[Linux-kernel-mentees] [PATCH RFC] checkpatch: extend same_email_address check to load mailmap entries

[Dwaipayan Ray]

Checkpatch throws a NO_AUTHOR_SIGN_OFF warning whenever either the
name or email address of author doesn't match any signed-off-by
entry. But it has no mechanism to check whether different email
addresses belong to the same author.

As a result, there have been multiple commits where the author has
signed off with a different email address which caused checkpatch
to product that warning.

An example is commit dc5bdb68b5b3 ("drm/fb-helper: Fix vt restore"),
where the author uses two different mail addresses, and checkpatch
generates a NO_AUTHOR_SIGN_OFF warning.

This was fixed by adding support for loading .mailmap entries.
If a mismatch in name or email address then occurs, the
entries in mailmap can be looked up to deterime the actual author
name and email address.

Signed-off-by: Dwaipayan Ray <dwaipayanray1 at gmail.com>
---
 scripts/checkpatch.pl | 113 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 111 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 9e65d21456f1..bfa06c9b9625 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1128,6 +1128,78 @@ sub top_of_kernel_tree {
 	return 1;
 }
 
+my $mailmap;
+
+sub read_mailmap {
+    $mailmap = {
+	names => {},
+	addresses => {}
+    };
+
+    return if (!defined($root) || !(-f "${root}/.mailmap"));
+
+    open(my $mailmap_file, '<', "${root}/.mailmap")
+	or warn "$P: Can't open .mailmap: $!\n";
+
+    while (<$mailmap_file>) {
+	s/#.*$//; #strip comments
+	s/^\s+|\s+$//g; #trim
+
+	next if (/^\s*$/); #skip empty lines
+	#entries have one of the following formats:
+	# name1 <mail1>
+	# <mail1> <mail2>
+	# name1 <mail1> <mail2>
+	# name1 <mail1> name2 <mail2>
+	# (see man git-shortlog)
+
+	if (/^([^<]+)<([^>]+)>$/) {
+	    my $real_name = $1;
+	    my $address = $2;
+
+	    $real_name =~ s/\s+$//;
+	    ($real_name, $address) = parse_email("$real_name <$address>");
+	    $mailmap->{names}->{$address} = $real_name;
+
+	} elsif (/^<([^>]+)>\s*<([^>]+)>$/) {
+	    my $real_address = $1;
+	    my $wrong_address = $2;
+
+	    $mailmap->{addresses}->{$wrong_address} = $real_address;
+
+	} elsif (/^(.+)<([^>]+)>\s*<([^>]+)>$/) {
+	    my $real_name = $1;
+	    my $real_address = $2;
+	    my $wrong_address = $3;
+
+	    $real_name =~ s/\s+$//;
+	    ($real_name, $real_address) =
+		parse_email("$real_name <$real_address>");
+	    $mailmap->{names}->{$wrong_address} = $real_name;
+	    $mailmap->{addresses}->{$wrong_address} = $real_address;
+
+	} elsif (/^(.+)<([^>]+)>\s*(.+)\s*<([^>]+)>$/) {
+	    my $real_name = $1;
+	    my $real_address = $2;
+	    my $wrong_name = $3;
+	    my $wrong_address = $4;
+
+	    $real_name =~ s/\s+$//;
+	    ($real_name, $real_address) =
+		parse_email("$real_name <$real_address>");
+
+	    $wrong_name =~ s/\s+$//;
+	    ($wrong_name, $wrong_address) =
+		parse_email("$wrong_name <$wrong_address>");
+
+	    my $wrong_email = format_email($wrong_name, $wrong_address);
+	    $mailmap->{names}->{$wrong_email} = $real_name;
+	    $mailmap->{addresses}->{$wrong_email} = $real_address;
+	}
+    }
+    close($mailmap_file);
+}
+
 sub parse_email {
 	my ($formatted_email) = @_;
 
@@ -1210,14 +1282,50 @@ sub reformat_email {
 	return format_email($email_name, $email_address);
 }
 
+sub mailmap_email {
+    my ($name, $address) = @_;
+
+    my $email = format_email($name, $address);
+    my $real_name = $name;
+    my $real_address = $address;
+
+    if (exists $mailmap->{names}->{$email} ||
+	exists $mailmap->{addresses}->{$email}) {
+	if (exists $mailmap->{names}->{$email}) {
+	    $real_name = $mailmap->{names}->{$email};
+	}
+	if (exists $mailmap->{addresses}->{$email}) {
+	    $real_address = $mailmap->{addresses}->{$email};
+	}
+    } else {
+	if (exists $mailmap->{names}->{$address}) {
+	    $real_name = $mailmap->{names}->{$address};
+	}
+	if (exists $mailmap->{addresses}->{$address}) {
+	    $real_address = $mailmap->{addresses}->{$address};
+	}
+    }
+    return ($real_name, $real_address);
+}
+
 sub same_email_addresses {
 	my ($email1, $email2) = @_;
 
 	my ($email1_name, $name1_comment, $email1_address, $comment1) = parse_email($email1);
 	my ($email2_name, $name2_comment, $email2_address, $comment2) = parse_email($email2);
 
-	return $email1_name eq $email2_name &&
-	       $email1_address eq $email2_address;
+	my $name_match = $email1_name eq $email2_name;
+	my $address_match = $email1_address eq $email2_address;
+
+	if(!$name_match || !$address_match) {
+		my ($real_name1, $real_address1) = mailmap_email($email1_name, $email1_address);
+		my ($real_name2, $real_address2) = mailmap_email($email2_name, $email2_address);
+
+		$name_match |= ($real_name1 eq $real_name2);
+		$address_match |= ($real_address1 eq $real_address2);
+	}
+
+	return $name_match && $address_match;
 }
 
 sub which {
@@ -2400,6 +2508,7 @@ sub process {
 
 	my $checklicenseline = 1;
 
+	read_mailmap();
 	sanitise_line_reset();
 	my $line;
 	foreach my $rawline (@rawlines) {
-- 
2.27.0