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1 | Like other projects, we also have some guidelines to keep to the |
2 | code. For git in general, three rough rules are: | |
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 | ||
21 | ||
22 | As for more concrete guidelines, just imitate the existing code | |
23 | (this is a good guideline, no matter which project you are | |
dfb047b9 NS |
24 | contributing to). It is always preferable to match the _local_ |
25 | convention. New code added to git suite is expected to match | |
26 | the overall style of existing code. Modifications to existing | |
27 | code is expected to match the style the surrounding code already | |
28 | uses (even if it doesn't match the overall style of existing code). | |
29 | ||
30 | But if you must have a list of rules, here they are. | |
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31 | |
32 | For shell scripts specifically (not exhaustive): | |
33 | ||
f36a4fa8 GB |
34 | - We use tabs for indentation. |
35 | ||
36 | - Case arms are indented at the same depth as case and esac lines. | |
37 | ||
6d0618a8 JS |
38 | - We prefer $( ... ) for command substitution; unlike ``, it |
39 | properly nests. It should have been the way Bourne spelled | |
40 | it from day one, but unfortunately isn't. | |
41 | ||
bc979945 JH |
42 | - We use POSIX compliant parameter substitutions and avoid bashisms; |
43 | namely: | |
6d0618a8 | 44 | |
bc979945 JH |
45 | - We use ${parameter-word} and its [-=?+] siblings, and their |
46 | colon'ed "unset or null" form. | |
6d0618a8 | 47 | |
bc979945 JH |
48 | - We use ${parameter#word} and its [#%] siblings, and their |
49 | doubled "longest matching" form. | |
6d0618a8 | 50 | |
bc979945 | 51 | - No "Substring Expansion" ${parameter:offset:length}. |
055467dd | 52 | |
bc979945 | 53 | - No shell arrays. |
6d0618a8 | 54 | |
bc979945 | 55 | - No strlen ${#parameter}. |
6d0618a8 | 56 | |
bc979945 | 57 | - No pattern replacement ${parameter/pattern/string}. |
6d0618a8 | 58 | |
bc979945 JH |
59 | - We use Arithmetic Expansion $(( ... )). |
60 | ||
61 | - Inside Arithmetic Expansion, spell shell variables with $ in front | |
62 | of them, as some shells do not grok $((x)) while accepting $(($x)) | |
63 | just fine (e.g. dash older than 0.5.4). | |
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64 | |
65 | - We do not use Process Substitution <(list) or >(list). | |
66 | ||
67 | - We prefer "test" over "[ ... ]". | |
68 | ||
69 | - We do not write the noiseword "function" in front of shell | |
70 | functions. | |
71 | ||
009c98ee JH |
72 | - As to use of grep, stick to a subset of BRE (namely, no \{m,n\}, |
73 | [::], [==], nor [..]) for portability. | |
74 | ||
75 | - We do not use \{m,n\}; | |
76 | ||
77 | - We do not use -E; | |
78 | ||
79 | - We do not use ? nor + (which are \{0,1\} and \{1,\} | |
80 | respectively in BRE) but that goes without saying as these | |
81 | are ERE elements not BRE (note that \? and \+ are not even part | |
82 | of BRE -- making them accessible from BRE is a GNU extension). | |
83 | ||
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84 | For C programs: |
85 | ||
86 | - We use tabs to indent, and interpret tabs as taking up to | |
87 | 8 spaces. | |
88 | ||
89 | - We try to keep to at most 80 characters per line. | |
90 | ||
91 | - When declaring pointers, the star sides with the variable | |
92 | name, i.e. "char *string", not "char* string" or | |
93 | "char * string". This makes it easier to understand code | |
94 | like "char *string, c;". | |
95 | ||
96 | - We avoid using braces unnecessarily. I.e. | |
97 | ||
98 | if (bla) { | |
99 | x = 1; | |
100 | } | |
101 | ||
102 | is frowned upon. A gray area is when the statement extends | |
103 | over a few lines, and/or you have a lengthy comment atop of | |
104 | it. Also, like in the Linux kernel, if there is a long list | |
105 | of "else if" statements, it can make sense to add braces to | |
106 | single line blocks. | |
107 | ||
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108 | - We try to avoid assignments inside if(). |
109 | ||
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110 | - Try to make your code understandable. You may put comments |
111 | in, but comments invariably tend to stale out when the code | |
112 | they were describing changes. Often splitting a function | |
113 | into two makes the intention of the code much clearer. | |
114 | ||
115 | - Double negation is often harder to understand than no negation | |
116 | at all. | |
117 | ||
118 | - Some clever tricks, like using the !! operator with arithmetic | |
119 | constructs, can be extremely confusing to others. Avoid them, | |
120 | unless there is a compelling reason to use them. | |
121 | ||
122 | - Use the API. No, really. We have a strbuf (variable length | |
123 | string), several arrays with the ALLOC_GROW() macro, a | |
c455c87c | 124 | string_list for sorted string lists, a hash map (mapping struct |
6d0618a8 JS |
125 | objects) named "struct decorate", amongst other things. |
126 | ||
127 | - When you come up with an API, document it. | |
128 | ||
129 | - The first #include in C files, except in platform specific | |
130 | compat/ implementations, should be git-compat-util.h or another | |
131 | header file that includes it, such as cache.h or builtin.h. | |
132 | ||
133 | - If you are planning a new command, consider writing it in shell | |
134 | or perl first, so that changes in semantics can be easily | |
135 | changed and discussed. Many git commands started out like | |
136 | that, and a few are still scripts. | |
137 | ||
138 | - Avoid introducing a new dependency into git. This means you | |
139 | usually should stay away from scripting languages not already | |
140 | used in the git core command set (unless your command is clearly | |
141 | separate from it, such as an importer to convert random-scm-X | |
142 | repositories to git). | |
57199892 KB |
143 | |
144 | - When we pass <string, length> pair to functions, we should try to | |
145 | pass them in that order. | |
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146 | |
147 | Writing Documentation: | |
148 | ||
149 | Every user-visible change should be reflected in the documentation. | |
150 | The same general rule as for code applies -- imitate the existing | |
151 | conventions. A few commented examples follow to provide reference | |
152 | when writing or modifying command usage strings and synopsis sections | |
153 | in the manual pages: | |
154 | ||
b1afe49d | 155 | Placeholders are spelled in lowercase and enclosed in angle brackets: |
c455bd89 ŠN |
156 | <file> |
157 | --sort=<key> | |
158 | --abbrev[=<n>] | |
159 | ||
469bfc96 | 160 | Possibility of multiple occurrences is indicated by three dots: |
c455bd89 ŠN |
161 | <file>... |
162 | (One or more of <file>.) | |
163 | ||
164 | Optional parts are enclosed in square brackets: | |
165 | [<extra>] | |
166 | (Zero or one <extra>.) | |
167 | ||
168 | --exec-path[=<path>] | |
169 | (Option with an optional argument. Note that the "=" is inside the | |
170 | brackets.) | |
171 | ||
172 | [<patch>...] | |
173 | (Zero or more of <patch>. Note that the dots are inside, not | |
174 | outside the brackets.) | |
175 | ||
176 | Multiple alternatives are indicated with vertical bar: | |
177 | [-q | --quiet] | |
178 | [--utf8 | --no-utf8] | |
179 | ||
180 | Parentheses are used for grouping: | |
181 | [(<rev>|<range>)...] | |
182 | (Any number of either <rev> or <range>. Parens are needed to make | |
183 | it clear that "..." pertains to both <rev> and <range>.) | |
184 | ||
185 | [(-p <parent>)...] | |
186 | (Any number of option -p, each with one <parent> argument.) | |
187 | ||
188 | git remote set-head <name> (-a | -d | <branch>) | |
189 | (One and only one of "-a", "-d" or "<branch>" _must_ (no square | |
190 | brackets) be provided.) | |
191 | ||
192 | And a somewhat more contrived example: | |
193 | --diff-filter=[(A|C|D|M|R|T|U|X|B)...[*]] | |
194 | Here "=" is outside the brackets, because "--diff-filter=" is a | |
195 | valid usage. "*" has its own pair of brackets, because it can | |
196 | (optionally) be specified only when one or more of the letters is | |
197 | also provided. |