Rename {% doc %} constant strictly validates the abscense of args

lib/liquid/locales/en.yml

@@ -2,12 +2,14 @@
   errors:
     syntax:
       tag_unexpected_args: "Syntax Error in '%{tag}' - Valid syntax: %{tag}"
+      block_tag_unexpected_args: "Syntax Error in '%{tag}' - Valid syntax: {% %{tag} %}{% end%{tag} %}"
       assign: "Syntax Error in 'assign' - Valid syntax: assign [var] = [source]"
       capture: "Syntax Error in 'capture' - Valid syntax: capture [var]"
       case: "Syntax Error in 'case' - Valid syntax: case [condition]"
       case_invalid_when: "Syntax Error in tag 'case' - Valid when condition: {% when [condition] [or condition2...] %}"
       case_invalid_else: "Syntax Error in tag 'case' - Valid else condition: {% else %} (no parameters) "
       cycle: "Syntax Error in 'cycle' - Valid syntax: cycle [name :] var [, var2, var3 ...]"
+      doc_invalid_nested: "Syntax Error in 'doc' - Nested doc tags are not allowed"
       for: "Syntax Error in 'for loop' - Valid syntax: for [item] in [collection]"
       for_invalid_in: "For loops require an 'in' clause"
       for_invalid_attribute: "Invalid attribute in for loop. Valid attributes are limit and offset"

lib/liquid/tags.rb

@@ -19,6 +19,7 @@ require_relative "tags/comment"
 require_relative "tags/raw"
 require_relative "tags/render"
 require_relative "tags/cycle"
+require_relative "tags/doc"
 
 module Liquid
   module Tags
@@ -42,6 +43,7 @@ module Liquid
       'if' => If,
       'echo' => Echo,
       'tablerow' => TableRow,
+      'doc' => Doc,
     }.freeze
   end
 end

lib/liquid/tags/doc.rb

@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+module Liquid
+  # @liquid_public_docs
+  # @liquid_type tag
+  # @liquid_category syntax
+  # @liquid_name doc
+  # @liquid_summary
+  #   Documents template elements with annotations.
+  # @liquid_description
+  #   The `doc` tag allows developers to include documentation within Liquid
+  #   templates. Any content inside `doc` tags is not rendered or outputted.
+  #   Liquid code inside will be parsed but not executed. This facilitates
+  #   tooling support for features like code completion, linting, and inline
+  #   documentation.
+  # @liquid_syntax
+  #   {% doc %}
+  #     Renders a message.
+  #
+  #     @param {string} foo - A foo value.
+  #     @param {string} [bar] - An optional bar value.
+  #
+  #     @example
+  #     {% render 'message', foo: 'Hello', bar: 'World' %}
+  #   {% enddoc %}
+  #   {{ foo }}, {{ bar }}!
+  class Doc < Block
+    NO_UNEXPECTED_ARGS = /\A\s*\z/
+
+    def initialize(tag_name, markup, parse_context)
+      super
+      ensure_valid_markup(tag_name, markup, parse_context)
+    end
+
+    def parse(tokens)
+      while (token = tokens.shift)
+        tag_name = token =~ BlockBody::FullTokenPossiblyInvalid && Regexp.last_match(2)
+
+        raise_nested_doc_error if tag_name == @tag_name
+
+        if tag_name == block_delimiter
+          parse_context.trim_whitespace = (token[-3] == WhitespaceControl)
+          return
+        end
+      end
+
+      raise_tag_never_closed(block_name)
+    end
+
+    def render_to_output_buffer(_context, output)
+      output
+    end
+
+    def blank?
+      true
+    end
+
+    private
+
+    def ensure_valid_markup(tag_name, markup, parse_context)
+      unless NO_UNEXPECTED_ARGS.match?(markup)
+        raise SyntaxError, parse_context.locale.t("errors.syntax.block_tag_unexpected_args", tag: tag_name)
+      end
+    end
+
+    def raise_nested_doc_error
+      raise SyntaxError, parse_context.locale.t("errors.syntax.doc_invalid_nested")
+    end
+  end
+end

test/unit/block_unit_test.rb

@@ -47,12 +47,18 @@ class BlockUnitTest < Minitest::Test
     )
   end
 
-  def test_with_block
+  def test_comment_tag_with_block
     template = Liquid::Template.parse("  {% comment %} {% endcomment %} ")
     assert_equal([String, Comment, String], block_types(template.root.nodelist))
     assert_equal(3, template.root.nodelist.size)
   end
 
+  def test_doc_tag_with_block
+    template = Liquid::Template.parse("  {% doc %} {% enddoc %} ")
+    assert_equal([String, Doc, String], block_types(template.root.nodelist))
+    assert_equal(3, template.root.nodelist.size)
+  end
+
   private
 
   def block_types(nodelist)

test/unit/tags/doc_tag_unit_test.rb

@@ -0,0 +1,160 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class DocTagUnitTest < Minitest::Test
+  def test_doc_tag
+    template = <<~LIQUID.chomp
+      {% doc %}
+        Renders loading-spinner.
+
+        @param {string} foo - some foo
+        @param {string} [bar] - optional bar
+
+        @example
+        {% render 'loading-spinner', foo: 'foo' %}
+        {% render 'loading-spinner', foo: 'foo', bar: 'bar' %}
+      {% enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_does_not_support_extra_arguments
+    error = assert_raises(Liquid::SyntaxError) do
+      template = <<~LIQUID.chomp
+        {% doc extra %}
+        {% enddoc %}
+      LIQUID
+
+      Liquid::Template.parse(template)
+    end
+
+    exp_error = "Liquid syntax error: Syntax Error in 'doc' - Valid syntax: {% doc %}{% enddoc %}"
+    act_error = error.message
+
+    assert_equal(exp_error, act_error)
+  end
+
+  def test_doc_tag_must_support_valid_tags
+    assert_match_syntax_error("Liquid syntax error (line 1): 'doc' tag was never closed", '{% doc %} foo')
+    assert_match_syntax_error("Liquid syntax error (line 1): Syntax Error in 'doc' - Valid syntax: {% doc %}{% enddoc %}", '{% doc } foo {% enddoc %}')
+    assert_match_syntax_error("Liquid syntax error (line 1): Syntax Error in 'doc' - Valid syntax: {% doc %}{% enddoc %}", '{% doc } foo %}{% enddoc %}')
+  end
+
+  def test_doc_tag_ignores_liquid_nodes
+    template = <<~LIQUID.chomp
+      {% doc %}
+        {% if true %}
+        {% if ... %}
+        {%- for ? -%}
+        {% while true %}
+        {%
+          unless if
+        %}
+        {% endcase %}
+      {% enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_ignores_unclosed_liquid_tags
+    template = <<~LIQUID.chomp
+      {% doc %}
+        {% if true %}
+      {% enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_does_not_allow_nested_docs
+    error = assert_raises(Liquid::SyntaxError) do
+      template = <<~LIQUID.chomp
+        {% doc %}
+          {% doc %}
+            {% doc %}
+        {% enddoc %}
+      LIQUID
+
+      Liquid::Template.parse(template)
+    end
+
+    exp_error = "Liquid syntax error: Syntax Error in 'doc' - Nested doc tags are not allowed"
+    act_error = error.message
+
+    assert_equal(exp_error, act_error)
+  end
+
+  def test_doc_tag_ignores_nested_raw_tags
+    template = <<~LIQUID.chomp
+      {% doc %}
+        {% raw %}
+      {% enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_ignores_unclosed_assign
+    template = <<~LIQUID.chomp
+      {% doc %}
+        {% assign foo = "1"
+      {% enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_ignores_malformed_syntax
+    template = <<~LIQUID.chomp
+      {% doc %}
+      {% {{ {%- enddoc %}
+    LIQUID
+
+    assert_template_result('', template)
+  end
+
+  def test_doc_tag_preserves_error_line_numbers
+    template = Liquid::Template.parse(<<~LIQUID.chomp, line_numbers: true)
+      {% doc %}
+        {% if true %}
+      {% enddoc %}
+      {{ errors.standard_error }}
+    LIQUID
+
+    expected = <<~TEXT.chomp
+
+      Liquid error (line 4): standard error
+    TEXT
+
+    assert_equal(expected, template.render('errors' => ErrorDrop.new))
+  end
+
+  def test_doc_tag_whitespace_control
+    # Basic whitespace control
+    assert_template_result("Hello!", "      {%- doc -%}123{%- enddoc -%}Hello!")
+    assert_template_result("Hello!", "{%- doc -%}123{%- enddoc -%}     Hello!")
+    assert_template_result("Hello!", "      {%- doc -%}123{%- enddoc -%}     Hello!")
+    assert_template_result("Hello!", <<~LIQUID.chomp)
+      {%- doc %}Whitespace control!{% enddoc -%}
+      Hello!
+    LIQUID
+  end
+
+  def test_doc_tag_delimiter_handling
+    assert_template_result('', <<~LIQUID.chomp)
+      {% if true %}
+        {% doc %}
+          {% docEXTRA %}wut{% enddocEXTRA %}xyz
+        {% enddoc %}
+      {% endif %}
+    LIQUID
+
+    assert_template_result('', "{% doc %}123{% enddoc xyz %}")
+    assert_template_result('', "{% doc %}123{% enddoc\txyz %}")
+    assert_template_result('', "{% doc %}123{% enddoc\nxyz %}")
+    assert_template_result('', "{% doc %}123{% enddoc\n   xyz  enddoc %}")
+  end
+end