From fe66edb8254a4af4af3a69a32884178e2263c421 Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Fri, 23 Oct 2020 10:53:16 -0400
Subject: [PATCH] Freeze block body after parsing completes

---
 Gemfile                  | 2 +-
 lib/liquid/block.rb      | 1 +
 lib/liquid/block_body.rb | 9 +++++++++
 lib/liquid/document.rb   | 1 +
 lib/liquid/tags/case.rb  | 6 +++++-
 lib/liquid/tags/for.rb   | 2 ++
 lib/liquid/tags/if.rb    | 1 +
 7 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Gemfile b/Gemfile
index 14537c6..338fe56 100644
--- a/Gemfile
+++ b/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: 'pz-block-body-buffer'
   end
 end
diff --git a/lib/liquid/block.rb b/lib/liquid/block.rb
index 47d5f25..d6619f9 100644
--- a/lib/liquid/block.rb
+++ b/lib/liquid/block.rb
@@ -13,6 +13,7 @@ module Liquid
       @body = new_body
       while parse_body(@body, tokens)
       end
+      @body.freeze(parse_context)
     end
 
     # For backwards compatibility
diff --git a/lib/liquid/block_body.rb b/lib/liquid/block_body.rb
index 67d5d63..f61ae87 100644
--- a/lib/liquid/block_body.rb
+++ b/lib/liquid/block_body.rb
@@ -16,9 +16,12 @@ module Liquid
     def initialize
       @nodelist = []
       @blank    = true
+      @frozen   = false
     end
 
     def parse(tokenizer, parse_context, &block)
+      raise FrozenError, "can't modify frozen Liquid::BlockBody" if @frozen
+
       parse_context.line_number = tokenizer.line_number
 
       if tokenizer.for_liquid_tag
@@ -28,6 +31,10 @@ module Liquid
       end
     end
 
+    def freeze(_context)
+      @frozen = true
+    end
+
     private def parse_for_liquid_tag(tokenizer, parse_context)
       while (token = tokenizer.shift)
         unless token.empty? || token =~ WhitespaceOrNothing
@@ -192,6 +199,8 @@ module Liquid
     end
 
     def render_to_output_buffer(context, output)
+      raise "Can only render when frozen" unless @frozen
+
       context.resource_limits.increment_render_score(@nodelist.length)
 
       idx = 0
diff --git a/lib/liquid/document.rb b/lib/liquid/document.rb
index 2e47ffb..21ddec2 100644
--- a/lib/liquid/document.rb
+++ b/lib/liquid/document.rb
@@ -22,6 +22,7 @@ module Liquid
     def parse(tokenizer, parse_context)
       while parse_body(tokenizer)
       end
+      @body.freeze(parse_context)
     rescue SyntaxError => e
       e.line_number ||= parse_context.line_number
       raise
diff --git a/lib/liquid/tags/case.rb b/lib/liquid/tags/case.rb
index b46fa05..cc85ed4 100644
--- a/lib/liquid/tags/case.rb
+++ b/lib/liquid/tags/case.rb
@@ -20,7 +20,11 @@ module Liquid
 
     def parse(tokens)
       body = new_body
-      body = @blocks.last.attachment while parse_body(body, tokens)
+      while parse_body(body, tokens)
+        body.freeze(parse_context)
+        body = @blocks.last.attachment
+      end
+      body.freeze(parse_context)
       if blank?
         @blocks.each { |condition| condition.attachment.remove_blank_strings }
       end
diff --git a/lib/liquid/tags/for.rb b/lib/liquid/tags/for.rb
index 6f66ebd..9a81b4d 100644
--- a/lib/liquid/tags/for.rb
+++ b/lib/liquid/tags/for.rb
@@ -61,7 +61,9 @@ module Liquid
     def parse(tokens)
       if parse_body(@for_block, tokens)
         parse_body(@else_block, tokens)
+        @else_block.freeze(parse_context)
       end
+      @for_block.freeze(parse_context)
       if blank?
         @for_block.remove_blank_strings
         @else_block&.remove_blank_strings
diff --git a/lib/liquid/tags/if.rb b/lib/liquid/tags/if.rb
index c910b0b..7632be9 100644
--- a/lib/liquid/tags/if.rb
+++ b/lib/liquid/tags/if.rb
@@ -31,6 +31,7 @@ module Liquid
     def parse(tokens)
       while parse_body(@blocks.last.attachment, tokens)
       end
+      @blocks.each { |block| block.attachment.freeze(parse_context) }
       if blank?
         @blocks.each { |condition| condition.attachment.remove_blank_strings }
       end