Move RDF classes from preprocess to templates

Thanks for the patch @tuutti!

+++ b/core/modules/rdf/templates/rdf-metadata.html.twig
@@ -13,5 +13,11 @@
+  <span{{ attributes }}{{ attributes.addClass(classes) }}></span>

This would result in double attributes. Should be:

<span{{ attributes.addClass(classes) }}></span>

It looks as though $attributes are not set sometimes when $variables is passed to the prerprocess function. The non-patched file sets $attributes['class'] to an array every time so it was not noticed. This patch sets $attributes to an empty array if it was not set.

Thanks @cilefen!

1. +++ b/core/modules/rdf/rdf.module
   @@ -567,10 +567,9 @@ function rdf_preprocess_image(&$variables) {
   +    if (!isset($attributes)) {
   +      $attributes = array();
   +    }
   

   I think we should probably add a short code comment to explain why this is being added.

2. +++ b/core/modules/rdf/templates/rdf-metadata.html.twig
   @@ -13,5 +13,11 @@
   +  {%
   +    set classes = [
   +      'rdf-meta',
   +      'hidden',
   +    ]
   +  %}
   +  <span{{ attributes.addClass(classes) }}></span>
   

   Since this is just two simple classes, maybe we should just do it inline?

   {{ attributes.addClass('rdf-meta', 'hidden') }}
   

Thanks!

To me that code comment just explains the code but not the "why", maybe something along the lines of:

In some cases $attributes is not set, in those cases make it an array for when we construct the Attribute object below.

Edit: or, shorter:

If $attributes is not set make it an empty array for constructing the Attribute object below.

Makes sense to me, thanks @cilefen!

+++ b/core/modules/rdf/rdf.module
@@ -567,10 +567,11 @@ function rdf_preprocess_image(&$variables) {
+    // In some cases $attributes is not set. In those cases make it an array
+    // for when we construct the Attribute object below.
+    if (!isset($attributes)) {

It is not that it is not set. It is that is null. This could be a if else too just set $variables['metadata'][$key] = new Attribute(); and then the comment could be shorter. Also the comment below about the doctype looks like it should be move to the twig template - can someone open a followup.

Those are good suggestions @alexpott. I think we can do without a comment altogether this way.

#2336965: Move the XHTML inline comment in template_preprocess_rdf_metadata to the template file

That seems reasonable to me, is_array() might be better than !is_null potentially but that's about it. Not sure if there any performance differences between the two.

Committed b29ad66 and pushed to 8.0.x. Thanks!