Incorporate relative_url within post_url tag

docs/_docs/upgrading/3-to-4.md

@@ -22,6 +22,25 @@ and fetch the latest version of Jekyll:
 gem update jekyll
 ```
 
+<div class="note warning">
+  <h5><code>post_url</code> Tag and Baseurl</h5>
+  <p>&nbsp;</p>
+  <p>
+    The <code>post_url</code> tag now incorporates the <code>relative_url</code> filter within itself
+    and therefore automatically prepends your site's <code>baseurl</code> to the post's <code>url</code>
+    value.
+  </p>
+  <p>
+    Please ensure that you change all instances of the <code>post_url</code> usage as following:
+  </p>
+
+{% highlight diff %}
+- {{ site.baseurl }}/{% post_url 2018-03-20-hello-world.markdown %}
++ {% post_url 2018-03-20-hello-world.markdown %}
+{% endhighlight %}
+</div>
+
+
 ## Template rendering
 
 We've slightly altered the way Jekyll parses and renders your various templates

docs/_sass/_style.scss

@@ -708,6 +708,15 @@ h5 > code,
     0 -1px 0 rgba(0,0,0,.5));
 }
 
+.note .highlight {
+  width: 94%;
+  pre code {
+    font-size: 0.9em;
+    background-color: transparent;
+    box-shadow: none;
+  }
+}
+
 .note code {
   background-color: #333;
   background-color: rgba(0,0,0,0.2);

features/post_url_tag.feature

@@ -71,7 +71,7 @@ Feature: PostUrl Tag
     When I run jekyll build
     Then I should get a zero exit status
     And the _site directory should exist
-    And I should see "<p><a href=\"/2019/02/04/hello-world.html\">Welcome</a></p>" in "_site/index.html"
+    And I should see "<p><a href=\"/blog/2019/02/04/hello-world.html\">Welcome</a></p>" in "_site/index.html"
 
   Scenario: Posts with categories
     Given I have a _posts directory

jekyll.gemspec

@@ -56,6 +56,10 @@ Gem::Specification.new do |s|
         You should no longer prepend `{{ site.baseurl }}` to `{% link foo.md %}`
         For further details: https://github.com/jekyll/jekyll/pull/6727
 
+      * Our `post_url` tag now comes with the `relative_url` filter incorporated into it.
+        You shouldn't prepend `{{ site.baseurl }}` to `{% post_url 2019-03-27-hello %}`
+        For further details: https://github.com/jekyll/jekyll/pull/7589
+
       * Our `highlight` tag no longer parses Liquid and Liquid-like constructs in the
         tag's content body. While this means you no longer need to enclose the content
         within a `{% raw %}{% endraw %}` block, it also means that you can no longer

lib/jekyll/tags/post_url.rb

@@ -57,6 +57,8 @@ def post_slug(other)
     end
 
     class PostUrl < Liquid::Tag
+      include Jekyll::Filters::URLFilters
+
       def initialize(tag_name, post, tokens)
         super
         @orig_post = post.strip
@@ -72,24 +74,25 @@ def initialize(tag_name, post, tokens)
       end
 
       def render(context)
+        @context = context
         site = context.registers[:site]
 
-        site.posts.docs.each do |p|
-          return p.url if @post == p
+        site.posts.docs.each do |document|
+          return relative_url(document) if @post == document
         end
 
         # New matching method did not match, fall back to old method
         # with deprecation warning if this matches
 
-        site.posts.docs.each do |p|
-          next unless @post.deprecated_equality p
+        site.posts.docs.each do |document|
+          next unless @post.deprecated_equality document
 
           Jekyll::Deprecator.deprecation_message "A call to "\
             "'{% post_url #{@post.name} %}' did not match " \
             "a post using the new matching method of checking name " \
             "(path-date-slug) equality. Please make sure that you " \
             "change this tag to match the post's name exactly."
-          return p.url
+          return relative_url(document)
         end
 
         raise Jekyll::Errors::PostURLError, <<~MSG