git-send-email: introduce quote_subject()

The quote_rfc2047() always adds RFC2047 quoting. To avoid
quoting ASCII subjects, before calling quote_rfc2047()
subject must be tested for non-ASCII characters. This patch
introduces a new quote_subject() function, which performs
the test and calls quote_rfc2047 only if necessary.

Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: Jeff King <peff@peff.net>

git-send-email.perl

@@ -657,9 +657,7 @@ sub get_patch_subject {
 			$initial_subject = $1;
 			my $subject = $initial_subject;
 			$_ = "Subject: " .
-				($subject =~ /[^[:ascii:]]/ ?
-				 quote_rfc2047($subject, $compose_encoding) :
-				 $subject) .
+				quote_subject($subject, $compose_encoding) .
 				"\n";
 		} elsif (/^In-Reply-To:\s*(.+)\s*$/i) {
 			$initial_reply_to = $1;
@@ -907,6 +905,22 @@ sub is_rfc2047_quoted {
 	$s =~ m/^(?:"[[:ascii:]]*"|=\?$token\?$token\?$encoded_text\?=)$/o;
 }
 
+sub subject_needs_rfc2047_quoting {
+	my $s = shift;
+
+	return ($s =~ /[^[:ascii:]]/);
+}
+
+sub quote_subject {
+	local $subject = shift;
+	my $encoding = shift || 'UTF-8';
+
+	if (subject_needs_rfc2047_quoting($subject)) {
+		return quote_rfc2047($subject, $encoding);
+	}
+	return $subject;
+}
+
 # use the simplest quoting being able to handle the recipient
 sub sanitize_address {
 	my ($recipient) = @_;
@@ -1327,9 +1341,8 @@ sub send_message {
 		$body_encoding = $auto_8bit_encoding;
 	}
 
-	if ($broken_encoding{$t} && !is_rfc2047_quoted($subject) &&
-			($subject =~ /[^[:ascii:]]/)) {
-		$subject = quote_rfc2047($subject, $auto_8bit_encoding);
+	if ($broken_encoding{$t} && !is_rfc2047_quoted($subject)) {
+		$subject = quote_subject($subject, $auto_8bit_encoding);
 	}
 
 	if (defined $author and $author ne $sender) {