Apply Par margin to previous box in some cases in PGML.

Apply the spacing between paragraphs added by the Par block in
in HTML to the previous block instead of inserting an empty div
with a margin. This adds the margin from the Par block to the
previous Indent div (including adding a div around an indent of zero),
list, or list item block.

Based on the code from @dpvc in #1355.

Author: somiaj

macros/core/PGML.pl

@@ -1266,19 +1266,22 @@ sub format {
 }
 
 sub string {
-	my $self    = shift;
-	my $block   = shift;
+	my ($self, $block) = @_;
+	my $stack   = $block->{stack};
+	my $n       = scalar(@$stack);
 	my @strings = ();
 	my $string;
-	foreach my $item (@{ $block->{stack} }) {
+	for my $i (0 .. $n - 1) {
+		my $item     = $stack->[$i];
+		my $next_par = $i + 1 < $n && $stack->[ $i + 1 ]{type} eq 'par' ? $stack->[ $i + 1 ] : undef;
 		$self->{item} = $item;
 		$self->{nl}   = (!defined($strings[-1]) || $strings[-1] =~ m/\n$/ ? "" : "\n");
 		for ($item->{type}) {
-			/indent/   && do { $string = $self->Indent($item);                    last };
+			/indent/   && do { $string = $self->Indent($item, $next_par);         last };
 			/align/    && do { $string = $self->Align($item);                     last };
 			/par/      && do { $string = $self->Par($item);                       last };
-			/list/     && do { $string = $self->List($item);                      last };
-			/bullet/   && do { $string = $self->Bullet($item);                    last };
+			/list/     && do { $string = $self->List($item, $next_par);           last };
+			/bullet/   && do { $string = $self->Bullet($item, $next_par);         last };
 			/text/     && do { $string = $self->Text($item);                      last };
 			/variable/ && do { $string = $self->Variable($item, $block);          last };
 			/command/  && do { $string = $self->Command($item);                   last };
@@ -1523,17 +1526,14 @@ sub Escape {
 }
 
 sub Indent {
-	my $self = shift;
-	my $item = shift;
-	return $self->string($item) if $item->{indent} == 0;
-	my $em = 2.25 * $item->{indent};
-	return
-		$self->nl
-		. '<div style="margin:0 0 0 '
-		. $em . 'em">' . "\n"
-		. $self->string($item)
-		. $self->nl
-		. "</div>\n";
+	my ($self, $item, $next_par) = @_;
+	my $left   = $item->{indent} ? (2.25 * $item->{indent}) . 'em' : '0';
+	my $bottom = '0';
+	if ($next_par) {
+		$next_par->{used_on_prev_item} = 1;
+		$bottom = '1em';
+	}
+	return $self->nl . "<div style=\"margin: 0 0 $bottom $left;\">\n" . $self->string($item) . $self->nl . "</div>\n";
 }
 
 sub Align {
@@ -1562,20 +1562,27 @@ sub Align {
 );
 
 sub List {
-	my $self = shift;
-	my $item = shift;
-	my $list = $bullet{ $item->{bullet} };
+	my ($self, $item, $next_par) = @_;
+	my $list   = $bullet{ $item->{bullet} };
+	my $margin = '0';
+	if ($next_par) {
+		$next_par->{used_on_prev_item} = 1;
+		$margin = '0 0 1em 0';
+	}
 	return $self->nl
 		. main::tag(
 			$list->[0],
-			style => "margin:0; padding-left:2.25em; $list->[1]",
+			style => "margin: $margin; padding-left: 2.25em; $list->[1]",
 			$self->string($item) . $self->nl
 		);
 }
 
 sub Bullet {
-	my $self = shift;
-	my $item = shift;
+	my ($self, $item, $next_par) = @_;
+	if ($next_par) {
+		$next_par->{used_on_prev_item} = 1;
+		return $self->nl . '<li style="margin-bottom: 1em;">' . $self->string($item) . "</li>\n";
+	}
 	return $self->nl . '<li>' . $self->string($item) . "</li>\n";
 }
 
@@ -1603,9 +1610,8 @@ sub Heading {
 }
 
 sub Par {
-	my $self = shift;
-	my $item = shift;
-	return $self->nl . '<div style="margin-top:1em"></div>' . "\n";
+	my ($self, $item) = @_;
+	return $item->{used_on_prev_item} ? '' : $self->nl . '<div style="margin-top:1em"></div>' . "\n";
 }
 
 sub Break {"<br />\n"}

t/pg_problems/problem_file.t

@@ -21,6 +21,7 @@ is($pg->{post_header_text}, '', 'post_header_text is empty');
 is(
 	$pg->{body_text},
 	qq{<div class="PGML">\n}
+		. qq{<div style="margin: 0 0 0 0;">\n}
 		. qq{Enter a value for <script type="math/tex">\\pi</script>.\n}
 		. qq{<div style="margin-top:1em"></div>\n}
 		. qq{<div class="text-nowrap d-inline">}
@@ -29,6 +30,7 @@ is(
 		. qq{<input id="MaThQuIlL_AnSwEr0001" name="MaThQuIlL_AnSwEr0001" type="hidden" value="">}
 		. qq{</div>}
 		. qq{<input name="previous_AnSwEr0001" type="hidden" value="3.14159">\n}
+		. qq{</div>\n}
 		. qq{</div>\n},
 	'body_text has correct content'
 );