[PATCH] scripts/checkpatch.pl: Improve guidance for LONG_LINE

[PATCH] scripts/checkpatch.pl: Improve guidance for LONG_LINE

[Josh Triplett]

Currently, LONG_LINE just informs the user about the line length,
leaving them to shorten the line.  Too many users run checkpatch and
blindly follow its recommendation by splitting long lines, which almost
invariably results in worse code.  On rare occasions, the line-width
limit encourages sensible refactoring of nested code into functions, but
more frequently it just results in painfully over-wrapped code.

Improve the guidance by detecting long lines that start with 4+ tabs and
explicitly suggesting simplification or refactoring in that case.

This does not introduce or remove any warnings; it just changes the text
of a warning that checkpatch would already emit, to emphasize a
preference for simplifying or refactoring complex, deeply nested code,
rather than just wrapping it but leaving it complex.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---

Of the ~267000 80+ character lines in the current kernel source, this
new guidance would trigger on ~67000 of them.

Other things I tested, but did not include in this patch, to minimize
controversy or subjectivity: flagging long lines with 2 or more logical
operations (&& or ||) to suggest wrapping at the operators, and flagging
long lines with 30+ character identifiers to suggest consideration of
whether the identifier could remain self-documenting if shortened.

 scripts/checkpatch.pl | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 010b18e..6e82f19 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2146,8 +2146,16 @@ sub process {
 		    $line =~ /^\+\s*"[^"]*"\s*(?:\s*|,|\)\s*;)\s*$/) &&
 		    $length > $max_line_length)
 		{
-			WARN("LONG_LINE",
-			     "line over $max_line_length characters\n" . $herecurr);
+			if ($line =~ /^\+\t{4,}/) {
+				WARN("LONG_LINE_DEEP_NESTING",
+				     "line over $max_line_length characters with excessive nesting (4+ tabs)\n"
+				     . "Consider simplifying or refactoring to eliminate excessive nesting.\n"
+				     . $herecurr);
+			} else {
+				WARN("LONG_LINE",
+				     "line over $max_line_length characters\n"
+				     . $herecurr);
+			}
 		}
 
 # Check for user-visible strings broken across lines, which breaks the ability
-- 
2.0.0

Re: [PATCH] scripts/checkpatch.pl: Improve guidance for LONG_LINE

[Joe Perches]

On Wed, 2014-06-25 at 23:01 -0700, Josh Triplett wrote:
> Currently, LONG_LINE just informs the user about the line length,
> leaving them to shorten the line.  Too many users run checkpatch and
> blindly follow its recommendation by splitting long lines, which almost
> invariably results in worse code.  On rare occasions, the line-width
> limit encourages sensible refactoring of nested code into functions, but
> more frequently it just results in painfully over-wrapped code.
> 
> Improve the guidance by detecting long lines that start with 4+ tabs and
> explicitly suggesting simplification or refactoring in that case.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -2146,8 +2146,16 @@ sub process {
>  		    $line =~ /^\+\s*"[^"]*"\s*(?:\s*|,|\)\s*;)\s*$/) &&
>  		    $length > $max_line_length)
>  		{
> -			WARN("LONG_LINE",
> -			     "line over $max_line_length characters\n" . $herecurr);
> +			if ($line =~ /^\+\t{4,}/) {
> +				WARN("LONG_LINE_DEEP_NESTING",
> +				     "line over $max_line_length characters with excessive nesting (4+ tabs)\n"
> +				     . "Consider simplifying or refactoring to eliminate excessive nesting.\n"
> +				     . $herecurr);

This is not the test you want.

This is also emitting on lines that are
merely continued like
			pr_warning(format,
				   arg1,
				   arg2,
				   arg3
				   ...
				   argN);

Better would be to test only for the lines
that increase indents (like the DEEP_INDENTATION test)

$line =~ /^\+\t{4,}(?:if|for|while|do|switch)\b/

This is the treewide distribution I get for the lines
that generally produce extra indentation:

 608432 1
 242180 2
  71260 3
  16953 4
   3688 5
    758 6
    187 7
     74 8
     23 9
     17 10
      8 11
      4 12
      1 13