[PATCH v3] Add Documentation/CodingGuidelines

From

Johannes Schindelin <johannes.schindelin@gmx.de>

Date

Nov 7, 2007, 22:35 UTC

Message-ID

<Pine.LNX.4.64.0711072233010.4362@racer.site>

In-Reply-To

<200711072243.21086.robin.rosenberg.lists@dewire.com>

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	I think I owe this list an apology for starting yet another
	thread which seems to instigate comments by not many
	code contributors.

	My intention was to make things simpler, but it appears
	that the human brain was created such that it needs complexity
	and creates it when it is absent.

	For example, when I wrote "guidelines" I fully expected that
	it was understood that these are no natural laws which you
	cannot break, should the circumstances afford it.

	Given the discussion, I am half convinced that even this
	patch is a bad idea, and am quite willing to just stop sending
	updates to it.

 Documentation/CodingGuidelines |  106 ++++++++++++++++++++++++++++++++++++++++
 1 files changed, 106 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/CodingGuidelines

diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
new file mode 100644
index 0000000..2d8656f
--- /dev/null
+++ b/Documentation/CodingGuidelines
@@ -0,0 +1,106 @@
+As a popular project, we also have some guidelines to keep to the
+code.  For git in general, two rough rules are:
+
+ - Most importantly, we never say "It's in POSIX; we'll happily
+   ignore your needs should your system that does not conform."
+   We live in the real world.
+
+ - However, we often say "Let's stay away from that construct,
+   it's not even in POSIX".
+
+ - In spite of the above two rules, we sometimes say "Although
+   this is not in POSIX, it (is so convenient | makes the code
+   much more readable | has other good characteristics) and
+   practically all the platforms we care about support it, so
+   let's use it".  Again, we live in the real world, and it is
+   sometimes a judgement call, decided based more on real world
+   constraints people face than what the paper standard says.
+
+
+As for more concrete guidelines, just imitate the existing code
+(this is a good guideline, no matter which project you are contributing
+to...).  But if you must have some list of rules, here they are.
+
+For shell scripts specifically (not exhaustive):
+
+ - We prefer $( ... ) for command substitution; unlike ``, it
+   properly nests.  It should have been the way Bourne spelled
+   it from day one, but unfortunately isn't.
+
+ - We use ${parameter-word} and its [-=?+] siblings, and their
+   colon'ed "unset or null" form.
+
+ - We use ${parameter#word} and its [#%] siblings, and their
+   doubled "longest matching" form.
+
+ - We use Arithmetic Expansion $(( ... )).
+
+ - No "Substring Expansion" ${parameter:offset:length}.
+
+ - No shell arrays.
+
+ - No strlen ${#parameter}.
+
+ - No regexp ${parameter/pattern/string}.
+
+ - We do not use Process Substitution <(list) or >(list).
+
+ - We prefer "test" over "[ ... ]".
+
+ - We do not write noiseword "function" in front of shell
+   functions.
+
+For C programs:
+
+ - Use tabs to indent, and interpret tabs as taking up to 8 spaces
+
+ - Try to keep to at most 80 characters per line
+
+ - When declaring pointers, the star sides with the variable name, i.e.
+   "char *string", not "char* string" or "char * string".  This makes
+   it easier to understand "char *string, c;"
+
+ - Do not use curly brackets unnecessarily.  I.e.
+
+	if (bla) {
+		x = 1;
+	}
+
+   is frowned upon.  A gray area is when the statement extends over a
+   few lines, and/or you have a lengthy comment atop of it.  Also,
+   like in the Linux kernel, if there is a long list of "else if"
+   statements, it can make sense to add curly brackets to single
+   line blocks.
+
+ - Try to make your code understandable.  You may put comments in, but
+   comments invariably tend to stale out when the code they were
+   describing changes.  Often splitting a function into two makes the
+   intention of the code much clearer.
+
+   Double negation is often harder to understand than no negation at
+   all.
+
+   Some clever tricks, like using the !! operator with arithmetic
+   constructs, can be extremely confusing to others.  Avoid them,
+   unless there is a compelling reason to use them.
+
+ - Use the API.  No, really.  We have a strbuf (variable length string),
+   several arrays with the ALLOC_GROW() macro, a path_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.
+
+ - #include system headers in git-compat-util.h.  Some headers on some
+   systems show subtle breakages when you change the order, so it is
+   best to keep them in one place.
+
+ - if you are planning a new command, consider writing it in shell or
+   perl first, so that changes in semantics can be easily changed and
+   discussed.  Many git commands started out like that, and a few are
+   still scripts.
+
+ - Avoid introducing a new dependency into git. This means you usually
+   should stay away from scripting languages not already used in the git
+   core command set (unless your command is clearly separate from it,
+   such as an importer to convert random-scm-X repositories to git).

-- 
1.5.3.5.1597.g7191