135 lines
4.8 KiB
Plaintext
135 lines
4.8 KiB
Plaintext
Like other projects, we also have some guidelines to keep to the
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code. For git in general, three rough rules are:
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- Most importantly, we never say "It's in POSIX; we'll happily
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ignore your needs should your system not conform to it."
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We live in the real world.
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- However, we often say "Let's stay away from that construct,
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it's not even in POSIX".
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- In spite of the above two rules, we sometimes say "Although
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this is not in POSIX, it (is so convenient | makes the code
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much more readable | has other good characteristics) and
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practically all the platforms we care about support it, so
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let's use it".
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Again, we live in the real world, and it is sometimes a
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judgement call, the decision based more on real world
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constraints people face than what the paper standard says.
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As for more concrete guidelines, just imitate the existing code
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(this is a good guideline, no matter which project you are
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contributing to). It is always preferable to match the _local_
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convention. New code added to git suite is expected to match
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the overall style of existing code. Modifications to existing
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code is expected to match the style the surrounding code already
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uses (even if it doesn't match the overall style of existing code).
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But if you must have a list of rules, here they are.
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For shell scripts specifically (not exhaustive):
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- We prefer $( ... ) for command substitution; unlike ``, it
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properly nests. It should have been the way Bourne spelled
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it from day one, but unfortunately isn't.
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- We use ${parameter-word} and its [-=?+] siblings, and their
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colon'ed "unset or null" form.
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- We use ${parameter#word} and its [#%] siblings, and their
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doubled "longest matching" form.
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- We use Arithmetic Expansion $(( ... )).
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- No "Substring Expansion" ${parameter:offset:length}.
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- No shell arrays.
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- No strlen ${#parameter}.
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- No regexp ${parameter/pattern/string}.
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- We do not use Process Substitution <(list) or >(list).
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- We prefer "test" over "[ ... ]".
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- We do not write the noiseword "function" in front of shell
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functions.
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- As to use of grep, stick to a subset of BRE (namely, no \{m,n\},
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[::], [==], nor [..]) for portability.
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- We do not use \{m,n\};
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- We do not use -E;
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- We do not use ? nor + (which are \{0,1\} and \{1,\}
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respectively in BRE) but that goes without saying as these
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are ERE elements not BRE (note that \? and \+ are not even part
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of BRE -- making them accessible from BRE is a GNU extension).
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For C programs:
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- We use tabs to indent, and interpret tabs as taking up to
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8 spaces.
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- We try to keep to at most 80 characters per line.
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- When declaring pointers, the star sides with the variable
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name, i.e. "char *string", not "char* string" or
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"char * string". This makes it easier to understand code
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like "char *string, c;".
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- We avoid using braces unnecessarily. I.e.
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if (bla) {
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x = 1;
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}
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is frowned upon. A gray area is when the statement extends
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over a few lines, and/or you have a lengthy comment atop of
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it. Also, like in the Linux kernel, if there is a long list
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of "else if" statements, it can make sense to add braces to
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single line blocks.
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- We try to avoid assignments inside if().
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- Try to make your code understandable. You may put comments
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in, but comments invariably tend to stale out when the code
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they were describing changes. Often splitting a function
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into two makes the intention of the code much clearer.
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- Double negation is often harder to understand than no negation
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at all.
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- Some clever tricks, like using the !! operator with arithmetic
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constructs, can be extremely confusing to others. Avoid them,
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unless there is a compelling reason to use them.
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- Use the API. No, really. We have a strbuf (variable length
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string), several arrays with the ALLOC_GROW() macro, a
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string_list for sorted string lists, a hash map (mapping struct
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objects) named "struct decorate", amongst other things.
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- When you come up with an API, document it.
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- The first #include in C files, except in platform specific
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compat/ implementations, should be git-compat-util.h or another
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header file that includes it, such as cache.h or builtin.h.
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- If you are planning a new command, consider writing it in shell
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or perl first, so that changes in semantics can be easily
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changed and discussed. Many git commands started out like
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that, and a few are still scripts.
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- Avoid introducing a new dependency into git. This means you
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usually should stay away from scripting languages not already
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used in the git core command set (unless your command is clearly
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separate from it, such as an importer to convert random-scm-X
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repositories to git).
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- When we pass <string, length> pair to functions, we should try to
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pass them in that order.
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