Reserve future support for comment line before a tag name

Gemfile

@@ -22,6 +22,6 @@ group :test do
   gem 'rubocop-performance', require: false
 
   platform :mri, :truffleruby do
-    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'master'
+    gem 'liquid-c', github: 'Shopify/liquid-c', ref: 'inline-comment'
   end
 end

History.md

@@ -1,5 +1,10 @@
 # Liquid Change Log
 
+## Unreleased
+
+### Features
+* Allow `#` to be used as an inline comment tag (#1401) [Dylan Thacker-Smith]
+
 ## 5.0.0 / 2021-01-06
 
 ### Features

lib/liquid/block_body.rb

@@ -4,8 +4,8 @@ require 'English'
 
 module Liquid
   class BlockBody
-    LiquidTagToken      = /\A\s*(\w+)\s*(.*?)\z/o
+    LiquidTagToken      = /\A\s*(\w+|#)\s*(.*?)\z/o
-    FullToken           = /\A#{TagStart}#{WhitespaceControl}?(\s*)(\w+)(\s*)(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
+    FullToken           = /\A#{TagStart}#{WhitespaceControl}?(\s*)(\w+|#)(\s*)(.*?)#{WhitespaceControl}?#{TagEnd}\z/om
     ContentOfVariable   = /\A#{VariableStart}#{WhitespaceControl}?(.*?)#{WhitespaceControl}?#{VariableEnd}\z/om
     WhitespaceOrNothing = /\A\s*\z/
     TAGSTART            = "{%"

lib/liquid/locales/en.yml

@@ -22,6 +22,7 @@
       tag_never_closed: "'%{block_name}' tag was never closed"
       table_row: "Syntax Error in 'table_row loop' - Valid syntax: table_row [item] in [collection] cols=3"
       render: "Syntax error in tag 'render' - Template name must be a quoted string"
+      inline_comment_invalid: "Syntax error in tag '#' - Each line of comments must be prefixed by the '#' character"
     argument:
       include: "Argument error in tag 'include' - Illegal template name"
     disabled:

lib/liquid/tags/inline_comment.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module Liquid
+  class InlineComment < Tag
+    def initialize(tag_name, markup, options)
+      super
+      # Semantically, a comment should only ignore everything after it on the line.
+      # Currently, this implementation doesn't support mixing a comment with another tag
+      # but we need to reserve future support for this.
+      if markup.match?(/\n\s*[^#]/)
+        raise SyntaxError, options[:locale].t("errors.syntax.inline_comment_invalid")
+      end
+    end
+
+    def render_to_output_buffer(_context, output)
+      output
+    end
+
+    def blank?
+      true
+    end
+  end
+
+  Template.register_tag('#', InlineComment)
+end

test/integration/tags/inline_comment_test.rb

@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class InlineCommentTest < Minitest::Test
+  include Liquid
+
+  def test_tag_in_different_styles
+    assert_template_result('', '{% # This text gets ignored %}')
+    assert_template_result('', '{%# This text gets ignored #%}')
+    assert_template_result('', '{%# This text gets ignored %}')
+    assert_template_result('', '{%#- This text gets ignored -#%}')
+  end
+
+  def test_test_syntax_error
+    assert_template_result('fail', '{% #This doesnt work %}')
+
+    assert false 
+  rescue 
+    # ok good
+  end
+
+  def test_tag_ws_stripping
+    assert_template_result('', '   {%#- This text gets ignored -#%}    ')
+  end
+
+  def test_comment_inline_tag
+    assert_template_result('ok', '{% echo "ok" # output something from a tag %}')
+  end
+
+  def test_comment_line_before_tag
+    assert_template_result('ok', '{% # this sort of comment also
+      echo "ok" %}')
+  end
+
+  def test_comment_inline_variable
+    assert_template_result('ok', '{{ "ok" # output something from a variable }}')
+    assert_template_result('ok', '{{ "OK" | downcase # output something from a variable }}')
+  end
+
+  def test_inside_liquid_tag
+    source = <<~LIQUID
+      {%- liquid
+        echo "before("
+        # This text gets ignored
+        echo ")after"
+      -%}
+    LIQUID
+    assert_template_result('before()after', source)
+  end
+
+  def test_multiline
+    assert_template_result('', '{% # this sort of comment also
+      # will just work, because it parses
+      # as a single call to the "#" tag %}')   
+
+  end
+
+end