Convert theme_feed_icon() to Twig

Indeed the widow must stay. Quick review:

+++ b/core/includes/theme.incundefined
@@ -3199,7 +3209,8 @@ function drupal_common_theme() {
-      'variables' => array('url' => NULL, 'title' => NULL),
+      'variables' => array('url' => NULL, 'title' => NULL, 'attributes' => array()),

Is adding 'attributes' here necessary? Can't we just add it in the preprocess function?

+++ b/core/modules/system/templates/feed-icon.html.twigundefined
@@ -0,0 +1,19 @@
+ * - attributes: An array of attributes for the feed link, with the following children:

This goes over 80 characters, and shouldn't use the word "array", especially because in this case I think it's an Attribute object. I'm wondering if we can have a boilerplate of sorts for 'attributes' since it's such a common variable. It might be worth looking at some of the other Twig conversion issues (or in the Twig sandbox) to see if there's a good description in one of the other patches :)

One teensy tiny tweak, then RTBC from me :)

+++ b/core/modules/system/templates/feed-icon.html.twigundefined
@@ -0,0 +1,19 @@
+ * - attributes.class: HTML Classes to be applied to the feed link.

HTML classes (lower c).

+++ b/core/modules/system/templates/feed-icon.html.twigundefined
@@ -0,0 +1,19 @@
+ * - attributes: Remaining HTML attributes for the feed link.
+ * - attributes.title: A descriptive title of the feed link.
+ * - attributes.class: HTML classes to be applied to the feed link.

Missed this before, I think we should indent attributes.title and attributes.class here.

 * - attributes: …
 *   - attributes.title: …
 *   - attributes.class: …

Also, can we please replace the theme function instead of adding the new preprocess function above drupal_common_theme()? I think that would be better (same as #1939088-17: Convert theme_meter() to Twig).

This looks great, tested manually and markup matches exactly. Great work guys!

Needs some touch-ups, things have changed :)

+++ b/core/includes/theme.inc
@@ -2411,19 +2411,29 @@ function theme_more_help_link($variables) {
+  $variables['attributes'] = new Attribute(array());

We don't need this line anymore, see #1982024: Lazy-load Attribute objects later in the rendering process only if needed.

+++ b/core/modules/system/templates/feed-icon.html.twig
@@ -0,0 +1,19 @@
+ * - attributes: Remaining HTML attributes for the feed link.
+ *   - attributes.title: A descriptive title of the feed link.
+ *   - attributes.class: HTML classes to be applied to the feed link.

The indented lines should just say 'title' and 'class'. Indent means 'add a dot'/drill down.

+++ b/core/modules/system/templates/feed-icon.html.twig
@@ -0,0 +1,19 @@
+ * @see template_preprocess()

This line should be removed - see #2013094: [policy adopted, patch needed] Stop saying '@see template_preprocess()' in every twig file.

Another quick round of manual testing would be great before we go ahead with the profiling, re-tagging.

I will take care of manually testing and profiling this one.

This looks good to me.

Markup comparison

(debug output in place to show that the markup is in fact coming from the new Twig template…)

Profiling

Scenario: default homepage.

=== 8.x..8.x compared (5219624c55207..521962849973a):

ct  : 34,314|34,314|0|0.0%
wt  : 191,228|191,175|-53|-0.0%
cpu : 165,799|165,925|126|0.1%
mu  : 13,882,272|13,882,272|0|0.0%
pmu : 13,926,944|13,926,944|0|0.0%

http://www.lionsad.de/xhprof-kit/xhprof/xhprof_html/?run1=5219624c55207&...

=== 8.x..theme_feed_icon-1939096-38 compared (5219624c55207..521962a927d49):

ct  : 34,314|34,389|75|0.2%
wt  : 191,228|191,693|465|0.2%
cpu : 165,799|166,748|949|0.6%
mu  : 13,882,272|13,910,952|28,680|0.2%
pmu : 13,926,944|13,956,376|29,432|0.2%

http://www.lionsad.de/xhprof-kit/xhprof/xhprof_html/?run1=5219624c55207&...