Mojo::DOM renders valueless attributes in XML mode

[jast]

If you parse something like <a b> as XML, rendering gives <a b /> which is not actually valid XML due to the missing attribute value. I'm not sure what the best way to "fix" the output would be... probably <a b="b" /> or <a b="" />.

To reproduce: print Mojo::DOM->new->xml(1)->parse('<a b>')->to_string

I guess fixing broken XML (or "converting" HTML to XHTML, which is what I'm doing) isn't really the aim of Mojo::DOM but this would be a fairly straightforward change... uncertainty about which fix is the right one aside.

[Grinnz]

XML mode as you mentioned is designed exactly for this purpose. If XML mode is not set, valid XML input/output cannot be expected.

Edit: Whoops, read it wrong. Disregard

[zoffixznet]

I think this is just a side-effect of the ability to parse broken XHTML. Adding logic to guestimate fixes for broken XHTML on output would probably be beyond the scope of this module.

This trick might be helpful for your purposes:

perl -MMojo::DOM -wle 'print Mojo::DOM->new->xml(1)->parse("<a b>")->at(q{a[b=""]})->attr("b", "")->to_string';
<a b="" />

[zoffixznet]

Here's a more generic approach for you that fixes all attributes on all elements:

perl -MMojo::DOM -wle 'print Mojo::DOM->new->xml(1)->parse(q{<a b c d/><b x y z c="42"/>})->find("*")->each(sub{for (values %$_){$_="" unless defined;}})->join'
<a b="" c="" d="" /><b c="42" x="" y="" z="" />

[kraih]

I believe <a b="b" /> would be the correct result, if we decide to repair the XML here. But i'm not sure if we should. Maybe if there's a more elegant solution than what i've come up with so far.

diff --git a/lib/Mojo/DOM/HTML.pm b/lib/Mojo/DOM/HTML.pm
index 016989a..12a75e4 100644
--- a/lib/Mojo/DOM/HTML.pm
+++ b/lib/Mojo/DOM/HTML.pm
@@ -228,8 +228,9 @@ sub _render {

   # Attributes
   for my $key (sort keys %{$tree->[2]}) {
-    $result .= " $key" and next unless defined(my $value = $tree->[2]{$key});
-    $result .= " $key" . '="' . xml_escape($value) . '"';
+    my $value = $tree->[2]{$key};
+    $result .= " $key" and next if !$xml && !defined $value;
+    $result .= " $key" . '="' . xml_escape($value // $key) . '"';
   }

   # No children
diff --git a/t/mojo/dom.t b/t/mojo/dom.t
index 14867c9..52d7e2f 100644
--- a/t/mojo/dom.t
+++ b/t/mojo/dom.t
@@ -1918,7 +1918,8 @@ is $element->parent->tag, 'XMLTest', 'right parent';
 ok $element->root->xml, 'XML mode active';
 $dom->replace('<XMLTest2 /><XMLTest3 just="works" />');
 ok $dom->xml, 'XML mode active';
-is $dom, '<XMLTest2 /><XMLTest3 just="works" />', 'right result';
+$dom->at('XMLTest2')->{foo} = undef;
+is $dom, '<XMLTest2 foo="foo" /><XMLTest3 just="works" />', 'right result';

 # Ensure HTML semantics
 ok !Mojo::DOM->new->xml(undef)->parse('<?xml version="1.0"?>')->xml,