Update error handling for keeping backward-compatibility on error messages in the render tag

This commit updates the render method to share parts
of the snippet and block rendering logic to enable
inline snippets to support `with`, `for`, and `as`
syntax

lib/liquid.rb

@@ -67,6 +67,7 @@ require 'liquid/i18n'
 require 'liquid/drop'
 require 'liquid/tablerowloop_drop'
 require 'liquid/forloop_drop'
+require 'liquid/snippet_drop'
 require 'liquid/extensions'
 require 'liquid/errors'
 require 'liquid/interrupts'

lib/liquid/locales/en.yml

@@ -5,6 +5,7 @@
       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]"
+      snippet: "Syntax Error in 'snippet' - Valid syntax: snippet [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) "
@@ -19,6 +20,7 @@
       invalid_delimiter: "'%{tag}' is not a valid delimiter for %{block_name} tags. use %{block_delimiter}"
       invalid_template_encoding: "Invalid template encoding"
       render: "Syntax error in tag 'render' - Template name must be a quoted string"
+      render_invalid_template_name: "Syntax error in tag 'render' - Expected a string or identifier, found %{found}"
       table_row: "Syntax Error in 'table_row loop' - Valid syntax: table_row [item] in [collection] cols=3"
       table_row_invalid_attribute: "Invalid attribute '%{attribute}' in tablerow loop. Valid attributes are cols, limit, offset, and range"
       tag_never_closed: "'%{block_name}' tag was never closed"
@@ -29,5 +31,6 @@
       variable_termination: "Variable '%{token}' was not properly terminated with regexp: %{tag_end}"
     argument:
       include: "Argument error in tag 'include' - Illegal template name"
+      render: "Argument error in tag 'render' - Dynamically chosen templates are not allowed"
     disabled:
       tag: "usage is not allowed in this context"

lib/liquid/snippet_drop.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Liquid
+  class SnippetDrop < Drop
+    attr_reader :body, :name, :filename
+
+    def initialize(body, name, filename)
+      super()
+      @body = body
+      @name = name
+      @filename = filename
+    end
+
+    def to_partial
+      @body
+    end
+
+    def to_s
+      'SnippetDrop'
+    end
+  end
+end

lib/liquid/tags.rb

@@ -20,6 +20,7 @@ require_relative "tags/raw"
 require_relative "tags/render"
 require_relative "tags/cycle"
 require_relative "tags/doc"
+require_relative "tags/snippet"
 
 module Liquid
   module Tags
@@ -44,6 +45,7 @@ module Liquid
       'echo' => Echo,
       'tablerow' => TableRow,
       'doc' => Doc,
+      'snippet' => Snippet,
     }.freeze
   end
 end

lib/liquid/tags/render.rb

@@ -27,7 +27,7 @@ module Liquid
   # @liquid_syntax_keyword filename The name of the snippet to render, without the `.liquid` extension.
   class Render < Tag
     FOR = 'for'
-    SYNTAX = /(#{QuotedString}+)(\s+(with|#{FOR})\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
+    SYNTAX = /(#{QuotedString}+|#{VariableSegment}+)(\s+(with|#{FOR})\s+(#{QuotedFragment}+))?(\s+(?:as)\s+(#{VariableSegment}+))?/o
 
     disable_tags "include"
 
@@ -47,21 +47,23 @@ module Liquid
     end
 
     def render_tag(context, output)
-      # The expression should be a String literal, which parses to a String object
-      template_name = @template_name_expr
-      raise ::ArgumentError unless template_name.is_a?(String)
+      template = context.evaluate(@template_name_expr)
 
-      partial = PartialCache.load(
-        template_name,
-        context: context,
-        parse_context: parse_context,
-      )
-
-      context_variable_name = @alias_name || template_name.split('/').last
+      if template.respond_to?(:to_partial)
+        partial = template.to_partial
+        template_name = template.filename
+        context_variable_name = @alias_name || template.name
+      elsif @template_name_expr.is_a?(String)
+        partial = PartialCache.load(template, context: context, parse_context: parse_context)
+        template_name = partial.name
+        context_variable_name = @alias_name || template_name.split('/').last
+      else
+        raise ::ArgumentError
+      end
 
       render_partial_func = ->(var, forloop) {
         inner_context               = context.new_isolated_subcontext
-        inner_context.template_name = partial.name
+        inner_context.template_name = template_name
         inner_context.partial       = true
         inner_context['forloop']    = forloop if forloop
 
@@ -101,14 +103,18 @@ module Liquid
         key = p.consume
         p.consume(:colon)
         @attributes[key] = safe_parse_expression(p)
-        p.consume?(:comma)
+        p.consume?(:comma) # optional comma
       end
 
       p.consume(:end_of_string)
     end
 
     def rigid_template_name(p)
-      p.consume(:string)
+      return p.consume(:string) if p.look(:string)
+      return p.consume(:id) if p.look(:id)
+
+      found = p.consume || "nothing"
+      raise SyntaxError, options[:locale].t("errors.syntax.render_invalid_template_name", found: found)
     end
 
     def strict_parse(markup)

lib/liquid/tags/snippet.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module Liquid
+  # @liquid_public_docs
+  # @liquid_type tag
+  # @liquid_category variable
+  # @liquid_name snippet
+  # @liquid_summary
+  #   Creates a new inline snippet.
+  # @liquid_description
+  #   You can create inline snippets to make your Liquid code more modular.
+  # @liquid_syntax
+  #   {% snippet snippet_name %}
+  #     value
+  #   {% endsnippet %}
+  class Snippet < Block
+    def initialize(tag_name, markup, options)
+      super
+      p = @parse_context.new_parser(markup)
+      if p.look(:id)
+        @to = p.consume(:id)
+        p.consume(:end_of_string)
+      else
+        raise SyntaxError, options[:locale].t("errors.syntax.snippet")
+      end
+    end
+
+    def render_to_output_buffer(context, output)
+      snippet_drop = SnippetDrop.new(@body, @to, context.template_name)
+      context.scopes.last[@to] = snippet_drop
+      context.resource_limits.increment_assign_score(assign_score_of(snippet_drop))
+      output
+    end
+
+    def blank?
+      true
+    end
+
+    private
+
+    def assign_score_of(snippet_drop)
+      snippet_drop.body.nodelist.sum { |node| node.to_s.bytesize }
+    end
+  end
+end

test/integration/tags/render_tag_test.rb

@@ -101,10 +101,6 @@ class RenderTagTest < Minitest::Test
     end
   end
 
-  def test_dynamically_choosen_templates_are_not_allowed
-    assert_syntax_error("{% assign name = 'snippet' %}{% render name %}")
-  end
-
   def test_rigid_parsing_errors
     with_error_modes(:lax, :strict) do
       assert_template_result(
@@ -294,6 +290,13 @@ class RenderTagTest < Minitest::Test
     )
   end
 
+  def test_render_tag_with_snippet_drop
+    assert_template_result(
+      "Hello from snippet",
+      "{% snippet my_snippet %}Hello from snippet{% endsnippet %}{% render my_snippet %}",
+    )
+  end
+
   def test_render_tag_renders_error_with_template_name
     assert_template_result(
       'Liquid error (foo line 1): standard error',