Add support for canonical URLs

Fixes #844

lib/miq/ref_page.rb

@@ -31,6 +31,7 @@ def initialize(site, base, dir, name)
       data['branch'] = @branch || data['doc_branch']
       data['legacy'] = @legacy
       data['branch_paths'] = RefVersions.instance.paths_for(@source)
+      data['canonical_url'] = RefVersions.instance.canonical_path_for(@source)
     end
 
     # Only render with liquid if markdown file

lib/miq/ref_versions.rb

@@ -21,7 +21,12 @@ def paths_for(path)
 
     def canonical_path_for(path)
       recent_path = self[path].first
-      path_version(recent_path) == "latest" ? recent_path : nil
+
+      # TODO: This case should not happen, but some docs do not conform to versioned docs (e.g. /api/)
+      #       Remove this when all docs conform.
+      recent_path ||= path.to_s.sub(%r{/docs/reference/(?:\w+)/}, "/docs/reference/latest/")
+
+      recent_path
     end
 
     private

site/_includes/head.html

@@ -7,9 +7,9 @@
   <title>{{ site.title | escape }}{% if page.title %} - {{ page.title | escape }}{% endif %}</title>
   <meta name="description" content="{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description }}{% endif %}">
   <meta property="og:image" content="http://manageiq.org/assets/images/logo/manageiq-logo-blue.png" />
-  
+
   {% css main %}
-  <link rel="canonical" href="{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">
+  <link rel="canonical" href="{{ page.canonical_url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}">
   <link rel="alternate" type="application/rss+xml" title="{{ site.title }}" href="{{ "/feed.xml" | prepend: site.baseurl | prepend: site.url }}">
 
   <link href="/assets/images/favicon.ico" rel="shortcut icon">

site/_plugins/canonical_url.rb

@@ -0,0 +1,20 @@
+# Jekyll::Page#url is memoized on first call, but this causes issues with the
+#   paginator.  As such, we get the URL and then remove the memoization.
+def extract_page_url(page)
+  had_url = page.instance_variable_defined?(:@url)
+  page.url.tap do
+    page.instance_variable_set(:@url, nil) unless had_url
+  end
+end
+
+Jekyll::Hooks.register :pages, :post_init do |page|
+  page.data['canonical_url'] ||= extract_page_url(page)
+end
+
+Jekyll::Hooks.register :posts, :post_init do |post|
+  post.data['canonical_url'] ||= extract_page_url(post)
+end
+
+Jekyll::Hooks.register :documents, :post_init do |doc|
+  doc.data['canonical_url'] ||= extract_page_url(doc)
+end

test/lib/miq/ref_versions_test.rb

@@ -26,4 +26,17 @@ def test_paths_for_with_ref_doc
     assert_equal "latest", paths.keys.first
     assert_equal "euwe",   paths.keys.last
   end
+
+  def test_canonical_path_for_with_ref_doc
+    path = Miq::RefVersions.instance.canonical_path_for("/docs/reference/latest/installing_on_google_compute_engine/index.html")
+    assert_equal "/docs/reference/latest/installing_on_google_compute_engine/index.html", path
+
+    path = Miq::RefVersions.instance.canonical_path_for("/docs/reference/jansa/installing_on_google_compute_engine/index.html")
+    assert_equal "/docs/reference/latest/installing_on_google_compute_engine/index.html", path
+  end
+
+  def test_canonical_path_for_with_legacy_ref_doc
+    path = Miq::RefVersions.instance.canonical_path_for("/docs/reference/ivanchuk/doc-Installing_on_Google_Compute_Engine/miq/index.html")
+    assert_equal "/docs/reference/latest/installing_on_google_compute_engine/index.html", path
+  end
 end