scripts: mandate that new files have SPDX-License-Identifier

Going forward we want all newly created source files to have an
SPDX-License-Identifier tag present.

Initially mandate this for C, Python, Perl, Shell source files,
as well as JSON (QAPI) and Makefiles, while encouraging users
to consider it for other file types.

Reviewed-by: Brian Cain <bcain@quicinc.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

scripts/checkpatch.pl

@@ -1378,6 +1378,8 @@ sub process {
 	my $in_imported_file = 0;
 	my $in_no_imported_file = 0;
 	my $non_utf8_charset = 0;
+	my $expect_spdx = 0;
+	my $expect_spdx_file;
 
 	our @report = ();
 	our $cnt_lines = 0;
@@ -1615,6 +1617,34 @@ sub process {
 			WARN("added, moved or deleted file(s), does MAINTAINERS need updating?\n" . $herecurr);
 		}
 
+# All new files should have a SPDX-License-Identifier tag
+		if ($line =~ /^new file mode\s*\d+\s*$/) {
+		    if ($expect_spdx) {
+			if ($expect_spdx_file =~
+			    /\.(c|h|py|pl|sh|json|inc|Makefile)$/) {
+			    # source code files MUST have SPDX license declared
+			    ERROR("New file '$expect_spdx_file' requires " .
+				  "'SPDX-License-Identifer'");
+			} else {
+			    # Other files MAY have SPDX license if appropriate
+			    WARNING("Does new file '$expect_spdx_file' need " .
+				    "'SPDX-License-Identifer'?");
+			}
+		    }
+		    $expect_spdx = 1;
+		    $expect_spdx_file = undef;
+		} elsif ($expect_spdx) {
+		    $expect_spdx_file = $realfile unless
+			defined $expect_spdx_file;
+
+		    # SPDX tags may occurr in comments which were
+		    # stripped from '$line', so use '$rawline'
+		    if ($rawline =~ /SPDX-License-Identifier/) {
+			$expect_spdx = 0;
+			$expect_spdx_file = undef;
+		    }
+		}
+
 # Check for wrappage within a valid hunk of the file
 		if ($realcnt != 0 && $line !~ m{^(?:\+|-| |\\ No newline|$)}) {
 			ERROR("patch seems to be corrupt (line wrapped?)\n" .