Merge branch 'jc/coding-guidelines'

* jc/coding-guidelines:
  CodingGuidelines: avoid "test <cond> -a/-o <cond>"
  CodingGuidelines: on splitting a long line
  CodingGuidelines: on comparison
  CodingGuidelines: do not call the conditional statement "if()"
  CodingGuidelines: give an example for shell function preamble
  CodingGuidelines: give an example for control statements
  CodingGuidelines: give an example for redirection
  CodingGuidelines: give an example for case/esac statement
  CodingGuidelines: once it is in, it is not worth the code churn

1 files changed, 145 insertions, 5 deletions

diff --git a/Documentation/CodingGuidelines b/Documentation/CodingGuidelines
index f424dbd75c..4d90c77c7b 100644
--- a/Documentation/CodingGuidelines
+++ b/Documentation/CodingGuidelines
@@ -18,6 +18,14 @@ code.  For Git in general, three rough rules are:
    judgement call, the decision based more on real world
    constraints people face than what the paper standard says.
 
+ - Fixing style violations while working on a real change as a
+   preparatory clean-up step is good, but otherwise avoid useless code
+   churn for the sake of conforming to the style.
+
+   "Once it _is_ in the tree, it's not really worth the patch noise to
+   go and fix it up."
+   Cf. http://article.gmane.org/gmane.linux.kernel/943020
+
 Make your code readable and sensible, and don't try to be clever.
 
 As for more concrete guidelines, just imitate the existing code
@@ -34,7 +42,17 @@ For shell scripts specifically (not exhaustive):
 
  - We use tabs for indentation.
 
- - Case arms are indented at the same depth as case and esac lines.
+ - Case arms are indented at the same depth as case and esac lines,
+   like this:
+
+	case "$variable" in
+	pattern1)
+		do this
+		;;
+	pattern2)
+		do that
+		;;
+	esac
 
  - Redirection operators should be written with space before, but no
    space after them.  In other words, write 'echo test >"$file"'
@@ -43,6 +61,14 @@ For shell scripts specifically (not exhaustive):
    redirection target in a variable (as shown above), our code does so
    because some versions of bash issue a warning without the quotes.
 
+	(incorrect)
+	cat hello > world < universe
+	echo hello >$world
+
+	(correct)
+	cat hello >world <universe
+	echo hello >"$world"
+
  - 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.
@@ -81,14 +107,33 @@ For shell scripts specifically (not exhaustive):
    "then" should be on the next line for if statements, and "do"
    should be on the next line for "while" and "for".
 
+	(incorrect)
+	if test -f hello; then
+		do this
+	fi
+
+	(correct)
+	if test -f hello
+	then
+		do this
+	fi
+
  - We prefer "test" over "[ ... ]".
 
  - We do not write the noiseword "function" in front of shell
    functions.
 
- - We prefer a space between the function name and the parentheses. The
-   opening "{" should also be on the same line.
-   E.g.: my_function () {
+ - We prefer a space between the function name and the parentheses,
+   and no space inside the parentheses. The opening "{" should also
+   be on the same line.
+
+	(incorrect)
+	my_function(){
+		...
+
+	(correct)
+	my_function () {
+		...
 
  - As to use of grep, stick to a subset of BRE (namely, no \{m,n\},
    [::], [==], or [..]) for portability.
@@ -106,6 +151,19 @@ For shell scripts specifically (not exhaustive):
    interface translatable. See "Marking strings for translation" in
    po/README.
 
+ - We do not write our "test" command with "-a" and "-o" and use "&&"
+   or "||" to concatenate multiple "test" commands instead, because
+   the use of "-a/-o" is often error-prone.  E.g.
+
+     test -n "$x" -a "$a" = "$b"
+
+   is buggy and breaks when $x is "=", but
+
+     test -n "$x" && test "$a" = "$b"
+
+   does not have such a problem.
+
+
 For C programs:
 
  - We use tabs to indent, and interpret tabs as taking up to
@@ -149,7 +207,7 @@ For C programs:
    of "else if" statements, it can make sense to add braces to
    single line blocks.
 
- - We try to avoid assignments inside if().
+ - We try to avoid assignments in the condition of an "if" statement.
 
  - Try to make your code understandable.  You may put comments
    in, but comments invariably tend to stale out when the code
@@ -177,6 +235,88 @@ For C programs:
  - Double negation is often harder to understand than no negation
    at all.
 
+ - There are two schools of thought when it comes to comparison,
+   especially inside a loop. Some people prefer to have the less stable
+   value on the left hand side and the more stable value on the right hand
+   side, e.g. if you have a loop that counts variable i down to the
+   lower bound,
+
+	while (i > lower_bound) {
+		do something;
+		i--;
+	}
+
+   Other people prefer to have the textual order of values match the
+   actual order of values in their comparison, so that they can
+   mentally draw a number line from left to right and place these
+   values in order, i.e.
+
+	while (lower_bound < i) {
+		do something;
+		i--;
+	}
+
+   Both are valid, and we use both.  However, the more "stable" the
+   stable side becomes, the more we tend to prefer the former
+   (comparison with a constant, "i > 0", is an extreme example).
+   Just do not mix styles in the same part of the code and mimic
+   existing styles in the neighbourhood.
+
+ - There are two schools of thought when it comes to splitting a long
+   logical line into multiple lines.  Some people push the second and
+   subsequent lines far enough to the right with tabs and align them:
+
+        if (the_beginning_of_a_very_long_expression_that_has_to ||
+		span_more_than_a_single_line_of ||
+		the_source_text) {
+                ...
+
+   while other people prefer to align the second and the subsequent
+   lines with the column immediately inside the opening parenthesis,
+   with tabs and spaces, following our "tabstop is always a multiple
+   of 8" convention:
+
+        if (the_beginning_of_a_very_long_expression_that_has_to ||
+	    span_more_than_a_single_line_of ||
+	    the_source_text) {
+                ...
+
+   Both are valid, and we use both.  Again, just do not mix styles in
+   the same part of the code and mimic existing styles in the
+   neighbourhood.
+
+ - When splitting a long logical line, some people change line before
+   a binary operator, so that the result looks like a parse tree when
+   you turn your head 90-degrees counterclockwise:
+
+        if (the_beginning_of_a_very_long_expression_that_has_to
+	    || span_more_than_a_single_line_of_the_source_text) {
+
+   while other people prefer to leave the operator at the end of the
+   line:
+
+        if (the_beginning_of_a_very_long_expression_that_has_to ||
+	    span_more_than_a_single_line_of_the_source_text) {
+
+   Both are valid, but we tend to use the latter more, unless the
+   expression gets fairly complex, in which case the former tends to
+   be easier to read.  Again, just do not mix styles in the same part
+   of the code and mimic existing styles in the neighbourhood.
+
+ - When splitting a long logical line, with everything else being
+   equal, it is preferable to split after the operator at higher
+   level in the parse tree.  That is, this is more preferable:
+
+	if (a_very_long_variable * that_is_used_in +
+	    a_very_long_expression) {
+		...
+
+   than
+
+	if (a_very_long_variable *
+	    that_is_used_in + a_very_long_expression) {
+		...
+
  - 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.