
235 | ||
236 | /* TRANSLATORS: here is a comment that explains the string | |
237 | to be translated, that follows immediately after it */ | |
238 | _("Here is a translatable string explained by the above."); | |
239 | ||
6d0618a8 JS |
240 | - Double negation is often harder to understand than no negation |
241 | at all. | |
242 | ||
5db9ab82 JH |
243 | - There are two schools of thought when it comes to comparison, |
244 | especially inside a loop. Some people prefer to have the less stable | |
245 | value on the left hand side and the more stable value on the right hand | |
246 | side, e.g. if you have a loop that counts variable i down to the | |
247 | lower bound, | |
248 | ||
249 | while (i > lower_bound) { | |
250 | do something; | |
251 | i--; | |
252 | } | |
253 | ||
254 | Other people prefer to have the textual order of values match the | |
255 | actual order of values in their comparison, so that they can | |
256 | mentally draw a number line from left to right and place these | |
257 | values in order, i.e. | |
258 | ||
259 | while (lower_bound < i) { | |
260 | do something; | |
261 | i--; | |
262 | } | |
263 | ||
264 | Both are valid, and we use both. However, the more "stable" the | |
265 | stable side becomes, the more we tend to prefer the former | |
266 | (comparison with a constant, "i > 0", is an extreme example). | |
267 | Just do not mix styles in the same part of the code and mimic | |
268 | existing styles in the neighbourhood. | |
269 | ||
f26443da JH |
270 | - There are two schools of thought when it comes to splitting a long |
271 | logical line into multiple lines. Some people push the second and | |
272 | subsequent lines far enough to the right with tabs and align them: | |
273 | ||
274 | if (the_beginning_of_a_very_long_expression_that_has_to || | |
275 | span_more_than_a_single_line_of || | |
276 | the_source_text) { | |
277 | ... | |
278 | ||
279 | while other people prefer to align the second and the subsequent | |
280 | lines with the column immediately inside the opening parenthesis, | |
281 | with tabs and spaces, following our "tabstop is always a multiple | |
282 | of 8" convention: | |
283 | ||
284 | if (the_beginning_of_a_very_long_expression_that_has_to || | |
285 | span_more_than_a_single_line_of || | |
286 | the_source_text) { | |
287 | ... | |
288 | ||
289 | Both are valid, and we use both. Again, just do not mix styles in | |
290 | the same part of the code and mimic existing styles in the | |
291 | neighbourhood. | |
292 | ||
293 | - When splitting a long logical line, some people change line before | |
294 | a binary operator, so that the result looks like a parse tree when | |
295 | you turn your head 90-degrees counterclockwise: | |
296 | ||
297 | if (the_beginning_of_a_very_long_expression_that_has_to | |
298 | || span_more_than_a_single_line_of_the_source_text) { | |
299 | ||
300 | while other people prefer to leave the operator at the end of the | |
301 | line: | |
302 | ||
303 | if (the_beginning_of_a_very_long_expression_that_has_to || | |
304 | span_more_than_a_single_line_of_the_source_text) { | |
305 | ||
306 | Both are valid, but we tend to use the latter more, unless the | |
307 | expression gets fairly complex, in which case the former tends to | |
308 | be easier to read. Again, just do not mix styles in the same part | |
309 | of the code and mimic existing styles in the neighbourhood. | |
310 | ||
311 | - When splitting a long logical line, with everything else being | |
312 | equal, it is preferable to split after the operator at higher | |
313 | level in the parse tree. That is, this is more preferable: | |
314 | ||
315 | if (a_very_long_variable * that_is_used_in + | |
316 | a_very_long_expression) { | |
317 | ... | |
318 | ||
319 | than | |
320 | ||
321 | if (a_very_long_variable * | |
322 | that_is_used_in + a_very_long_expression) { | |
323 | ... | |
324 | ||
6d0618a8 JS |
325 | - Some clever tricks, like using the !! operator with arithmetic |
326 | constructs, can be extremely confusing to others. Avoid them, | |
327 | unless there is a compelling reason to use them. | |
328 | ||
329 | - Use the API. No, really. We have a strbuf (variable length | |
330 | string), several arrays with the ALLOC_GROW() macro, a | |
c455c87c | 331 | string_list for sorted string lists, a hash map (mapping struct |
6d0618a8 JS |
332 | objects) named "struct decorate", amongst other things. |
333 | ||
334 | - When you come up with an API, document it. | |
335 | ||
412cb2ec JH |
336 | - The first #include in C files, except in platform specific compat/ |
337 | implementations, must be either "git-compat-util.h", "cache.h" or | |
338 | "builtin.h". You do not have to include more than one of these. | |
339 | ||
340 | - A C file must directly include the header files that declare the | |
341 | functions and the types it uses, except for the functions and types | |
342 | that are made available to it by including one of the header files | |
343 | it must include by the previous rule. | |
6d0618a8 JS |
344 | |
345 | - If you are planning a new command, consider writing it in shell | |
346 | or perl first, so that changes in semantics can be easily | |
2de9b711 | 347 | changed and discussed. Many Git commands started out like |
6d0618a8 JS |
348 | that, and a few are still scripts. |
349 | ||
2de9b711 | 350 | - Avoid introducing a new dependency into Git. This means you |
6d0618a8 | 351 | usually should stay away from scripting languages not already |
2de9b711 | 352 | used in the Git core command set (unless your command is clearly |
6d0618a8 | 353 | separate from it, such as an importer to convert random-scm-X |
2de9b711 | 354 | repositories to Git). |
57199892 KB |
355 | |
356 | - When we pass <string, length> pair to functions, we should try to | |
357 | pass them in that order. | |
c455bd89 | 358 | |
5e9637c6 ÆAB |
359 | - Use Git's gettext wrappers to make the user interface |
360 | translatable. See "Marking strings for translation" in po/README. | |
361 | ||
c5e366b1 TZ |
362 | For Perl programs: |
363 | ||
364 | - Most of the C guidelines above apply. | |
365 | ||
366 | - We try to support Perl 5.8 and later ("use Perl 5.008"). | |
367 | ||
368 | - use strict and use warnings are strongly preferred. | |
369 | ||
370 | - Don't overuse statement modifiers unless using them makes the | |
371 | result easier to follow. | |
372 | ||
373 | ... do something ... | |
374 | do_this() unless (condition); | |
375 | ... do something else ... | |
376 | ||
377 | is more readable than: | |
378 | ||
379 | ... do something ... | |
380 | unless (condition) { | |
381 | do_this(); | |
382 | } | |
383 | ... do something else ... | |
384 | ||
385 | *only* when the condition is so rare that do_this() will be almost | |
386 | always called. | |
387 | ||
388 | - We try to avoid assignments inside "if ()" conditions. | |
389 | ||
390 | - Learn and use Git.pm if you need that functionality. | |
391 | ||
392 | - For Emacs, it's useful to put the following in | |
393 | GIT_CHECKOUT/.dir-locals.el, assuming you use cperl-mode: | |
394 | ||
395 | ;; note the first part is useful for C editing, too | |
396 | ((nil . ((indent-tabs-mode . t) | |
397 | (tab-width . 8) | |
398 | (fill-column . 80))) | |
399 | (cperl-mode . ((cperl-indent-level . 8) | |
400 | (cperl-extra-newline-before-brace . nil) | |
401 | (cperl-merge-trailing-else . t)))) | |
402 | ||
9ef43dd7 JK |
403 | For Python scripts: |
404 | ||
405 | - We follow PEP-8 (http://www.python.org/dev/peps/pep-0008/). | |
406 | ||
407 | - As a minimum, we aim to be compatible with Python 2.6 and 2.7. | |
408 | ||
409 | - Where required libraries do not restrict us to Python 2, we try to | |
410 | also be compatible with Python 3.1 and later. | |
411 | ||
412 | - When you must differentiate between Unicode literals and byte string | |
413 | literals, it is OK to use the 'b' prefix. Even though the Python | |
414 | documentation for version 2.6 does not mention this prefix, it has | |
415 | been supported since version 2.6.0. | |
416 | ||
0ae0e882 PO |
417 | Error Messages |
418 | ||
419 | - Do not end error messages with a full stop. | |
420 | ||
421 | - Do not capitalize ("unable to open %s", not "Unable to open %s") | |
422 | ||
423 | - Say what the error is first ("cannot open %s", not "%s: cannot open") | |
424 | ||
425 | ||
35840a3e JH |
426 | Externally Visible Names |
427 | ||
428 | - For configuration variable names, follow the existing convention: | |
429 | ||
430 | . The section name indicates the affected subsystem. | |
431 | ||
432 | . The subsection name, if any, indicates which of an unbounded set | |
433 | of things to set the value for. | |
434 | ||
435 | . The variable name describes the effect of tweaking this knob. | |
436 | ||
437 | The section and variable names that consist of multiple words are | |
438 | formed by concatenating the words without punctuations (e.g. `-`), | |
439 | and are broken using bumpyCaps in documentation as a hint to the | |
440 | reader. | |
441 | ||
442 | When choosing the variable namespace, do not use variable name for | |
443 | specifying possibly unbounded set of things, most notably anything | |
444 | an end user can freely come up with (e.g. branch names). Instead, | |
445 | use subsection names or variable values, like the existing variable | |
446 | branch.<name>.description does. | |
447 | ||
448 | ||
c455bd89 ŠN |
449 | Writing Documentation: |
450 | ||
48bc1755 DW |
451 | Most (if not all) of the documentation pages are written in the |
452 | AsciiDoc format in *.txt files (e.g. Documentation/git.txt), and | |
453 | processed into HTML and manpages (e.g. git.html and git.1 in the | |
454 | same directory). | |
bb9f2aec | 455 | |
42e0fae9 MB |
456 | The documentation liberally mixes US and UK English (en_US/UK) |
457 | norms for spelling and grammar, which is somewhat unfortunate. | |
458 | In an ideal world, it would have been better if it consistently | |
459 | used only one and not the other, and we would have picked en_US | |
460 | (if you wish to correct the English of some of the existing | |
461 | documentation, please see the documentation-related advice in the | |
462 | Documentation/SubmittingPatches file). | |
463 | ||
c455bd89 ŠN |
464 | Every user-visible change should be reflected in the documentation. |
465 | The same general rule as for code applies -- imitate the existing | |
ca03c368 JSJ |
466 | conventions. |
467 | ||
468 | A few commented examples follow to provide reference when writing or | |
469 | modifying command usage strings and synopsis sections in the manual | |
470 | pages: | |
c455bd89 | 471 | |
b1afe49d | 472 | Placeholders are spelled in lowercase and enclosed in angle brackets: |
c455bd89 ŠN |
473 | <file> |
474 | --sort=<key> | |
475 | --abbrev[=<n>] | |
476 | ||
9c9b4f2f AH |
477 | If a placeholder has multiple words, they are separated by dashes: |
478 | <new-branch-name> | |
479 | --template=<template-directory> | |
480 | ||
469bfc96 | 481 | Possibility of multiple occurrences is indicated by three dots: |
c455bd89 ŠN |
482 | <file>... |
483 | (One or more of <file>.) | |
484 | ||
485 | Optional parts are enclosed in square brackets: | |
486 | [<extra>] | |
487 | (Zero or one <extra>.) | |
488 | ||
489 | --exec-path[=<path>] | |
490 | (Option with an optional argument. Note that the "=" is inside the | |
491 | brackets.) | |
492 | ||
493 | [<patch>...] | |
494 | (Zero or more of <patch>. Note that the dots are inside, not | |
495 | outside the brackets.) | |
496 | ||
9c9b4f2f | 497 | Multiple alternatives are indicated with vertical bars: |
c455bd89 ŠN |
498 | [-q | --quiet] |
499 | [--utf8 | --no-utf8] | |
500 | ||
501 | Parentheses are used for grouping: | |
9c9b4f2f | 502 | [(<rev> | <range>)...] |
c455bd89 ŠN |
503 | (Any number of either <rev> or <range>. Parens are needed to make |
504 | it clear that "..." pertains to both <rev> and <range>.) | |
505 | ||
506 | [(-p <parent>)...] | |
507 | (Any number of option -p, each with one <parent> argument.) | |
508 | ||
509 | git remote set-head <name> (-a | -d | <branch>) | |
510 | (One and only one of "-a", "-d" or "<branch>" _must_ (no square | |
511 | brackets) be provided.) | |
512 | ||
513 | And a somewhat more contrived example: | |
514 | --diff-filter=[(A|C|D|M|R|T|U|X|B)...[*]] | |
515 | Here "=" is outside the brackets, because "--diff-filter=" is a | |
516 | valid usage. "*" has its own pair of brackets, because it can | |
517 | (optionally) be specified only when one or more of the letters is | |
518 | also provided. | |
48a8c26c TA |
519 | |
520 | A note on notation: | |
521 | Use 'git' (all lowercase) when talking about commands i.e. something | |
522 | the user would type into a shell and use 'Git' (uppercase first letter) | |
523 | when talking about the version control system and its properties. | |
ca03c368 JSJ |
524 | |
525 | A few commented examples follow to provide reference when writing or | |
526 | modifying paragraphs or option/command explanations that contain options | |
527 | or commands: | |
528 | ||
41f5b21f TR |
529 | Literal examples (e.g. use of command-line options, command names, |
530 | configuration and environment variables) must be typeset in monospace (i.e. | |
531 | wrapped with backticks): | |
ca03c368 JSJ |
532 | `--pretty=oneline` |
533 | `git rev-list` | |
da0005b8 | 534 | `remote.pushDefault` |
41f5b21f TR |
535 | `GIT_DIR` |
536 | ||
537 | An environment variable must be prefixed with "$" only when referring to its | |
538 | value and not when referring to the variable itself, in this case there is | |
539 | nothing to add except the backticks: | |
540 | `GIT_DIR` is specified | |
541 | `$GIT_DIR/hooks/pre-receive` | |
ca03c368 JSJ |
542 | |
543 | Word phrases enclosed in `backtick characters` are rendered literally | |
544 | and will not be further expanded. The use of `backticks` to achieve the | |
545 | previous rule means that literal examples should not use AsciiDoc | |
546 | escapes. | |
547 | Correct: | |
548 | `--pretty=oneline` | |
549 | Incorrect: | |
550 | `\--pretty=oneline` | |
551 | ||
552 | If some place in the documentation needs to typeset a command usage | |
553 | example with inline substitutions, it is fine to use +monospaced and | |
554 | inline substituted text+ instead of `monospaced literal text`, and with | |
555 | the former, the part that should not get substituted must be | |
556 | quoted/escaped. |