checkpatch: prefer fallthrough; over fallthrough comments

commit 294f69e6 ("compiler_attributes.h: Add 'fallthrough' pseudo
keyword for switch/case use") added the pseudo keyword so add a test for
it to checkpatch.

Warn on a patch or use --strict for files.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/8b6c1b9031ab9f3cdebada06b8d46467f1492d68.camel@perches.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2294,6 +2294,19 @@ sub pos_last_openparen {
 	return length(expand_tabs(substr($line, 0, $last_openparen))) + 1;
 }
 
+sub get_raw_comment {
+	my ($line, $rawline) = @_;
+	my $comment = '';
+
+	for my $i (0 .. (length($line) - 1)) {
+		if (substr($line, $i, 1) eq "$;") {
+			$comment .= substr($rawline, $i, 1);
+		}
+	}
+
+	return $comment;
+}
+
 sub process {
 	my $filename = shift;
 
@@ -2455,6 +2468,7 @@ sub process {
 		$sline =~ s/$;/ /g;	#with comments as spaces
 
 		my $rawline = $rawlines[$linenr - 1];
+		my $raw_comment = get_raw_comment($line, $rawline);
 
 # check if it's a mode change, rename or start of a patch
 		if (!$in_commit_log &&
@@ -6408,6 +6422,28 @@ sub process {
 			}
 		}
 
+# check for /* fallthrough */ like comment, prefer fallthrough;
+		my @fallthroughs = (
+			'fallthrough',
+			'@fallthrough@',
+			'lint -fallthrough[ \t]*',
+			'intentional(?:ly)?[ \t]*fall(?:(?:s | |-)[Tt]|t)hr(?:ough|u|ew)',
+			'(?:else,?\s*)?FALL(?:S | |-)?THR(?:OUGH|U|EW)[ \t.!]*(?:-[^\n\r]*)?',
+			'Fall(?:(?:s | |-)[Tt]|t)hr(?:ough|u|ew)[ \t.!]*(?:-[^\n\r]*)?',
+			'fall(?:s | |-)?thr(?:ough|u|ew)[ \t.!]*(?:-[^\n\r]*)?',
+		    );
+		if ($raw_comment ne '') {
+			foreach my $ft (@fallthroughs) {
+				if ($raw_comment =~ /$ft/) {
+					my $msg_level = \&WARN;
+					$msg_level = \&CHK if ($file);
+					&{$msg_level}("PREFER_FALLTHROUGH",
+						      "Prefer 'fallthrough;' over fallthrough comment\n" . $herecurr);
+					last;
+				}
+			}
+		}
+
 # check for switch/default statements without a break;
 		if ($perl_version_ok &&
 		    defined $stat &&