Potential fix

lib/liquid/tags/comment.rb

@@ -2,6 +2,19 @@
 
 module Liquid
   class Comment < Block
+    # Potential fix
+    FullTokenPossiblyInvalid = /\A(.*)#{TagStart}#{WhitespaceControl}?\s*(\w+)\s*(.*)?#{WhitespaceControl}?#{TagEnd}\z/om
+
+    def parse(tokens)
+      while (token = tokens.shift)
+        if token =~ FullTokenPossiblyInvalid && block_delimiter == Regexp.last_match(2)
+          return
+        end
+      end
+
+      raise_tag_never_closed(block_name)
+    end
+
     def render_to_output_buffer(_context, output)
       output
     end

lib/liquid/tags/echo.rb

@@ -15,15 +15,19 @@ module Liquid
     attr_reader :variable
 
     def initialize(tag_name, markup, parse_context)
+      puts "Initializing Echo tag"
       super
       @variable = Variable.new(markup, parse_context)
     end
 
     def render(context)
+      puts "Render Echo tag"
       @variable.render_to_output_buffer(context, +'')
     end
 
     class ParseTreeVisitor < Liquid::ParseTreeVisitor
+      puts "ParseTreeVisitor Echo tag"
+
       def children
         [@node.variable]
       end

test/integration/tags/comment_tag_test.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class CommentTagTest < Minitest::Test
+  include Liquid
+
+  def test_single_line_comments_parse
+    assert_template_result('Before comment', <<~LIQUID)
+      Before comment
+      {%- comment -%}
+        Regular text comment
+        Liquid in comment: {% echo 'Hi from comment' %}
+      {%- endcomment -%}
+    LIQUID
+  end
+
+  def test_multi_line_comments_parse
+    assert_template_result('Before comment', <<~LIQUID)
+      Before comment
+      {%- comment -%} Regular text comment {%- endcomment -%}
+      {%- comment -%} Liquid in comment: {% echo 'Hi from comment' %} {%- endcomment -%}
+    LIQUID
+  end
+end # CommentTagTest