[PATCH] checkpatch.pl: Add SPDX license tag check

[Rob Herring <robh@kernel.org>]

Add SPDX license tag check based on the rules defined in
Documentation/process/license-rules.rst. To summarize, SPDX license tags
should be on the 1st line (or 2nd line in scripts) using the appropriate
comment style for the file type.

Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Rob Herring <robh@kernel.org>
---
I didn't get around to resending once license-rules.rst landed in -next. 
Hopefully, this can be picked up for 4.16 so folks can start using it. 
SPDX tags have already become a frequent review comment.

Rob

 scripts/checkpatch.pl | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index ba03f17ff662..cf1b5a90b20a 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2225,6 +2225,8 @@ sub process {
 
 	my $camelcase_file_seeded = 0;
 
+	my $checklicenseline = 1;
+
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
@@ -2416,6 +2418,7 @@ sub process {
 			} else {
 				$check = $check_orig;
 			}
+			$checklicenseline = 1;
 			next;
 		}
 
@@ -2866,6 +2869,30 @@ sub process {
 			}
 		}
 
+# check for using SPDX license tag at beginning of files
+		if ($realline == $checklicenseline) {
+			if ($realfile =~ /\.(?:sh|pl|py)/ && $rawline =~ /\[ \+]\s*\!\#/) {
+				$checklicenseline = 2;
+			} elsif ($rawline =~ /^\+/) {
+				my $comment = "";
+				if ($realfile =~ /\.(h|s|S)$/) {
+					$comment = '/*';
+				} elsif ($realfile =~ /\.(c|dts|dtsi)$/) {
+					$comment = '//';
+				} elsif ($realfile =~ /\.(sh|pl|py)$/) {
+					$comment = '#';
+				} elsif ($realfile =~ /\.rst$/) {
+					$comment = '..';
+				}
+
+				if ($comment !~ /^$/ &&
+				    $rawline !~ /^\+\Q$comment\E SPDX-License-Identifier: /) {
+					WARN("SPDX_LICENSE_TAG",
+					     "Missing or malformed SPDX-License-Identifier tag in 1st (or 2nd for scripts) line\n" . $herecurr);
+				}
+			}
+		}
+
 # check we are in a valid source file if not then ignore this hunk
 		next if ($realfile !~ /\.(h|c|s|S|sh|dtsi|dts)$/);
 
-- 
2.14.1