Re: [PATCH] checkpatch: make the line length warnings match the coding style document

[Joe Perches <joe@perches.com>]

On Thu, 2020-12-10 at 20:09 +0000, Matthew Wilcox wrote:
> On Thu, Dec 10, 2020 at 12:05:04PM -0800, Joe Perches wrote:
> > Also, given the ever increasing average identifier length, strict
> > adherence to 80 columns is sometimes just not possible without silly
> > visual gymnastics.  The kernel now has quite a lot of 30+ character
> > length function names, constants, and structs.
> 
> maybe checkpatch should warn for identifiers that are 30+ characters
> long?  address the problem at its source ..

Hard to know when to warn as patches could just add uses of already
existing names and emitting warnings for those would just be annoying.

Maybe something that tests long identifier additions of
defines/functions/macros/structs but not their uses and maybe only
then in patches and not files.

Perhaps:
---
 scripts/checkpatch.pl | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7b086d1cd6c2..8579be987fc0 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -54,6 +54,7 @@ my @ignore = ();
 my $help = 0;
 my $configuration_file = ".checkpatch.conf";
 my $max_line_length = 100;
+my $max_identifier_length = 30;
 my $ignore_perl_version = 0;
 my $minimum_perl_version = 5.10.0;
 my $min_conf_desc_length = 4;
@@ -103,6 +104,8 @@ Options:
   --max-line-length=n        set the maximum line length, (default $max_line_length)
                              if exceeded, warn on patches
                              requires --strict for use with --file
+  --max-identifier-length=n  set the maximum identifier length, (default $max_identifier_length)
+                             only used with patches, not output with --file
   --min-conf-desc-length=n   set the min description length, if shorter, warn
   --tab-size=n               set the number of spaces for tab (default $tabsize)
   --root=PATH                PATH to the kernel tree root
@@ -223,6 +226,7 @@ GetOptions(
 	'show-types!'	=> \$show_types,
 	'list-types!'	=> \$list_types,
 	'max-line-length=i' => \$max_line_length,
+	'max-identifier-length=i' => \$max_identifier_length,
 	'min-conf-desc-length=i' => \$min_conf_desc_length,
 	'tab-size=i'	=> \$tabsize,
 	'root=s'	=> \$root,
@@ -2489,6 +2493,7 @@ sub process {
 	my $suppress_statement = 0;
 
 	my %signatures = ();
+	my %long_identifiers = ();
 
 	# Pre-scan the patch sanitizing the lines.
 	# Pre-scan the patch looking for any __setup documentation.
@@ -3840,6 +3845,33 @@ sub process {
 # check we are in a valid C source file if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c)$/);
 
+# check for long identifiers in defines/macros/functions/structs/types/labels
+		if (!$file) {
+			while ($sline =~ /^\+.*\b(\w{$max_identifier_length,})\b/g) {
+				my $id = $1;
+				next if (exists($long_identifiers{$id}));
+				my $use = "";
+				if ($sline =~ /^\+\s*\#\s*define\s+$id(?!\()/) {
+					$use = "define";
+				} elsif ($sline =~ /^\+\s*\#\s*define\s+$id\(/) {
+					$use = "function-like macro";
+				} elsif ($sline =~ /^\+\s*(?!define)$Declare?$id\s*\(/) {
+					$use = "function";
+				} elsif ($sline =~ /^\+\s*(struct|union|enum)\s+$id\b/) {
+					$use = "$1";
+				} elsif ($sline =~ /^\+\s*$Declare$id\b/) {
+					$use = "declaration";
+				} elsif ($sline =~ /^\+\s*$id\s*:\s*$/) {
+					$use = "label";
+				}
+				if ($use ne "") {
+					$long_identifiers{$id} = $id;
+					WARN("LONG_IDENTIFIER",
+					     "$use '$id' is " . length($id) . " characters - avoid using identifiers with $max_identifier_length+ characters\n" . $herecurr);
+				}
+			}
+		}
+
 # check for unusual line ending [ or (
 		if ($line =~ /^\+.*([\[\(])\s*$/) {
 			CHK("OPEN_ENDED_LINE",