Add liquid-spec for conformance testing

- Add liquid-spec gem from GitHub to :spec group
- Create spec/ruby-liquid.rb adapter for the reference implementation
- Add spec job to CI workflow to run liquid-spec tests

.github/workflows/liquid.yml

@@ -42,6 +42,16 @@ jobs:
         env:
           RUBYOPT: ${{ matrix.entry.rubyopt }}
 
+  spec:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+      - uses: ruby/setup-ruby@a25f1e45f0e65a92fcb1e95e8847f78fb0a7197a # v1.273.0
+        with:
+          bundler-cache: true
+          bundler: latest
+      - run: bundle exec liquid-spec run spec/ruby-liquid.rb --no-max-failures
+
   memory_profile:
     runs-on: ubuntu-latest
     steps:

Gemfile

@@ -30,3 +30,7 @@ group :test do
   gem 'rubocop-shopify', '~> 2.18.0', require: false
   gem 'rubocop-performance', require: false
 end
+
+group :spec do
+  gem 'liquid-spec', github: 'Shopify/liquid-spec'
+end

spec/ruby-liquid.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+# Liquid Spec Adapter for Shopify/liquid (Ruby reference implementation)
+#
+# Run with: bundle exec liquid-spec run spec/ruby-liquid.rb
+
+$LOAD_PATH.unshift(File.expand_path('../lib', __dir__))
+require 'liquid'
+
+LiquidSpec.configure do |config|
+  # Run core Liquid specs
+  config.features = [:core]
+end
+
+# Compile a template string into a Liquid::Template
+LiquidSpec.compile do |source, options|
+  Liquid::Template.parse(source, **options)
+end
+
+# Render a compiled template with the given context
+LiquidSpec.render do |template, ctx|
+  static_registers = ctx.registers
+  registers = Liquid::Registers.new(static_registers)
+
+  context = Liquid::Context.build(
+    static_environments: ctx.environment,
+    registers: registers,
+    rethrow_errors: ctx.rethrow_errors?
+  )
+
+  context.exception_renderer = ctx.exception_renderer if ctx.exception_renderer
+
+  template.render(context)
+end