enhanced subject line formatting options for email

conf/defaults.config

@@ -73,7 +73,7 @@ $mail{feedbackRecipients}    = [
 #   %% = literal percent sign
 #
 
-$mail{feedbackSubjectFormat} = "[WWfeedback] course:%c user:%u set:%s prob:%p sec:%x rec:%r";
+$mail{feedbackSubjectFormat} = '[WWfeedback] course:%c user:%u{ set:%s}{ prob:%p}{ sec:%x}{ rec:%r}';
 
 # feedbackVerbosity:
 #  0: send only the feedback comment and context link

lib/WeBWorK/ConfigValues.pm

@@ -829,13 +829,15 @@ sub getConfigValues ($ce) {
 			x('E-Mail'),
 			{
 				var  => 'mail{feedbackSubjectFormat}',
-				doc  => x('Format for the subject line in feedback emails'),
+				doc  => x('Format for the subject of feedback emails'),
 				doc2 => x(
-					'When students click the <em>Email Instructor</em> button to send feedback, WeBWorK fills in the '
-						. 'subject line. Here you can set the subject line. In it, you can have various bits of '
-						. 'information filled in with the following escape sequences.<p><ul><li>%c = course ID</li>'
+					'<p>When students click the <em>Email Instructor</em> button to send feedback, WeBWorK fills in '
+						. 'the subject line. Here you can set the subject line. In it, you can have various bits of '
+						. 'information filled in with the following escape sequences.</p><ul><li>%c = course ID</li>'
 						. '<li>%u = user ID</li><li>%s = set ID</li><li>%p = problem ID</li><li>%x = section</li>'
-						. '<li>%r = recitation</li><li>%% = literal percent sign</li></ul>'
+						. '<li>%r = recitation</li><li>%% = literal percent sign</li></ul><p>If content is between '
+						. "a brace pair, like '{ rec:%r}', then it will only be included in the subject line if all "
+						. 'substitutions within the double brace pair are defined and nonempty.'
 				),
 				width => 45,
 				type  => 'text'

lib/WeBWorK/ContentGenerator/Feedback.pm

@@ -12,7 +12,7 @@ use Email::Stuffer;
 use Try::Tiny;
 
 use WeBWorK::Upload;
-use WeBWorK::Utils qw(createEmailSenderTransportSMTP fetchEmailRecipients);
+use WeBWorK::Utils qw(createEmailSenderTransportSMTP fetchEmailRecipients formatEmailSubject);
 
 # request paramaters used
 #
@@ -108,18 +108,15 @@ sub initialize ($c) {
 			}
 		}
 
-		my %subject_map = (
-			'c' => $courseID,
-			'u' => $user    ? $user->user_id       : undef,
-			's' => $set     ? $set->set_id         : undef,
-			'p' => $problem ? $problem->problem_id : undef,
-			'x' => $user    ? $user->section       : undef,
-			'r' => $user    ? $user->recitation    : undef,
-			'%' => '%',
+		my $subject = formatEmailSubject(
+			$ce->{mail}{feedbackSubjectFormat},
+			$courseID,
+			$user    ? $user->user_id       : '',
+			$set     ? $set->set_id         : '',
+			$problem ? $problem->problem_id : '',
+			$user    ? $user->section       : '',
+			$user    ? $user->recitation    : ''
 		);
-		my $chars   = join('', keys %subject_map);
-		my $subject = $ce->{mail}{feedbackSubjectFormat} || 'WeBWorK question from %c: %u set %s/prob %p';
-		$subject =~ s/%([$chars])/defined $subject_map{$1} ? $subject_map{$1} : ''/eg;
 
 		my %data = (
 			user         => $user,

lib/WeBWorK/Utils.pm

@@ -30,6 +30,7 @@ our @EXPORT_OK = qw(
 	processEmailMessage
 	createEmailSenderTransportSMTP
 	generateURLs
+	formatEmailSubject
 	getAssetURL
 	x
 );
@@ -382,6 +383,35 @@ sub generateURLs ($c, %params) {
 	}
 }
 
+sub formatEmailSubject ($formatString, $courseID, $userID, $setID, $problemID, $section, $recitation) {
+	my %subject_map = (
+		c   => $courseID,
+		u   => $userID,
+		s   => $setID,
+		p   => $problemID,
+		x   => $section,
+		r   => $recitation,
+		'%' => '%',
+	);
+	my $chars   = join('', keys %subject_map);
+	my $subject = $formatString;
+	# extract the brace pairs
+	my @braces = $formatString =~ /(\{(?:[^{}]*|(?0))*\})/xg;
+	if (@braces) {
+		# for each brace pair, do substitutions, but leave %c etc when variable is empty
+		my %braces = map { $_ => $_ =~ s/%([$chars])/$subject_map{$1} ne '' ? $subject_map{$1} : "%$1"/egr } @braces;
+		# if there is an instance of %c, etc, nullify the whole thing
+		%braces = map { $_ => $braces{$_} =~ /%[$chars]/ ? '' : $braces{$_} } keys %braces;
+		# remove outer braces
+		%braces = map { $_ => $braces{$_} =~ s/\{(.*)\}/$1/egr } keys %braces;
+		my $regex = join('|', keys %braces);
+		$regex = qr/$regex/;
+		$subject =~ s/($regex)/$braces{$1}/g;
+	}
+	$subject =~ s/%([$chars])/$subject_map{$1} ne '' ? $subject_map{$1} : ''/eg;
+	return $subject;
+}
+
 my $staticWWAssets;
 my $staticPGAssets;
 my $thirdPartyWWDependencies;

lib/WeBWorK/Utils/ProblemProcessing.pm

@@ -13,7 +13,7 @@ use Try::Tiny;
 use Mojo::JSON qw(encode_json decode_json);
 
 use WeBWorK::Debug;
-use WeBWorK::Utils                      qw(encodeAnswers createEmailSenderTransportSMTP);
+use WeBWorK::Utils                      qw(encodeAnswers createEmailSenderTransportSMTP formatEmailSubject);
 use WeBWorK::Utils::DateTime            qw(before after);
 use WeBWorK::Utils::JITAR               qw(jitar_id_to_seq jitar_problem_adjusted_status);
 use WeBWorK::Utils::Logs                qw(writeLog writeCourseLog);
@@ -383,19 +383,12 @@ sub jitar_send_warning_email ($c, $userProblem) {
 
 	$problemID = join('.', jitar_id_to_seq($problemID));
 
-	my %subject_map = (
-		'c' => $courseID,
-		'u' => $userID,
-		's' => $setID,
-		'p' => $problemID,
-		'x' => $user->section,
-		'r' => $user->recitation,
-		'%' => '%',
+	my $subject = formatEmailSubject(
+		$ce->{mail}{feedbackSubjectFormat},
+		$courseID, $userID, $setID, $problemID,
+		$user ? $user->section    : '',
+		$user ? $user->recitation : ''
 	);
-	my $chars   = join('', keys %subject_map);
-	my $subject = $ce->{mail}{feedbackSubjectFormat}
-		|| 'WeBWorK question from %c: %u set %s/prob %p';    # default if not entered
-	$subject =~ s/%([$chars])/defined $subject_map{$1} ? $subject_map{$1} : ""/eg;
 
 	my $full_name     = $user->full_name;
 	my $email_address = $user->email_address;