Support RDFa output in link field formatter

Great progress here, Jamie!!

+++ b/core/modules/rdf/lib/Drupal/rdf/Tests/Field/LinkFieldRdfaTest.php
@@ -0,0 +1,61 @@
+ * Tests the placement of RDFa in email field formatters.

There is a reference to the email field here, it should say "link field".

We should also test some cases where the link has a title (along with the url value), and various field formatter settings, such as 'Add rel="nofollow" to links' or 'Open link in new window'. These should not impact the RDFa, but we should test them anyways. It should be trivial to test with the help of #2203065: Adjust assertFormatterRdfa() parameters to allow for more advanced testing. Feel free to include that patch in this issue for now (commit it locally in your issue branch) while devising the test for the link formatter, once #2203065 is committed, we can remove and RTBC this link formatter issue.

1. +++ b/core/modules/rdf/src/Tests/Field/EmailFieldRdfaTest.php
   @@ -53,8 +53,9 @@ public function setUp() {
   -    $this->assertFormatterRdfa(array('type'=>'string'), 'http://schema.org/email', array('value' => $this->testValue));
   +    $this->assertFormatterRdfa(array('type' => 'string'), 'http://schema.org/email', array('value' => $this->testValue));
   +
        // Test the mailto formatter.
   -    $this->assertFormatterRdfa(array('type'=>'email_mailto'), 'http://schema.org/email', array('value' => $this->testValue));
   +    $this->assertFormatterRdfa(array('type' => 'email_mailto'), 'http://schema.org/email', array('value' => $this->testValue));
   

   Those are coding standard fixes, please create a follow up issue to fix those.

2. +++ b/core/modules/rdf/src/Tests/Field/FieldRdfaTestBase.php
   @@ -74,6 +74,7 @@ public function setUp() {
   +    // Merge in the default value type of "literal" if one wasn't given.
   

   ditto.

3. +++ b/core/modules/rdf/src/Tests/Field/FieldRdfaTestBase.php
   --- /dev/null
   +++ b/core/modules/rdf/src/Tests/Field/LinkFieldRdfaTest.php
   
   +++ b/core/modules/rdf/src/Tests/Field/LinkFieldRdfaTest.php
   @@ -0,0 +1,175 @@
   +    // change the expected value here to literal. When formatted as plaintext
   +    // then the RDF is expecting a 'literal' not a 'uri'
   

   The coding standards need to be verified throughout LinkFieldRdfaTest.php.

4. +++ b/core/modules/rdf/src/Tests/Field/LinkFieldRdfaTest.php
   @@ -0,0 +1,175 @@
   +    $this->runTestAllFormatters('External');
   

   Given that those are not UI facing, let's spell the types 'external', 'internal' and 'front' all in lower case.

Why does assertFormatterRdfa() expect an absolute URL when we pass in a relative URL?

The RDFa will still be parsed and extract full URLs, even if those are relative, they will get expanded to match the localhost site.

Probably the expected value should be set up inside the testAllFormattersX() functions.

good idea.

1. +++ b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
   @@ -147,6 +147,12 @@ public function viewElements(FieldItemListInterface $items) {
   +        if (!empty($item->_attributes)) {
   +          // Take the fallback behavior of ___ by just setting the
   +          // _attributes directly.
   +          $item->_attributes += array('content' => $item->url);
   

   The comment here should say something like: Piggyback on the metadata attributes which will be placed in the field template wrapper, and set the URL value in a content attribute.

2. +++ b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
   @@ -154,6 +160,7 @@ public function viewElements(FieldItemListInterface $items) {
              '#options' => $url->getOptions(),
            );
   +
            if ($url->isExternal()) {
              $element[$delta]['#href'] = $url->getPath();
            }
   

   let's keep the patch small (new line here).

3. +++ b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkSeparateFormatter.php
   @@ -77,6 +77,14 @@ public function viewElements(FieldItemListInterface $items) {
   +      if (!empty($item->_attributes)) {
   +        $url->setOption('attributes', $item->_attributes);
   

   Add a comment to say that we're generating a 'a' element here, which is a perfect fit for the RDFa metadata attribute.

4. +++ b/core/modules/rdf/src/Tests/Field/EmailFieldRdfaTest.php
   @@ -54,6 +54,7 @@ public function setUp() {
      public function testAllFormatters() {
        // Test the plain formatter.
        $this->assertFormatterRdfa(array('type'=>'string'), 'http://schema.org/email', array('value' => $this->testValue));
   +
        // Test the mailto formatter.
        $this->assertFormatterRdfa(array('type'=>'email_mailto'), 'http://schema.org/email', array('value' => $this->testValue));
   

   rogue newline.

5. +++ b/core/modules/rdf/src/Tests/Field/LinkFieldRdfaTest.php
   @@ -0,0 +1,183 @@
   +    // set up the expected result
   

   s/set/Set and missing period.

+++ b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
@@ -147,6 +147,13 @@ public function viewElements(FieldItemListInterface $items) {
+          // Piggyback on the metadata attributes,
+          // which will be placed in the field template wrapper,
+          // and set the URL value in a content attribute.
+          $item->_attributes += array('content' => $item->url);

comments should span to 80 chars

Patch looks good now thanks to the recent fixes by Charu. Good to go.

URL is now more than 80 charracter long. back to RTBC.

and congrats @CharuAg for your first patch to core!